From: Sean C (Upp_and_Upp@hotmail.com)
Date: Fri May 27 2005 - 10:47:39 GMT-3
Hey Tim,
Hold on a moment -
iBGP AD is 200
eBGP AD is 20.
external EIGRP AD is 170 (perhaps that is what you're thinking of).
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094195.shtml#topic2
Using the BGP network backdoor command will change the AD of the eBGP route
to an AD of 200 - so the eBGP prefix AD will be equal to the AD of an iBGP
prefix. But please understand, the backdoor command wasn't created to equal
the route selection of an eBGP and a iBGP route. Like you wrote, all things
being equal, the router will still take choose the eBGP route over the iBGP
route - even if at an AD of 200. The backdoor command was created so the
router will now select an IGP route (not necessarily an iBGP route) over an
eBGP prefix with the default AD of 20.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/iprrp_r/ip2_n1g.htm#wp1041089
HTH,
Sean
----- Original Message -----
From: "ccie2be" <ccie2be@nyc.rr.com>
To: "'CCIE6296'" <ccie6296@aces-star.com>; "'Group Study'"
<ccielab@groupstudy.com>
Sent: Friday, May 27, 2005 8:54 AM
Subject: RE: BGP Load-balancing betw ibgp and ebgp paths
> 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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