draft-ietf-6man-udpzero-05.txt   draft-ietf-6man-udpzero-06.txt 
Internet Engineering Task Force G. Fairhurst Internet Engineering Task Force G. Fairhurst
Internet-Draft University of Aberdeen Internet-Draft University of Aberdeen
Intended status: Informational M. Westerlund Intended status: Informational M. Westerlund
Expires: June 25, 2012 Ericsson Expires: December 20, 2012 Ericsson
December 23, 2011 June 20, 2012
IPv6 UDP Checksum Considerations IPv6 UDP Checksum Considerations
draft-ietf-6man-udpzero-05 draft-ietf-6man-udpzero-06
Abstract Abstract
This document examines the role of the UDP transport checksum when This document examines the role of the UDP transport checksum when
used with IPv6, as defined in RFC2460. It presents a summary of the used with IPv6, as defined in RFC2460. It presents a summary of the
trade-offs for evaluating the safety of updating RFC 2460 to permit trade-offs for evaluating the safety of updating RFC 2460 to permit
an IPv6 UDP endpoint to use a zero value in the checksum field as an an IPv6 UDP endpoint to use a zero value in the checksum field as an
indication that no checksum is present. This method is compared with indication that no checksum is present. This method is compared with
some other possibilities. The document also describes the issues and some other possibilities. The document also describes the issues and
design principles that need to be considered when UDP is used with design principles that need to be considered when UDP is used with
IPv6 to support tunnel encapsulations. It concludes that UDP with a IPv6 to support tunnel encapsulations. It concludes that UDP with a
zero checksum in IPv6 can safely be used for this purpose, provided zero checksum in IPv6 can safely be used for this purpose, provided
that this usage is governed by a set of constraints. that this usage is governed by a set of constraints.
Status of this Memo Status of this Memo
skipping to change at page 1, line 40 skipping to change at page 1, line 40
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 25, 2012. This Internet-Draft will expire on December 20, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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carefully, as they describe your rights and restrictions with respect and restrictions with respect to this document. Code Components
to this document. Code Components extracted from this document must extracted from this document must include Simplified BSD License text
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described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Document Structure . . . . . . . . . . . . . . . . . . . . 4 1.1. Document Structure . . . . . . . . . . . . . . . . . . . . 3
1.2. Background . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2. Background . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1. The Role of a Transport Endpoint . . . . . . . . . . . 5 1.2.1. The Role of a Transport Endpoint . . . . . . . . . . . 4
1.2.2. The UDP Checksum . . . . . . . . . . . . . . . . . . . 5 1.2.2. The UDP Checksum . . . . . . . . . . . . . . . . . . . 4
1.2.3. Differences between IPv6 and IPv4 . . . . . . . . . . 7 1.2.3. Differences between IPv6 and IPv4 . . . . . . . . . . 6
1.3. Use of UDP Tunnels . . . . . . . . . . . . . . . . . . . . 7 1.3. Use of UDP Tunnels . . . . . . . . . . . . . . . . . . . . 6
1.3.1. Motivation for new approaches . . . . . . . . . . . . 8 1.3.1. Motivation for new approaches . . . . . . . . . . . . 6
1.3.2. Reducing forwarding cost . . . . . . . . . . . . . . . 8 1.3.2. Reducing forwarding cost . . . . . . . . . . . . . . . 7
1.3.3. Need to inspect the entire packet . . . . . . . . . . 9 1.3.3. Need to inspect the entire packet . . . . . . . . . . 8
1.3.4. Interactions with middleboxes . . . . . . . . . . . . 9 1.3.4. Interactions with middleboxes . . . . . . . . . . . . 8
1.3.5. Support for load balancing . . . . . . . . . . . . . . 10 1.3.5. Support for load balancing . . . . . . . . . . . . . . 8
2. Standards-Track Transports . . . . . . . . . . . . . . . . . . 10 2. Standards-Track Transports . . . . . . . . . . . . . . . . . . 9
2.1. UDP with Standard Checksum . . . . . . . . . . . . . . . . 10 2.1. UDP with Standard Checksum . . . . . . . . . . . . . . . . 9
2.2. UDP-Lite . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2. UDP-Lite . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.1. Using UDP-Lite as a Tunnel Encapsulation . . . . . . . 11 2.2.1. Using UDP-Lite as a Tunnel Encapsulation . . . . . . . 10
2.3. General Tunnel Encapsulations . . . . . . . . . . . . . . 11 2.3. General Tunnel Encapsulations . . . . . . . . . . . . . . 10
3. Issues Requiring Consideration . . . . . . . . . . . . . . . . 12 3. Issues Requiring Consideration . . . . . . . . . . . . . . . . 11
3.1. Effect of packet modification in the network . . . . . . . 13 3.1. Effect of packet modification in the network . . . . . . . 11
3.1.1. Corruption of the destination IP address . . . . . . . 14 3.1.1. Corruption of the destination IP address . . . . . . . 12
3.1.2. Corruption of the source IP address . . . . . . . . . 14 3.1.2. Corruption of the source IP address . . . . . . . . . 13
3.1.3. Corruption of Port Information . . . . . . . . . . . . 15 3.1.3. Corruption of Port Information . . . . . . . . . . . . 14
3.1.4. Delivery to an unexpected port . . . . . . . . . . . . 15 3.1.4. Delivery to an unexpected port . . . . . . . . . . . . 14
3.1.5. Corruption of Fragmentation Information . . . . . . . 16 3.1.5. Corruption of Fragmentation Information . . . . . . . 15
3.2. Validating the network path . . . . . . . . . . . . . . . 18 3.2. Validating the network path . . . . . . . . . . . . . . . 17
3.3. Applicability of method . . . . . . . . . . . . . . . . . 19 3.3. Applicability of method . . . . . . . . . . . . . . . . . 18
3.4. Impact on non-supporting devices or applications . . . . . 20 3.4. Impact on non-supporting devices or applications . . . . . 19
4. Evaluation of proposal to update RFC 2460 to support zero 4. Evaluation of proposal to update RFC 2460 to support zero
checksum . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 checksum . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.1. Alternatives to the Standard Checksum . . . . . . . . . . 20 4.1. Alternatives to the Standard Checksum . . . . . . . . . . 19
4.2. Comparison . . . . . . . . . . . . . . . . . . . . . . . . 22 4.2. Comparison . . . . . . . . . . . . . . . . . . . . . . . . 21
4.2.1. Middlebox Traversal . . . . . . . . . . . . . . . . . 22 4.2.1. Middlebox Traversal . . . . . . . . . . . . . . . . . 21
4.2.2. Load Balancing . . . . . . . . . . . . . . . . . . . . 23 4.2.2. Load Balancing . . . . . . . . . . . . . . . . . . . . 22
4.2.3. Ingress and Egress Performance Implications . . . . . 23 4.2.3. Ingress and Egress Performance Implications . . . . . 22
4.2.4. Deployability . . . . . . . . . . . . . . . . . . . . 23 4.2.4. Deployability . . . . . . . . . . . . . . . . . . . . 22
4.2.5. Corruption Detection Strength . . . . . . . . . . . . 24 4.2.5. Corruption Detection Strength . . . . . . . . . . . . 23
4.2.6. Comparison Summary . . . . . . . . . . . . . . . . . . 24 4.2.6. Comparison Summary . . . . . . . . . . . . . . . . . . 23
5. Requirements on the specification of transported protocols . . 26 5. Requirements on the specification of transported protocols . . 25
5.1. Constraints required on usage of a zero checksum . . . . . 27 5.1. Constraints required on usage of a zero checksum . . . . . 25
6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 30 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
9. Security Considerations . . . . . . . . . . . . . . . . . . . 30 9. Security Considerations . . . . . . . . . . . . . . . . . . . 28
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
10.1. Normative References . . . . . . . . . . . . . . . . . . . 30 10.1. Normative References . . . . . . . . . . . . . . . . . . 28
10.2. Informative References . . . . . . . . . . . . . . . . . . 30 10.2. Informative References . . . . . . . . . . . . . . . . . 29
Appendix A. Document Change History . . . . . . . . . . . . . . . 32 Appendix A. Document Change History . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction 1. Introduction
The User Datagram Protocol (UDP) [RFC0768] transport is defined for The User Datagram Protocol (UDP) [RFC0768] transport is defined for
the Internet Protocol (IPv4) [RFC0791] and is defined in Internet the Internet Protocol (IPv4) [RFC0791] and is defined in Internet
Protocol, Version 6 (IPv6) [RFC2460] for IPv6 hosts and routers. The Protocol, Version 6 (IPv6) [RFC2460] for IPv6 hosts and routers. The
UDP transport protocol has a minimal set of features. This limited UDP transport protocol has a minimal set of features. This limited
set has enabled a wide range of applications to use UDP, but these set has enabled a wide range of applications to use UDP, but these
application do need to provide many important transport functions on application do need to provide many important transport functions on
top of UDP. The UDP Usage Guidelines [RFC5405] provides overall top of UDP. The UDP Usage Guidelines [RFC5405] provides overall
guidance for application designers, including the use of UDP to guidance for application designers, including the use of UDP to
support tunneling. The key difference between UDP usage with IPv4 support tunneling. The key difference between UDP usage with IPv4
and IPv6 is that IPv6 mandates use of the UDP checksum, i.e. a non- and IPv6 is that IPv6 mandates use of the UDP checksum, i.e. a non-
zero value, due to the lack of an IPv6 header checksum. zero value, due to the lack of an IPv6 header checksum.
The lack of a possibility to use UDP with a zero-checksum in IPv6 has The lack of a possibility to use UDP with a zero-checksum in IPv6 has
been observed as a real problem for certain classes of application, been observed as a real problem for certain classes of application,
primarily tunnel applications. This class of application has been primarily tunnel applications. This class of application has been
deployed with a zero checksum using IPv4. The design of IPv6 raises deployed with a zero checksum using IPv4. The design of IPv6 raises
different issues when considering the safety of using a zero checksum different issues when considering the safety of using a zero checksum
for UDP with IPv6. These issues can significantly affect for UDP with IPv6. These issues can significantly affect
applications, both when an endpoint is the intended user and when an applications, both when an endpoint is the intended user and when an
innocent bystander (received by a different endpoint to that innocent bystander (received by a different endpoint to that
intended). The document examines these issues and compares the intended). The document examines these issues and compares the
strengths and weaknesses of a number of proposed solutions. This strengths and weaknesses of a number of proposed solutions. This
analysis presents a set of issues that must be considered and analysis presents a set of issues that must be considered and
mitigated to be able to safely deploy UDP with a zero checksum over mitigated to be able to safely deploy UDP with a zero checksum over
IPv6. The provided comparison of methods is expected to also be IPv6. The provided comparison of methods is expected to also be
useful when considering applications that have different goals from useful when considering applications that have different goals from
the ones that initiated the writing of this document, especially the the ones that initiated the writing of this document, especially the
use of already standardized methods. use of already standardized methods.
