BFD multihop with Junos

[Ondrej Zajicek]

On Tue, Mar 12, 2019 at 01:04:28PM -0400, Arzhel Younsi wrote:
> Bingo! As soon as I the system TTL to 255, the session went up. Thanks a lot!
>
> Now that we know where to look, we started to dig a bit in the code to not have to change the TTL system wide but only for Bird.
> 
> It seems like there a TODO to make the TTL value customizable: https://github.com/BIRD/bird/blob/master/proto/bfd/packets.c#L453
> And in some (so far unknown) cases, it sets the TTL to 255 https://github.com/BIRD/bird/blob/master/proto/bfd/packets.c#L456

That is for single-hop BFD cases. As i wrote in the previous e-mail:

> For single-hop BFD sessions, the RFC 5880 requires TTL security
> mechanism and therefore BIRD specifies outgoing TTL 255.

You can just change it to "sk->ttl = 255;" and recompile.

Is this 'min-recv-TTL 254' some special setting in Juniper, or its
default BFD behavior? If the second case, then perhaps it would be best
to make a bugreport to Juniper as they have packet checks that are not
requested by BFD specifications.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."