State of LDPv6 and 6PE

One of my readers successfully deployed LDPv6 in their production network:

We are using LDPv6 since we started using MPLS with IPv6 because I was used to OSPF/OSPFv3 in dual-stack deployments, and it simply worked.

Not everyone seems to be sharing his enthusiasm:

Now some consultants tell me that they know no-one else that is using LDPv6. According to them “everyone” is using 6PE and the future of LDPv6 is not certain.

I would believe that the future of LDPv6 is uncertain because the vendors are furiously pushing segment routing, be it as a control-plane addition to MPLS data plane or as a completely new IPv6-based data plane.

However, let’s start with the basics. If plan to use IPv4+IPv6 throughout your network, and already use LDP, then LDPv6 is the natural way to go. However:

  • While you can run LDPv6 on Junos, IOS XR, and Nokia/ALU1, there’s still no LDPv6 on Arista EOS or Cisco IOS XE (more details)
  • LDP/IGP interactions are tricky, and introducing LDPv6 will more than double your headaches – now you’ll have to deal with OSPF/LDP and OSPFv3/LDPv6 interactions.

6PE is an obvious alternative, and since L3VPN and EVPN often cannot use IPv6 next hops, it might still make sense to stay with an IPv4-only core transport network if you plan to offer more than simple IPv4/IPv6 transport. 6PE is also supported on a wider variety of platforms than LDPv6.

In greenfield networks, SR-MPLSv62 would be a viable alternative to LDPv6, assuming it’s supported by the platforms you’re interested in3. It would also simplify your protocol stack, particularly if you use IS-IS as the routing protocol.

Finally, if you need an excuse to burn way too much money replacing still-working gear with the latest gizmos while ensuring job security for the next decade or so, you could decide to go for an IPv6-only network implementing all services with SRv6. I wish you plenty of luck, and would love to hear how well it worked out for you.

Update: June 2023

Mark Tinka, the author of the LDPv6 in the Real World presentation sent me a brief update on the state of LDPv6 in Cisco gear:

We have been running LDPv6 since 2019, and while we had initial issues with varying levels of interoperability between Junos and IOS XR back then, everything has been smoothed out and it’s all working nicely and stably.

Sadly, IOS XE still has no support, while IOS XR does. Cisco have no interest in adding support to IOS XE, for obvious reasons. In fact, they aren’t even suggesting SR-MPLS or 6PE as an option, but rather SRv6. What’s worse, on IOS XE platforms where Cisco support SR-MPLS, they don’t support it for IPv6 signaling in the IGP.

For whatever unfathomable reason, the product mix in their network shifted heavily toward Juniper. Who would have thought…

Revision History

Added an update on the lack of LDPv6 in Cisco IOS XE

  1. At least we did make some progress since the last time someone mentioned LDPv6 on my blog in 2009. ↩︎

  2. Or however we should write that combo of acronyms ↩︎

  3. According to netlab SR-MPLS implementations, Arista EOS, Junos, Nokia SR Linux and Nokia SR OS support IPv6 SID while Cisco IOS XE does not. ↩︎

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