Internet Engineering Task Force (IETF) R. Gagliano Request for Comments: 5963 Cisco Systems Category: Informational August 2010 ISSN: 2070-1721
IPv6 Deployment in Internet Exchange Points (IXPs)
This document provides guidance on IPv6 deployment in Internet Exchange Points (IXPs). It includes information regarding the switch fabric configuration, the addressing plan and general organizational tasks that need to be performed. IXPs are mainly a Layer 2 infrastructure, and, in many cases, the best recommendations suggest that the IPv6 data, control, and management plane should not be handled differently than in IPv4.
Status of This Memo
This document is not an Internet Standards Track specification; it is published for informational purposes.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5963.
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.
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Table of Contents
1. Introduction ....................................................2 2. Switch Fabric Configuration .....................................2 3. Addressing Plan .................................................3 4. Multicast IPv6 ..................................................5 4.1. Multicast Support and Monitoring for Neighbor Discovery at an IXP ........................................6 4.2. IPv6 Multicast Traffic Exchange at an IXP ..................6 5. Reverse DNS .....................................................7 6. Route-Server ....................................................7 7. External and Internal Support ...................................7 8. IXP Policies and IPv6 ...........................................8 9. Security Considerations .........................................8 10. Acknowledgements ...............................................8 11. Informative References .........................................8
Most Internet Exchange Points (IXPs) work at the Layer 2 level, making the adoption of IPv6 an easy task. However, IXPs normally implement additional services such as statistics, route servers, looking glasses, and broadcast controls that may be impacted by the implementation of IPv6. This document clarifies the impact of IPv6 on a new or an existing IXP. The document assumes an Ethernet switch fabric, although other Layer 2 configurations could be deployed.
2. Switch Fabric Configuration
An Ethernet-based IXP switch fabric implements IPv6 over Ethernet as described in [RFC2464] . Therefore, the switching of IPv6 traffic happens in the same way as in IPv4. However, some management functions (such as switch management, SNMP (Simple Network Management Protocol) [RFC3411] support, or flow analysis exportation) may require IPv6 as an underlying layer, and this should be assessed by the IXP operator.
There are two common configurations of IXP switch ports to support IPv6:
1. dual-stack LAN (Local Area Network): when both IPv4 and IPv6 traffic share a common LAN. No extra configuration is required in the switch.
2. independent VLAN (Virtual Local Area Network)[IEEE.P802-1Q.1998]: when an IXP logically separates IPv4 and IPv6 traffic in different VLANs.
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In both configurations, IPv6 and IPv4 traffic can either share a common physical port or use independent physical ports. The use of independent ports can be more costly in both capital expenses (as new ports are needed) and operational expenses.
When using the same physical port for both IPv4 and IPv6 traffic, some changes may be needed at the participants' interfaces' configurations. If the IXP implements the "dual-stack configuration", IXP's participants will configure dual-stack interfaces. On the other hand, if the IXP implements the "independent VLAN configuration", IXP participants are required to pass one additional VLAN tag across the interconnection. In this case, if the IXP did not originally use VLAN tagging, VLAN tagging should be established and the previously configured LAN may continue untagged as a "native VLAN" or be transitioned to a tagged VLAN. The "independent VLAN" configuration provides a logical separation of IPv4 and IPv6 traffic, simplifying separate statistical analysis for IPv4 and IPv6 traffic. Conversely, the "dual-stack" configuration (when performing separate statistical analysis for IPv4 and IPv6 traffic) would require the use of flow techniques such as IPFIX (IP Flow Information Export) [RFC5101] to classify traffic based on the different Ethertypes (0x0800 for IPv4, 0x0806 for ARP (Address Resolution Protocol), and 0x86DD for IPv6).
The only technical requirement for IPv6 referring link MTUs is that they need to be greater than or equal to 1280 octets [RFC2460]. The MTU size for every LAN in an IXP should be well known by all its participants.
3. Addressing Plan
Regional Internet Registries (RIRs) have specific address policies to assign Provider Independent (PI) IPv6 addresses to IXPs. Those allocations are usually /48 or shorter prefixes [RIR_IXP_POLICIES]. Depending on the country and region of operation, address assignments may be made by NIRs (National Internet Registries). Unique Local IPv6 Unicast Addresses ([RFC4193]) are normally not used in an IXP LAN as global reverse DNS resolution and whois services are required.
IXPs will normally use manual address configuration. The manual configuration of IPv6 addresses allows IXP participants to replace network interfaces with no need to reconfigure Border Gateway Protocol (BGP) sessions' information, and it also facilitates management tasks. The IPv6 Addressing Architecture [RFC4291] requires that interface identifiers are 64 bits in size for prefixes not starting with binary 000, resulting in a maximum prefix length of /64. Longer prefix lengths up to /127 have been used operationally.
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If prefix lengths longer than 64 bits are chosen, the implications described in [RFC3627] need to be considered. A /48 prefix allows the addressing of 65536 /64 LANs.
