Basic Questions on OSPF

What is OSPF(Open Shortest Path First)?

Ans: Open Shortest Path First(OSPF) is a link state Interior Gateway routing protocol. OSPF is a vendor-independent routing protocol, can be used in a multivendor environment. OSPF can be run on the router of Cisco, HP, Juniper, etc.

What is the multicast address used by OSPF?

Ans: Multicast address is used to send Hello packets to all OSPF routers on a network segment. And is used to send OSPF routing information to designated routers on a network segment.

What is the hello and dead interval of OSPF?

Ans: Hello time is 10 seconds and the Dead Interval is 40 seconds.

What is the AD  value of OSPF?

Ans: AD value of OSPF is 110.

How the metric is calculated in OSPF?

Ans: Metric of OSPF is called  COST. Cost = Reference bandwidth / Interface bandwidth in bps.

Where to use OSPF routing protocol?

Ans: OSPF routing protocol can be used in a multi-vendor environment.

What is the difference between neighbor and adjacent in OSPF?

Ans: If routers have exchanged only Hello Packets then they are neighbor only. If routers have exchanged Hello Packets and LSA then they are Adjacent.

What parameters should match for OSPF neighbor formation?

Ans: The following parameter must match: Hello and Dead interval, Network Mask, Area ID, Authentication password.

Which is elected first DR or BDR in OSPF?

Ans: BDR.

What is the router-id selection process in OSPF?

Ans: OSPF router-id selection algorithm works as below:

  • Any Manually configured OSPF Router ID is selected as the OSPF Router ID.
  • If there is no OSPF Router ID configured then Highest IP address on any Loopback Interfaces of the router is selected as the OSPF Router ID.
  • If there are no Loopback Interfaces configured then Highest IP address on its active interfaces is selected as the OSPF Router ID.


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