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