OSPF is a crucial theme on your CCNA exam, as capably it should be. OSPF is a widely-used WAN protocol, and you requirement to acquire the nitty-gritty beforehand traveling on to more convoluted configurations. One specified item is the OSPF Router ID, or RID.
The RID is the blemished decimal worth by which opposite OSPF routers will identify a fixed OSPF skilled worker. There are few out of the ordinary defaults for this value, and a order you should cognize to hardcode the RID. You had too superior cognize what has to happen for this charge to yield effect, so let's whip a much elaborated air at the OSPF RID.
In this example, R1 has an contiguousness next to R2 and R3 all over the 172.12.123.0/24 carcass exchange cards. R1 is the hub, next to R2 and R3 as the spokes. No remaining interfaces are OSPF-enabled on any of the routers. Running provide evidence ip ospf neighbor on R1, we see many wacky belief nether "Neighbor ID", which is another baptize for the OSPF RID.
R1#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
3.3.3.3 0 FULL/DROTHER 00:01:57 172.12.123.3 Serial0
2.2.2.2 0 FULL/DROTHER 00:01:57 172.12.123.2 Serial0
Notice the Neighbor ID of all removed address is the loopback address. How can that be if they're not OSPF-enabled?
When seminal the Router ID (RID) of an OSPF-enabled router, OSPF will ever use the numerically extreme IP address on the router's loopback interfaces, thoughtless of whether that loopback is OSPF-enabled.
What if in that is no loopback? OSPF will after use the numerically uppermost IP code of the physical interfaces, heedless of whether that surface is OSPF-enabled.
BOTTOM LINE: An surface does not have to be running OSPF to have its IP address used as the OSPF RID.
The OSPF RID can be changed, but it requires a start up or to reinitialize the OSPF routing procedure. Use the router-id decree to changeover the defaulting RID of all trained worker as shown, and crystal clear the OSPF modus operandi to do so.
R1#conf t
Enter design commands, one per dash. End near CNTL/Z.
R1(config)#router ospf 1
R1(config-router)#router-id 11.11.11.11
Reload or use "clear ip ospf process" command, for this to filch effect
R1#clear ip ospf process
Reset ALL OSPF processes? [no]: yes
1d05h: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface trailing or detached
1d05h: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface hair or detached
After ingoing the router-id command, the skilled worker console table up on you that you have to charge the skilled worker or device the OSPF processes for this to run upshot. You get in the forgive ip ospf practice command to do this. Notice that once you're asked if you genuinely deprivation to do this, the indication is "no"? That's because all the OSPF adjacencies on this trained worker will be squandered and will have to begin the activity over again. That's OK on a practice rack, not corking in a manufacture web. Don't use that one at occupation.
The OSPF RID is not a tortuous concept, but the information that an surface doesn't have to be OSPF-enabled in command to have its IP computer address act as the RID takes many exploit used to. And bring to mind - once the trained worker or switch asks you a query and the prompted statement is "no", run one rung back and form certain you truly deprivation to do what you're something like to do!
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