We are running IGP as OSPF with multiple areas and observing high CPU only in couple of routers. These routers are configured ABR and the router CPU is constantly peaking due to OSPF. Though there are many other routers which are configured as ABR with less CPU only these routers are heavily loaded with CPU.
Is there any way to specifically troubleshoot the OSPF issue
How do we identify the cause of the issue due to what process in OSPF
If your high CPU is indeed caused by OSPF, often OSPF area topology calculation is the culprit caused by topology instability (e.g. link flapping).
Is yours a pure Cisco environment, or is there any brand "X"? Reason I ask, Cisco's implementation of OSPF has some "tweaks" that many other implementations don't offer which can impact OSPF.
At the moment, unable to offer any other suggestions, although Cisco's web site might offer some additional tech notes or white papers on the subject. Other posters might yet offer some additional suggestions.
Assuming you find and fix the cause of the issue, longer term, you might want to carefully review you OSPF topology. How OSPF is implemented has much control over how it responds to adverse situations. That's why you have general rules like no more then 3 areas per ABR or 50 routers per OSPF area, but such general rules aren't really "one size fits all".
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