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New Member

ospf question

Hi all, I have a little bit of a problem understanding the output of some ospf show commands and I was wondering if someone here can help me. Basically I don't understand why the loopback int is showing up on the output command. (see attached configuration and results of show commands)

Thank you very much in advance for your help.

Cheers!

  • WAN Routing and Switching
1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Bronze

Re: ospf question

I don't understand why the loopback int is showing up on the output command.

It's the concept of the OSPF router-ID where the router selects the highest loopback interface, if available, or the highest IP address of any of the physical interfaces as router-ID.

Here is a good tutorial:

http://www.thebryantadvantage.com/CCNACertificationExamTutorialOSPFRouterIDRID.htm

2 REPLIES
Hall of Fame Super Bronze

Re: ospf question

I don't understand why the loopback int is showing up on the output command.

It's the concept of the OSPF router-ID where the router selects the highest loopback interface, if available, or the highest IP address of any of the physical interfaces as router-ID.

Here is a good tutorial:

http://www.thebryantadvantage.com/CCNACertificationExamTutorialOSPFRouterIDRID.htm

New Member

Re: ospf question

If you do a "show ip ospf neighbor" You should see that your loopback will be the router-id unless you specify. OSPF will always choose the loopback as such before any interface even if it has a higher 32 bit number. Thats why it shows up as an advertised router.

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