The analysis concludes that using UDP with a zero checksum is the The analysis concludes that using UDP with a zero checksum is the
best method of the proposed alternatives to meet the goals for best method of the proposed alternatives to meet the goals for
certain tunnel applications. Unfortunately, this usage is expected certain tunnel applications. Unfortunately, this usage is expected
to have some deployment issues related to middleboxes, limiting the to have some deployment issues related to middleboxes, limiting the
usability more than desired in the currently deployed internet. usability more than desired in the currently deployed internet.
However, this limitation will be largest initially and will reduce as However, this limitation will be largest initially and will reduce as
updates for support of UDP zero checksum for IPv6 are provided to updates for support of UDP zero checksum for IPv6 are provided to
middleboxes. The document therefore derives a set of constraints middleboxes. The document therefore derives a set of constraints
required to ensure safe deployment of zero checksum in UDP. It also required to ensure safe deployment of zero checksum in UDP. It also
identifies some issues that require future consideration and possibly identifies some issues that require future consideration and possibly
additional research. additional research.
1.1. Document Structure 1.1. Document Structure
Section 1 provides a background to key issues, and introduces the use Section 1 provides a background to key issues, and introduces the use
of UDP as a tunnel transport protocol. of UDP as a tunnel transport protocol.
Section 2 describes a set of standards-track datagram transport Section 2 describes a set of standards-track datagram transport
protocols that may be used to support tunnels. protocols that may be used to support tunnels.
Section 3 discusses issues with a zero checksum in UDP for IPv6. It Section 3 discusses issues with a zero checksum in UDP for IPv6. It
considers the impact of corruption, the need for validation of the considers the impact of corruption, the need for validation of the
path and when it is suitable to use a zero checksum. path and when it is suitable to use a zero checksum.
Section 4 evaluates a set of proposals to update the UDP transport Section 4 evaluates a set of proposals to update the UDP transport
behaviour and other alternatives intended to improve support for behaviour and other alternatives intended to improve support for
tunnel protocols. It focuses on a proposal to allow a zero checksum tunnel protocols. It focuses on a proposal to allow a zero checksum
for this use-case with IPv6 and assesses the trade-offs that would for this use-case with IPv6 and assesses the trade-offs that would
arise. arise.
Section 5.1 lists the constraints perceived for safe deployment of Section 5.1 lists the constraints perceived for safe deployment of
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internal state. internal state.
o Pre-filtering by the endpoint of erroneous data, to protect the o Pre-filtering by the endpoint of erroneous data, to protect the
transport from unnecessary processing and from corruption that it transport from unnecessary processing and from corruption that it
can not itself reject. can not itself reject.
o Pre-filtering of incorrectly addressed destination packets, before o Pre-filtering of incorrectly addressed destination packets, before
responding to a source address. responding to a source address.
1.2.2. The UDP Checksum 1.2.2. The UDP Checksum
UDP, as defined in [RFC0768], supports two checksum behaviours when UDP, as defined in [RFC0768], supports two checksum behaviours when
used with IPv4. The normal behaviour is for the sender to calculate used with IPv4. The normal behaviour is for the sender to calculate a
a checksum over a block of data that includes a pseudo header and the checksum over a block of data that includes a pseudo header and the
UDP datagram payload. The UDP header includes a 16-bit one's UDP datagram payload. The UDP header includes a 16-bit one's
complement checksum that provides a statistical guarantee that the complement checksum that provides a statistical guarantee that the
payload was not corrupted in transit. This also allows a receiver to payload was not corrupted in transit. This also allows a receiver to
verify that the endpoint was the intended destination of the verify that the endpoint was the intended destination of the
datagram, because the transport pseudo header covers the IP datagram, because the transport pseudo header covers the IP
addresses, port numbers, transport payload length, and Next Header/ addresses, port numbers, transport payload length, and Next Header/
Protocol value corresponding to the UDP transport protocol [RFC1071]. Protocol value corresponding to the UDP transport protocol [RFC1071].
The length field verifies that the datagram is not truncated or The length field verifies that the datagram is not truncated or
padded. The checksum therefore protects an application against padded. The checksum therefore protects an application against
receiving corrupted payload data in place of, or in addition to, the receiving corrupted payload data in place of, or in addition to, the
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o Endpoint IP destination address (always included in the pseudo o Endpoint IP destination address (always included in the pseudo
header of the checksum) header of the checksum)
o Upper layer payload type (always included in the pseudo header of o Upper layer payload type (always included in the pseudo header of
the checksum) the checksum)
o IP length of payload (always included in the pseudo header of the o IP length of payload (always included in the pseudo header of the
checksum) checksum)
o Length of the network layer extension headers (i.e. by correct o Length of the network layer extension headers (i.e. by correct
position of the checksum bytes) position of the checksum bytes)
The transport-layer fields that are validated by a transport checksum The transport-layer fields that are validated by a transport checksum
are: are:
o Transport demultiplexing, i.e. ports (always included in the o Transport demultiplexing, i.e. ports (always included in the
checksum) checksum)
o Transport payload size (always included in the checksum) o Transport payload size (always included in the checksum)
Transport endpoints also need to verify the correctness of reassembly Transport endpoints also need to verify the correctness of reassembly
of any fragmented datagram. For UDP, this is normally provided as a of any fragmented datagram. For UDP, this is normally provided as a
part of the integrity check. Disabling the IPv4 checksum prevents part of the integrity check. Disabling the IPv4 checksum prevents
this check. A lack of the UDP header and checksum in fragments can this check. A lack of the UDP header and checksum in fragments can
lead to issues in a translator or middlebox. For example, many IPv4 lead to issues in a translator or middlebox. For example, many IPv4
Network Address Translators, NATs, rely on port numbers to find the Network Address Translators, NATs, rely on port numbers to find the
mappings, packet fragments do not carry port numbers, so fragments mappings, packet fragments do not carry port numbers, so fragments
get dropped. IP/ICMP Translation Algorithm [RFC6145] provides some get dropped. IP/ICMP Translation Algorithm [RFC6145] provides some
guidance on the processing of fragmented IPv4 UDP datagrams that do guidance on the processing of fragmented IPv4 UDP datagrams that do
not carry a UDP checksum. not carry a UDP checksum.
IPv4 UDP checksum control is often a kernel-wide configuration IPv4 UDP checksum control is often a kernel-wide configuration
control (e.g. In Linux and BSD), rather than a per socket call. control (e.g. In Linux and BSD), rather than a per socket call.
There are also Networking Interface Cards (NICs) that automatically There are also Networking Interface Cards (NICs) that automatically
calculate TCP [RFC0793] and UDP checksums on transmission when a calculate TCP [RFC0793] and UDP checksums on transmission when a
checksum of zero is sent to the NIC, using a method known as checksum checksum of zero is sent to the NIC, using a method known as checksum
offloading. offloading.
1.2.3. Differences between IPv6 and IPv4 1.2.3. Differences between IPv6 and IPv4
IPv6 does not provide a network-layer integrity check. The removal IPv6 does not provide a network-layer integrity check. The removal
of the header checksum from the IPv6 specification released routers of the header checksum from the IPv6 specification released routers
from a need to update a network-layer checksum for each router hop as from a need to update a network-layer checksum for each router hop as
the IPv6 Hop Count is changed (in contrast to the checksum update the IPv6 Hop Count is changed (in contrast to the checksum update
needed when an IPv4 router modifies the Time-To-Live (TTL)). needed when an IPv4 router modifies the Time-To-Live (TTL)).
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[RFC2460] when endpoint applications transmit UDP datagrams over [RFC2460] when endpoint applications transmit UDP datagrams over
IPv6. IPv6.
1.3. Use of UDP Tunnels 1.3. Use of UDP Tunnels
One increasingly popular use of UDP is as a tunneling protocol, where One increasingly popular use of UDP is as a tunneling protocol, where
a tunnel endpoint encapsulates the packets of another protocol inside a tunnel endpoint encapsulates the packets of another protocol inside
UDP datagrams and transmits them to another tunnel endpoint. Using UDP datagrams and transmits them to another tunnel endpoint. Using
UDP as a tunneling protocol is attractive when the payload protocol UDP as a tunneling protocol is attractive when the payload protocol
is not supported by the middleboxes that may exist along the path, is not supported by the middleboxes that may exist along the path,
because many middleboxes support transmission using UDP. In this because many middleboxes support transmission using UDP. In this use,
use, the receiving endpoint decapsulates the UDP datagrams and the receiving endpoint decapsulates the UDP datagrams and forwards
forwards the original packets contained in the payload [RFC5405]. the original packets contained in the payload [RFC5405]. Tunnels
Tunnels establish virtual links that appear to directly connect establish virtual links that appear to directly connect locations
locations that are distant in the physical Internet topology and can that are distant in the physical Internet topology and can be used to
be used to create virtual (private) networks. create virtual (private) networks.
1.3.1. Motivation for new approaches 1.3.1. Motivation for new approaches
A number of tunnel encapsulations deployed over IPv4 have used the A number of tunnel encapsulations deployed over IPv4 have used the
UDP transport with a zero checksum. Users of these protocols expect UDP transport with a zero checksum. Users of these protocols expect
a similar solution for IPv6. a similar solution for IPv6.
A number of tunnel protocols are also currently being defined (e.g. A number of tunnel protocols are also currently being defined (e.g.
Automated Multicast Tunnels, AMT [I-D.ietf-mboned-auto-multicast], Automated Multicast Tunnels, AMT [I-D.ietf-mboned-auto-multicast],
and the Locator/Identifier Separation Protocol, LISP [LISP]). These and the Locator/Identifier Separation Protocol, LISP [LISP]). These
protocols have proposed an update to IPv6 UDP checksum processing. protocols have proposed an update to IPv6 UDP checksum processing.
