I have two statments on OSPF, are they correct?

1- If I split a single area OSPF to an OSPF domain with area 0 and area 1, and there is just one ABR between area 0 and area 1, The load on CPU will decrease, but there will be no impact on routing table size (RAM usage)

2- If I add one redundant ABR between area 0 and area 1(so, there will be two ABRs) the routing table of each router will increas as much as other area subnets. The CPU load will increases too. So, in terms of RAM usage (routing table size), single-area OSPF uses less RAM than dual-areas OSPF with two ABRs!

  • 1
    In terms of ABRs, you are right. Life is always hard for ABRs :). For the other routers, it depends on the Area Properties. Think of routers that reside in a totally stub/stub area. They will use much less resource. Jul 28, 2022 at 17:00
  • @kayaatabey, think of standard area...non ABRs wil have impact on their resource usage like I said?
    – A.A
    Jul 29, 2022 at 5:15

1 Answer 1


Statement one partly incorrect. At the ABR will contain a LSDB for each area. So the RAM consumption will increase, even if the RIB remains the same. IF the number of prefixes dosn't change, then the CPU impact will result in a negligible increase, but the CPU usage will not decrease. On the internal routers within area 0 and 1 your statement would be correct, but you didn't specify the router type in the statement.

Statement 2 adds even more burden on the ABRs (see above). As far as the internal routers within Area 1, they can see a reduction of CPU/Memory if you are implementing Area 1 as a Stub or Totally Stubby environment. Area 0 will see the additional path options within the LSDB and will ne to process things accordingly (yes increased CPU).

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