When selecting the use of static Interface Identifiers (IIDs), there are different options on how to fill its 64 bits (or 16 hexadecimal characters). A non-exhaustive list of possible IID selection mechanisms is the following:
1. Some IXPs like to include the decimal encoding of each participant's ASN (Autonomous System Number) inside its correspondent IPv6 address. The ASN decimal number is used as the BCD (binary code decimal) encoding of the upper part of the IID such as shown in this example:
equivalent representation 2001:db8::6:4496:1/64
In this example, we are right-justifying the participant's ASN number from the 112nd bit. Remember that 32-bit ASNs require a maximum of 10 characters. With this example, up to 2^16 IPv6 addresses can be configured per ASN.
2. Although BCD encoding is more "human-readable", some IXPs prefer to use the hexadecimal encoding of the ASNs number as the upper part of the IID as follow:
equivalent representation 2001:db8::fbf0:1/64
In this case, a maximum of 8 characters will be needed to represent 32-bit ASNs.
3. A third scheme for statically assigning IPv6 addresses on an IXP LAN could be to relate some portions of a participant's IPv6 address to its IPv4 address. In the following example, the last four decimals of the IPv4 address are copied to the last hexadecimals of the IPv6 address, using the decimal number as the BCD encoding for the last three characters of the IID such as in the following example:
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4. A fourth approach might be based on the IXPs ID for that participant.
IPv6 prefixes for IXP LANs are typically publicly well known and taken from dedicated IPv6 blocks for IXP assignments reserved for this purpose by the different RIRs. These blocks are usually only meant for addressing the exchange fabric, and may be filtered out by DFZ (Default Free Zone) operators. When considering the routing of the IXP LANs two options are identified:
o IXPs may decide that LANs should not to be globally routed in order to limit the possible origins of a Denial-of-Service (DoS) attack to its participants' AS (Autonomous System) boundaries. In this configuration, participants may route these prefixes inside their networks (e.g., using BGP no-export communities or routing the IXP LANs within the participants' IGP) to perform fault management. Using this configuration, the monitoring of the IXP LANs from outside of its participants' AS boundaries is not possible.
o IXP may decide that LANs should (attempt to) be globally routed. In this case, IXP LANs monitoring from outside its participants' AS boundaries may be possible, but the IXP LANs will be vulnerable to DoS from outside of those boundaries.
Additionally, possible IXP external services (such as DNS, web pages, FTP servers) need to be globally routed. These should be addressed from separate address blocks, either from upstream providers' address space or separate independent assignments. Strict prefix length filtering could be a reason for requesting more than one /48 assignment from a RIR (i.e., requesting one /48 assignment for the IXPs LANs that may not be globally routed and a different, non-IXP /48 assignment for the IXP external services that will be globally routed).
4. Multicast IPv6
There are two elements that need to be evaluated when studying IPv6 multicast in an IXP: multicast support for neighbor discovery and multicast peering.
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4.1. Multicast Support and Monitoring for Neighbor Discovery at an IXP
IXPs typically control broadcast traffic across the switching fabric in order to avoid broadcast storms by only allowing limited ARP [RFC0826] traffic for address resolution. In IPv6 there is not broadcast support, but IXPs may intend to control multicast traffic in each LAN instead. ICMPv6 Neighbor Discovery [RFC4861] implements the following necessary functions in an IXP switching fabric: Address Resolution, Neighbor Unreachability Detection, and Duplicate Address Detection. In order to perform these functions, Neighbor Solicitation and Neighbor Advertisement packets are exchanged using the link-local all-nodes multicast address (ff02::1) and/or solicited-node multicast addresses (ff02:0:0:0:0:1:ff00:0000 to ff02: 0:0:0:0:1:ffff:ffff). As described in [RFC4861], routers will initialize their interfaces by joining their solicited-node multicast addresses using either Multicast Listener Discovery (MLD) [RFC2710] or MLDv2 [RFC3810]. MLD messages may be sent to the corresponding group address: ff02::2 (MLD) or ff02::16 (MLDv2). Depending on the addressing plan selected by the IXP, each solicited-node multicast group may be shared by a sub-set of participants' conditioned by how the last three octets of the addresses are selected. In Section 3, example 1, only participants with ASNs with the same last two digits are going to share the same solicited-node multicast group.
Similar to the ARP policy, an IXP may limit multicast traffic across the switching fabric in order to only allow ICMPv6 Neighbor Solicitation, Neighbor Advertisement, and MLD messages. Configuring default routes in an IXP LAN without an agreement between the parties is normally against IXP policies. ICMPv6 Router Advertisement packets should neither be issued nor accepted by routers connected to the IXP. Where possible, the IXP operator should block link-local RA (Router Advertisement) packets using IPv6 RA-GUARD [V6OPS-RA-GUARD] . If this is not possible, the IXP operator should monitor the exchange for rogue Router Advertisement packets as described in [V6OPS-ROGUE-RA] .
