When an OSPF design is planned, which implementation can help a router not have memory resource issues?

A. Have a backbone area (area 0) with 40 routers and use default routes to reach external destinations.

B. Have a backbone area (area 0) with 4 routers and 30,000 external routes injected into OSPF.

C. Have less OSPF areas to reduce the need for interarea route summarizations.










 

Suggested Answer: D. Have multiple OSPF processes on each OSPF router. Example, router ospf 1, router ospf 2.

Memory issues usually come up when too many external routes are injected in the OSPF domain. A backbone area with 40 routers and a default route to the outside world would have less memory issues compared with a backbone area with 4 routers and 33,000 external routes being injected into OSPF. Router memory could also be conserved by using a good OSPF design. Summarization at the area border routers and use of stub areas could further minimize the number of routes exchanged.
The total memory used by OSPF is the sum of the memory used in the routing table ( show ip route summary ) and the memory used in the LSDB. The following numbers are a "rule of thumb" estimate. Each entry in the routing table will consume between approximately 200 and 280 bytes plus 44 bytes per extra path. Each
LSA will consume a 100 byte overhead plus the size of the actual LSA, possibly another 60 to 100 bytes (For router links, this depends on the number of interfaces on the router). These amounts should be added to memory already used by other processes and by the IOS itself.
If you really want to know the exact number, you can do a show memory with and without OSPF being turned on. The difference in the processor memory used would be the answer.

This question is in 300-101 Cisco Implementing Cisco IP Routing (ROUTE) Exam
For getting Cisco Certified Network Professional (CCNP) Routing and Switching Certificate




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