From: Brown, Nelson (Nelson.Brown@nasdaq.com)
Date: Wed Oct 20 2004 - 12:57:21 GMT-3
I've been trying to solve this problem for a while, and I haven't been able to come up with a solution. Given the following topology:
R1 R2
| |
------------------------
| |
R3 R4
* R1 and R2 have no routing protocol enabled.
* R1 and R2 have specific static routes via both R3 and R4.
* R1, R2, R3, and R4 all have CDP enabled and see each other in their neighbor tables.
* R3 and R4 both have router odr configured.
* R1 and R2 both learn of R3 and R4 as default gateways via ODR, with R4 being preferred.
* This is fine in the case of R2.
* R1 should only use R3 as a default gateway.
* R1-R4 are all connected via shared media (i.e. there is no intelligent intermediate device on which to filter the CDP messages)
So, I guess my question is how to accomplish one of the following:
1.) filter only R4 CDP announcements from being processed by R1.
2.) receive the R4 CDP announcementss, but not install the default route to R4.
3.) manipulate the distance of ODR default routes on a per-destination basis.
I've tried turning this into a bridging/filtering question by using access-expression filters on R1's e0 interface to block CDP (protocol -0x2000) or destination MAC 0100:0ccc:cccc from R4's source MAC, while moving the IP address up to a BVI. Unfortunately, the router seems to process the CDP/ODR at the e0, rather than bridging it up to the BVI, so the access-expression is never evaluated.
Also, I don't see any way to manipulate the generated default route to keep it from being installed. Creating a static default with AD 255 to R4 doesn't black-hole the route from being installed, as ODR comes in and installs it with AD 160. I'm also not aware of any CDP commands that I could use to
Any suggestions? Thanks for any light you can shed.
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