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By Administrator in All, Cisco, Routing protocols

We are publishing this short post as we noticed a number of visitors to our website who have landed here via related search queries.

So, the main advantages of using a loopback interface on a Cisco router with OSPF enabled are:

  • Since the loopback interface is a virtual interface, it is always up and this gives you a stable, never-changing Router ID. Using a loopback address is the preferred way of setting the Router ID as compared to the router-id command. (At least according to some big Cisco books :)CCNP BSCI Official Exam Certification Guide, Fourth Edition, Brent D. Stewart)
  • As the OSPF interface priority is usually left at the default value of 1, the Designated Router is practically elected based on the highest Router ID. Using a loopback interface, you could afford to directly manipulate the Designated Router and Backup Designated Router election process by more or less setting loopback addresses of your choice. Any additional changes to the network topology (any routers or physical interfaces being added or removed from the segment) would not lead to DR and BDR changes either as you would be able to set the loopback addresses accordingly.

In a nutshell, using a loopback interface on a router with OSPF enabled would help you to have a more stable, converged OSPF segment.

Note: We actually believe that in a network which would not utilize the BGP protocol, it might be more appropriate to use the router-id command as problems are only likely to occur if both BGP and OSPF are running.

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4 Responses

  1. GopikumarJune 9, 2012 @ 11:16 amReply

    Great work… The whole site is really amazing with technical contents….

    Thank You

  2. WOW! I studied on it but never noticed that DR and BDR could be manipulated this way!
    Interesting and Thank you! :-)



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