Categories Cisco


Cisco Pete’s company uses OSPF for their dynamic routing protocol. R-1 has been having some issues since R-4 was added to the network. After troubleshooting you notice that R-1 is an older router that could probably use a memory upgrade and it’s processor is not optimal. Cisco Pete is low on money due to COVID-19…So hitting up Cisco for a new router is out of the option. Instead you want to consolidate your routing table to free up processes and make management of R-1’s routing table easier. Thus you research and come across stubbing OSPF.

Advantages of stub:

  • Minimize the size of routing table / Cleaner management
  • Minimize the number of LSA type 1 advertisements

Things to remember:

  • Area 0 can’t become a stub because it’s considered backbone.
  • Area doing ASBR can’t be stubbed. This wold stop the route redistribution. (e1/e2 routes)
  • Area with Virtual links (Virtual area) can’t be a stub.
  • Every router in the area must be stubbed in order for the neighborship to form. Otherwise you will see the stub flap due to stub mismatch.

When I stub area 10 I am expecting all my E1/E2 routers to become a single O *IA route. On all routers for area 10 we will need to configure 1 command.

router ospf 1
area 10 stub

Notice now I have no route listed for the 14.x.x.x networks. However, we’re still able to ping it. This is because router 3 is the ABR and redistributing those E1/E2 routes from R4 as a default route advertisement.

If we check our OSPF routing table on R-3 (This is the ABR). It will still hold the more specific routes.

All lab configurations will be on next pages.