Basic OSPF Single Area Configuration Part 1

Question 1

What are the required OSPF router configuration lines?

Answer 1

router ospf#
ospf router-id
network statements
interface statements
passive interfaces

Question 2

what is the ospf process id?

Answer 2

router(conf t )# router ospf 500
here 500 is the ospf process id
process-id is different than the router-id

Question 3

Is the OSPF process ID locally or globally significant?

Answer 3

OSPF process id is locally significant. You can use different process id on each of the OSPF routers

Question 4

What is the ospf router-id?

Answer 4

OSPF router-id is the router-id for the OSPF process.
Router-id is the unique number with which the OSPF router is identified. Router-id is what is used to identify the OSPF router.

Question 5

How is OSPF different from EIGRP?

Answer 5

OSPF tries to get to the neighbor which knows the destination using the shortest path. Whereas EIGRP tries for the best way to get to the destination directly.
OSPF tries to get to the node which has the link state information for the network the router is trying to reach

Question 6

How does OSPF select the router-id?

Answer 6

1. Checks if router-id is configured
2. If not, it takes the highest loopback interface IP configured
3. If not it takes the highest physical interface IP which is UP
4. If there is no router-id, no loopback interface, no physical interface, then OSPF will not start at all. We need a routeid to start OSPF

Question 7

What are passive and non passive interfaces in OSPF?

Answer 7

Passive interface are the ones which do not have a OSPF neighbor on that link, or any OSPF neighborship established over that link. There will be no hello packets sent over a passive interface.
Non passive interfaces are the ones which have a OSPF neighbor on that link, used to establish and maintain the OSPF neighborship on that link. OSPF hellos’s will be sent on non passive interafces

Question 8

How and where to specify about which interfaces will be passive and non-passive in OSPF config?

Answer 8

router…14:34:17(config)#router ospf 500
router…14:34:27(config-router-ospf)#passive-interface default
^ The above will set all interfaces to passive by default.
router…14:34:32(config-router-ospf)#no passive-interface ethernet 1
router…14:34:58(config-router-ospf)#no passive-interface ethernet 5
^ Above commands used to specify non passive interfaces