Cisco CCNA Certification Exam Tutorial: The OSPF RID
De BISAWiki
OSPF is just a major subject in your bridge saw CCNA examination, as well it ought to be. OSPF is just a widely-used WAN protocol, and you'll need to understand the basic principles before moving forward to more difficult configurations. One particular detail may be the OSPF Router ID, or RID.
The RID may be the dotted decimal value through which a given OSPF router will be identifyed by other OSPF routers. There are several interesting defaults used cnc with this value, and a command you need to know to hardcode the RID. You had also better understand what needs to happen with this command to take effect, so let us take a far more step-by-step consider the OSPF RID.
In this example, R1 has an adjacency with R2 and R3 within the 172.12.123.0/24 frame network. R1 may be the center, with R2 and R3 because the spokes. No other interfaces are OSPF-enabled on the hubs. Running show ip address ospf neighbor on R1, some unusual values are seen by us under "Neighbor ID", that is another name for the OSPF RID.
R1#show ip address 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 every remote address may be the loopback address. Just how can that be if theyre not OSPF-enabled?
The numerically highest IP address will be always used by OSPF on the routers loopback interfaces, whether or not that loopback is OSPF-enabled, when identifying the Router ID (RID) of an OSPF-enabled modem.
What if there is no loopback? OSPF will make use of the numerically highest IP of the physical interfaces, whether or not that software is OSPF-enabled.
BOTTOM LINE: An interface does not have to be running OSPF to have its IP used because the OSPF RID.
The OSPF RID could be changed, however it takes a restart or to reinitialize the OSPF routing process. Make use of the router-id command as shown to change the default GONE each router, and clear the OSPF process to do this.
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1( config )#router ospf 1
R1( config-router )#router-id 11.11.11.11
Reload or use "clear ip address ospf process" command, for this to take effect
R1#clear ip address ospf process
Reset ALL OSPF techniques? [no]: yes
1d05h: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or separate
1d05h: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or separate
After entering the router-id order, the router console informed you that you have to reload the router or reset the OSPF techniques with this to take effect. The clear ip ospf process command is entered by you to achieve this. Realize that if you truly might like to do this when youre asked, the prompt is not any? Thats since most of the OSPF adjacencies with this router will be lost and will need to start the method again. Thats OKAY on a training sheet, negative in a production network. Dont use any particular one at the job.
The OSPF RID isn't an intricate bridge saw idea, but the undeniable fact that so as to have its IP become the RID a screen does not have to be OSPF-enabled takes some getting used to. And remember - if the hub or switch asks you a question and the encouraged response is "no", just take one step back and ensure you really would like to do what you're planning to do!
