Go CCIE Go!! - A Cisco Certified Internetwork Expert

Synchronization is off BTW.
For a moment I was thinking that BGP somehow levitated above the IGP layer and operated regardless of the IGP decision process.
Thanks for putting my straight!

—–Original Message—– From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of adufour@metlife.com Sent: 27 May 2008 18:54 To: Chris Gray Cc: ccielab@groupstudy.com; nobody@groupstudy.com; adufour@metlife.com Subject: Re: Having a bad moment with BGP / IGP
Hello Chris,
Is synchronization on? If so, turn it off. Also, either way, the IGP packet will still have a destination to a subnet that it does not know about (IGP back-hole). If the IGP does not know about the destination network and there’s no default route, the packet will be dropped. Basically, the intermediate router does a route look-up on the final destination (not next hop at this point) and says, I don’t have the route to the final destination in my routing table. In a CCIE lab-type of scenario, a tunnel could be used between the 2 bgp speaking neighbors so that the intermediate igp router never sees the final true destination on any packets sent it’s way; it will only see the source/destination as being the points of the tunnel rather than in a remote AS (for example).
Synchronization being off will allow the routes to be advertised even if the IGP is not in synch with BGP, it does not, however, changes the basic “laws” of routing and route lookups.
Just my 2 cents.
Andre

“Chris Gray” Sent by: nobody@groupstudy.com 05/27/2008 01:41 PM Please respond to “Chris Gray”
To ccielab@groupstudy.com cc
Subject Having a bad moment with BGP / IGP

Hi,
This may sound like a stupid question, but I have been studying now for 5 days solid so my brain may be fried..
I seem to have lost grip on BGP and how it interacts with IGP.
I have a set of routes in by BGP table , for which the next hop is known and pingable by my IGP on the same router. When I try and ping the BGP routes I get timeouts from an intermediate IGP router because it doesn’t know the route to my BGP destination. It does however know the route to the BGP next hop.
If I put a static default route out to my BGP Backbone router in this intermediate IGP router I get a ping, but this isn’t correct or practical..
Have tried all the usual next-hop-self tricks but this just changes the BGP next hop to another IGP address which is also accessible through my IGP and I get the same timeout.
Have also advertised my LO0 networks in BGP and run an extended ping from my LO0 as source, makes no difference.
I am definitely missing something here.
Where am I going wrong people!
Thanks in advance
Kriz