OSPF STUB
Scenario:
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.
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