From: Frank Jimenez (franjime@xxxxxxxxx)
Date: Mon May 06 2002 - 22:20:20 GMT-3
Howard, does this feature, intoduced in 12.2(4)T, match what you're
discussing below?
BGP Conditional Route Injection
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft
/122t/122t4/ftbgpri.htm
Thanks,
Frank Jimenez, CCIE #5738
franjime@cisco.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Howard C. Berkowitz
Sent: Monday, May 06, 2002 6:03 PM
To: ccielab@groupstudy.com
Subject: RE: Redist: Filtering vs Fail-over
I'm going to back up a bit and explore the problem that is to be
solved, which I recognize may or may not have anything to do with the
lab solution.
First, let's look for a moment at "optimal routing." Unless both
links have enough capacity to handle the entire workload, either of
them going down is going to result in suboptimal performance,
assuming the IGPs use a closest exit routing policy.
Second, much of large scale routing aims less at always finding the
optimal route than minimizing routing protocol churn. So, I'll ask
again, what is being optimized? In a real-world situation, an
oscillating route situation can crash routers and/or produce huge
amounts of protocol traffic.
There are several different ways I could conceive of this problem.
Let's start with the Doyle example. With the 5 router test network,
real performance isn't an issue, but with many more routers, it might
be a good and conscious decision to let Bumble be blackholed in the
interest of the overall network.
If BGP were involved, this might be a very good thing to handle with
conditional advertisement, even putting a simple BGP "shim" AS on
Bumble and Grimwig.
I hope Cisco will extend the idea of conditional advertisements to
IGPs, and/or do something that Bay RS does. In Bay RS, if any
component of a summary address goes down, the summary is no longer
advertised, just the more-specifics. Unfortunately, in the Doyle
example, the addresses aren't aggregatable, so this sort of solution,
common in BGP even without conditional advertisement, isn't available.
If the idea of optimization is for Bumble never to be blackholed than
yes, the book solution is probably quite reasonable. It's somewhat
analogous to restoring a partitioned OSPF backbone with a virtual
link.
Simply remember, when you are "optimizing," you need to be clear WHAT
and WHY you are optimizing.
-- "What Problem are you trying to solve?" ***send Cisco questions to the list, so all can benefit -- not directly to me*** ************************************************************************ ******** Howard C. Berkowitz hcb@gettcomm.com Chief Technology Officer, GettLab/Gett Communications http://www.gettlabs.com Technical Director, CertificationZone.com http://www.certificationzone.com "retired" Certified Cisco Systems Instructor (CID) #93005
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