What’s New With LDPv6 and Where We Are on the Updated Protocol

techabstract2014Now that IPv6 is progressing and being deployed more and more, there is a need for a change to the underlying infrastructure. Most providers today use MPLS as their core technology to support a vast number of services to their customers, including Layer 3 VPNs. Larger enterprise networks have also implemented MPLS within their own core in a private MPLS cloud.

Passing labels within the MPLS cloud is being handled by Label Distribution Protocol (LDP) and will pass a label for every IPv4 route within the Routing Information Table (RIB), except those learned from BGP. BGP has had extensions written to pass its own set of labels to other BGP peers.

Now that we are deploying IPv6, the issue is how are we going to pass labels for them?

BGP has the ability to pass labels for both IPv4 and IPv6. The support of labels with BGP for IPv6 is an additional Layer 3 VPN option and is referred to as either 6PE or 6VPE. But, the underlying label switch path (LSP) is derived from IPv4, not IPv6. To be able to natively use IPv6 for the LSP, LDP needs to be modified to support both IPv4 and IPv6. The process for the IETF to modify LDP started in 2008 with a draft RFC.

Current State LDPv6
We are still under draft of the RFC. Once approved, it will modify or update RFC 5036 (LDP Specification). We are up to draft 12, which was published on February 5, 2014, and expires January 2015. The draft RFC purposes the following changes to LDP:

  • Adding TTL Security (for both IPv4 and IPv6)
  • Adding the ability to form LDP session over IPv6, including peer discovery over either IPv4 or IPv6
  • Modifying the Forwarding Equivalence Class to support both IPv4 and IPv6
  • Modifying how the LDP Identifier is used; this is still 32 bit, but it does not have to be reachable or applied anywhere on the router
  • Adding address families to support both IPv4 and IPv6
  • Link local address will NOT get labels generated or passed

Once the update is approved, we will be able to configure an LDP session between routers either with IPv4 or IPv6. Once the session is established, labels for either or both IPv4 and IPv6 will be passed over the LDP session. If the routers are able to form an LDP session over both IPv4 and IPv6, the IPv6 session will be preferred and the IPv4 session will be terminated.

The current draft has a lot of support for the vendors. In fact, it was authored by employees of Cisco, Hewlett Packard and Huawei. It looks fairly complete, and at this point, we are waiting for others to look for issues. If no issues are found, hopefully the IETF will approve this version, and we could see code from the vendors in 2015.

Stay tuned.

Related Courses
SPCORE – Implementing Cisco Service Provider Next-Generation Core Network Services v1.0
AMPLS – Advanced Implementing and Troubleshooting MPLS VPN Networks

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