Re: AS_PATH length and route selection (WAS: Strange BGP announcement)

[Ben Black <black () layer8 net>]

The key to this is that the administrative preference in question has domain
scope.  Assuming you are correctly implementing iBGP, whether with a full
mesh, reflectors, or confederations, and assuming consistent announcements
from external route originators, then you can't make a loop because the
same policy is in effect for all the routers in the AS.

Incomplete iBGP implementations and router-local administrative preferences
can easily be used to create loops, but that is certainly not a problem
with BGP.


Ben

On Tue, Nov 17, 1998 at 05:49:21PM -0800, Tony Li wrote:
> |  This, of course, leads to many, many other questions (such as the
> |  possibility routing loops caused by different local policies as was seen
> |  with implementations of BGP4), but few of which are of a truly operational
> |  issue.  So I will apologize for starting a thread based on mis-information
> |  and go back to my cave.
>
>
> Different local policies should all be reflected in the LOCAL_PREF, which
> should be distributed to all nodes within the domain.  This should lead to
> consistent decisions within the domain and thus should avoid stable
> forwarding loops.
>
> Tony