--- 1/draft-ietf-v6ops-tunnel-loops-06.txt 2011-05-07 01:15:30.000000000 +0200 +++ 2/draft-ietf-v6ops-tunnel-loops-07.txt 2011-05-07 01:15:30.000000000 +0200 @@ -1,49 +1,52 @@ Network Working Group G. Nakibly Internet-Draft National EW Research & Intended status: Informational Simulation Center -Expires: October 1, 2011 F. Templin +Expires: November 8, 2011 F. Templin Boeing Research & Technology - March 30, 2011 + May 7, 2011 Routing Loop Attack using IPv6 Automatic Tunnels: Problem Statement and Proposed Mitigations - draft-ietf-v6ops-tunnel-loops-06.txt + draft-ietf-v6ops-tunnel-loops-07.txt Abstract This document is concerned with security vulnerabilities in IPv6-in- IPv4 automatic tunnels. These vulnerabilities allow an attacker to take advantage of inconsistencies between the IPv4 routing state and the IPv6 routing state. The attack forms a routing loop which can be abused as a vehicle for traffic amplification to facilitate DoS attacks. The first aim of this document is to inform on this attack and its root causes. The second aim is to present some possible - mitigation measures. + mitigation measures. It should be noted that at the time of this + writing there are no known reports of malicious attacks exploiting + these vulnerabilities. Nonetheless, these vulnerabilities can be + activated by accidental misconfiguarion. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on October 1, 2011. + This Internet-Draft will expire on November 8, 2011. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -62,39 +65,39 @@ 3.1.1. Neighbor Cache Check . . . . . . . . . . . . . . . . . 7 3.1.2. Known IPv4 Address Check . . . . . . . . . . . . . . . 8 3.2. Operational Measures . . . . . . . . . . . . . . . . . . . 8 3.2.1. Avoiding a Shared IPv4 Link . . . . . . . . . . . . . 8 3.2.2. A Single Border Router . . . . . . . . . . . . . . . . 9 3.2.3. A Comprehensive List of Tunnel Routers . . . . . . . . 9 3.2.4. Avoidance of On-link Prefixes . . . . . . . . . . . . 10 3.3. Destination and Source Address Checks . . . . . . . . . . 15 3.3.1. Known IPv6 Prefix Check . . . . . . . . . . . . . . . 16 4. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 17 - 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 + 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 6. Security Considerations . . . . . . . . . . . . . . . . . . . 18 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 8.1. Normative References . . . . . . . . . . . . . . . . . . . 18 8.2. Informative References . . . . . . . . . . . . . . . . . . 19 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 1. Introduction IPv6-in-IPv4 tunnels are an essential part of many migration plans for IPv6. They allow two IPv6 nodes to communicate over an IPv4-only - network. Automatic tunnels that assign non-link-local IPv6 prefixes - with stateless address mapping properties (hereafter called - "automatic tunnels") are a category of tunnels in which a tunneled - packet's egress IPv4 address is embedded within the destination IPv6 - address of the packet. An automatic tunnel's router is a router that - respectively encapsulates and decapsulates the IPv6 packets into and - out of the tunnel. + network. Automatic tunnels that assign IPv6 prefixes with stateless + address mapping properties (hereafter called "automatic tunnels") are + a category of tunnels in which a tunneled packet's egress IPv4 + address is embedded within the destination IPv6 address of the + packet. An automatic tunnel's router is a router that respectively + encapsulates and decapsulates the IPv6 packets into and out of the + tunnel. Ref. [USENIX09] pointed out the existence of a vulnerability in the design of IPv6 automatic tunnels. Tunnel routers operate on the implicit assumption that the destination address of an incoming IPv6 packet is always an address of a valid node that can be reached via the tunnel. The assumption of path validity can introduce routing loops as the inconsistency between the IPv4 routing state and the IPv6 routing state allows a routing loop to be formed. Although those loops will not trap normal data, they will catch traffic targeted at addresses that have become unavailable, and misconfigured @@ -227,21 +230,21 @@ Figure 2: Routing loop attack between two tunnels' routers The crux of the attack is as follows. The attacker exploits the fact that R2 does not know that R1 does not configure addresses from Prf2 and that R1 does not know that R2 does not configure addresses from Prf1. The IPv4 network acts as a shared link layer for the two tunnels. Hence, the packet is repeatedly forwarded by both routers. It is noted that the attack will fail when the IPv4 network can not transport packets between the tunnels. For example, when the two routers belong to different IPv4 address realms or when ingress/ - egress filtering is exercised between the routes. + egress filtering is exercised between the routers. The loop will stop when the Hop Limit field of the packet reaches zero. After a single loop the Hop Limit field is decreased by the number of IPv6 routers on path from R1 to R2. Therefore, the number of loops is inversely proportional to the number of IPv6 hops between R1 and R2. The tunnels used by R1 and R2 may be any combination of automatic tunnel types, e.g., ISATAP, 6to4 and 6rd. This has the exception that both tunnels can not be of type 6to4, since two 6to4 routers @@ -334,21 +337,24 @@ shared link-layer between more than one tunnel. From this the following two mitigation measures arise: 3.2.1.1. Filtering IPv4 Protocol-41 Packets In this measure a tunnel router may drop all IPv4 protocol-41 packets received or sent over interfaces that are attached to an untrusted IPv4 network. This will cut-off any IPv4 network as a shared link. This measure has the advantage of simplicity. However, such a measure may not always be suitable for scenarios where IPv4 - connectivity is essential on all interfaces. + connectivity is essential on all interfaces. Most notably, filtering + of IPv4 protocol-41 packets that belong to a 6to4 tunnel can have + real adverse affects on unsuspecting users + [I-D.ietf-v6ops-6to4-advisory]. 3.2.1.2. Operational Avoidance of Multiple Tunnels This measure mitigates the attack by simply allowing for a single IPv6 tunnel to operate in a bounded IPv4 network. For example, the attack can not take place in broadband home networks. In such cases there is a small home network having a single residential gateway which serves as a tunnel router. A tunnel router is vulnerable to the attack only if it has at least two interfaces with a path to the Internet: a tunnel interface and a native IPv6 interface (as depicted @@ -383,85 +389,86 @@ router. This condition is essentially translated to a scenario in which the tunnel router is the only border router between the IPv6 network and the IPv4 network to which it is attached (as in broadband home network scenario mentioned above). 3.2.3. A Comprehensive List of Tunnel Routers If a tunnel router can be configured with a comprehensive list of IPv4 addresses of all other tunnel routers in the network, then the router can use the list as a filter to discard any tunneled packets - coming from other routers. For example, a tunnel router can use the - network's ISATAP Potential Router List (PRL) [RFC5214] as a filter as - long as there is operational assurance that all ISATAP routers are - listed and that no other types of tunnel routers are present in the - network. + coming from or destined to other routers. For example, a tunnel + router can use the network's ISATAP Potential Router List (PRL) + [RFC5214] as a filter as long as there is operational assurance that + all ISATAP routers are listed and that no other types of tunnel + routers are present in the network. This measure parallels the one proposed for 6rd in [RFC5969] where the 6rd BR filters all known relay addresses of other tunnels inside the ISP's network. This measure is especially useful for intra-site tunneling mechanisms, such as ISATAP and 6rd, since filtering can be exercised - on well-defined site borders. + on well-defined site borders. A specific ISATAP operational scenario + for which this mitigation applies is described in Section 3 of + [I-D.templin-v6ops-isops]. 