On 16/Jul/20 19:34, Mark Tinka wrote:

BFD on LAG's on IOS XR platforms in a LAN environment don't work. A point-to-point mechanism is required, so we disabled it there. Junos and IOS XE have no problems running BFD on LAG's in LAN's, so we have it on there. This is for within the data centre.

So for the archives, I thought I'd update this comment in case anyone comes across this issue in the future.

If you want to run BFD on a LAG in IOS XR, you need to tell it to do so with the below command:

    conf
     bfd
      mutlipath include location <location-id>

This ensures that at least one physical line card (where a member link may live) hosts the BFD sessions. Without this, the router tries to host the session on the RP, which doesn't work. This also applies to fixed form factor IOS XR-based routers.

In previous versions of IOS XR, enabling BFD without this feature simply kept the BFD sessions down. At some point (not sure when, but we saw this in 6.7.1), IS-IS will remain down if BFD remains down, i.e., having this command is now mandatory.

The error log to signal you to this requirement is not particularly user-friendly:

    %L2-BFD-6-SESSION_NO_RESOURCES

We won't be messing around with BFD on LAG's in IOS XR still, as a matter of course. Too many moving parts compared to how it's done in Junos.

But for anyone who may need this, here you go.

Mark.