From: john matijevic (matijevi@bellsouth.net)
Date: Wed Sep 15 2004 - 14:10:55 GMT-3
Carlos,
Can you tell us which version of 12.2(T) version it is listed under? I
could not find it documented anywhere, and I also tried on a T version
and did not see it listed as well.
Sincerely,
John Matijevic, CCIE #13254, MCSE, CNE, CCEA
CEO
IgorTek Inc.
151 Crandon Blvd. #402
Key Biscayne, FL 33149
Hablo Espanol
305-321-6232
http://home.bellsouth.net/p/PWP-CCIE
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Carlos G Mendioroz
Sent: Wednesday, September 15, 2004 12:59 PM
To: James
Cc: Jongsoo.Kim@Intelsat.com; ziutek@mac.com; ccielab@groupstudy.com
Subject: Re: BGP reachability issues Lab 2 Cisco Press
Be VERY careful with next-hop-unchanged implementation of some 12.2T
versions. The command works but it does not make it to the stored
config, so a reload will make it vanish :-(
James wrote:
> On Wed, Sep 15, 2004 at 11:43:52AM -0400, Jongsoo.Kim@Intelsat.com
wrote:
>
>>James
>>
>>BGP protocol will choose which next hop to use for a BGP route.
>>But still it is IGP's decision which interface to use to reach the
next hop.
>>
>>Nexthop 10.90.90.1 for 2.2.2.0/29 is selected on R6 by iBGP process
learned
>>from R1.
>>However, which interface R6 to use to reach 10.90.90.1 is based on IGP
>>process ( OSPF in this case).
>>So R6 will forward any packet of 2.2.2.0/29 to R4 via F/R interface.
>>
>>In the same way, R4 learned 2.2.2.0/29 from two eBGP connections from
R1 and
>>R6.
>>But it chooses R6's peer address as nexthop as you said higher IP
address
>>(unless bgp loadbalance is enable.)
>>To determine which interface to use to reach 10.6.6.6, R4 will check
IGP and
>>forward to F/R interface going to R6.
>>
>>If you make bgp nexthop unchanged on R1 so that R4 choose 10.90.90.1
as
>>nexthop for 2.2.2.0/29, then still R4 will rely on IGP to select the
proper
>>interface to forward.
>
>
> Yes, being a programmer myself writing own BGPd implementation, I am
familiar
> with how BGP works to select best path ;-)
>
> I think it was more of confusion between us in previous email
exchanges.
> I may have misunderstood what you were saying in the first email..
>
> Anyhow, 10.90.x.x is clearly closer to reach via R1 in R4's
perspective at
> least if your setup your IGP as the book requested. IGP may reroute,
but as
> you say, things like that in lab is probably rare.
>
> Thanks,
> -J
>
>
-- Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
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