CastelloReece916
OSPF is a significant topic on your CCNA exam, as effectively it must be. OSPF is a widely-utilised WAN protocol, and you need to have to understand the fundamentals before moving on to far more complicated configurations. A single such detail is the OSPF Router ID, or RID.
The RID is the dotted decimal worth by which other OSPF routers will identify a provided OSPF router. There are some fascinating defaults for this value, and a command you must know to hardcode the RID. You had also far better know what has to occur for this command to take effect, so let's take a a lot more detailed look at the OSPF RID.
In this example, R1 has an adjacency with R2 and R3 over 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. Running show ip ospf neighbor on R1, we see some uncommon values below "Neighbor ID", which is another name for the OSPF RID.
R1#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
3.3.3.three Complete/DROTHER 00:01:57 172.12.123.3 Serial0
two.2.two.2 Full/DROTHER 00:01:57 172.12.123.two Serial0
Notice the Neighbor ID of every remote address is the loopback address. How can that be if theyre not OSPF-enabled?
When figuring out the Router ID (RID) of an OSPF-enabled router, OSPF will always use the numerically highest IP address on the routers loopback interfaces, regardless of regardless of whether that loopback is OSPF-enabled.
What if there is no loopback? OSPF will then use the numerically highest IP address of the physical interfaces, regardless of regardless of whether that interface is OSPF-enabled.
BOTTOM LINE: An interface does not have to be running OSPF to have its IP address employed as the OSPF RID.
The OSPF RID can be changed, but it needs a restart or to reinitialize the OSPF routing process. Use the router-id command to adjust the default RID of every router as shown, and clear the OSPF process to do so.
R1#conf t
Enter configuration commands, a single per line. Finish with CNTL/Z.
R1(config)#router ospf 1
R1(config-router)#router-id 11.11.11.11
Reload or use "clear ip ospf method" command, for this to take effect
R1#clear ip ospf procedure
Reset ALL OSPF processes? [no]: yes
1d05h: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.three.three on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached
1d05h: %OSPF-5-ADJCHG: Process 1, Nbr two.two.2.2 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached
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 take impact. You enter the clear ip ospf procedure command to do this. Notice that when youre asked if you genuinely want to do this, the prompt is no? Thats due to the fact all the OSPF adjacencies on this router will be lost and will have to begin the approach once more. Thats OK on a practice rack, not excellent in a production network. Dont use that a single at operate.
The OSPF RID is not a difficult concept, but the reality that an interface doesn't have to be OSPF-enabled in order to have its IP address act as the RID takes some getting utilised to. And keep in mind - when the router or switch asks you a query and the prompted answer is "no", take one particular step back and make positive you genuinely want to do what you happen to be about to do! click here for
