[56302] in North American Network Operators' Group
Re: BGP to doom us all
daemon@ATHENA.MIT.EDU (Iljitsch van Beijnum)
Sun Mar 2 06:35:11 2003
Date: Sun, 2 Mar 2003 12:33:47 +0100 (CET)
From: Iljitsch van Beijnum <iljitsch@muada.com>
To: Avi Freedman <freedman@freedman.net>
Cc: <nanog@merit.edu>
In-Reply-To: <200303021112.GAA26972@freedman.net>
Errors-To: owner-nanog-outgoing@merit.edu
On Sun, 2 Mar 2003, Avi Freedman wrote:
> In article <10322.05320.15507@avi.netaxs.com> The Great Sean wrote:
^^^^^^^^^^^^^^
> : I'll be stupid, and ask some questions I've always wondered about.
> : Why should routes learned by eBGP have a higher priority than iBGP?
> Love to know myself.
Consider the situation where two routers have an external path to a
destination, but they both prefer the path over the other. This can
create routing loops and BGP instability as routers keep revoking and
reannouncing their external routes over iBGP.
However, the "external first" rule is a relatively weak one, as it only
kicks in when the BGP route selection algorithm can't decide which route
is better. If you use the local preference, AS path or multi-exit
discriminator to prefer one of the BGP routes, all routers will use this
one, regardless of whether they learn it over eBGP or iBGP.