These tunnel protocols could benefit from simpler checksum processing These tunnel protocols could benefit from simpler checksum processing
for various reasons: for various reasons:
o Reducing forwarding costs, motivated by redundancy present in the o Reducing forwarding costs, motivated by redundancy present in the
encapsulated packet header, since in tunnel encapsulations, encapsulated packet header, since in tunnel encapsulations,
payload integrity and length verification may be provided by payload integrity and length verification may be provided by
higher layer encapsulations (often using the IPv4, UDP, UDP-Lite, higher layer encapsulations (often using the IPv4, UDP, UDP-Lite,
or TCP checksums). or TCP checksums).
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Address Translators, NATs. Address Translators, NATs.
o A desire to use the port number space to enable load-sharing. o A desire to use the port number space to enable load-sharing.
1.3.2. Reducing forwarding cost 1.3.2. Reducing forwarding cost
It is a common requirement to terminate a large number of tunnels on It is a common requirement to terminate a large number of tunnels on
a single router/host. Processing per tunnel concerns both state a single router/host. Processing per tunnel concerns both state
(memory requirements) and per-packet processing costs. (memory requirements) and per-packet processing costs.
Automatic IP Multicast Tunneling, known as AMT Automatic IP Multicast Tunneling, known as AMT [I-D.ietf-mboned-auto-
[I-D.ietf-mboned-auto-multicast] currently specifies UDP as the multicast] currently specifies UDP as the transport protocol for
transport protocol for packets carrying tunneled IP multicast packets carrying tunneled IP multicast packets. The current
packets. The current specification for AMT requires that the UDP specification for AMT requires that the UDP checksum in the outer
checksum in the outer packet header should be 0 (see Section 6.6 of packet header should be 0 (see Section 6.6 of [I-D.ietf-mboned-auto-
[I-D.ietf-mboned-auto-multicast]). It argues that the computation of multicast]). It argues that the computation of an additional
an additional checksum, when an inner packet is already adequately checksum, when an inner packet is already adequately protected, is an
protected, is an unwarranted burden on nodes implementing lightweight unwarranted burden on nodes implementing lightweight tunneling
tunneling protocols. The AMT protocol needs to replicate a multicast protocols. The AMT protocol needs to replicate a multicast packet to
packet to each gateway tunnel. In this case, the outer IP addresses each gateway tunnel. In this case, the outer IP addresses are
are different for each tunnel and therefore require a different different for each tunnel and therefore require a different pseudo
pseudo header to be built for each UDP replicated encapsulation. header to be built for each UDP replicated encapsulation.
The argument concerning redundant processing costs is valid regarding The argument concerning redundant processing costs is valid regarding
the integrity of a tunneled packet. In some architectures (e.g. PC- the integrity of a tunneled packet. In some architectures (e.g. PC-
based routers), other mechanisms may also significantly reduce based routers), other mechanisms may also significantly reduce
checksum processing costs: There are implementations that have checksum processing costs: There are implementations that have
optimised checksum processing algorithms, including the use of optimised checksum processing algorithms, including the use of
checksum-offloading. This processing is readily available for IPv4 checksum-offloading. This processing is readily available for IPv4
packets at high line rates. Such processing may be anticipated for packets at high line rates. Such processing may be anticipated for
IPv6 endpoints, allowing receivers to reject corrupted packets IPv6 endpoints, allowing receivers to reject corrupted packets
without further processing. However, there are certain classes of without further processing. However, there are certain classes of
tunnel end-points where this off-loading is not available and tunnel end-points where this off-loading is not available and
unlikely to become available in the near future. unlikely to become available in the near future.
1.3.3. Need to inspect the entire packet 1.3.3. Need to inspect the entire packet
The currently-deployed hardware in many routers uses a fast-path The currently-deployed hardware in many routers uses a fast-path
processing that only provides the first n bytes of a packet to the processing that only provides the first n bytes of a packet to the
forwarding engine, where typically n <= 128. This prevents fast forwarding engine, where typically n <= 128. This prevents fast
processing of a transport checksum over an entire (large) packet. processing of a transport checksum over an entire (large) packet.
Hence the currently defined IPv6 UDP checksum is poorly suited to use Hence the currently defined IPv6 UDP checksum is poorly suited to use
within a router that is unable to access the entire packet and does within a router that is unable to access the entire packet and does
not provide checksum-offloading. Thus enabling checksum calculation not provide checksum-offloading. Thus enabling checksum calculation
over the complete packet can impact router design, performance over the complete packet can impact router design, performance
improvement, energy consumption and/or cost. improvement, energy consumption and/or cost.
1.3.4. Interactions with middleboxes 1.3.4. Interactions with middleboxes
In IPv4, UDP-encapsulation may be desirable for NAT traversal, since In IPv4, UDP-encapsulation may be desirable for NAT traversal, since
UDP support is commonly provided. It is also necessary due to the UDP support is commonly provided. It is also necessary due to the
almost ubiquitous deployment of IPv4 NATs. There has also been almost ubiquitous deployment of IPv4 NATs. There has also been
discussion of NAT for IPv6, although not for the same reason as in discussion of NAT for IPv6, although not for the same reason as in
IPv4. If IPv6 NAT becomes a reality they hopefully do not present IPv4. If IPv6 NAT becomes a reality they hopefully do not present the
the same protocol issues as for IPv4. If NAT is defined for IPv6, it same protocol issues as for IPv4. If NAT is defined for IPv6, it
should take UDP zero checksum into consideration. should take UDP zero checksum into consideration.
The requirements for IPv6 firewall traversal are likely be to be The requirements for IPv6 firewall traversal are likely be to be
similar to those for IPv4. In addition, it can be reasonably similar to those for IPv4. In addition, it can be reasonably expected
expected that a firewall conforming to RFC 2460 will not regard UDP that a firewall conforming to RFC 2460 will not regard UDP datagrams
datagrams with a zero checksum as valid packets. If a zero-checksum with a zero checksum as valid packets. If a zero-checksum for UDP
for UDP were to be allowed for IPv6, this would need firewalls to be were to be allowed for IPv6, this would need firewalls to be updated
updated before full utility of the change is available. before full utility of the change is available.
It can be expected that UDP with zero-checksum will initially not It can be expected that UDP with zero-checksum will initially not
have the same middlebox traversal characteristics as regular UDP. have the same middlebox traversal characteristics as regular UDP.
However, if standardized we can expect an improvement over time of However, if standardized we can expect an improvement over time of
the traversal capabilities. We also note that deployment of IPv6- the traversal capabilities. We also note that deployment of
capable middleboxes is still in its initial phases. Thus, it might IPv6-capable middleboxes is still in its initial phases. Thus, it
be that the number of non-updated boxes quickly become a very small might be that the number of non-updated boxes quickly become a very
percentage of the deployed middleboxes. small percentage of the deployed middleboxes.
1.3.5. Support for load balancing 1.3.5. Support for load balancing
The UDP port number fields have been used as a basis to design load- The UDP port number fields have been used as a basis to design load-
balancing solutions for IPv4. This approach has also been leveraged balancing solutions for IPv4. This approach has also been leveraged
for IPv6. An alternate method would be to utilise the IPv6 Flow for IPv6. An alternate method would be to utilise the IPv6 Flow Label
Label as basis for entropy for the load balancing. This would have as basis for entropy for the load balancing. This would have the
the desirable effect of releasing IPv6 load-balancing devices from desirable effect of releasing IPv6 load-balancing devices from the
the need to assume semantics for the use of the transport port field need to assume semantics for the use of the transport port field and
and also works for all type of transport protocols. This use of the also works for all type of transport protocols. This use of the
flow-label is consistent with the intended use, although further flow-label is consistent with the intended use, although further
clarity may be needed to ensure the field can be consistently used clarity may be needed to ensure the field can be consistently used
for this purpose, (e.g. Equal-Cost Multi-Path routing, ECMP [ECMP]). for this purpose, (e.g. Equal-Cost Multi-Path routing, ECMP [ECMP]).
Router vendors could be encouraged to start using the IPv6 Flow Label Router vendors could be encouraged to start using the IPv6 Flow Label
as a part of the flow hash, providing support for ECMP without as a part of the flow hash, providing support for ECMP without
requiring use of UDP. However, the method for populating the outer requiring use of UDP. However, the method for populating the outer
IPv6 header with a value for the flow label is not trivial: If the IPv6 header with a value for the flow label is not trivial: If the
inner packet uses IPv6, then the flow label value could be copied to inner packet uses IPv6, then the flow label value could be copied to
the outer packet header. However, many current end-points set the the outer packet header. However, many current end-points set the
flow label to a zero value (thus no entropy). The ingress of a flow label to a zero value (thus no entropy). The ingress of a tunnel
tunnel seeking to provide good entropy in the flow label field would seeking to provide good entropy in the flow label field would
therefore need to create a random flow label value and keep therefore need to create a random flow label value and keep
corresponding state, so that all packets that were associated with a corresponding state, so that all packets that were associated with a
flow would be consistently given the same flow label. Although flow would be consistently given the same flow label. Although
possible, this complexity may not be desirable in a tunnel ingress. possible, this complexity may not be desirable in a tunnel ingress.
The end-to-end use of flow labels for load balancing is a long-term The end-to-end use of flow labels for load balancing is a long-term
solution. Even if the usage of the flow label is clarified, there solution. Even if the usage of the flow label is clarified, there
would be a transition time before a significant proportion of end- would be a transition time before a significant proportion of end-
points start to assign a good quality flow label to the flows that points start to assign a good quality flow label to the flows that
they originate, with continued use of load balancing using the they originate, with continued use of load balancing using the
transport header fields until any widespread deployment is finally transport header fields until any widespread deployment is finally
achieved. achieved.
2. Standards-Track Transports 2. Standards-Track Transports
The IETF has defined a set of transport protocols that may be The IETF has defined a set of transport protocols that may be
applicable for tunnels with IPv6. There are also a set of network applicable for tunnels with IPv6. There are also a set of network
layer encapsulation tunnels such as IP-in-IP and GRE. These already layer encapsulation tunnels such as IP-in-IP and GRE. These already
standardized solutions are discussed here prior to the issues, as standardized solutions are discussed here prior to the issues, as
background for the issue description and some comparison of where the background for the issue description and some comparison of where the
issue may already occur. issue may already occur.
