draft-ietf-bfd-v4v6-1hop-07.txt   draft-ietf-bfd-v4v6-1hop-08.txt 
Network Working Group D. Katz Network Working Group D. Katz
Internet Draft Juniper Networks Internet Draft Juniper Networks
D. Ward D. Ward
Cisco Systems Cisco Systems
Expires: July, 2008 January, 2008 Expires: September, 2008 March, 2008
BFD for IPv4 and IPv6 (Single Hop) BFD for IPv4 and IPv6 (Single Hop)
draft-ietf-bfd-v4v6-1hop-07.txt draft-ietf-bfd-v4v6-1hop-08.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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to monitor router-host connectivity, among other applications. to monitor router-host connectivity, among other applications.
This document describes the particulars necessary to use BFD in this This document describes the particulars necessary to use BFD in this
environment. Interactions between BFD and other protocols and system environment. Interactions between BFD and other protocols and system
functions are described in the BFD Generic Applications document functions are described in the BFD Generic Applications document
[BFD-GENERIC]. [BFD-GENERIC].
2. Applications and Limitations 2. Applications and Limitations
This application of BFD can be used by any pair of systems This application of BFD can be used by any pair of systems
communicating via IPv4 and/or IPv6 across a single IP hop that can be communicating via IPv4 and/or IPv6 across a single IP hop that is
associated with an incoming interface. This includes, but is not associated with an incoming interface. This includes, but is not
limited to, physical media, virtual circuits, and tunnels. limited to, physical media, virtual circuits, and tunnels.
Each BFD session between a pair of systems MUST traverse a separate Each BFD session between a pair of systems MUST traverse a separate
path in both directions. path in both directions.
If BFD is to be used in conjunction with both IPv4 and IPv6 on a If BFD is to be used in conjunction with both IPv4 and IPv6 on a
particular link, a separate BFD session MUST be established for each particular link, a separate BFD session MUST be established for each
protocol (and thus encapsulated by that protocol) over that link. protocol (and thus encapsulated by that protocol) over that link.
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demultiplexing incoming BFD Control packets, but ultimately the demultiplexing incoming BFD Control packets, but ultimately the
mechanisms in [BFD] MUST be used to demultiplex incoming packets to mechanisms in [BFD] MUST be used to demultiplex incoming packets to
the proper session. the proper session.
BFD Echo packets MUST be transmitted in UDP packets with destination BFD Echo packets MUST be transmitted in UDP packets with destination
UDP port 3785 in an IPv4 packet. The setting of the UDP source port UDP port 3785 in an IPv4 packet. The setting of the UDP source port
is outside the scope of this specification. The destination address is outside the scope of this specification. The destination address
MUST be chosen in such a way as to cause the remote system to forward MUST be chosen in such a way as to cause the remote system to forward
the packet back to the local system. The source address MUST be the packet back to the local system. The source address MUST be
chosen in such a way as to preclude the remote system from generating chosen in such a way as to preclude the remote system from generating
ICMP Redirect messages. In particular, the source address MUST NOT ICMP Redirect messages. In particular, the source address SHOULD NOT
be part of the subnet bound to the interface over which the BFD Echo be part of the subnet bound to the interface over which the BFD Echo
packet is being transmitted. packet is being transmitted, unless it is known by other means that
the remote system will not send Redirects.
4.2. BFD for IPv6 4.2. BFD for IPv6
In the case of IPv6, BFD Control packets MUST be transmitted in UDP In the case of IPv6, BFD Control packets MUST be transmitted in UDP
packets with destination port 3784, within an IPv6 packet. The packets with destination port 3784, within an IPv6 packet. The
source port MUST be in the range 49152 through 65535. The same UDP source port MUST be in the range 49152 through 65535. The same UDP
source port number MUST be used for all BFD Control packets source port number MUST be used for all BFD Control packets
associated with a particular session. The source port number SHOULD associated with a particular session. The source port number SHOULD
be unique among all BFD sessions on the system. If more than 16384 be unique among all BFD sessions on the system. If more than 16384
BFD sessions are simultaneously active, UDP source port numbers MAY BFD sessions are simultaneously active, UDP source port numbers MAY
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mechanisms in [BFD] MUST be used to demultiplex incoming packets to mechanisms in [BFD] MUST be used to demultiplex incoming packets to
the proper session. the proper session.
