Where to from here? Probably OSPF…

Well, being away from a while presents me with the dilemma of trying to decide where to go from here for the next few weeks and months. I could ramble on whatever's on my mind that day, changing topics each time, or try to get something more cohesive going. Should I talk about the value of certs? Lab gear (again)? Pick a techie topic? Alas, so many choices, so little time.

I'll probably jump around a bit in the coming month or two, but I've decided to start out with a post or two on OSPF. Not new, not snazzy, but in my most recent survey in this blog, asking about CCNA topics people might like to hear about, OSPF was near the top. (IPv6 is there already, and I did a few posts on it this past June, here and here.)

I also surveyed on CCNP topics, if you want to look there - so maybe I'll do something on MPLS or BGP coming up.

To do this right, I need your help. I'm wondering what is it about OSPF that makes it a challenge for CCNA candidates. Is it the link state theory? Is it figuring out how much Link State theory you need to really know? Is it the trickier-than-average config? Is it the sometimes-confusing output from the various "show ip ospf..." commands? If it's hands on, maybe I could post a lab exercise that could be done on gear, or maybe not, something like this:

Three routers connect to one LAN switch, with the switch placing all three routers in the same VLAN. Assume all hardware is cabled and has no physical problems. Each router uses their respective Fa0/0 interfaces. Configure each router as shown here, and save the configs. Then reload the switch. Finally, using show commands, determine:

  1. The Router ID of each router
  2. The DR (if it exists)
  3. The BDR (if it exists)                 
  4. OSPF intra-area routes learned at each router
  5. OSPF inter-area routes learned at each router
  6. Number of Type 2 LSAs known on each router
  7. Number of Type 3 LSAs known on each router
  8. Number of neighbors in the full state on each router

That's not a lot of detail on a lab, but it's enough to try if you've got three routers handy. If you don't, you could look at the config, and think about what should happen just based on the configuration.

Just for grins, while I give you some time to weigh in on what in particular is troublesome about OSPF, you try the above "lab" with the following configs. Note that this lab, in my opinion, requires much more thought and time than any particular CCNA exam question - it's just a tool for learning and discussing. Some of this may well even be more like CCNP level topics, but it makes for a more interesting discussion.

R1:

  • Hostname R1
  • Interface loopback 0
  •  Shutdown
  •  Ip address 5.5.5.5 255.255.255.255
  • Interface fa0/0
  •  Ip addr 10.1.1.1 255.255.255.192
  •  No shutdown
  • Router ospf 1
  •  Network 10.1.1.0 0.0.0.255 area 0
  •  Network 5.5.5.5 0.0.0.0 area 1

R2:

  • Hostname R2
  • Interface Fa0/0
  •  Ip address 10.1.1.222 255.255.255.192
  •  No shutdown
  • Router ospf 1
  •  Network 10.1.1.0 0.0.0.255 area 0

R3:

  • Hostname R3
  • Interface loopback 2
  •  Ip address 3.3.3.3 255.255.255.0
  • Interface loopback 4
  •  Ip address 2.2.2.2 255.255.255.255
  • Interface fa0/0
  •  Ip address 10.1.1.33 255.255.255.192
  •  No shutdown
  • Router ospf 2
  •  Network 10.0.0.0 0.255.255.255 area 0
  •  Network 2.2.2.2 0.0.0.0 area 0
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