From: McNeace, Roger (RMcNeace@ciena.com)
Date: Thu Mar 03 2005 - 17:41:48 GMT-3
Usually a static route to a null interface is used for summary routes
to prevent route loops.
Example
------> Default Gateway
-------10.1.1.x----R1------R2------------------------R3 send packet
10.1.1.1/24
10.1.2.0 <-----summary
10.1.0.0/26
10.1.3.0
etc
1. R2 has default to R3
2. R2 has summary for 10.1.0.0/16 and specific routes, advertises
summary to R3
3. 10.1.1.0/24 route goes away at R1
4. R2 now has no specific route to 10.1.1.0/24
5. R3 send packet to 10.1.1.1 via R2
6. R2 finds no match to 10.1.1.0/24, sends packet back to R3 -Default
route
7. R3 sends packet back to R2, route is now in a loop unitl ttl expires
If R2 had static route 10.1.0.0/16 to a NULL interface, R2 would have
dumped packet to the bitbucket, thus preventing a route loop.
Roger McNeace CCIE#12777
Prinicipal Network Engineer
Ciena Corporation
410-694-5805
rmcneace@ciena.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
jacque vincent
Sent: Thursday, March 03, 2005 3:09 PM
To: ccielab@groupstudy.com
Subject: BGP and null0 interface
I start doing bgp practice labs and I do not understand the use of tha
NULL0 interface. It is the first time I am using the static routes with
NULL0 interface.
Can somebody explain me when do we need to use the static route directed
to NULL0 interface in BGP ?
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