Cisco Hands On Training Podcast
Summary: These podcasts include recordings of hands-on Cisco exercises. I recommend you scrounge or buy 3 routers, build a triangle, and follow along.
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- Artist: Darrell Root
Podcasts:
In BGP, MED stands for Multi Exit Discriminator. It is a well-known optional attribute which allows one autonomous system to inject it's IGP route metrics into its BGP advertisements to another BGP autonomous system. This allows the second autonomous system to make intelligent routing decisions regarding which of multiple paths to take to send traffic to a particular destination in the first autonomous system. Because different AS's use different IGP's and can calculate metrics in different ways, by default MEDs are only compared when multiple paths exist between the same two autonomous systems. BGP MEDs are fairly late in the BGP route selection process, coming after local-preference and AS-PATH length. In this episode we show how to inject MEDs into BGP advertisements, and how they are used to influence routing decisions.
We filter BGP routes in 4 different ways.
We put together what we learned about eBGP, iBGP, and OSPF.
An iBGP example with 1 autonomous system with 3 routers.
An eBGP example with 3 autonomous systems with 1 router each.
An introduction to BGP theory.
OSPF routes should be filtered or summarized at area border routers.
OSPF's fundamental design is that all routers in an area have the same exact view of the network topology. This is fundamentally incompatible with filtering routes within an area. As a result OSPF distribute lists do not have the same effect as RIP distribute lists. In fact, using distribute-lists within an OSPF area is dangerous.
OSPF totally stubby areas and not-so-stubby areas are ways to improve OSPF scalability. But they can be very confusing.
We cover OSPF stub areas and neighbor synchronization.
We redistribute from RIPv2 into OSPF and introduce autonomous system boundry summary LSAs and external summary LSAs.
We introduce multiple OSPF areas and network summary LSA's.
We show a single area OSPF network and go into router and network link state advertisements (LSA's) in detail.
A brief tutorial on Dijkstra's Shortest Path First Algorithm. This algorithm is used by most link state routing protocols, including OSPF and IS-IS.
RIP version 2 includes subnet information in the route advertisement. It also improves efficiency by multicasting to RIPv2 routers instead of broadcasting to all hosts.