2.1. UDP with Standard Checksum 2.1. UDP with Standard Checksum
UDP [RFC0768] with standard checksum behaviour, as defined in RFC UDP [RFC0768] with standard checksum behaviour, as defined in RFC
2460, has already been discussed. UDP usage guidelines are provided 2460, has already been discussed. UDP usage guidelines are provided
in [RFC5405]. in [RFC5405].
2.2. UDP-Lite 2.2. UDP-Lite
UDP-Lite [RFC3828] offers an alternate transport to UDP, specified as UDP-Lite [RFC3828] offers an alternate transport to UDP, specified as
a proposed standard, RFC 3828. A MIB is defined in RFC 5097 and a proposed standard, RFC 3828. A MIB is defined in RFC 5097 and
unicast usage guidelines in [RFC5405]. There is at least one open unicast usage guidelines in [RFC5405]. There is at least one open
source implementation as a part of the Linux kernel since version source implementation as a part of the Linux kernel since version
2.6.20. 2.6.20.
UDP-Lite provides a checksum with optional partial coverage. When UDP-Lite provides a checksum with optional partial coverage. When
using this option, a datagram is divided into a sensitive part using this option, a datagram is divided into a sensitive part
(covered by the checksum) and an insensitive part (not covered by the (covered by the checksum) and an insensitive part (not covered by the
checksum). When the checksum covers the entire packet, UDP-Lite is checksum). When the checksum covers the entire packet, UDP-Lite is
fully equivalent with UDP. Errors/corruption in the insensitive part fully equivalent with UDP. Errors/corruption in the insensitive part
will not cause the datagram to be discarded by the transport layer at will not cause the datagram to be discarded by the transport layer at
the receiving endpoint. A minor side-effect of using UDP-Lite is the receiving endpoint. A minor side-effect of using UDP-Lite is
that this was specified for damage-tolerant payloads, and some link- that this was specified for damage-tolerant payloads, and some link-
layers may employ different link encapsulations when forwarding UDP- layers may employ different link encapsulations when forwarding UDP-
Lite segments (e.g. radio access bearers). Most link-layers will Lite segments (e.g. radio access bearers). Most link-layers will
cover the insensitive part with the same strong layer 2 frame CRC cover the insensitive part with the same strong layer 2 frame CRC
that covers the sensitive part. that covers the sensitive part.
2.2.1. Using UDP-Lite as a Tunnel Encapsulation 2.2.1. Using UDP-Lite as a Tunnel Encapsulation
Tunnel encapsulations can use UDP-Lite (e.g. Control And Tunnel encapsulations can use UDP-Lite (e.g. Control And
Provisioning of Wireless Access Points, CAPWAP [RFC5415]), since UDP- Provisioning of Wireless Access Points, CAPWAP [RFC5415]), since UDP-
Lite provides a transport-layer checksum, including an IP pseudo Lite provides a transport-layer checksum, including an IP pseudo
header checksum, in IPv6, without the need for a router/middelbox to header checksum, in IPv6, without the need for a router/middelbox to
traverse the entire packet payload. This provides most of the traverse the entire packet payload. This provides most of the
delivery verifications and still keeps the complexity of the verification required for delivery and still keeps the complexity of
checksumming operation low. UDP-Lite may set the length of checksum the checksumming operation low. UDP-Lite may set the length of
coverage on a per packet basis. This feature could be used if a checksum coverage on a per packet basis. This feature could be used
tunnel protocol is designed to only verify delivery of the tunneled if a tunnel protocol is designed to only verify delivery of the
payload and uses full checksumming for control information. tunneled payload and uses full checksumming for control information.
There is currently poor support for middlebox traversal using UDP- There is currently poor support for middlebox traversal using UDP-
Lite, because UDP-Lite uses a different IPv6 network-layer Next Lite, because UDP-Lite uses a different IPv6 network-layer Next
Header value to that of UDP, and few middleboxes are able to Header value to that of UDP, and few middleboxes are able to
interpret UDP-Lite and take appropriate actions when forwarding the interpret UDP-Lite and take appropriate actions when forwarding the
packet. This makes UDP-Lite less suited to protocols needing general packet. This makes UDP-Lite less suited to protocols needing general
Internet support, until such time that UDP-Lite has achieved better Internet support, until such time that UDP-Lite has achieved better
support in middleboxes and end-points. support in middleboxes and end-points.
2.3. General Tunnel Encapsulations 2.3. General Tunnel Encapsulations
The IETF has defined a set of tunneling protocols or network layer The IETF has defined a set of tunneling protocols or network layer
encapsulations, e.g., IP-in-IP and GRE. These either do not include encapsulations, e.g., IP-in-IP and GRE. These either do not include a
a checksum or use a checksum that is optional, since tunnel checksum or use a checksum that is optional, since tunnel
encapsulations are typically layered directly over the Internet layer encapsulations are typically layered directly over the Internet layer
(identified by the upper layer type in the IPv6 Next Header field) (identified by the upper layer type in the IPv6 Next Header field)
and are also not used as endpoint transport protocols. There is and are also not used as endpoint transport protocols. There is
little chance of confusing a tunnel-encapsulated packet with other little chance of confusing a tunnel-encapsulated packet with other
application data that could result in corruption of application state application data that could result in corruption of application state
or data. or data.
From the end-to-end perspective, the principal difference is that the From the end-to-end perspective, the principal difference is that the
network-layer Next Header field identifies a separate transport, network-layer Next Header field identifies a separate transport,
which reduces the probability that corruption could result in the which reduces the probability that corruption could result in the
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checksum. checksum.
In IPv6, these checks occur within the endpoint stack using the UDP In IPv6, these checks occur within the endpoint stack using the UDP
checksum information. An IPv6 node also relies on the header checksum information. An IPv6 node also relies on the header
information to determine whether to send an ICMPv6 error message information to determine whether to send an ICMPv6 error message
[RFC4443] and to determine the node to which this is sent. Corrupted [RFC4443] and to determine the node to which this is sent. Corrupted
information may lead to misdelivery to an unintended application information may lead to misdelivery to an unintended application
socket on an unexpected host. socket on an unexpected host.
3.1. Effect of packet modification in the network 3.1. Effect of packet modification in the network
IP packets may be corrupted as they traverse an Internet path. IP packets may be corrupted as they traverse an Internet path.
Evidence has been presented [Sigcomm2000] to show that this was once Evidence has been presented [Sigcomm2000] to show that this was once
an issue with IPv4 routers, and occasional corruption could result an issue with IPv4 routers, and occasional corruption could result
from bad internal router processing in routers or hosts. These from bad internal router processing in routers or hosts. These
errors are not detected by the strong frame checksums employed at the errors are not detected by the strong frame checksums employed at the
link-layer [RFC3819]. There is no current evidence that such cases link-layer [RFC3819]. There is no current evidence that such cases
are rare in the modern Internet, nor that they may not be applicable are rare in the modern Internet, nor that they may not be applicable
to IPv6. It therefore seems prudent not to relax this constraint. to IPv6. It therefore seems prudent not to relax this constraint.
The emergence of low-end IPv6 routers and the proposed use of NAT The emergence of low-end IPv6 routers and the proposed use of NAT
with IPv6 further motivate the need to protect from this type of with IPv6 further motivate the need to protect from this type of
error. error.
Corruption in the network may result in: Corruption in the network may result in:
o A datagram being mis-delivered to the wrong host/router or the o A datagram being mis-delivered to the wrong host/router or the
wrong transport entity within an endpoint. Such a datagram needs wrong transport entity within an endpoint. Such a datagram needs
to be discarded; to be discarded;
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errors, reducing the probability of undetected corruption of state errors, reducing the probability of undetected corruption of state
(and data) on both the host stack and the applications using the (and data) on both the host stack and the applications using the
transport service. transport service.
The following sections examine the impact of modifying each of these The following sections examine the impact of modifying each of these
header fields. header fields.
3.1.1. Corruption of the destination IP address 3.1.1. Corruption of the destination IP address
An IP endpoint destination address could be modified in the network An IP endpoint destination address could be modified in the network
(e.g. corrupted by an error). This is not a concern for IPv4, (e.g. corrupted by an error). This is not a concern for IPv4,
because the IP header checksum will result in this packet being because the IP header checksum will result in this packet being
discarded by the receiving IP stack. Such modification in the discarded by the receiving IP stack. Such modification in the
network can not be detected at the network layer when using IPv6. network can not be detected at the network layer when using IPv6.
There are two possible outcomes: There are two possible outcomes:
o Delivery to a destination address that is not in use (the packet o Delivery to a destination address that is not in use (the packet
will not be delivered, but could result in an error report); will not be delivered, but could result in an error report);
o Delivery to a different destination address. This modification o Delivery to a different destination address. This modification
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3.1.4. Delivery to an unexpected port 3.1.4. Delivery to an unexpected port
If one combines the corruption effects, such as destination address If one combines the corruption effects, such as destination address
and ports, there is a number of potential outcomes when traffic and ports, there is a number of potential outcomes when traffic
arrives at an unexpected port. This section discusses these arrives at an unexpected port. This section discusses these
possibilities and their outcomes for a packet that does not use the possibilities and their outcomes for a packet that does not use the
UDP checksum validation: UDP checksum validation:
o Delivery to a port that is not in use. The packet is discarded, o Delivery to a port that is not in use. The packet is discarded,
but could generate an ICMPv6 message (e.g. port unreachable). but could generate an ICMPv6 message (e.g. port unreachable).
o It could be delivered to a different node that implements the same o It could be delivered to a different node that implements the same
application, where the packet may be accepted, generating side- application, where the packet may be accepted, generating side-
effects or accumulated state. effects or accumulated state.
o It could be delivered to an application that does not implement o It could be delivered to an application that does not implement
the tunnel protocol, where the packet may be incorrectly parsed, the tunnel protocol, where the packet may be incorrectly parsed,
and may be misinterpreted, generating side-effects or accumulated and may be misinterpreted, generating side-effects or accumulated
state. state.
