RE: BGP Load-balancing betw ibgp and ebgp paths

From: ccie2be (ccie2be@nyc.rr.com)
Date: Fri May 27 2005 - 09:54:43 GMT-3

Hi,

Thanks for that idea. It's a very interesting idea but I'm not sure this
will work. Do you know for sure? Have you tested this? At the moment, I
can't test this.

Here's my thinking:

A bgp router knows through it's configuration which peers are ibgp or ebgp.
Because it knows that, I suspect it uses that knowledge to decide what AD to
assign to routes it learns from its peers. And, if it learns a route from
an ibgp peer, it assigns it an AD of 170. But, if it learns a route from an
ebgp peer, it assigns it an AD of 20.

So, I can't imagine that manually changing the AD of ibgp learned routes
will enable load balancing between ibgp and ebgp routes but I do like your
idea. And, maybe for some reason I can't think of it would work.

Thanks, Tim

-----Original Message-----
From: CCIE6296 [mailto:ccie6296@aces-star.com]
Sent: Friday, May 27, 2005 8:11 AM
To: 'ccie2be'; 'Group Study'
Subject: RE: BGP Load-balancing betw ibgp and ebgp paths

Hi Tim,

Use the backdoor command so that the AD for the route learn is same for both
iBGP and eBGP.

Cheers!
csyeo

CS Yeo
CCIE6296, CISSP, PMP, MCSE
http://www.aces-star.com
Your Asia rack rental source.
Ace the CCIE lab

-----Original Message-----
From: ccie2be [mailto:ccie2be@nyc.rr.com]
Sent: Friday, May 27, 2005 4:58 AM
To: Group Study
Subject: BGP Load-balancing betw ibgp and ebgp paths

Hi guys,
 
I now know how to configure BGP to load-balance between paths learned from
either multiple ebgp peers or from multiple ibgp peers.
 
maximum-paths # --- for ebgp peers
 
maximum-paths ibgp # -- for ibgp peers
 
 
But, how is load balancing configured when the same route is learned from
both an ibgp and an ebgp peer?
 
I looked at all the bgp commands available under the bgp process but none
appear to do the trick.
 
Any ideas?
 
TIA, Tim
 
R6(config-router)#bgp ?
  always-compare-med Allow comparing MED from different neighbors
  bestpath Change the default bestpath selection
  client-to-client Configure client to client route reflection
  cluster-id Configure Route-Reflector Cluster-id
  confederation AS confederation parameters
  dampening Enable route-flap dampening
  default Configure BGP defaults
  deterministic-med Pick the best-MED path among paths advertised from
                          the neighboring AS
  dmzlink-bw Use DMZ Link Bandwidth as weight for BGP
multipaths
  fast-external-fallover Immediately reset session if a link to a directly
                          connected external peer goes down
  inject-map Routemap which specifies prefixes to inject
  log-neighbor-changes Log neighbor up/down and reset reason
  redistribute-internal Allow redistribution of iBGP into IGPs (dangerous)
  router-id Override configured router identifier
  scan-time Configure background scanner interval
 
R6(config-router)#bgp best ?
  compare-routerid Compare router-id for identical EBGP paths
  dampening Enable route-flap dampening
  dmzlink-bw Use DMZ Link Bandwidth as weight for BGP multipaths
  inject-map Routemap which specifies prefixes to inject
  med MED attribute
  scan-time Configure background scanner interval

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