From: Scott Morris (smorris@ipexpert.com)
Date: Wed Oct 17 2007 - 21:35:20 ART
Ahhh... Then yes, you'd need to get rid of the null route as that's more
specific than 0/0!
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE-M
#153, JNCIS-ER, CISSP, et al.
CCSI/JNCI-M/JNCI-ER
VP - Technical Training - IPexpert, Inc.
IPexpert Sr. Technical Instructor
A Cisco Learning Partner - We Accept Learning Credits!
smorris@ipexpert.com
Telephone: +1.810.326.1444
Fax: +1.810.454.0130
http://www.ipexpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Con
Spathas
Sent: Wednesday, October 17, 2007 1:13 PM
To: smorris@ipexpert.com; 'Cisco certification'
Subject: RE: BGP aggregate-address and null0 route
I don't have the 10.1.3.0/24 subnet in R1's local routing table.
R1 gets a 0/0 from R3 via RIP (which does have the 10.1.3.0/24 in it's local
routing table) which in turn allows R1 to then get to the 10.1.3.0/24
subnet.
However R1 then generates the null route after advertising the 10.1.0.0/16
aggregate into BGP.
R1 then prefers the 10.1.0.0/16 route to null0 as opposed to the 0/0 route
to R3.
I think the distance command is what I was looking for tbh!
Thx...
-----Original Message-----
From: Scott Morris [mailto:smorris@ipexpert.com]
Sent: Wednesday, 17 October 2007 18:00
To: 'Con Spathas'; 'Cisco certification'
Subject: RE: BGP aggregate-address and null0 route
I'm confused on how you are losing connectivity there, since most-specific
routing always wins. So IF you still have the 10.1.3.0/24 network in your
local table anyway, you will never route their packets to Null0.
I might suggest using debug ip packet when you're trying to see the
connectivity issues you're having. That will tell you what's happening and
where it's going!
To make your own life more sane, use an ACL to limit what packets you debug!
On a side note, look at the BGP Distance command and keep in mind that
aggregate null0 routes are considered "local" in nature.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE-M
#153, JNCIS-ER, CISSP, et al.
CCSI/JNCI-M/JNCI-ER
VP - Technical Training - IPexpert, Inc.
IPexpert Sr. Technical Instructor
A Cisco Learning Partner - We Accept Learning Credits!
smorris@ipexpert.com
Telephone: +1.810.326.1444
Fax: +1.810.454.0130
http://www.ipexpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Con
Spathas
Sent: Wednesday, October 17, 2007 12:30 PM
To: 'Cisco certification'
Subject: BGP aggregate-address and null0 route
I think I'm missing something here but for the life of me I can't work it
out...
When you configure an aggregate-address summary in BGP it adds the relevant
summary into the routing table pointing to null0.
Is there any way to remove this?
I have a scenario where a router (R1) running BGP is advertising a summary
to a peer (R2). However another router (R3) is sending R1 a default-route
via RIP.
R3 knows how to get to say 10.1.3.0/24 and R1 uses the default route to R3
to get to this subnet. Things work nicely up to this point.
However when R1 advertises the 10.1.0.0/16 summary into BGP - the route to
null0 is matched on R1 and I lose connectivity to 10.1.3.0/24 from R1.
Thx.
This archive was generated by hypermail 2.1.4 : Fri Nov 16 2007 - 13:11:15 ART