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The information in this article applies only to single-topology IS-IS setup. Multi-topology IS-IS works correctly.

It’s a shame but it looks like IPv6 and MPLS TE don’t work together in current IOS releases. The standards are there, but Cisco didn’t find the motivation to implement them yet. The situation is particularly grave if you happen to:

  • run IS-IS as your routing protocol (many large Service Provider networks do);
  • use IS-IS for both IPv4 and IPv6 (makes perfect sense) in single-topology mode (not the best idea);
  • use MPLS TE for traffic engineering and/or fast reroute (not uncommon);
  • use autoroute on MPLS TE tunnels (most people do);
  • run IPv6 natively (without end-to-end MPLS LSP and 6PE).

In this scenario, IS-IS will install autoroute-enabled MPLS TE tunnels in the SPF tree (see autoroute basics for more details) but as IPv6 and MPLS TE tunnels don’t mix, the IPv6 destinations behind the MPLS TE tunnels will not be reachable at all.

MPLS TE issues in IPv6 networks are covered in Building IPv6 Service Provider core webinar (register here).


  1. It’s a shame too, IPv6 cannot be used for a network management (syslog/snmp) - not VRF aware ;(
  2. 6PE != VRF. That's 6VPE. Whether management over IPv6 works in 6PE environment is another issue (GRE tunnels over IPv6 don't).
  3. yes, for 6PE ipv6-based management (syslog/snmp) was ok (not tested in last two years)!
    but for 6VPE it is still impossible. btw AAA is the next challenge...
  4. Anyhow, I would try to keep as much management as possible on IPv4. Easier with fewer bugs and compatibility problems.
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