Bird 2.0 AS path prepending

[Ondrej Zajicek]

On Wed, Dec 20, 2017 at 06:11:42PM +0100, Daniel Czerwonk wrote:
> Hello bird users,
> 
> I just started to test bird 2.0 and converted the existing bird 1.6
> configuration to bird 2.0. I compiled bird 2.0.0 on my fedora test VM
> and got it running. But when I use path prepending in BGP (the same way
> I did in 1.6) bird throws an error and does not export the route. Does
> anyone have the same problem?

Hello

The problem is related to the change that in BIRD 2.0.0, an export filter
is called before BGP-specific export route modifications (including
implicit ASN prepend), while in older versions it was after these route
modifications. But i forgot to describe the change in the documentation
and/or 2.0 migration guidelines, sorry.

The side effect of the change is that when 'bgp_path.prepend(202739)' is
called for non-BGP route, the bgp_path attribute is not yet defined.
A workaround is to use something like:

if !defined(bgp_path) then bgp_path.empty();

before the first prepend, which will define the bgp_path attribute, so it
can be prepended. We will fix it to make prepend() automatically define
the attribute if not defined.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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