3.2.4. Avoidance of On-link Prefixes The looping attack exploits the fact that a router is permitted to assign non-link-local IPv6 prefixes on its tunnel interfaces, which could cause it to send tunneled packets to other routers that do not configure an address from the prefix. Therefore, if the router does not assign non-link-local IPv6 prefixes on its tunnel interfaces there is no opportunity for it to initiate the loop. If the router further ensures that the routing state is consistent for the packets it receives on its tunnel interfaces there is no opportunity for it to propagate a loop initiated by a different router. This mitigation is available only to ISATAP routers, since the ISATAP stateless address mapping operates only on the Interface Identifier - portion of the IPv6 address, and not on the IPv6 prefix. . The + portion of the IPv6 address, and not on the IPv6 prefix. The mitigation is also only applicable on ISATAP links on which IPv4 source address spoofing is disabled. The following sections discuss the operational configurations necessary to implement the mitigation. 3.2.4.1. ISATAP Router Interface Types ISATAP provides a Potential Router List (PRL) to further ensure a - loop-free topology. Routers that are members of the provider network - PRL configure their provider network ISATAP interfaces as advertising - router interfaces (see: [RFC4861], Section 6.2.2), and therefore may - send Router Advertisement (RA) messages that include non-zero Router - Lifetimes. Routers that are not members of the provider network PRL - configure their provider network ISATAP interfaces as non-advertising - router interfaces. + loop-free topology. Routers that are members of the PRL for the site + configure their site-facing ISATAP interfaces as advertising router + interfaces (see: [RFC4861], Section 6.2.2), and therefore may send RA + messages that include non-zero Router Lifetimes. Routers that are + not members of the PRL for the site configure their site-facing + ISATAP interfaces as non-advertising router interfaces. 3.2.4.2. ISATAP Source Address Verification ISATAP nodes employ the source address verification checks specified in Section 7.3 of [RFC5214] as a prerequisite for decapsulation of packets received on an ISATAP interface. To enable the on-link prefix avoidance procedures outlined in this section, ISATAP nodes must employ an additional source address verification check; namely, the node also considers the outer IPv4 source address correct for the inner IPv6 source address if: o a forwarding table entry exists that lists the packet's IPv4 source address as the link-layer address corresponding to the inner IPv6 source address via the ISATAP interface. 3.2.4.3. ISATAP Host Behavior - ISATAP hosts send Router Solicitation (RS) messages to obtain RA - messages from an advertising ISATAP router. Whether or not non-link- - local IPv6 prefixes are advertised, the host can acquire IPv6 - addresses, e.g., through the use of DHCPv6 stateful address - autoconfiguration [RFC3315]. + ISATAP hosts send RS messages to obtain RA messages from an + advertising ISATAP router. Whether or not non-link-local IPv6 + prefixes are advertised, the host can acquire IPv6 addresses, e.g., + through the use of DHCPv6 stateful address autoconfiguration + [RFC3315]. To acquire addresses, the host performs standard DHCPv6 exchanges while mapping the IPv6 "All_DHCP_Relay_Agents_and_Servers" link- scoped multicast address to the IPv4 address of the advertising router (hence, the advertising router must configure either a DHCPv6 relay or server function). The host should also use DHCPv6 Authentication in environments where authentication of the DHCPv6 exchanges is required. After the host receives IPv6 addresses, it assigns them to its ISATAP @@ -469,179 +476,187 @@ advertising router as a default router. The advertising router in turn maintains IPv6 forwarding table entries that list the IPv4 address of the host as the link-layer address of the delegated IPv6 addresses. 