From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Tue Oct 12 2004 - 14:01:52 GMT-3
Sam,
I would speculate that it's picking the one from the neighbor
that originated it because it would be learned sooner that the one from
the route reflector. Everything is equal up to the oldest route
decision. Do a hard clear between the router and the neighbor that is
originating the prefix, and see if the best path moves over to the
route-reflector.
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Sameh El Tawil
> Sent: Monday, October 11, 2004 3:28 PM
> To: ccielab@groupstudy.com
> Subject: BGP best path selection with route reflectors
>
> Hi Group,
> I have seen in one of the examples in the Karl Solie book volume-2
that he
> was
> using the route-reflector-client command for all neighbors in an AS
with
> three
> fully-meshed routers. The result is to have every route appearing
twice in
> the
> BGP table; one time from the direct session with the originating
neighbor,
> and
> the second time reflected from the other router.
>
> When I configured this example in the lab, I was surprised to see that
the
> route coming from the originator directly is always preferred over the
> reflected one. I am wondering which step in the best path selection
> algorithm
> tells the router to make this choice. Unless I am missing something,
there
> is
> no rule to choose the route learned from the route's next hop over the
> same
> information coming from the route reflector.
>
> Any ideas?
>
> Here is some output to illustrate:
>
> - 10.2.2.0 is originated by the neighbor (by the network command on
the
> neighbor)
> - 62.121.0.0 is originated by neighbor (learned from an EBGP
session on
> that neighbor)
>
> 2612#sh ip bgp 10.2.2.0
> BGP routing table entry for 10.2.2.0/24, version 27
> Paths: (2 available, best #1, table Default-IP-Routing-Table)
> Advertised to non peer-group peers:
> 108.201.14.1
> Local
> 192.168.1.2 (metric 74) from 192.168.1.2 (192.168.253.4)
> Origin IGP, metric 0, localpref 100, valid, internal, best
> Local
> 192.168.1.2 (metric 74) from 10.1.1.2 (192.168.254.1)
> Origin IGP, metric 0, localpref 100, valid, internal
> Originator: 192.168.253.4, Cluster list: 192.168.254.1
>
> 2612#sh ip bgp 62.121.0.0
> BGP routing table entry for 62.121.0.0/16, version 25
> Paths: (2 available, best #2, table Default-IP-Routing-Table)
> Advertised to non peer-group peers:
> 108.201.14.1
> 203
> 10.1.1.2 from 192.168.1.2 (192.168.253.4)
> Origin IGP, metric 0, localpref 100, valid, internal
> Originator: 192.168.254.1, Cluster list: 10.2.5.1
> 203
> 10.1.1.2 from 10.1.1.2 (192.168.254.1)
> Origin IGP, metric 0, localpref 100, valid, internal, best
> 2612#
>
> Cheers,
> Sameh
>
>
This archive was generated by hypermail 2.1.4 : Sat Nov 06 2004 - 17:11:46 GMT-3