Cisco CCNA Certification Exam Tutorial: The OSPF RID

OSPF is a big subject on your CCNA test, as nicely it should be. OSPF is a greatly-utilized WAN protocol, and you need to find out the fundamentals prior to shifting on to additional challenging configurations. One particular such element is the OSPF Router ID, or RID.

The RID is the dotted decimal benefit by which other OSPF routers will establish a specified OSPF router. There are some appealing defaults for this value, and a command you need to know to hardcode the RID. You experienced also improved know what has to take place for this command to acquire result, so let us take a much more in-depth search at the OSPF RID.

In this case in point, R1 has an adjacency with R2 and R3 about the 172.12.123./24 frame network. R1 is the hub, with R2 and R3 as the spokes. No other interfaces are OSPF-enabled on any of the routers. Operating exhibit ip ospf neighbor on R1, we see some unconventional values below “Neighbor ID”, which is a different name for the OSPF RID.

R1#display ip ospf neighbor

Neighbor ID Pri Condition Dead Time Address Interface

3.3.3.3 Entire/DROTHER 00:01:57 172.12.123.3 Serial0

2.2.2.2 Entire/DROTHER 00:01:57 172.12.123.2 Serial0

Recognize the Neighbor ID of each distant address is the loopback tackle. How can that be if they are not OSPF-enabled?

When determining the Router ID (RID) of an OSPF-enabled router, OSPF will normally use the numerically maximum IP address on the router’s loopback interfaces, no matter of whether that loopback is OSPF-enabled.

What if there is no loopback? OSPF will then use the numerically optimum IP handle of the actual physical interfaces, regardless of no matter if that interface is OSPF-enabled.

Bottom LINE: An interface does not have to be managing OSPF to have its IP deal with applied as the OSPF RID.

The OSPF RID can be improved, but it needs a restart or to reinitialize the OSPF routing system. Use the router-id command to change the default RID of each and every router as revealed, and obvious the OSPF system to do so.

R1#conf t

Enter configuration commands, 1 per line. Conclude with CNTL/Z.

R1(config)#router ospf 1

R1(config-router)#router-id 11.11.11.11

Reload or use “obvious ip ospf process” command, for this to take influence

R1#very clear ip ospf process

Reset ALL OSPF processes? [no]: yes

1d05h: %OSPF-5-ADJCHG: Approach 1, Nbr 3.3.3.3 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached

1d05h: %OSPF-5-ADJCHG: System 1, Nbr 2.2.2.2 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached

Soon after entering the router-id command, the router console knowledgeable you that you have to reload the router or reset the OSPF procedures for this to consider outcome. You enter the obvious ip ospf course of action command to do this. Observe that when you are requested if you definitely want to do this, the prompt is “no”? That is mainly because all the OSPF adjacencies on this router will be misplaced and will have to commence the approach once again. Which is Okay on a practice rack, not excellent in a generation network. Don’t use that a person at get the job done.

The OSPF RID is not a intricate strategy, but the reality that an interface isn’t going to have to be OSPF-enabled in order to have its IP deal with act as the RID will take some receiving utilised to. And remember – when the router or change asks you a issue and the prompted response is “no”, just take 1 step again and make sure you actually want to do what you might be about to do!