OSPF is a main topic on your CCNA examination, as well it must be. OSPF is a greatly-used WAN protocol, and you want to find out the fundamentals ahead of relocating on to additional challenging configurations. One these types of element is the OSPF Router ID, or RID.
The RID is the dotted decimal price by which other OSPF routers will establish a offered OSPF router. There are some intriguing defaults for this price, and a command you ought to know to hardcode the RID. You had also far better know what has to materialize for this command to just take result, so let us just take a extra in-depth glance 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 unconventional values under “Neighbor ID”, which is another identify for the OSPF RID.
R1#show ip ospf neighbor
Neighbor ID Pri Condition Dead Time Address Interface
3.3.3.3 Comprehensive/DROTHER 00:01:57 172.12.123.3 Serial0
2.2.2.2 Comprehensive/DROTHER 00:01:57 172.12.123.2 Serial0
See the Neighbor ID of every single remote handle is the loopback deal with. How can that be if they’re not OSPF-enabled?
When deciding the Router ID (RID) of an OSPF-enabled router, OSPF will always use the numerically best IP tackle on the router’s loopback interfaces, regardless of no matter if that loopback is OSPF-enabled.
What if there is no loopback? OSPF will then use the numerically best IP tackle of the bodily interfaces, regardless of regardless of whether that interface is OSPF-enabled.
Bottom LINE: An interface does not have to be working OSPF to have its IP address used as the OSPF RID.
The OSPF RID can be improved, but it necessitates a restart or to reinitialize the OSPF routing procedure. Use the router-id command to adjust the default RID of each individual router as demonstrated, and obvious the OSPF approach to do so.
R1#conf t
Enter configuration instructions, a single for each line. Conclusion with CNTL/Z.
R1(config)#router ospf 1
R1(config-router)#router-id 11.11.11.11
Reload or use “distinct ip ospf system” command, for this to get influence
R1#distinct ip ospf method
Reset ALL OSPF procedures? [no]: certainly
1d05h: %OSPF-5-ADJCHG: Course of action 1, Nbr 3.3.3.3 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached
1d05h: %OSPF-5-ADJCHG: Course of action 1, Nbr 2.2.2.2 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached
Immediately after coming into the router-id command, the router console knowledgeable you that you have to reload the router or reset the OSPF procedures for this to choose impact. You enter the clear ip ospf system command to do this. Detect that when you might be requested if you actually want to do this, the prompt is “no”? That is mainly because all the OSPF adjacencies on this router will be dropped and will have to start off the approach yet again. That’s Alright on a observe rack, not good in a manufacturing network. You should not use that one particular at work.
The OSPF RID is not a complicated strategy, but the point that an interface isn’t going to have to be OSPF-enabled in get to have its IP handle act as the RID will take some receiving utilised to. And don’t forget – when the router or switch asks you a dilemma and the prompted response is “no”, consider just one stage back and make sure you truly want to do what you are about to do!