Loopback interface and OSPF

Is this loopback address also called the logical address, and the Router ID should be the highest logical address?

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Is there any other reason to configure a loopback address for OSPF other than changing the Routers ID? Such as, ensures that an interface is always active for OSPF?

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Steve C

as far as i have studdied loopbacks are logical interfaces and are used to manage the priority of the routers in one area. so basicly you can set them manualy to the highest IP address in one area making that router the DR, also they never go down (unless the router is physicly turned off), so they solve problems with flapping connections, please correct me if im wrong, thanks allot

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also... if you dont use RIDs you will find troubleshooting OSPF can be nasty. I tend to use low numbers for all routers except the DR/BDR. This makes the "sh ip ospf nei" command a lot easier to read/understand.

also... ospf virtual-links require RID information when being configured.


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be carefull with that statement.

you may actually get hit with a question such as this on the ccna test.

The RID will NOT ... I repeat *NOT* be the one with the highest logical interface.

Remember, loopbacks are not the only logical interfaces on a router. There are also subinterfaces.

To be completely accurate, you should make the statement ...

"The RID will be the highest physical interface on the router ... unless a loopback interface has been configured. If a loop is configured, the RID will be the highest loop address."

Gotta be carefull with wording ... Cisco is very good at tripping you up on semantics.

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