Cisco CCNA Certification Test Tutorial: The OSPF RID

OSPF is a big topic on your CCNA examination, as perfectly it ought to be. OSPF is a broadly-utilised WAN protocol, and you need to have to study the fundamentals just before transferring on to more challenging configurations. A person these depth is the OSPF Router ID, or RID.

The RID is the dotted decimal benefit by which other OSPF routers will recognize a specified OSPF router. There are some interesting defaults for this worth, and a command you should know to hardcode the RID. You had also greater know what has to happen for this command to consider result, so let us just take a far more in-depth look at the OSPF RID.

In this instance, R1 has an adjacency with R2 and R3 more than the 172.12.123./24 frame community. R1 is the hub, with R2 and R3 as the spokes. No other interfaces are OSPF-enabled on any of the routers. Operating present ip ospf neighbor on R1, we see some strange values underneath “Neighbor ID”, which is yet another name for the OSPF RID.

R1#clearly show ip ospf neighbor

Neighbor ID Pri Point out Lifeless Time Address Interface

3.3.3.3 Total/DROTHER 00:01:57 172.12.123.3 Serial0

2.2.2.2 Whole/DROTHER 00:01:57 172.12.123.2 Serial0

Observe the Neighbor ID of every single distant address is the loopback tackle. How can that be if they’re not OSPF-enabled?

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

What if there is no loopback? OSPF will then use the numerically greatest IP handle of the bodily interfaces, irrespective of whether that interface is OSPF-enabled.

Base LINE: An interface does not have to be running OSPF to have its IP deal with made use of as the OSPF RID.

The OSPF RID can be changed, but it necessitates a restart or to reinitialize the OSPF routing process. Use the router-id command to modify the default RID of each and every router as proven, and crystal clear the OSPF system to do so.

R1#conf t

Enter configuration commands, a single per line. Conclusion with CNTL/Z.

R1(config)#router ospf 1

R1(config-router)#router-id 11.11.11.11

Reload or use “crystal clear ip ospf approach” command, for this to get influence

R1#crystal clear ip ospf procedure

Reset ALL OSPF processes? [no]: indeed

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

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

After entering the router-id command, the router console educated you that you have to reload the router or reset the OSPF procedures for this to get impact. You enter the apparent ip ospf approach command to do this. Notice that when you happen to be questioned if you truly want to do this, the prompt is “no”? Which is because all the OSPF adjacencies on this router will be missing and will have to begin the method all over again. Which is Alright on a apply rack, not excellent in a generation network. Will not use that one particular at operate.

The OSPF RID is not a sophisticated strategy, but the actuality that an interface would not have to be OSPF-enabled in purchase to have its IP tackle act as the RID will take some finding used to. And try to remember – when the router or switch asks you a concern and the prompted respond to is “no”, consider 1 move back again and make guaranteed you genuinely want to do what you are about to do!