3.2.4.4. ISATAP Router Behavior In many use case scenarios (e.g., enterprise networks, MANETs, etc.), advertising and non-advertising ISATAP routers can engage in a proactive dynamic IPv6 routing protocol (e.g., OSPFv3, RIPng, etc.) - so that IPv6 routing/forwarding tables can be populated and standard - IPv6 forwarding between ISATAP routers can be used. In other - scenarios (e.g., large ISP networks, etc.), this might be impractical - dues to scaling issues. When a proactive dynamic routing protocol - cannot be used, non-advertising ISATAP routers send RS messages to - obtain RA messages from an advertising ISATAP router, i.e., they act - as "hosts" on their non-advertising ISATAP interfaces. + over their ISATAP interfaces so that IPv6 routing/forwarding tables + can be populated and standard IPv6 forwarding between ISATAP routers + can be used. In other scenarios (e.g., large enterprise networks, + etc.), this might be impractical due to scaling issues. When a + proactive dynamic routing protocol cannot be used, non-advertising + ISATAP routers send RS messages to obtain RA messages from an + advertising ISATAP router, i.e., they act as "hosts" on their non- + advertising ISATAP interfaces. - Non-advertising routers can also acquire IPv6 prefixes, e.g., through - the use of DHCPv6 Prefix Delegation [RFC3633] via an advertising - router in the same fashion as described above for host-based DHCPv6 - stateful address autoconfiguration. The advertising router in turn - maintains IPv6 forwarding table entries that list the IPv4 address of - the non-advertising router as the link-layer address of the next hop - toward the delegated IPv6 prefixes. + Non-advertising ISATAP routers can also acquire IPv6 prefixes, e.g., + through the use of DHCPv6 Prefix Delegation [RFC3633] via an + advertising router in the same fashion as described above for host- + based DHCPv6 stateful address autoconfiguration. The advertising + router in turn maintains IPv6 forwarding table entries that list the + IPv4 address of the non-advertising router as the link-layer address + of the next hop toward the delegated IPv6 prefixes. After the non-advertising router acquires IPv6 prefixes, it can sub- delegate them to routers and links within its attached IPv6 edge networks, then can forward any outbound IPv6 packets coming from its edge networks via other ISATAP nodes on the link. 3.2.4.5. Reference Operational Scenario Figure 3 depicts a reference ISATAP network topology for operational avoidance of on-link non-link-local IPv6 prefixes. The scenario - shows an advertising ISATAP router ('A'), two non-advertising ISATAP - routers ('B', 'D'), an ISATAP host ('F'), and three ordinary IPv6 - hosts ('C', 'E', 'G') in a typical deployment configuration: + shows two advertising ISATAP routers ('A', 'B'), two non-advertising + ISATAP routers ('C', 'E'), an ISATAP host ('G'), and three ordinary + IPv6 hosts ('D', 'F', 'H') in a typical deployment configuration: + .-(::::::::) 2001:db8:3::1 .-(::: IPv6 :::)-. +-------------+ - (:::: Internet ::::) | IPv6 Host G | + (:::: Internet ::::) | IPv6 Host H | `-(::::::::::::)-' +-------------+ `-(::::::)-' - ,-. - ,-----+-/-+--' \+------. - / ,~~~~~~~~~~~~~~~~~, : - / |companion gateway| |. - ,-' '~~~~~~~~~~~~~~~~~' `. - ; +--------------+ ) - : | Router A | / fe80::5efe:192.0.2.4 - : | (isatap) | ; 2001:db8:2::1 - +- +--------------+ -+ +--------------+ - ; fe80::5efe:192.0.2.1 : | (isatap) | - | ; | Host F | - : IPv4 Provider Network -+-' +--------------+ - `-. (PRL: 192.0.2.1) .) + ,~~~~~~~~~~~~~~~~~, + ,----|companion gateway|--. + / '~~~~~~~~~~~~~~~~~' : + / |. + ,-' `. + ; +------------+ +------------+ ) + : | Router A | | Router B | / fe80::*192.0.2.5 + : | (isatap) | | (isatap) | ; 2001:db8:2::1 + + +------------+ +------------+ \ +--------------+ + ; fe80::*192.0.2.1 fe80::*192.0.2.2 : | (isatap) | + | ; | Host G | + : IPv4 Site -+-' +--------------+ + `-. (PRL: 192.0.2.1, 192.0.2.2) .) \ _) `-----+--------)----+'----' - fe80::5efe:192.0.2.2 fe80::5efe:192.0.2.3 .-. + fe80::*192.0.2.3 fe80::*192.0.2.4 .-. +--------------+ +--------------+ ,-( _)-. | (isatap) | | (isatap) | .-(_ IPv6 )-. - | Router B | | Router D |--(__Edge Network ) + | Router C | | Router E |--(__Edge Network ) +--------------+ +--------------+ `-(______)-' - 2001:db8::/48 2001:db8:1::/48 | + 2001:db8:0::/48 2001:db8:1::/48 | | 2001:db8:1::1 .-. +-------------+ - ,-( _)-. 2001:db8::1 | IPv6 Host E | + ,-( _)-. 2001:db8::1 | IPv6 Host F | .