The probability of each outcome depends on the statistical The probability of each outcome depends on the statistical
probability that the address or the port information for the source probability that the address or the port information for the source
or destination becomes corrupt in the datagram such that they match or destination becomes corrupt in the datagram such that they match
those of an existing flow or server port. Unfortunately, such a those of an existing flow or server port. Unfortunately, such a
match may be more likely for UDP than for connection-oriented match may be more likely for UDP than for connection-oriented
transports, because: transports, because:
1. There is no handshake prior to communication and no sequence 1. There is no handshake prior to communication and no sequence
numbers (as in TCP, DCCP, or SCTP). Together, this makes it hard numbers (as in TCP, DCCP, or SCTP). Together, this makes it hard
to verify that an application is given only the data associated to verify that an application is given only the data associated
with a transport session. with a transport session.
2. Applications writers often bind to wild-card values in endpoint 2. Applications writers often bind to wild-card values in endpoint
identifiers and do not always validate correctness of datagrams identifiers and do not always validate correctness of datagrams
they receive (guidance on this topic is provided in [RFC5405]). they receive (guidance on this topic is provided in [RFC5405]).
While these rules could, in principle, be revised to declare naive While these rules could, in principle, be revised to declare naive
applications as "Historic". This remedy is not realistic: the applications as "Historic". This remedy is not realistic: the
transport owes it to the stack to do its best to reject bogus transport owes it to the stack to do its best to reject bogus
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packets may contain corrupted data or data associated with a packets may contain corrupted data or data associated with a
completely different protocol. completely different protocol.
3.1.5. Corruption of Fragmentation Information 3.1.5. Corruption of Fragmentation Information
The fragmentation information in IPv6 employs a 32-bit identity The fragmentation information in IPv6 employs a 32-bit identity
field, compared to only a 16-bit field in IPv4, a 13-bit fragment field, compared to only a 16-bit field in IPv4, a 13-bit fragment
offset and a 1-bit flag, indicating if there are more fragments. offset and a 1-bit flag, indicating if there are more fragments.
Corruption of any of these field may result in one of two outcomes: Corruption of any of these field may result in one of two outcomes:
Reassembly failure: An error in the "More Fragments" field for the Reassembly failure: An error in the "More Fragments" field for the
last fragment will for example result in the packet never being last fragment will for example result in the packet never being
considered complete and will eventually be timed out and considered complete and will eventually be timed out and
discarded. A corruption in the ID field will result in the discarded. A corruption in the ID field will result in the
fragment not being delivered to the intended context thus leaving fragment not being delivered to the intended context thus leaving
the rest incomplete, unless that packet has been duplicated prior the rest incomplete, unless that packet has been duplicated prior
to corruption. The incomplete packet will eventually be timed out to corruption. The incomplete packet will eventually be timed out
and discarded. and discarded.
Erroneous reassembly: The re-assemblied packet did not match the Erroneous reassembly: The re-assemblied packet did not match the
original packet. This can occur when the ID field of a fragment original packet. This can occur when the ID field of a fragment
is corrupted, resulting in a fragment becoming associated with is corrupted, resulting in a fragment becoming associated with
another packet and taking the place of another fragment. another packet and taking the place of another fragment.
Corruption in the offset information can cause the fragment to be Corruption in the offset information can cause the fragment to be
misaligned in the reassembly buffer, resulting in incorrect misaligned in the reassembly buffer, resulting in incorrect
reassembly. Corruption can cause the packet to become shorter or reassembly. Corruption can cause the packet to become shorter or
longer, however completion of reassembly is much less probable, longer, however completion of reassembly is much less probable,
since this would requires consistent corruption of the IPv6 since this would requires consistent corruption of the IPv6
headers payload length field and the offset field. The headers payload length field and the offset field. The
possibility of mis-assembly requires the reassembling stack to possibility of mis-assembly requires the reassembling stack to
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however that this is not guaranteed and has recently been however that this is not guaranteed and has recently been
clarified in "Handling of Overlapping IPv6 Fragments" [RFC5722]. clarified in "Handling of Overlapping IPv6 Fragments" [RFC5722].
The erroneous reassembly of packets is a general concern and such The erroneous reassembly of packets is a general concern and such
packets should be discarded instead of being passed to higher layer packets should be discarded instead of being passed to higher layer
processes. The primary detector of packet length changes is the IP processes. The primary detector of packet length changes is the IP
payload length field, with a secondary check by the transport payload length field, with a secondary check by the transport
checksum. The Upper-Layer Packet length field included in the pseudo checksum. The Upper-Layer Packet length field included in the pseudo
header assists in verifying correct reassembly, since the Internet header assists in verifying correct reassembly, since the Internet
checksum has a low probability of detecting insertion of data or checksum has a low probability of detecting insertion of data or
overlap errors (due to misplacement of data). The checksum is also overlap errors (due to misplacement of data). The checksum is also
incapable of detecting insertion or removal of all zero-data that incapable of detecting insertion or removal of all zero-data that
occurs in a multiple of a 16-bit chunk. occurs in a multiple of a 16-bit chunk.
The most significant risk of corruption results following mis- The most significant risk of corruption results following mis-
association of a fragment with a different packet. This risk can be association of a fragment with a different packet. This risk can be
significant, since the size of fragments is often the same (e.g. significant, since the size of fragments is often the same (e.g.
fragments resulting when the path MTU results in fragmentation of a fragments resulting when the path MTU results in fragmentation of a
larger packet, common when addition of a tunnel encapsulation header larger packet, common when addition of a tunnel encapsulation header
expands the size of a packet). Detection of this type of error expands the size of a packet). Detection of this type of error
requires a checksum or other integrity check of the headers and the requires a checksum or other integrity check of the headers and the
payload. Such protection is anyway desirable for tunnel payload. Such protection is anyway desirable for tunnel
encapsulations using IPv4, since the small fragmentation ID can encapsulations using IPv4, since the small fragmentation ID can
easily result in wrap-around [RFC4963], this is especially the case easily result in wrap-around [RFC4963], this is especially the case
for tunnels that perform flow aggregation [I-D.ietf-intarea-tunnels]. for tunnels that perform flow aggregation [I-D.ietf-intarea-tunnels].
Tunnel fragmentation behavior matters. There can be outer or inner Tunnel fragmentation behavior matters. There can be outer or inner
fragmentation "Tunnels in the Internet Architecture" fragmentation "Tunnels in the Internet Architecture" [I-D.ietf-
[I-D.ietf-intarea-tunnels]. If there is inner fragmentation by the intarea-tunnels]. If there is inner fragmentation by the tunnel, the
tunnel, the outer headers will never be fragmented and thus a zero- outer headers will never be fragmented and thus a zero-checksum in
checksum in the outer header will not affect the reassembly process. the outer header will not affect the reassembly process. When a
When a tunnel performs outer header fragmentation, the tunnel egress tunnel performs outer header fragmentation, the tunnel egress needs
needs to perform reassembly of the outer fragments into an inner to perform reassembly of the outer fragments into an inner packet.
packet. The inner packet is either a complete packet or a fragment. The inner packet is either a complete packet or a fragment. If it is
If it is a fragment, the destination endpoint of the fragment will a fragment, the destination endpoint of the fragment will perform
perform reassembly of the received fragments. The complete packet or reassembly of the received fragments. The complete packet or the
the reassembled fragments will then be processed according to the reassembled fragments will then be processed according to the packet
packet next header field. The receiver may only detect reassembly next header field. The receiver may only detect reassembly anomalies
anomalies when it uses a protocol with a checksum. The larger the when it uses a protocol with a checksum. The larger the number of
number of reassembly processes to which a packet has been subjected, reassembly processes to which a packet has been subjected, the
the greater the probability of an error. greater the probability of an error.
o An IP-in-IP tunnel that performs inner fragmentation has similar o An IP-in-IP tunnel that performs inner fragmentation has similar
properties to a UDP tunnel with a zero-checksum that also performs properties to a UDP tunnel with a zero-checksum that also performs
inner fragmentation. inner fragmentation.
o An IP-in-IP tunnel that performs outer fragmentation has similar o An IP-in-IP tunnel that performs outer fragmentation has similar
properties to a UDP tunnel with a zero checksum that performs properties to a UDP tunnel with a zero checksum that performs
outer fragmentation. outer fragmentation.
o A tunnel that performs outer fragmentation can result in a higher o A tunnel that performs outer fragmentation can result in a higher
level of corruption due to both inner and outer fragmentation, level of corruption due to both inner and outer fragmentation,
enabling more chances for reassembly errors to occur. enabling more chances for reassembly errors to occur.
o Recursive tunneling can result in fragmentation at more than one o Recursive tunneling can result in fragmentation at more than one
header level, even for inner fragmentation unless it goes to the header level, even for inner fragmentation unless it goes to the
inner most IP header. inner most IP header.
o Unless there is verification at each reassembly, the probability o Unless there is verification at each reassembly, the probability
for undetected error will increase with the number of times for undetected error will increase with the number of times
fragmentation is recursively applied, making IP-in-IP and UDP with fragmentation is recursively applied, making IP-in-IP and UDP with
zero checksum both vulnberable to undetected errors. zero checksum both vulnerable to undetected errors.
In conclusion fragmentation of packets with a zero-checksum does not In conclusion fragmentation of packets with a zero-checksum does not
worsen the situation compared to some other commonly used tunnel worsen the situation compared to some other commonly used tunnel
encapsulations. However, caution is needed for recursive tunneling encapsulations. However, caution is needed for recursive tunneling
without any additional verification at the different tunnel layers. without any additional verification at the different tunnel layers.
3.2. Validating the network path 3.2. Validating the network path
IP transports designed for use in the general Internet should not IP transports designed for use in the general Internet should not
assume specific path characteristics. Network protocols may reroute assume specific path characteristics. Network protocols may reroute
packets that change the set of routers and middleboxes along a path. packets that change the set of routers and middleboxes along a path.
Therefore transports such as TCP, SCTP and DCCP have been designed to Therefore transports such as TCP, SCTP and DCCP have been designed to
negotiate protocol parameters, adapt to different network path negotiate protocol parameters, adapt to different network path
characteristics, and receive feedback to verify that the current path characteristics, and receive feedback to verify that the current path
is suited to the intended application. Applications using UDP and is suited to the intended application. Applications using UDP and
UDP-Lite need to provide their own mechanisms to confirm the validity UDP-Lite need to provide their own mechanisms to confirm the validity
of the current network path. of the current network path.
