Route selection

Mikdilly

Just came across this concept while searching for something else on Yahoo, i've searched thru the ciscopress icnd book and see no mention of it. What else does the odom book not cover but might show up on the 801 exam?

empc4000xl

route selection? Can you be a little more specific on what you are asking. Are you asking about the metrics that determine the best route for a certain protocol, or are you asking about something else?

Mikdilly

Say the router has this in it's routing table:

router# show ip route
....
D 192.168.32.0/26 [90/25789217] via 10.1.1.1
R 192.168.32.0/24 [120/4] via 10.1.1.2
O 192.168.32.0/19 [110/229840] via 10.1.1.3

You want to send something to 192.168.32.100, which route does the router use to send the packet? Since .100 falls within the range for both 192.168.32.0/24 and 192.168.32.0/19, you would think it would be thru 10.1.1.3 since ospf has a lower admin. distance but the router actually will use the rip route because it has a longer prefix.

I don't remember anywhere in the odom book where this was ever discussed. Seems like a pretty important point in terms of routing to me. Do a search on cisco's site for document 8651, it explains it.

Bill Kaster

It won't use rip, it'll use EIGRP which has an AD of 90. Unless the links you're referring to aren't of equal bandwidth, which changes things considerably.

networker050184

The router will use the longest match when routing a packet, in other words the most specific route is chosen to the destination. So in your example it would use the RIP route.