December 7, 2023

Network System

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Cisco CCNA Certification Exam Tutorial: The OSPF RID

3 min read

OSPF is a key topic on your CCNA examination, as properly it really should be. OSPF is a greatly-applied WAN protocol, and you will need to master the fundamentals in advance of shifting on to additional sophisticated configurations. 1 this kind of detail is the OSPF Router ID, or RID.

The RID is the dotted decimal value by which other OSPF routers will recognize a given OSPF router. There are some exciting defaults for this benefit, and a command you should really know to hardcode the RID. You experienced also improved know what has to come about for this command to take impact, so let us choose a additional in-depth glimpse at the OSPF RID.

In this example, R1 has an adjacency with R2 and R3 more than the 172.12.123./24 body community. R1 is the hub, with R2 and R3 as the spokes. No other interfaces are OSPF-enabled on any of the routers. Running exhibit ip ospf neighbor on R1, we see some uncommon values underneath “Neighbor ID”, which is another title for the OSPF RID.

R1#display ip ospf neighbor

Neighbor ID Pri State Lifeless Time Handle Interface Total/DROTHER 00:01:57 Serial0 Comprehensive/DROTHER 00:01:57 Serial0

Discover the Neighbor ID of just about every distant tackle is the loopback address. How can that be if they are not OSPF-enabled?

When pinpointing the Router ID (RID) of an OSPF-enabled router, OSPF will constantly use the numerically maximum IP tackle on the router’s loopback interfaces, irrespective of whether that loopback is OSPF-enabled.

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

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

The OSPF RID can be transformed, but it needs a restart or to reinitialize the OSPF routing course of action. Use the router-id command to adjust the default RID of just about every router as revealed, and clear the OSPF system to do so.

R1#conf t

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

R1(config)#router ospf 1


Reload or use “crystal clear ip ospf method” command, for this to choose influence

R1#very clear ip ospf method

Reset ALL OSPF processes? [no]: indeed

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

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

Just after entering the router-id command, the router console informed you that you have to reload the router or reset the OSPF processes for this to just take result. You enter the crystal clear ip ospf course of action command to do this. Observe that when you are asked if you definitely want to do this, the prompt is “no”? That’s due to the fact all the OSPF adjacencies on this router will be misplaced and will have to get started the course of action once again. That is Ok on a practice rack, not superior in a output community. Will not use that 1 at work.

The OSPF RID is not a sophisticated strategy, but the reality that an interface won’t have to be OSPF-enabled in buy to have its IP address act as the RID can take some getting employed to. And recall – when the router or swap asks you a dilemma and the prompted remedy is “no”, acquire one move back and make sure you truly want to do what you might be about to do!

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