BIRDs allowas-in functionality

Ondrej Zajicek santiago at
Tue Jan 18 14:05:07 CET 2011

On Sun, Jan 16, 2011 at 06:20:43PM +0100, Bartek Kois wrote:
> Hi 
> I`ve got two networks in different locations without any connection between
> them. In each of them I`ve got two BGP routers connected to two separate
> ISP`s. Both networks have the same AS number but their BGP routers propagate
> different prefixes (different /23 prefix for each network). The thing is
> that hosts inside one network don`t see hosts in the second network, because
> of BGP anti-loop mechanism.
> Typically this problem can be solved by using "allowas-in" directive. How to
> achieve the same functionality in BIRD configuration?

It is not possible to do currently (such behavior is not really standard).
But it would not be a problem to add an option for ignoring loop check to
the next version.

If you are able to modify sources and recompile BIRD, you could just remove
these lines (1418-1419) from proto/bgp/attrs.c:

  if (bgp_as_path_loopy(bgp, a)) 
      goto loop;

Elen sila lumenn' omentielvo

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