The zero-checksum in UDP is explicitly disallowed in RFC2460. Thus The zero-checksum in UDP is explicitly disallowed in RFC2460. Thus it
it may be expected that any device on the path that has a reason to may be expected that any device on the path that has a reason to look
look beyond the IP header will consider such a packet as erroneous or beyond the IP header will consider such a packet as erroneous or
illegal and may likely discard it, unless the device is updated to illegal and may likely discard it, unless the device is updated to
support a new behavior. A pair of end-points intending to use a new support a new behavior. A pair of end-points intending to use a new
behavior will therefore not only need to ensure support at each end- behavior will therefore not only need to ensure support at each end-
point, but also that the path between them will deliver packets with point, but also that the path between them will deliver packets with
the new behavior. This may require negotiation or an explicit the new behavior. This may require negotiation or an explicit
mandate to use the new behavior by all nodes intended to use a new mandate to use the new behavior by all nodes intended to use a new
protocol. protocol.
Support along the path between end points may be guaranteed in Support along the path between end points may be guaranteed in
limited deployments by appropriate configuration. In general, it can limited deployments by appropriate configuration. In general, it can
be expected to take time for deployment of any updated behaviour to be expected to take time for deployment of any updated behaviour to
become ubiquitous. A sender will need to probe the path to verify become ubiquitous. A sender will need to probe the path to verify
the expected behavior. Path characteristics may change, and usage the expected behavior. Path characteristics may change, and usage
therefore should be robust and able to detect a failure of the path therefore should be robust and able to detect a failure of the path
under normal usage and re-negotiate. This will require periodic under normal usage and re-negotiate. This will require periodic
validation of the path, adding complexity to any solution using the validation of the path, adding complexity to any solution using the
new behavior. new behavior.
3.3. Applicability of method 3.3. Applicability of method
The expectation of the present proposal defined in The expectation of the present proposal defined in [I-D.ietf-6man-
[I-D.ietf-6man-udpchecksums] is that this change would only apply to udpchecksums] is that this change would only apply to IPv6 router
IPv6 router nodes that implement specific protocols that permit nodes that implement specific protocols that permit omission of UDP
omission of UDP checksums. However, the distinction between a router checksums. However, the distinction between a router and a host is
and a host is not always clear, especially at the transport level. not always clear, especially at the transport level. Systems (such
Systems (such as unix-based operating systems) routinely provide both as unix-based operating systems) routinely provide both functions.
functions. There is also no way to identify the role of a receiver There is also no way to identify the role of a receiver from a
from a received packet. received packet.
Any new method would therefore need a specific applicability Any new method would therefore need a specific applicability
statement indicating when the mechanism can (and can not) be used. statement indicating when the mechanism can (and can not) be used.
Enabling this, and ensuring correct interactions with the stack, Enabling this, and ensuring correct interactions with the stack,
implies much more than simply disabling the checksum algorithm for implies much more than simply disabling the checksum algorithm for
specific packets at the transport interface. specific packets at the transport interface.
The IETF should carefully consider constraints on sanctioning the use The IETF should carefully consider constraints on sanctioning the use
of any new transport mode. If this is specified and widely of any new transport mode. If this is specified and widely
available, it may be expected to be used by applications that are available, it may be expected to be used by applications that are
skipping to change at page 21, line 22 skipping to change at page 20, line 23
[RFC1141]. This would not require access to the whole packet, but [RFC1141]. This would not require access to the whole packet, but
does require fields to be collected across the header, and does require fields to be collected across the header, and
arithmetic operations on each packet. The method would only work arithmetic operations on each packet. The method would only work
for packets that contain a 2's complement transport checksum (i.e. for packets that contain a 2's complement transport checksum (i.e.
it would not be appropriate for SCTP or when IP fragmentation is it would not be appropriate for SCTP or when IP fragmentation is
used). used).
o UDP-Lite with the checksum coverage set to only the header portion o UDP-Lite with the checksum coverage set to only the header portion
of a packet. This requires a pseudo header checksum calculation of a packet. This requires a pseudo header checksum calculation
only on the encapsulating packet header. The computed checksum only on the encapsulating packet header. The computed checksum
value may be cached (before adding the Length field) for each value may be cached (before adding the Length field) for each flow
flow/destination and subsequently combined with the Length of each /destination and subsequently combined with the Length of each
packet to minimise per-packet processing. This value is combined packet to minimise per-packet processing. This value is combined
with the UDP payload length for the pseudo header, however this with the UDP payload length for the pseudo header, however this
length is expected to be known when performing packet forwarding. length is expected to be known when performing packet forwarding.
o The proposed UDP Tunnel Transport, UDPTT [UDPTT] suggested a o The proposed UDP Tunnel Transport, UDPTT [UDPTT] suggested a
method where UDP would be modified to derive the checksum only method where UDP would be modified to derive the checksum only
from the encapsulating packet protocol header. This value does from the encapsulating packet protocol header. This value does
not change between packets in a single flow. The value may be not change between packets in a single flow. The value may be
cached per flow/destination to minimise per-packet processing. cached per flow/destination to minimise per-packet processing.
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to drop the packet. The main downside is that it would be to drop the packet. The main downside is that it would be
impossible to identify a UDP packet (in the network or an impossible to identify a UDP packet (in the network or an
endpoint) that is treated in this way compared to a packet that endpoint) that is treated in this way compared to a packet that
has actually been corrupted. has actually been corrupted.
o A method has been proposed that uses a new (to be defined) IPv6 o A method has been proposed that uses a new (to be defined) IPv6
Destination Options Header to provide an end-to-end validation Destination Options Header to provide an end-to-end validation
check at the network layer. This would allow an endpoint to check at the network layer. This would allow an endpoint to
verify delivery to an appropriate end point, but would also verify delivery to an appropriate end point, but would also
require IPv6 nodes to correctly handle the additional header, and require IPv6 nodes to correctly handle the additional header, and
would require changes to middlebox behavior (e.g. when used with a would require changes to middlebox behavior (e.g. when used with
NAT that always adjusts the checksum value). a NAT that always adjusts the checksum value).
o UDP modified to disable checksum processing o UDP modified to disable checksum processing [I-D.ietf-6man-
[I-D.ietf-6man-udpchecksums]. This requires no checksum udpchecksums]. This requires no checksum calculation, but would
calculation, but would require constraints on appropriate usage require constraints on appropriate usage and updates to end-points
and updates to end-points and middleboxes. and middleboxes.
o IP-in-IP tunneling. As this method completely dispenses with a o IP-in-IP tunneling. As this method completely dispenses with a
transport protocol in the outer-layer it has reduced overhead and transport protocol in the outer-layer it has reduced overhead and
complexity, but also reduced functionality. There is no outer complexity, but also reduced functionality. There is no outer
checksum over the packet and also no ports to perform checksum over the packet and also no ports to perform
demultiplexing between different tunnel types. This reduces the demultiplexing between different tunnel types. This reduces the
information available upon which a load balancer may act. information available upon which a load balancer may act.
These options are compared and discussed further in the following These options are compared and discussed further in the following
sections. sections.
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have a good probability of traversal, because most middleboxes have a good probability of traversal, because most middleboxes
perform an incremental checksum update. UDPTT may also traverse a perform an incremental checksum update. UDPTT may also traverse a
middlebox with this behaviour. However, a middlebox on the path that middlebox with this behaviour. However, a middlebox on the path that
attempts to verify a standard checksum will not forward packets using attempts to verify a standard checksum will not forward packets using
either of these methods, preventing traversal. The methods that either of these methods, preventing traversal. The methods that
ignores the checksum has an additional downside in that middlebox ignores the checksum has an additional downside in that middlebox
traversal can not be improved, because there is no way to identify traversal can not be improved, because there is no way to identify
which packets use the modified checksum behaviour. which packets use the modified checksum behaviour.
IP-in-IP or GRE tunnels offer good traversal of middleboxes that have IP-in-IP or GRE tunnels offer good traversal of middleboxes that have
not been designed for security, e.g. firewalls. However, firewalls not been designed for security, e.g. firewalls. However, firewalls
may be expected to be configured to block general tunnels as they may be expected to be configured to block general tunnels as they
present a large attack surface. present a large attack surface.
A new IPv6 Destination Options header will suffer traversal issues A new IPv6 Destination Options header will suffer traversal issues
with middleboxes, especially Firewalls and NATs, and will likely with middleboxes, especially Firewalls and NATs, and will likely
require them to be updated before the extension header is passed. require them to be updated before the extension header is passed.
Packets using UDP with a zero checksum will not be passed by any Packets using UDP with a zero checksum will not be passed by any
middlebox that validates the checksum using RFC 2460 or updates the middlebox that validates the checksum using RFC 2460 or updates the
checksum field, such as NAT or firewalls. This would require an checksum field, such as NAT or firewalls. This would require an
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number. Once enabled, the method to support incremental checksum number. Once enabled, the method to support incremental checksum
update would be identical to that for UDP, but different for checksum update would be identical to that for UDP, but different for checksum
validation. validation.
4.2.2. Load Balancing 4.2.2. Load Balancing
The usefulness of solutions for load balancers depends on the The usefulness of solutions for load balancers depends on the
difference in entropy in the headers for different flows that can be difference in entropy in the headers for different flows that can be
included in a hash function. All the proposals that use the UDP included in a hash function. All the proposals that use the UDP
protocol number have equal behavior. UDP-Lite has the potential for protocol number have equal behavior. UDP-Lite has the potential for
equally good behavior as for UDP. However, UDP-Lite is currently equally good behavior as for UDP. However, UDP-Lite is currently
likely to not be supported by deployed hashing mechanisms, which may likely to not be supported by deployed hashing mechanisms, which may
cause a load balancer to not use the transport header in the computed cause a load balancer to not use the transport header in the computed
hash. A load balancer that only uses the IP header will have low hash. A load balancer that only uses the IP header will have low
entropy, but could be improved by including the IPv6 the flow label, entropy, but could be improved by including the IPv6 the flow label,
providing that the tunnel ingress ensures that different flow labels providing that the tunnel ingress ensures that different flow labels
are assigned to different flows. However, a transition to the common are assigned to different flows. However, a transition to the common
use of good quality flow labels is likely to take time to deploy. use of good quality flow labels is likely to take time to deploy.
