Hi,

I have encountered what seems to be a bug of sorts in the Juniper implementation of BFD in at least their SRX340.

We have no issues with the QFX series, where BFD seems to work as expected with bird.

I'm wondering if there is anything we can do to handle this issue on the bird side, or if anyone has any insight that may shed some light on the behaviour we are seeing.

Here is the issue summary:

BFD timers are set quite conservatively

interval 4000 ms
multiplier 6

A BFD session between a bird endpoint and a juniper endpoint is up and running at the start - all fine
If the you stop bird on the server, after the Detection time [ currently 24 secs ], the BFD messages from the Juniper show status as Down with the Diagnostic message Control Detection Time Expired. You can then start bird on the server again, and the two sides will agree session info and BFD status goes Up. - This is expected.
However, if you stop bird, but start it again before the Detection time [ currently 24 secs ], like for a service restart, the BFD messages from the Juniper never show as Down, and the two sides never agree on a BFD session and BFD remains Down on the server but Up on the Juniper. - Should a new session be established at this point ?
Once the Juniper gets stuck in the BFD status Up state, then you can stop the bird for a long time [ over an hour at least ] , and the Juniper never seems to notice [ the BFD packets still show state Up ]. - This seems to be a bug n the juniper end - why should it never go Down in this state ?
If the BFD session info is reset on the Juniper side, then the two sides will agree session info and BFD status goes Up.

Does anyone have any thoughts ?

Is there a packet bird can send, gratuitous or not, that can make the juniper end realise it MUST reinitialize ?

Any config that can be tweaked to help ?

Cheers,

Just

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