BFD Echo packets MUST be transmitted in UDP packets with destination BFD Echo packets MUST be transmitted in UDP packets with destination
UDP port 3785 in an IPv6 packet. The setting of the UDP source port UDP port 3785 in an IPv6 packet. The setting of the UDP source port
is outside the scope of this specification. The source and is outside the scope of this specification. The source and
destination addresses MUST both be associated with the local system. destination addresses MUST both be associated with the local system.
The destination address MUST be chosen in such a way as to cause the The destination address MUST be chosen in such a way as to cause the
remote system to forward the packet back to the local system. remote system to forward the packet back to the local system.
5. TTL/Hop Count Issues 5. TTL/Hop Limit Issues
If BFD authentication is not in use on a session, all BFD Control If BFD authentication is not in use on a session, all BFD Control
packets for the session MUST be sent with a TTL or Hop Count value of packets for the session MUST be sent with a TTL or Hop Limit value of
255. All received BFD Control packets that are demultiplexed to the 255. All received BFD Control packets that are demultiplexed to the
session MUST be discarded if the received TTL or Hop Count is not session MUST be discarded if the received TTL or Hop Limit is not
equal to 255. A discussion of this mechanism can be found in [GTSM]. equal to 255. A discussion of this mechanism can be found in [GTSM].
If BFD authentication is in use on a session, all BFD Control packets If BFD authentication is in use on a session, all BFD Control packets
MUST be sent with a TTL or Hop Count value of 255. All received BFD MUST be sent with a TTL or Hop Limit value of 255. All received BFD
Control packets that are demultiplexed the session MAY be discarded Control packets that are demultiplexed the session MAY be discarded
if the received TTL or Hop Count is not equal to 255. if the received TTL or Hop Limit is not equal to 255.
In the context of this section, "authentication in use" means that In the context of this section, "authentication in use" means that
the system is sending BFD control packets with the Authentication bit the system is sending BFD control packets with the Authentication bit
set and with the Authentication Section included, and that all set and with the Authentication Section included, and that all
unauthenticated packets demultiplexed to the session are discarded, unauthenticated packets demultiplexed to the session are discarded,
per the BFD base specification. per the BFD base specification.
6. Addressing Issues 6. Addressing Issues
On a subnetted network, BFD Control packets MUST be transmitted with Implementations MUST ensure that all BFD Control packets are
source and destination addresses that are part of the subnet transmitted over the one-hop path being protected by BFD.
(addressed from and to interfaces on the subnet.)
On an addressed but unsubnetted point-to-point link, BFD Control On a multiaccess network, BFD Control packets MUST be transmitted
packets MUST be transmitted with source and destination addresses with source and destination addresses that are part of the subnet
that match the addresses configured on that link. (addressed from and to interfaces on the subnet.)
On an unnumbered point-to-point link, the source address of a BFD On a point-to-point link, the source address of a BFD Control packet
Control packet MUST NOT be used to identify the session. This means MUST NOT be used to identify the session. This means that the
that the initial BFD packet MUST be accepted with any source address, initial BFD packet MUST be accepted with any source address, and that
and that subsequent BFD packets MUST be demultiplexed solely by the subsequent BFD packets MUST be demultiplexed solely by the Your
My Discriminator field (as is always the case.) This allows the Discriminator field (as is always the case.) This allows the source
source address to change if necessary. If the received source address to change if necessary. If the received source address
address changes, the local system MUST NOT use that address as the changes, the local system MUST NOT use that address as the
destination in outgoing BFD Control packets; rather it MUST continue destination in outgoing BFD Control packets; rather it MUST continue
to use the address configured at session creation. An implementation to use the address configured at session creation. An implementation
MAY notify the application that the neighbor's source address has MAY notify the application that the neighbor's source address has
changed, so that the application might choose to change the changed, so that the application might choose to change the
destination address or take some other action. Note that the TTL/Hop destination address or take some other action. Note that the TTL/Hop
Count check described in section 5 (or the use of authentication) Limit check described in section 5 (or the use of authentication)
precludes the BFD packets from having come from any source other than precludes the BFD packets from having come from any source other than
the immediate neighbor. the immediate neighbor.
