SR/MPLS Security Framework

A long-time friend sent me this question:

I would like your advice or a reference to a security framework I must consider when building a green field backbone in SR/MPLS.

Before going into the details, keep in mind that the core SR/MPLS functionality is not much different than the traditional MPLS:

  • The data plane is the same. Ingress nodes add a stack of MPLS labels to each incoming layer-3 packet, and the rest of the network uses those labels for packet forwarding.
  • You still need a functioning IP network core, so you need a set of routing protocols to propagate end-user prefixes and next hops.

The only significant difference between traditional MPLS and SR/MPLS is the label allocation process:

  • Traditional MPLS uses locally-significant labels, whereas SR/MPLS uses network-wide Segment Identifiers.
  • Traditional MPLS uses LDP to assign labels to entries in the IP forwarding table. In contrast, SR/MPLS attaches node- or adjacency segment identifiers to routing protocol data structures, eliminating an extra control-plane protocol and synchronizing MPLS forwarding with IP forwarding.
You can use network-wide labels in novel solutions like TI-LFA, but that’s a topic for another day.

The security recommendations for an SR/MPLS backbone thus don’t differ from those I would make for a traditional MPLS backbone:

  • Make sure it’s impossible to enable core routing protocols or form routing protocol adjacencies on customer-facing interfaces.
  • Whenever someone breaks into the transport backbone, it’s game over. You could use encryption (but it has to be below MPLS encapsulation) to make the intruder’s life a bit more miserable (keeping in mind that the key distribution tends to be the most vulnerable bit).
  • Someone could attach a third-party device to a transport link, so you’d better use routing protocol authentication.
  • Finally, use the usual hardening practices on the PE- and P-devices. It doesn’t help if you do everything right just to have someone do a password recovery on one of your boxes.

Want more details? You can find them in the Security Framework for MPLS and GMPLS Networks (RFC 5920), or you can read the relevant chapter in the MPLS and VPN Architectures, Volume II book.


  1. MACSec on underlay core across the board would simplify upper layer protocols IMO, i.e. if MACSec is underlay, then you could probably skip extra work of auth config on the protocols. Just my opinion though, for doing less work than may be needed, but also simplifies stuff in an org, where you have lower level engineers who'd just mess stuff up the more complex the network gets.

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