Cisco CCNA Certification Exam Tutorial: The OSPF RID - 0 views
started by Cobb Riber on 12 Jun 13
started by Cobb Riber on 12 Jun 13
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started by Cobb Riber on 12 Jun 13
The RID is the dotted decimal worth by which other OSPF routers will recognize a offered OSPF router. There are some interesting defaults for this worth, and a command you need to know to hardcode the RID. If you think you know anything, you will likely require to compare about in english. In case you need to identify more on found it, there are thousands of online resources people might think about pursuing. You had also far better know what has to happen for this command to take effect, so let's take a more detailed appear at the OSPF RID.
In this instance, 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 unusual values below "Neighbor ID", which is an additional name for the OSPF RID.
R1#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
three.3.3.three Complete/DROTHER 00:01:57 172.12.123.three Serial0
two.two.two.2 Full/DROTHER 00:01:57 172.12.123.two Serial0
Notice the Neighbor ID of every single remote address is the loopback address. How can that be if theyre not OSPF-enabled?
When determining the Router ID (RID) of an OSPF-enabled router, OSPF will usually use the numerically highest IP address on the routers loopback interfaces, regardless of no matter 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 whether or not that interface is OSPF-enabled.
BOTTOM LINE: An interface does not have to be operating OSPF to have its IP address employed as the OSPF RID.
The OSPF RID can be changed, but it demands a restart or to reinitialize the OSPF routing method. Use the router-id command to change the default RID of each and every router as shown, and clear the OSPF approach to do so.
R1#conf t
Enter configuration commands, one 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 process" command, for this to take effect
R1#clear ip ospf method
Reset ALL OSPF processes? [no]: yes
1d05h: %OSPF-five-ADJCHG: Process 1, Nbr 3.3.3.three on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached
1d05h: %OSPF-five-ADJCHG: Approach 1, Nbr 2.2.two.2 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached
Soon 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 effect. You enter the clear ip ospf method command to do this. Notice that when youre asked if you actually want to do this, the prompt is no? Thats simply because all the OSPF adjacencies on this router will be lost and will have to begin the method once more. Thats OK on a practice rack, not excellent in a production network. Dont use that 1 at work.
The OSPF RID is not a difficult notion, but the reality that an interface does not have to be OSPF-enabled in order to have its IP address act as the RID requires some receiving utilized to. And remember - when the router or switch asks you a query and the prompted answer is "no", take 1 step back and make certain you really want to do what you're about to do!.