[Xorp-users] XORP BGP supports ECMP?

[Kristian Larsson]

On Sat, Oct 07, 2006 at 10:13:29AM +0200, Vincent Jardin wrote:
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> But, in any cases, ECMP cannot apply to BGP due to its policy of
> selection process of the next hop. Only, static routes, OSPF, RIP and
> ISIS can support it.
> 
> But, if there are any papers or recommandations that show that BGP can
> support ECMP as-is, I'd apprecieate to review it :)
> FYI, it is currently a working draft:
> ~  http://bgp.potaroo.net/ietf/idref/draft-bhatia-ecmp-routes-in-bgp/
> but right now, no implementation supports it.
I'm running a network powered mostly by Cisco
6500s and we're doing multipath
For example:
c6500.k.klm.se# sh ip bgp 216.221.5.0
BGP routing table entry for 216.221.5.0/24, version 6966311
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Multipath: eBGP iBGP
  Not advertised to any peer
  1299 3549 13609
    213.248.78.29 (metric 20) from 85.195.63.14 (85.195.63.14)
      Origin IGP, localpref 120, valid, internal, multipath
      Community: 35706:8 35706:10002
  1299 3549 13609
    213.248.101.53 (metric 20) from 85.195.63.4 (85.195.63.4)
      Origin IGP, metric 0, localpref 120, valid, internal, multipath, best
      Community: 35706:8 35706:10003

As you can see it has chosen a best path, which BGP always
does as it is that path that it tells it peers about, but
it has installed two routes in the FIB as shown by the 
"multipath".
c6500.k.klm.se# sh ip route 216.221.5.0
Routing entry for 216.221.5.0/24
  Known via "bgp 35706", distance 200, metric 0
  Tag 1299, type internal
  Last update from 213.248.101.53 6d16h ago
  Routing Descriptor Blocks:
  * 213.248.78.29, from 85.195.63.14, 6d21h ago
      Route metric is 0, traffic share count is 1
      AS Hops 3
      Route tag 1299
    213.248.101.53, from 85.195.63.4, 6d16h ago
      Route metric is 0, traffic share count is 1
      AS Hops 3
      Route tag 1299

So yes, it's possible with BGP but not with XORPs implementation
(just yet, at least :).

Regards,
   Kristian.

> Vincent
> 
> Pavlin Radoslavov wrote:
> |>Does XORP's BGP support multipath ECMP?
> |>I briefly looked at the code and didn't
> |>see any hint.  Nor did other protocols.
> |
> |
> | No, currently XORP doesn't support ECMP.
> | It is on our TODO list:
> |
> | http://www.xorp.org/bugzilla/show_bug.cgi?id=223
> |
> | Regards,
> | Pavlin
> |
> | _______________________________________________
> | Xorp-users mailing list
> | Xorp-users at xorp.org
> | http://mailman.ICSI.Berkeley.EDU/mailman/listinfo/xorp-users
> 
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-- 
Kristian Larsson                                   KLL-RIPE
Network Engineer                      Net at Once [AS35706]
+46 704 910401			     kristian at spritelink.se