Path on Aaron's Worthless Words

BGP Notes - Path Decision

Thu, 09 Jun 2011 00:00:00 +0000

This is required blogging…and reading for that matter. A good chunk of this is taken from my CCNP posts from last year. Corrections, please.

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How does a BGP router decide which BGP route is the best?

Next-hop : Does the router have a route to the next-hop?

Weight : This is a numeric value where bigger is better. Weight is not passed onto other peers and is a Cisco proprietary feature.

BGP Notes - Path Attribute Categories

Wed, 08 Jun 2011 00:00:00 +0000

Make my corrections! Please!

Well-known mandatory : These PAs must be recognized by all BGP routers and passed along to other peers.

Well-known discretionary : These PAs do not need to be in every update, but they must be recognized by all BGP routers.

Optional transitive : These PAs don’t have to be recognized but they must be passed along to other BGP peers if they are present in an update.

EIGRP Notes - Unequal Cost Path Load Balancing

Mon, 06 Jun 2011 00:00:00 +0000

Per the standard rules, please correct anything that’s wrong.

One of EIGRP’s big features is the ability to use unequal cost paths for load balancing. This is done with the variance command.

variance : A multiplier used to calculate which feasible successors can be used as active routes. The router takes integer and multiplies it by the successor’s feasible distance, and any FS with a an FD less than this new number gets submitted to the routing table manager.

ROUTE Notes - Controlling BGP

Tue, 06 Jul 2010 00:00:00 +0000

Corrections, please. I skipped a bunch of BGP intro stuff to get to the juicy center. I’ll see if I can come back later and finish the other parts for posterity.

Study Notes

Is BGP route selection a controversial subject?

Yes. If you ask 1000 network guys the best way to influence BGP, you’ll probably get 1000 different answers.

At what position in the PA list of a BGP update do you find the weight attribute?

You don’t. Weight is a Cisco-proprietary thing.

Stubby Post - Path Cost of EtherChannels

Tue, 27 Apr 2010 00:00:00 +0000

I was doing some STP labs tonight and found something that caught me off guard a bit. I had been meddling with some EtherChannels between a pair of 3750s earlier today, and I forgot to reset the configs before starting on the STP stuff. One my secondary root switch, I ran a show spanning-tree vlan 1 to see what status the ports were in, and I noticed the root path cost.