-(_ IPv6 )-. +-------------+ +-------------+ - (__Edge Network )--| IPv6 Host C | + (__Edge Network )--| IPv6 Host D | `-(______)-' +-------------+ + (* == "5efe:") Figure 3: Reference ISATAP Network Topology - In Figure 3, advertising ISATAP router 'A' within the IPv4 provider - network connects to the IPv6 Internet, either directly or via a - companion gateway. 'A' configures a provider network IPv4 interface - with address 192.0.2.1 and arranges to add the address to the - provider network PRL. 'A' next configures an advertising ISATAP - router interface with link-local IPv6 address fe80::5efe:192.0.2.1 - over the IPv4 interface. + In Figure 3, advertising ISATAP routers 'A' and 'B' within the IPv4 + site connect to the IPv6 Internet, either directly or via a companion + gateway. 'A' configures a provider network IPv4 interface with + address 192.0.2.1 and arranges to add the address to the provider + network PRL. 'A' next configures an advertising ISATAP router + interface with link-local IPv6 address fe80::5efe:192.0.2.1 over the + IPv4 interface. In the same fashion, 'B' configures the IPv4 + interface address 192.0.2.2, adds the address to the PRL, then + configures the IPv6 ISATAP interface link-local address fe80::5efe: + 192.0.2.2. - Non-advertising ISATAP router 'B' connects to one or more IPv6 edge - networks and also connects to the provider network via an IPv4 - interface with address 192.0.2.2, but it does not add the IPv4 - address to the provider network PRL. 'B' next configures a non- - advertising ISATAP router interface with link-local address fe80:: - 5efe:192.0.2.2, then receives the IPv6 prefix 2001:db8::/48 through a - DHCPv6 prefix delegation exchange via 'A'. 'B' then engages in an - IPv6 routing protocol over its ISATAP interface and announces the - delegated IPv6 prefix. 'B' finally sub-delegates the prefix to its - attached edge networks, where IPv6 host 'C' autoconfigures the - address 2001:db8::1. + Non-advertising ISATAP router 'C' connects to one or more IPv6 edge + networks and also connects to the site via an IPv4 interface with + address 192.0.2.3, but it does not add the IPv4 address to the site's + PRL. 'C' next configures a non-advertising ISATAP router interface + with link-local address fe80::5efe:192.0.2.3, then receives the IPv6 + prefix 2001:db8::/48 through a DHCPv6 prefix delegation exchange via + one of 'A' or 'B'. 'C' then engages in an IPv6 routing protocol over + its ISATAP interface and announces the delegated IPv6 prefix. 'C' + finally sub-delegates the prefix to its attached edge networks, where + IPv6 host 'D' autoconfigures the address 2001:db8::1. - Non-advertising ISATAP router 'D' connects to the provider network, - configures its ISATAP interface, receives a DHCPv6 prefix delegation, - and engages in the IPv6 routing protocol the same as for router 'B'. - In particular, 'D' configures the IPv4 address 192.0.2.3, the ISATAP - link-local address fe80::5efe:192.0.2.3, and the delegated IPv6 - prefix 2001:db8:1::/48. 'D' finally sub-delegates the prefix to its - attached edge networks, where IPv6 host 'E' autoconfigures IPv6 + Non-advertising ISATAP router 'E' connects to the site, configures + its ISATAP interface, receives a DHCPv6 prefix delegation, and + engages in the IPv6 routing protocol the same as for router 'C'. In + particular, 'E' configures the IPv4 address 192.0.2.4, the ISATAP + link-local address fe80::5efe:192.0.2.4, and the delegated IPv6 + prefix 2001:db8:1::/48. 'E' finally sub-delegates the prefix to its + attached edge networks, where IPv6 host 'F' autoconfigures IPv6 address 2001:db8:1::1. - ISATAP host 'F' connects to the provider network via an IPv4 - interface with address 192.0.2.4, and also configures an ISATAP host - interface with link-local address fe80::5efe:192.0.2.4 over the IPv4 - interface. 'F' next configures a default IPv6 route with next-hop - address fe80::5efe:192.0.2.1 via the ISATAP interface, then receives - the IPv6 address 2001:db8:2::1 from a DHCPv6 address configuration - exchange via 'A'. When 'F' receives the IPv6 address, it assigns the - address to the ISATAP interface but does not assign a non-link-local - IPv6 prefix to the interface. + ISATAP host 'G' connects to the site via an IPv4 interface with + address 192.0.2.5, and also configures an ISATAP host interface with + link-local address fe80::5efe:192.0.2.5 over the IPv4 interface. 