4.2.3. Ingress and Egress Performance Implications 4.2.3. Ingress and Egress Performance Implications
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checksum on reception, the Option Header, UDPTT and UDP-Lite will checksum on reception, the Option Header, UDPTT and UDP-Lite will
likely incur additional complexities in the application to likely incur additional complexities in the application to
incorporate a negotiation and validation mechanism. incorporate a negotiation and validation mechanism.
4.2.4. Deployability 4.2.4. Deployability
The major factors influencing deployability of these solutions are a The major factors influencing deployability of these solutions are a
need to update both end-points, a need for negotiation and the need need to update both end-points, a need for negotiation and the need
to update middleboxes. These are summarised below: to update middleboxes. These are summarised below:
o The solution with the best deployability is regular UDP. This o The solution with the best deployability is regular UDP. This
requires no changes and has good middlebox traversal requires no changes and has good middlebox traversal
characteristics. characteristics.
o The next easiest to deploy is the delta checksum solution. This o The next easiest to deploy is the delta checksum solution. This
does not modify the protocol on the wire and only needs changes in does not modify the protocol on the wire and only needs changes in
tunnel ingress. tunnel ingress.
o IP-in-IP tunnels should not require changes to the end-points, but o IP-in-IP tunnels should not require changes to the end-points, but
raise issues when traversing firewalls and other security-type raise issues when traversing firewalls and other security-type
devices, which are expected to require updates. devices, which are expected to require updates.
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intended to be processed by a specific tunnel egress or that the intended to be processed by a specific tunnel egress or that the
inner packet was correct. inner packet was correct.
4.2.6. Comparison Summary 4.2.6. Comparison Summary
The comparisons above may be summarised as "there is no silver bullet The comparisons above may be summarised as "there is no silver bullet
that will slay all the issues". One has to select which down side(s) that will slay all the issues". One has to select which down side(s)
can best be lived with. Focusing on the existing solutions, this can can best be lived with. Focusing on the existing solutions, this can
be summarized as: be summarized as:
Regular UDP: Good middlebox traversal and load balancing and Regular UDP: Good middlebox traversal and load balancing and
multiplexing, requiring a checksum in the outer headers covering multiplexing, requiring a checksum in the outer headers covering
the whole packet. the whole packet.
IP in IP: A low complexity encapsulation, with limited middlebox IP in IP: A low complexity encapsulation, with limited middlebox
traversal, no multiplexing support, and currently poor load traversal, no multiplexing support, and currently poor load
balancing support that could improve over time. balancing support that could improve over time.
UDP-Lite: A medium complexity encapsulation, with good multiplexing UDP-Lite: A medium complexity encapsulation, with good multiplexing
support, limited middlebox traversal, but possible to improve over support, limited middlebox traversal, but possible to improve over
time, currently poor load balancing support that could improve time, currently poor load balancing support that could improve
over time, in most cases requiring application level negotiation over time, in most cases requiring application level negotiation
and validation. and validation.
The delta-checksum is an optimization in the processing of UDP, as The delta-checksum is an optimization in the processing of UDP, as
such it exhibits some of the drawbacks of using regular UDP. such it exhibits some of the drawbacks of using regular UDP.
The remaining proposals may be described in similar terms: The remaining proposals may be described in similar terms:
Zero-Checksum: A low complexity encapsulation, with good Zero-Checksum: A low complexity encapsulation, with good multiplexing
multiplexing support, limited middlebox traversal that could support, limited middlebox traversal that could improve over time,
improve over time, good load balancing support, in most cases good load balancing support, in most cases requiring application
requiring application level negotiation and validation. level negotiation and validation.
UDPTT: A medium complexity encapsulation, with good multiplexing UDPTT: A medium complexity encapsulation, with good multiplexing
support, limited middlebox traversal, but possible to improve over support, limited middlebox traversal, but possible to improve over
time, good load balancing support, in most cases requiring time, good load balancing support, in most cases requiring
application level negotiation and validation. application level negotiation and validation.
IPv6 Destination Option IP in IP tunneling: A medium complexity, IPv6 Destination Option IP in IP tunneling: A medium complexity, with
with no multiplexing support, limited middlebox traversal, no multiplexing support, limited middlebox traversal, currently
currently poor load balancing support that could improve over poor load balancing support that could improve over time, in most
time, in most cases requiring application level negotiation and cases requiring application level negotiation and validation.
validation.
IPv6 Destination Option combined with UDP Zero-checksuming: A medium IPv6 Destination Option combined with UDP Zero-checksuming: A medium
complexity encapsulation, with good multiplexing support, limited complexity encapsulation, with good multiplexing support, limited
load balancing support that could improve over time, in most cases load balancing support that could improve over time, in most cases
requiring application level negotiation and validation. requiring application level negotiation and validation.
Ignore the checksum on reception: A low complexity encapsulation, Ignore the checksum on reception: A low complexity encapsulation,
with good multiplexing support, medium middlebox traversal that with good multiplexing support, medium middlebox traversal that
never can improve, good load balancing support, in most cases never can improve, good load balancing support, in most cases
requiring application level negotiation and validation. requiring application level negotiation and validation.
There is no clear single optimum solution. If the most important There is no clear single optimum solution. If the most important
need is to traverse middleboxes, then the best choice is to stay with need is to traverse middleboxes, then the best choice is to stay with
regular UDP and consider the optimizations that may be required to regular UDP and consider the optimizations that may be required to
perform the checksumming. If one can live with limited middlebox perform the checksumming. If one can live with limited middlebox
traversal, low complexity is necessary and one does not require load traversal, low complexity is necessary and one does not require load
balancing, then IP-in-IP tunneling is the simplest. If one wants balancing, then IP-in-IP tunneling is the simplest. If one wants
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8. If a method proposes recursive tunnels, it needs to provide 8. If a method proposes recursive tunnels, it needs to provide
guidance that is appropriate for all use-cases. Restrictions may guidance that is appropriate for all use-cases. Restrictions may
be needed to the use of a tunnel encapsulations and the use of be needed to the use of a tunnel encapsulations and the use of
recursive tunnels (e.g. Necessary when the endpoint is not recursive tunnels (e.g. Necessary when the endpoint is not
verified). verified).
9. IPv6 nodes that receive ICMPv6 messages that refer to packets 9. IPv6 nodes that receive ICMPv6 messages that refer to packets
with a zero UDP checksum must provide appropriate checks with a zero UDP checksum must provide appropriate checks
concerning the consistency of the reported packet to verify that concerning the consistency of the reported packet to verify that
the reported packet actually originated from the node, before the reported packet actually originated from the node, before
acting upon the information (e.g. validating the address and port acting upon the information (e.g. validating the address and
numbers in the ICMPv6 message body). port numbers in the ICMPv6 message body).
Deployment of the new method needs to remain restricted to endpoints Deployment of the new method needs to remain restricted to endpoints
that explicitly enable this mode and adopt the above procedures. Any that explicitly enable this mode and adopt the above procedures. Any
middlebox that examines or interacts with the UDP header over IPv6 middlebox that examines or interacts with the UDP header over IPv6
should support the new method. should support the new method.
6. Summary 6. Summary
This document examines the role of the transport checksum when used This document examines the role of the transport checksum when used
with IPv6, as defined in RFC2460. with IPv6, as defined in RFC2460.
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zero-checksum packets. Thus, the enabling of zero-checksum needs to zero-checksum packets. Thus, the enabling of zero-checksum needs to
be at a port level, not for the entire host or for all use of an be at a port level, not for the entire host or for all use of an
interface. interface.
The implications on firewalls, NATs and other middleboxes need to be The implications on firewalls, NATs and other middleboxes need to be
considered. It is not expected that IPv6 NATs handle IPv6 UDP considered. It is not expected that IPv6 NATs handle IPv6 UDP
datagrams in the same way that they handle IPv4 UDP datagrams. This datagrams in the same way that they handle IPv4 UDP datagrams. This
possibly reduces the need to update the checksum. Firewalls are possibly reduces the need to update the checksum. Firewalls are
intended to be configured, and therefore may need to be explicitly intended to be configured, and therefore may need to be explicitly
updated to allow new services or protocols. IPv6 middlebox updated to allow new services or protocols. IPv6 middlebox
deployment is not yet as prolific as it is in IPv4. Thus, relatively deployment is not yet as prolific as it is in IPv4. Thus, relatively
few current middleboxes may actually block IPv6 UDP with a zero few current middleboxes may actually block IPv6 UDP with a zero
checksum. checksum.
In general, UDP-based applications need to employ a mechanism that In general, UDP-based applications need to employ a mechanism that
allows a large percentage of the corrupted packets to be removed allows a large percentage of the corrupted packets to be removed
before they reach an application, both to protect the data stream of before they reach an application, both to protect the data stream of
the application and the control plane of higher layer protocols. the application and the control plane of higher layer protocols.
These checks are currently performed by the UDP checksum for IPv6, or These checks are currently performed by the UDP checksum for IPv6, or
the reduced checksum for UDP-Lite when used with IPv6. the reduced checksum for UDP-Lite when used with IPv6.
The use of UDP with no checksum has merits for some applications, The use of UDP with no checksum has merits for some applications,
such as tunnel encapsulation, and is widely used in IPv4. However, such as tunnel encapsulation, and is widely used in IPv4. However,
there are dangers for IPv6: There is a bigger risk of corruption and there are dangers for IPv6: There is a bigger risk of corruption and
miss-delivery when using zero-checksum in IPv6 compared to IPv4 due miss-delivery when using zero-checksum in IPv6 compared to IPv4 due
to the removed IP header checksum. Thus, applications need to make a to the removed IP header checksum. Thus, applications need to make a
new evaluation of the risks of enabling a zero-checksum. Some new evaluation of the risks of enabling a zero-checksum. Some
applications will need to re-consider their usage of zero-checksum, applications will need to re-consider their usage of zero-checksum,
and possibly consider a solution that at least provides the same and possibly consider a solution that at least provides the same
delivery protection as for IPv4, for example by utilizing UDP-Lite, delivery protection as for IPv4, for example by utilizing UDP-Lite,
or by enabling the UDP checksum. Tunnel applications using UDP for or by enabling the UDP checksum. Tunnel applications using UDP for
encapsulation can in many case use zero-checksum without significant encapsulation can in many case use zero-checksum without significant
impact on the corruption rate. In some cases, the use of checksum impact on the corruption rate. In some cases, the use of checksum
skipping to change at page 30, line 4 skipping to change at page 28, line 29
Recursive tunneling and fragmentation is a difficult issue relating Recursive tunneling and fragmentation is a difficult issue relating
to tunnels in general. There is an increased risk of an error in the to tunnels in general. There is an increased risk of an error in the
inner-most packet when fragmentation when several layers of tunneling inner-most packet when fragmentation when several layers of tunneling
and several different reassembly processes are run without any and several different reassembly processes are run without any
verification of correctness. This issue requires future thought and verification of correctness. This issue requires future thought and
consideration. consideration.
