[PATCH] bgp deterministic med

Ondrej Zajicek santiago at crfreenet.org
Sun Nov 27 22:50:08 CET 2011

On Wed, Nov 23, 2011 at 09:13:17PM +0400, Alexander V. Chernikov wrote:
>> But as you already wrote the patch i could look at it.
> It will be great. This version is rather hackish.

I found how this feature could be implemented in a much simpler
way - if we just add to a route some 'suppress' flag (which causes
the route to be skipped in the best route selection) and some
rte_suppress protocol callback that is called before the best
route selection that allows the protocol to suppress routes from
other instances of the protocol.

Because the deterministic-med best route selection can be considered
as two-level linear ordering (one within the group of routes with the
same neighbor ASN, and one with a slightly different ordering on
the best routes from groups) we could move the lower level to the
suppress protocol callback (when all routes besides the best in group
would be marked as suppressed) while the standard rte_recalculate
would process the unmarked best routes from groups.

This approach makes almost no changes to rte_recalculate() or
bgp_rte_better(), and as with a route update only one or two
best-in-group routes can change, we virtually cache the other
best-in-group routes so the best path selection would be probably faster
than with rte_best approach. It will also work consistently without
global deterministic-med option (which is problematic in BIRD approach).
I will implement it soon.

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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