By default, ospf will send 4 hello packet for every ten seconds, if there is no reply within 40 seconds, this ospf will be declared as down. If I want shorten the ospf time. Let's say, I want to declare the ospf neighbor is alive or not within 8 seconds. Then, which method below I need to choose?
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Method 1 unless you also desire to change the number of missed hellos.
BTW, later IOSs support subsecond and/or OSPF with BFD which allows you to detect down neighbors in under a seconds.