The conclusion is that UDP zero checksum in IPv6 should be The conclusion is that UDP zero checksum in IPv6 should be
standardized, as it satisfies usage requirements that are currently standardized, as it satisfies usage requirements that are currently
difficult to address. We do note that a safe deployment of zero- difficult to address. We do note that a safe deployment of zero-
checksum will need to follow a set of constraints listed in checksum will need to follow a set of constraints listed in Section
Section 5.1. 5.1.
7. Acknowledgements 7. Acknowledgements
Brian Haberman, Brian Carpenter, Magaret Wasserman, Lars Eggert, Brian Haberman, Brian Carpenter, Magaret Wasserman, Lars Eggert,
others in the TSV directorate. others in the TSV directorate.
Thanks also to: Remi Denis-Courmont, Pekka Savola and many others who Thanks also to: Remi Denis-Courmont, Pekka Savola and many others who
contributed comments and ideas via the 6man, behave, lisp and mboned contributed comments and ideas via the 6man, behave, lisp and mboned
lists. lists.
skipping to change at page 30, line 31 skipping to change at page 28, line 56
Transport checksums provide the first stage of protection for the Transport checksums provide the first stage of protection for the
stack, although they can not be considered authentication mechanisms. stack, although they can not be considered authentication mechanisms.
These checks are also desirable to ensure packet counters correctly These checks are also desirable to ensure packet counters correctly
log actual activity, and can be used to detect unusual behaviours. log actual activity, and can be used to detect unusual behaviours.
10. References 10. References
10.1. Normative References 10.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
September 1981. 1981.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
RFC 793, September 1981. 793, September 1981.
[RFC1071] Braden, R., Borman, D., Partridge, C., and W. Plummer, [RFC1071] Braden, R., Borman, D., Partridge, C. and W. Plummer,
"Computing the Internet checksum", RFC 1071, "Computing the Internet checksum", RFC 1071, September
September 1988. 1988.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC2460] Deering, S.E. and R.M. Hinden, "Internet Protocol, Version
(IPv6) Specification", RFC 2460, December 1998. 6 (IPv6) Specification", RFC 2460, December 1998.
10.2. Informative References 10.2. Informative References
[ECMP] "Using the IPv6 flow label for equal cost multipath [ECMP] "Using the IPv6 flow label for equal cost multipath
routing in tunnels (draft-carpenter-flow-ecmp)". routing in tunnels (draft-carpenter-flow-ecmp)", .
[I-D.ietf-6man-udpchecksums] [I-D.ietf-6man-udpchecksums]
Eubanks, M. and P. Chimento, "UDP Checksums for Tunneled Eubanks, M. and P. Chimento, "UDP Checksums for Tunneled
Packets", draft-ietf-6man-udpchecksums-01 (work in Packets", Internet-Draft draft-ietf-6man-udpchecksums-02,
progress), October 2011. March 2012.
[I-D.ietf-intarea-tunnels] [I-D.ietf-intarea-tunnels]
Touch, J. and M. Townsley, "Tunnels in the Internet Touch, J. and M. Townsley, "Tunnels in the Internet
Architecture", draft-ietf-intarea-tunnels-00 (work in Architecture", Internet-Draft draft-ietf-intarea-
progress), March 2010. tunnels-00, March 2010.
[I-D.ietf-mboned-auto-multicast] [I-D.ietf-mboned-auto-multicast]
Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., Bumgardner, G., "Automatic Multicast Tunneling", Internet-
Pusateri, T., and T. Morin, "Automatic IP Multicast Draft draft-ietf-mboned-auto-multicast-14, June 2012.
Tunneling", draft-ietf-mboned-auto-multicast-11 (work in
progress), July 2011.
[LISP] D. Farinacci et al, "Locator/ID Separation Protocol [LISP] D. Farinacci et al, , "Locator/ID Separation Protocol
(LISP)", March 2009. (LISP)", March 2009.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980. August 1980.
[RFC1141] Mallory, T. and A. Kullberg, "Incremental updating of the [RFC1141] Mallory, T. and A. Kullberg, "Incremental updating of the
Internet checksum", RFC 1141, January 1990. Internet checksum", RFC 1141, January 1990.
[RFC1624] Rijsinghani, A., "Computation of the Internet Checksum via [RFC1624] Rijsinghani, A., "Computation of the Internet Checksum via
Incremental Update", RFC 1624, May 1994. Incremental Update", RFC 1624, May 1994.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R. and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D., [RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J. and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89, Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, July 2004. RFC 3819, July 2004.
[RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., and [RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E. and
G. Fairhurst, "The Lightweight User Datagram Protocol G. Fairhurst, "The Lightweight User Datagram Protocol
(UDP-Lite)", RFC 3828, July 2004. (UDP-Lite)", RFC 3828, July 2004.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control [RFC4443] Conta, A., Deering, S. and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006. Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly [RFC4963] Heffner, J., Mathis, M. and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963, July 2007. Errors at High Data Rates", RFC 4963, July 2007.
[RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines [RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
for Application Designers", BCP 145, RFC 5405, for Application Designers", BCP 145, RFC 5405, November
November 2008. 2008.
[RFC5415] Calhoun, P., Montemurro, M., and D. Stanley, "Control And [RFC5415] Calhoun, P., Montemurro, M. and D. Stanley, "Control And
Provisioning of Wireless Access Points (CAPWAP) Protocol Provisioning of Wireless Access Points (CAPWAP) Protocol
Specification", RFC 5415, March 2009. Specification", RFC 5415, March 2009.
[RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments", [RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments",
RFC 5722, December 2009. RFC 5722, December 2009.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation [RFC6145] Li, X., Bao, C. and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, April 2011. Algorithm", RFC 6145, April 2011.
[Sigcomm2000] [Sigcomm2000]
Jonathan Stone and Craig Partridge , "When the CRC and TCP Jonathan Stone and Craig Partridge , , "When the CRC and
Checksum Disagree", 2000. TCP Checksum Disagree", 2000.
[UDPTT] G Fairhurst, "The UDP Tunnel Transport mode", Feb 2010. [UDPTT] G Fairhurst, , "The UDP Tunnel Transport mode", Feb 2010.
Appendix A. Document Change History Appendix A. Document Change History
{RFC EDITOR NOTE: This section must be deleted prior to publication} {RFC EDITOR NOTE: This section must be deleted prior to publication}
Individual Draft 00 This is the first DRAFT of this document - It Individual Draft 00 This is the first DRAFT of this document - It
contains a compilation of various discussions and contributions contains a compilation of various discussions and contributions
from a variety of IETF WGs, including: mboned, tsv, 6man, lisp, from a variety of IETF WGs, including: mboned, tsv, 6man, lisp,
and behave. This includes contributions from Magnus with text on and behave. This includes contributions from Magnus with text on
RTP, and various updates. RTP, and various updates.
Individual Draft 01 Individual Draft 01
* This version corrects some typos and editorial NiTs and adds * This version corrects some typos and editorial NiTs and adds
discussion of the need to negotiate and verify operation of a discussion of the need to negotiate and verify operation of a
new mechanism (3.3.4). new mechanism (3.3.4).
skipping to change at page 33, line 6 skipping to change at page 31, line 4
Individual Draft 02 Individual Draft 02
* Version -02 corrects some typos and editorial NiTs. * Version -02 corrects some typos and editorial NiTs.
* Added reference to ECMP for tunnels. * Added reference to ECMP for tunnels.
* Clarifies the recommendations at the end of the document. * Clarifies the recommendations at the end of the document.
Working Group Draft 00 Working Group Draft 00
* Working Group Version -00 corrects some typos and removes much * Working Group Version -00 corrects some typos and removes much
of rationale for UDPTT. It also adds some discussion of IPv6 of rationale for UDPTT. It also adds some discussion of IPv6
extension header. extension header.
Working Group Draft 01 Working Group Draft 01
* Working Group Version -01 updates the rules and incorporates * Working Group Version -01 updates the rules and incorporates
off-list feedback. This version is intended for wider review off-list feedback. This version is intended for wider review
within the 6man working group. within the 6man working group.
Working Group Draft 02 Working Group Draft 02
skipping to change at page 33, line 41 skipping to change at page 31, line 38
* Editorial updates * Editorial updates
Working Group Draft 04 Working Group Draft 04
* Resubmission only updating the AMT and RFC2765 references. * Resubmission only updating the AMT and RFC2765 references.
Working Group Draft 05 Working Group Draft 05
* Resubmission to correct editorial NiTs - thanks to Bill Atwood * Resubmission to correct editorial NiTs - thanks to Bill Atwood
for noting these. for noting these.Group Draft 05.
Working Group Draft 06
* Resubmission to keep draft alive (spelling updated from 05).
Authors' Addresses Authors' Addresses
Godred Fairhurst Godred Fairhurst
University of Aberdeen University of Aberdeen
School of Engineering School of Engineering
Aberdeen, AB24 3UE, Aberdeen, AB24 3UE,
Scotland, UK Scotland, UK
Phone:
Email: gorry@erg.abdn.ac.uk Email: gorry@erg.abdn.ac.uk
URI: http://www.erg.abdn.ac.uk/users/gorry URI: http://www.erg.abdn.ac.uk/users/gorry
Magnus Westerlund Magnus Westerlund
Ericsson Ericsson
Farogatan 6 Farogatan 6
Stockholm, SE-164 80 Stockholm, SE-164 80
Sweden Sweden
Phone: +46 8 719 0000 Phone: +46 8 719 0000
Fax:
Email: magnus.westerlund@ericsson.com Email: magnus.westerlund@ericsson.com
URI:
 End of changes. 96 change blocks. 
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