7. BFD for use with Tunnels 7. BFD for use with Tunnels
A number of mechanisms are available to tunnel IPv4 and IPv6 over A number of mechanisms are available to tunnel IPv4 and IPv6 over
arbitrary topologies. If the tunnel mechanism does not decrement the arbitrary topologies. If the tunnel mechanism does not decrement the
TTL or hop count of the network protocol carried within, the TTL or Hop Limit of the network protocol carried within, the
mechanism described in this document may be used to provide liveness mechanism described in this document may be used to provide liveness
detection for the tunnel. The BFD Authentication mechanism SHOULD be detection for the tunnel. The BFD Authentication mechanism SHOULD be
used and is strongly encouraged. used and is strongly encouraged.
Normative References Normative References
[BFD] Katz, D., and Ward, D., "Bidirectional Forwarding Detection", [BFD] Katz, D., and Ward, D., "Bidirectional Forwarding Detection",
draft-ietf-bfd-base-07.txt, January, 2008. draft-ietf-bfd-base-07.txt, January, 2008.
[BFD-GENERIC] Katz, D., and Ward, D., "Generic Application of BFD", [BFD-GENERIC] Katz, D., and Ward, D., "Generic Application of BFD",
draft-ietf-bfd-generic-04.txt, January, 2008. draft-ietf-bfd-generic-04.txt, January, 2008.
[GTSM] Gill, V., et al, "The Generalized TTL Security Mechanism [GTSM] Gill, V., et al, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, October, 2007. (GTSM)", RFC 5082, October, 2007.
[KEYWORD] Bradner, S., "Key words for use in RFCs to Indicate [KEYWORD] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997. Requirement Levels", RFC 2119, March 1997.
Security Considerations Security Considerations
In this application, the use of TTL=255 on transmit and receive is In this application, the use of TTL=255 on transmit and receive,
viewed as supplying equivalent security characteristics to other coupled with an association to an incoming interface, is viewed as
protocols used in the infrastructure, as it is not trivially supplying equivalent security characteristics to other protocols used
spoofable. The security implications of this mechanism are further in the infrastructure, as it is not trivially spoofable. The
discussed in [GTSM]. security implications of this mechanism are further discussed in
[GTSM].
The security implications of the use of BFD Authentication are The security implications of the use of BFD Authentication are
discussed in [BFD]. discussed in [BFD].
The use of the TTL=255 check simultaneously with BFD Authentication The use of the TTL=255 check simultaneously with BFD Authentication
provides a low overhead mechanism for discarding a class of provides a low overhead mechanism for discarding a class of
unauthorized packets and may be useful in implementations in which unauthorized packets and may be useful in implementations in which
cryptographic checksum use is susceptable to denial of service cryptographic checksum use is susceptable to denial of service
attacks. The use or non-use of this mechanism does not impact attacks. The use or non-use of this mechanism does not impact
interoperability. interoperability.
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Dave Ward Dave Ward
Cisco Systems Cisco Systems
170 W. Tasman Dr. 170 W. Tasman Dr.
San Jose, CA 95134 USA San Jose, CA 95134 USA
Phone: +1-408-526-4000 Phone: +1-408-526-4000
Email: dward@cisco.com Email: dward@cisco.com
Changes from the previous draft Changes from the previous draft
This is a reissue of the previous version. There are only minor Section 6 was changed to lump all point-to-point link types together.
editorial changes. Otherwise, only minor editorial changes were made.
IPR Disclaimer IPR Disclaimer
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this document or the extent to which any license under such rights this document or the extent to which any license under such rights
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made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
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THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
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Acknowledgement Acknowledgement
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
This document expires in July, 2008. This document expires in September, 2008.
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