'G' + next configures a default IPv6 route with next-hop address fe80:: + 5efe:192.0.2.2 via the ISATAP interface, then receives the IPv6 + address 2001:db8:2::1 from a DHCPv6 address configuration exchange + via 'B'. When 'G' receives the IPv6 address, it assigns the address + to the ISATAP interface but does not assign a non-link-local IPv6 + prefix to the interface. - Finally, IPv6 host 'G' connects to an IPv6 network outside of the - ISATAP domain. 'G' configures its IPv6 interface in a manner + Finally, IPv6 host 'H' connects to an IPv6 network outside of the + ISATAP domain. 'H' configures its IPv6 interface in a manner specific to its attached IPv6 link, and autoconfigures the IPv6 address 2001:db8:3::1. - Following this autoconfiguration, when host 'C' has an IPv6 packet to - send to host 'E', it prepares the packet with source address 2001: + Following this autoconfiguration, when host 'D' has an IPv6 packet to + send to host 'F', it prepares the packet with source address 2001: db8::1 and destination address 2001:db8:1::1, then sends the packet into the edge network where it will eventually be forwarded to router - 'B'. 'B' then uses ISATAP encapsulation to forward the packet to - router 'D', since it has discovered a route to 2001:db8:1::/48 with - next hop 'D' via dynamic routing over the ISATAP interface. Router - 'D' finally forwards the packet to host 'E'. + 'C'. 'C' then uses ISATAP encapsulation to forward the packet to + router 'E', since it has discovered a route to 2001:db8:1::/48 with + next hop 'E' via dynamic routing over the ISATAP interface. Router + 'E' finally forwards the packet to host 'F'. - In a second scenario, when 'C' has a packet to send to ISATAP host - 'F', it prepares the packet with source address 2001:db8::1 and + In a second scenario, when 'D' has a packet to send to ISATAP host + 'G', it prepares the packet with source address 2001:db8::1 and destination address 2001:db8:2::1, then sends the packet into the - edge network where it will eventually be forwarded to router 'B' the - same as above. 'B' then uses ISATAP encapsulation to forward the + edge network where it will eventually be forwarded to router 'C' the + same as above. 'C' then uses ISATAP encapsulation to forward the packet to router 'A' (i.e., a router that advertises "default"), - which in turn forwards the packet to 'F'. Note that this operation - entails two hops across the ISATAP link (i.e., one from 'B' to 'A', - and a second from 'A' to 'F'). If 'F' also participates in the - dynamic IPv6 routing protocol, however, 'B' could instead forward the - packet directly to 'F' without involving 'A'. + which in turn forwards the packet to 'G'. Note that this operation + entails two hops across the ISATAP link (i.e., one from 'C' to 'A', + and a second from 'A' to 'G'). If 'G' also participates in the + dynamic IPv6 routing protocol, however, 'C' could instead forward the + packet directly to 'G' without involving 'A'. - In a final scenario, when 'C' has a packet to send to host 'G' in the - IPv6 Internet, the packet is forwarded to 'B' the same as above. 'B' + In a third scenario, when 'D' has a packet to send to host 'H' in the + IPv6 Internet, the packet is forwarded to 'C' the same as above. 'C' then forwards the packet to 'A', which forwards the packet into the IPv6 Internet. + In a final scenario, when 'G' has a packet to send to host 'H' in the + IPv6 Internet, the packet is forwarded directly to 'B', which + forwards the packet into the IPv6 Internet. + 3.2.4.6. Scaling Considerations - Figure 3 depicts an ISATAP network topology with only a single - advertising ISATAP router within the provider network. In order to - support larger numbers of non-advertising ISATAP routers and ISATAP - hosts, the provider network can deploy more advertising ISATAP - routers to support load balancing and generally shortest-path - routing. + Figure 3 depicts an ISATAP network topology with only two advertising + ISATAP routers within