4.2. IPv6 Multicast Traffic Exchange at an IXP
For IPv6 Multicast traffic exchange, an IXP may decide to use either the same LAN being used for unicast IPv6 traffic exchange, the same LAN being used for IPv4 Multicast traffic exchange, or a dedicated LAN for IPv6 Multicast traffic exchange. The reason for having a dedicated LAN for multicast is to prevent unwanted multicast traffic from reaching participants that do not have multicast support. Protocol Independent Multicast (PIM) [RFC4601] messages will be sent to the link-local IPv6 'ALL-PIM-ROUTERS' multicast group ff02::d in the selected LAN and should be allowed. Implementing IPv6 PIM snooping will allow only the participants associated with a
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particular group to receive its multicast traffic. BGP reachability information for IPv6 multicast address family (SAFI=2) is normally exchanged using MP-BGP (Multi-Protocol BGP) [RFC4760] and is used for Reverse Path Forwarding (RPF) lookups performed by the IPv6 PIM. If a dedicated LAN is configured for Multicast IPv6 traffic exchange, reachability information for IPv6 Multicast address family should be carried in new BGP sessions. ICMPv6 Neighbor Discovery should be allowed in the Multicast IPv6 LAN as described in the previous paragraph.
5. Reverse DNS
The inclusion of PTR records for all addresses assigned to participants in the IXP reverse zone under "ip6.arpa" facilitates troubleshooting, particularly when using tools such as traceroute. If reverse DNS is configured, DNS servers should be reachable over IPv6 transport for complete IPv6 support.
IXPs may offer a route-server service, either for Multi-Lateral Peering Agreements (MLPA) service, looking-glass service, or route- collection service. IPv6 support needs to be added to the BGP speaking router. The equipment should be able to transport IPv6 traffic and to support MP-BGP extensions for IPv6 address family ([RFC2545] and [RFC4760]).
A good practice is that all BGP sessions used to exchange IPv6 network information are configured using IPv6 data transport. This configuration style ensures that both network reachability information and generic packet data transport use the same transport plane. Because of the size of the IPv6 space, limiting the maximum number of IPv6 prefixes in every session should be studied.
External services should be available for external IPv6 access, either by an IPv6 enabled web page or an IPv6 enabled console interface.
7. External and Internal Support
Some external services that need to have IPv6 support are traffic graphics, DNS, FTP, web, route server, and looking glass. Other external services such as NTP servers, or SIP Gateways need to be evaluated as well. In general, each service that is currently accessed through IPv4 or that handle IPv4 addresses should be evaluated for IPv6 support.
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Internal services are also important when considering IPv6 adoption at an IXP. Such services may not deal with IPv6 traffic, but may handle IPv6 addresses; that is the case of provisioning systems, logging tools and statistics analysis tools. Databases and tools should be evaluated for IPv6 support.
8. IXP Policies and IPv6
IXP policies and contracts should be revised as any mention of IP should be clarified if it refers to IPv4, IPv6, or both.
Policies for IPv6 traffic monitoring and filtering may be in place as described in Section 4.
9. Security Considerations
This memo includes references to procedures for monitoring and/or avoiding particular ICMPv6 traffic at IXPs' LANs. None of these procedures prevent Ethernet loops caused by mischief in the LAN. The document also mentions how to limit IPv6 DoS attacks to the IXP switch fabric by not globally announce the IXP LANs prefix.
The author would like to thank the contributions from Alain Aina, Bernard Tuy, Stig Venaas, Martin Levy, Nick Hilliard, Martin Pels, Bill Woodcock, Carlos Friacas, Arien Vijn, Fernando Gont, and Louis Lee.
11. Informative References
[IEEE.P802-1Q.1998] Institute of Electrical and Electronics Engineers, "Local and Metropolitan Area Networks: Virtual Bridged Local Area Networks", IEEE Draft P802.1Q, March 1998.
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or converting network protocol addresses to 48.bit Ethernet address for transmission on Ethernet hardware", STD 37, RFC 826, November 1982.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet Networks", RFC 2464, December 1998.
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[RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol Extensions for IPv6 Inter-Domain Routing", RFC 2545, March 1999.
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener Discovery (MLD) for IPv6", RFC 2710, October 1999.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An Architecture for Describing Simple Network Management Protocol (SNMP) Management Frameworks", STD 62, RFC 3411, December 2002.
[RFC3627] Savola, P., "Use of /127 Prefix Length Between Routers Considered Harmful", RFC 3627, September 2003.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast Addresses", RFC 4193, October 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", RFC 4601, August 2006.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007.
[RFC5101] Claise, B., "Specification of the IP Flow Information Export (IPFIX) Protocol for the Exchange of IP Traffic Flow Information", RFC 5101, January 2008.
[RIR_IXP_POLICIES] Numbers Resource Organization (NRO)., "RIRs Allocations Policies for IXP. NRO Comparison matrix", 2009, <http://www.nro.net/documents/comp-pol.html#3-4-2>.
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[V6OPS-RA-GUARD] Levy-Abegnoli, E., Velde, G., Popoviciu, C., and J. Mohacsi, "IPv6 RA-Guard", Work in Progress, June 2010.
[V6OPS-ROGUE-RA] Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement Problem Statement", Work in Progress, June 2010.
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