ospf question

Answered Question
Aug 20th, 2009
User Badges:

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!





Attachment: 
Correct Answer by Edison Ortiz about 7 years 8 months ago

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



  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (1 ratings)
Loading.
Correct Answer
Edison Ortiz Thu, 08/20/2009 - 05:55
User Badges:
  • Super Bronze, 10000 points or more
  • Hall of Fame,

    Founding Member

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



johnspaulding Thu, 08/20/2009 - 05:55
User Badges:

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.

Actions

This Discussion