the provider network. In order to support + larger numbers of non-advertising ISATAP routers and ISATAP hosts, + the provider network can deploy more advertising ISATAP routers to + support load balancing and generally shortest-path routing. Such an arrangement requires that the advertising ISATAP routers participate in an IPv6 routing protocol instance so that IPv6 address/prefix delegations can be mapped to the correct router. The routing protocol instance can be configured as either a full mesh topology involving all advertising ISATAP routers, or as a partial mesh topology with each advertising ISATAP router associating with - one or more companion gateways and a full mesh between companion - gateways. + one or more companion gateways. Each such companion gateway would in + turn participate in a full mesh between all companion gateways. 3.2.4.7. On-Demand Dynamic Routing With respect to the reference operational scenario depicted in Figure 3, there will be many use cases in which a proactive dynamic - IPv6 routing protocol cannot be used. For example, in large ISP - network deployments it would be impractical for all Customer-Edge and - Provider-Edge routers to engage in a common routing protocol instance - due to scaling considerations. + IPv6 routing protocol cannot be used. For example, in large + enterprise network deployments it would be impractical for all + routers to engage in a common routing protocol instance due to + scaling considerations. In those cases, an on-demand routing capability can be enabled in which ISATAP nodes send initial packets via an advertising ISATAP router and receive redirection messages back. For example, when a non-advertising ISATAP router 'B' has a packet to send to a host located behind non-advertising ISATAP router 'D', it can send the initial packets via advertising router 'A' which will return redirection messages to inform 'B' that 'D' is a better first hop. Protocol details for this ISATAP redirection are specified in [I-D.templin-aero]. @@ -676,21 +691,21 @@ prefix but embeds one of the router's configured IPv4 addresses. o When the router receives an IPv6 packet on a tunnel interface, it discards the packet if the IPv6 destination address has an off- link prefix but embeds one of the router's configured IPv4 addresses. This approach has the advantage that no ancillary state is required, since checking is through static lookup in the lists of IPv4 and IPv6 addresses belonging to the router. However, this approach has some - inherent limitations + inherent limitations: o The checks incur an overhead which is proportional to the number of IPv4 addresses assigned to the router. If a router is assigned many addresses, the additional processing overhead for each packet may be considerable. Note that an unmitigated attack packet would be repetitively processed by the router until the Hop Limit expires, which may require as many as 255 iterations. Hence, an unmitigated attack will consume far more aggregate processing overhead than per-packet address checks even if the router assigns a large number of addresses. @@ -831,25 +846,35 @@ Infrastructures (6rd) -- Protocol Specification", RFC 5969, August 2010. 8.2. Informative References [I-D.gont-6man-teredo-loops] Gont, F., "Mitigating Teredo Rooting Loop Attacks", draft-gont-6man-teredo-loops-00 (work in progress), September 2010. + [I-D.ietf-v6ops-6to4-advisory] + Carpenter, B., "Advisory Guidelines for 6to4 Deployment", + draft-ietf-v6ops-6to4-advisory-01 (work in progress), + April 2011. + [I-D.templin-aero] Templin, F., "Asymmetric Extended Route Optimization (AERO)", draft-templin-aero-00 (work in progress), March 2011. + [I-D.templin-v6ops-isops] + Templin, F., "Operational Guidance for IPv6 Deployment in + IPv4 Sites using ISATAP", draft-templin-v6ops-isops-00 + (work in progress), May 2011. + [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through Network Address Translations (NATs)", RFC 4380, February 2006. [RFC4732] Handley, M., Rescorla, E., and IAB, "Internet Denial-of- Service Considerations", RFC 4732, December 2006. [USENIX09] Nakibly, G. and M. Arov, "Routing Loop Attacks using IPv6 Tunnels", USENIX WOOT, August 2009.