CCIE Candidate

03/05/2007 - 1.25 hours. Chapter 9 EIGRP write-up starts.
03/10/2007 - 2.5 hours. Chapter 9 EIGRP write-up completes.
03/12/2007 - 1.0 hour. Reading chapter 10 OSPF, started it anyway. Read the first major section, about how LSA’s are managed, including a painful section on what happens if you were to totally misconfigure your frame-relay network [...]

path attribute - a BGP update field that any number of things about the included prefix
BGP table - the router’s table of BGP prefixes, not the same as the IP routing table
BGP Update - a message sent from one BGP router to another, contain prefixes with matching path attributes

Last but not least in this journey of BGP discovery, the BGP process has to actually put routes in the local router’s IP routing table. Often, this process is as simple as BGP choosing the best route (based on the criteria in last section of the chapter), and using that to populate the IP [...]

Whereas the previous section of the book focuses on building the local BGP table, the next section of the book focuses on how a BGP router advertises routes to neighbors and inject learned BGP prefixes into the local routing table.
BGP routers inform their neighbors about BGP routes with BGP Update messages. The format is [...]

We need to talk about how BGP builds its table with routing information. BGP is not all that different from an IGP - you can use “network” statements in the router bgp paragraph, you learn about routes from a neighbor, and you can redistribute routes from another routing protocol. It’s worth mentioning that [...]

Presumably, the basic operation of BGP isn’t news to you. If you’re brand new to BGP, then my synopsis of the OECG chapters on BGP are likely to leave you befuddled. You’ll need to get a good book on BGP, or spend some quality time with the many BGP papers available at cisco.com. [...]

The final entry of the week for chapter 11…the “definitions” at the end.
default route - the gateway of last resort, 0.0.0.0/0. The route used when no other route matches in the routing table
route redistribution - injecting routes from one routing protocol into another

Ah, our old friend the default route - the catch-all, the safety net. He’s the guy that says “If you don’t know where else to forward this packet, forward it here.” If all else fails, the default route has you covered. For a concept that seems so simple, there are considerations when [...]

Moving on in this chapter of miscellaneous nifty things you can do with routing protocols, we come to route summarization. The idea is that you can reduce the size of your routing table by summarizing a bunch of smaller routes into a single larger route. For instance, let’s say a router was connected [...]

When you get into mutually redistributing routes (routes from protocol A into protocol B and vice-versa) with multiple routers, you run the risk of redistributing an already redistributed route. Thus the router may prefer a route because of administrative distance, and not because of route metrics. This can lead to route inefficiency, and [...]

There are times that you don’t want to redistribute all routes from one protocol into another. Route maps can help you with this, allowing you to select which routes to redistribute. Also, you can use route maps to manipulate routes before you redistribute them.
Consider the following brief IOS code example:

Route redistribution is the black art of taking routes learned from one routing protocol, and injecting them into the advertisements of another routing protocol. Say you’ve got an OSPF network and and EIGRP network, side by side. The OSPF network runs 10.110.0.0/16 subnets. The EIGRP network runs 10.90.0.0/16 subnets. As is, [...]

In the context of the OECG, the book has spoken mostly about a single routing protocol at a time. Much of the purpose of this chapter is to highlight the issues that arise when running multiple routing protocols on a router at the same time. That introduces a number of challenges, including how [...]

Prefix lists are, for me, the big-boy way to make lists of routes. While they don’t give you the granular ability of an ACL when it comes to layer 4 matching (port numbers), prefix lists are easier to read and offer greater flexibility than access-lists if all you’re trying to do is generate a [...]

This chapter of the OECG covers IGP route redistribution, route summarization and default routing. That’s a wee bit long to put into the blog article title, so I abbreviated to “Redistribution, Etc.” If you don’t like it, sue me. It’s not a terribly long chapter, covering only 33 pages of [...]