Posts tagged CCIE
This is the first post in a series about OSPF Area Types. Today we’ll go over Stub areas. This one will be somewhat short on config, but should have a good amount of show commands.
Quick refresher, OSPF Stub Areas allow inter- and intra-area routes (Type 2 and Type 3 LSAs). External routes (Type 5 LSAs) are not allowed in stub areas.
(For more detailed information on LSAs and Area Types, check out this post.)
We’ll be using the same topology we used for OSPF Authentication:
I’m not going through the basic OSPF config, so assume everything is configured as the diagram suggests. I’ve also redistributed loopbacks on each router to give us some external routes, and I added 126.96.36.199/32 to Area 34 so we have an intra-area route to look at. Let’s look at some show commands BEFORE we make area 34 a stub:
This post is about the different OSPF authentication methods. It will be part of a series outlining OSPF commands/technologies.
We can configure OSPF to use authentication for an entire area, or just for a single interface. Today we’ll go over both. Here’s the topology:
First we’ll setup authentication for all of area 0:
R1(config)#interface FastEthernet0/0 R1(config-if)#ip ospf message-digest-key 1 md5 cisco R1(config-if)#ip ospf 100 area 0 R1(config-if)# R1(config-if)#router ospf 100 R1(config-router)#area 0 authentication message-digest R2(config)#interface FastEthernet0/0 R2(config-if)#ip ospf message-digest-key 1 md5 cisco R2(config-if)#ip ospf 100 area 0 R2(config-if)# R2(config-if)#router ospf 100 R2(config-router)#area 0 authentication message-digest R3(config)#interface FastEthernet0/0 R3(config-if)#ip ospf message-digest-key 1 md5 cisco R3(config-if)#ip ospf 100 area 0 R3(config-if)# R3(config-if)#router ospf 100 R3(config-router)#area 0 authentication message-digest
Nothing crazy here, we configure OSPF and an MD5 key under our area 0 interfaces, then we specify that all of area 0 should use MD5 authentication. Note that the commands differ slightly if we want to use clear-text, it would be “ip ospf authentication-key [key]” and “area 0 authentication” under the OSPF 100 process.
R1#sh ip ospf neigh Neighbor ID Pri State Dead Time Address Interface 188.8.131.52 1 FULL/DR 00:00:32 10.1.123.2 FastEthernet0/0 184.108.40.206 1 FULL/DROTHER 00:00:35 10.1.123.3 FastEthernet0/0 R1#sh ip ospf int fa0/0 ... Message digest authentication enabled Youngest key id is 1
Everything is working, our neighbors are up and we see that authentication is enabled with the key we specifcied. Note, if we leave off a key, the neigbhors will still form and MD5 will still be enabled, but it will say key 0:
This is the second OSPF post I’ll be doing for CCIE lab preparation. Today I’m posting the tasks, then tomorrow or the day after (or possibly after the weekend, depending how busy I am) I’ll post the walkthrough. If any of you work on this before the walkthrough, leave a comment.
Here’s the topology:
(Click image for fullsize)
Here are the tasks:
1. Configure R1, R2 and R3′s S0/0 interfaces in Area 0. Ensure that DR and BDR are elected. Advertise all loopback0s on all routers into OSPF.
2. Configure R1 as the default gateway for all OSPF routers. Do not use the “default-information” command.
3. Configure R6 to use the path through R4 to get to area 0 Do not use any interface level commands to accomplish this.
4. Configure R4 to filter any type 3, 4, 5 and 7 LSAs from entering area 45.
This is the walkthrough for OSPF Lab #1.
Here’s the topology:
Here is task one:
1. Configure R1′s s0/0.102 interface and R2′s s0/0.201 interface in area 12, this area should not receive any Type 5 LSAs. Configure R1′s s0/0.103 interface and R3′s s0/0.301 interface in area 13, R1 should only receive a default route from R3, no other OSPF routes should be in R1′s RIB (from R3). Do not use network statements to accomplish this task.
R1(config)#interface Serial0/0.102 point-to-point R1(config-subif)#ip ospf 100 area 12 R1(config-subif)# R1(config-subif)#interface Serial0/0.103 point-to-point R1(config-subif)#ip ospf 100 area 13 R1(config-subif)# R1(config-subif)#router ospf 100 R1(config-router)#area 12 stub R1(config-router)#area 13 stub R2(config)#interface Serial0/0.201 point-to-point R2(config-subif)#ip ospf 100 area 12 R2(config-subif)# R2(config-subif)#router ospf 100 R2(config-router)#area 12 stub R3(config)#interface Serial0/0.301 point-to-point R3(config-subif)#ip ospf 100 area 13 R3(config-subif)# R3(config-subif)#router ospf 100 R3(config-router)#area 13 stub no-summary
Here we configure OSPF 100 under the routers’ interfaces (avoiding network statements). Then we configure R1 and R2′s link/area as a stub. Last we configure R1 and R3′s link/area as a totally stubby area, preventing R3 from sending anything buy a default route to R1.
This is the first little challenge I’m posting on here. If you frequent the forums, you likely saw the one I had for OSPF. I thought of another challenge while talking to a buddy. Here’s the topology:
Make R1 prefer the path through R3 for the 192.168.1.0/24 network. The configuration must be on R1. Do not use Weight or Local Preference to accomplish this. Assume that all previous configuration is correct.
This one is a little different than the OSPF challenge in that there are many ways to accomplish it. I’ve thought of a few, I want to see what everyone else comes up with.