CCNA Skills Lab 3: Part 4

Today’s post wraps up the posts about this lab. Today, rather than leave you with the answers to another chunk of the lab, with some explanations, instead we’ll turn it around into both a troubleshooting and a configuration exercise. First, did the config I supplied for router R4, in the previous post, really work? And if you didn’t lab it yourself, are you confident enough in your OSPF config skills to confidently state whether it should work? Then, for the last lab tasks that I’ve not discussed, I’ll leave it as an open request for ya’ll to supply answers, and I’ll comment about those. And as always, it helps to read the original lab to make sense of all this.

In the last post, I purposefully chose some of R4’s configuration options to make us think. Example 13 repeats that configuration.

Example 13: OSPF Config, R4

interface loopback 1
 ip address 4.4.4.4 255.255.255.255
!
router ospf 4
 network 172.23.4.1 0.0.0.0 area 4
 network 172.23.0.190 0.0.0.1 area 4
!
interface F0/0
 ip address 172.23.4.1 255.255.255.192
!
interface serial 0/0/0
 encapsulation frame-relay
!
interface S0/0/0.1 point-to-point
 ip address 172.23.0.190 255.255.255.192
 frame-relay interface-dlci 101

So here are the questions that might have come to mind if you reviewed that configuration:

1. Does the OSPF process ID on the router ospf 4 command work, considering the other three routers use a router ospf 1 command? Will R4 exchanging routing information with the other routers?
2. Does R4’s network 172.23.4.1 0.0.0.0 area 4 command, with a wildcard mask of 0.0.0.0, allow R4 to truly advertise a route for subnet 172.23.4.0/26? Or does the wildcard mask change what route R4 advertises?
3. Does R4’s network 172.23.0.190 0.0.0.1 area 4 command enable OSPF? What interface IP addresses does this network command match?

Those are the questions, and it’s up to you to ponder and answer. If you answer them here, I’ll post back to comment.
The second part of today’s post is to toss it back to all of you to add the configuration to change the cost for some of the routes. Repeating the two related requirements from part 3 of the original lab:

5. Configure such that R2’s metric for its route to 172.23.3.0/26 is 98
6. Configure such that R3’s metric for its route to 172.23.4.0/26 is 104

To influence the cost of a route with OSPF, you have a couple of options. You can change the OSPF interface cost directly, using the ip ospf cost x interface subcommand. You can also change the cost as calculated by IOS if the interface cost isn’t directly configured, by configuring the interface bandwidth command. And, you can change all such calculations by changing the denominator of that calculation, using the router subcommand auto-cost reference-bandwidth mbps.
There are lots of config options that give you the right answer. If you’re interested, create your config, post it here, and I’ll make a comment. If you lab it up, check the interface costs with the show ip ospf interface command, and check the cost for each route with the usual show ip route command.
That’s it! Jump in and respond if interested.