OSPF Network Type Loopback

By Barooq
Reading across, I found something I didnt know and which I think is very cool.

Ref to RFC 2328

" looped back.
The interface may be looped back in hardware or software. The interface will be unavailable for regular data traffic. However, it may still be desirable to gain information on the quality of this interface, either through sending ICMP pings to the interface or through something like a bit error test. For this reason, IP packets may still be addressed to an interface in Loopback state. To facilitate this, such interfaces are advertised in router-LSAs as single host routes, whose destination is the IP interface address.[4]"

Which simply means that no matter what is the subent mask of my loopback address, it'll be advertised as host route in the OSPF domain, or say a loopback of 1.1.1.1/8 will appear as
"1.0.0.0/32 is subnetted, 1 subnets"

SO, what if I want my actual subnet mask to be advertised ?
All i have to do is to put "ip ospf network point-to-point" in loopback interface config.
 

3 comments so far.

  1. Anonymous January 20, 2009 at 6:58 AM
    i was doing a mock lab at work and ran into this problem, this post helped me out!! thanks, Matt
  2. Mark DeLong August 14, 2010 at 7:54 PM
    I noticed this command available for OSPF and OSPF version 3. But i have not found any reference to why you would want the actual mask (rather than a host route) advertised for a loopback interface. In what situations would you want this behavior??

    Thanks,

    Mark DeLong
  3. GCFA July 9, 2012 at 8:35 AM
    I am also awaiting Mark but this post helps many people like Anonymous.

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