Subject: RE: missing issue - implemented route selections not necessarily consistant with draft

From: "Natale, Jonathan" <[email-masked]>
Date: Thu, 24 Oct 2002 16:32:57 -0400

this is my unofficial understanding of this...

first the router id's were used

then there was a "bug" that said they should not be used,
and this bug was fixed so the oldest route was used

then they came up with "bgp bestpath compare-routerid"
to restore the older behavior

*i think* this applies to the peer ip (next step)

not sure how the clust-list applies here

-$0.02

-----Original Message-----
From: Pedro Roque Marques [mailto:[email-masked]] 
Sent: Thursday, October 24, 2002 2:26 PM
To: Jeffrey Haas
Cc: [email-masked]
Subject: missing issue - implemented route selections not necessarily
consistant with draft

Jeffrey Haas writes:

> Reviewing my inbox, I think we dropped an issue - or I've misplaced 
> the resolution of it.

> Our route selection tie-breaking process in -17 doesn't match at least 
> two of the $LARGE_ROUTER_VENDORs.

> Noted differences are (per vrishab sikand): 1) originator ID (to be 
> substituited for router id, when present in path attribute) 2) cluster 
> list length 3) peer id (configured ip address of peer in the neighbor 
> command)

- What about arrival time of a route as decision factor... ?
I believe there are implementations that choose the 'older' route (whatever
that is) before router-id in certain circunstances.

Which may seen as a behaviour in which the route selection does not depend
on the route attributes entirely...

  Pedro.

---

From: Daniel Walton <[email-masked]>
Date: Fri, 25 Oct 2002 09:02:14 -0400 (EDT)

> and this bug was fixed so the oldest route was used

The "prefer the oldest external" step was added to prevent a variation of the
MED churn.

> to restore the older behavior

Customers asked for a knob :)

> not sure how the clust-list applies here

The oldest external check only makes a difference if you are comparing two
external routes and this happens right before the router-ID check.  Comparing
peer addresses is the last step, after the router-ID and cluster-list length
have tied.

Daniel