EIGRP questions

Hi All,

I bought the CCNP module a few weeks back and am so far very impressed with the quality of the videos and content of the site - well done!

I have some questions around EIGRP which maybe you can help me with.

  1. Regarding default routes with EIGRP, which is the most commonly used way of injecting a default route into EIGRP? I know you can either redistribute, use the 'default-network' command or advertise a static of 0.0.0.0/0 using the 'network' command, but which do you use in a production environment and why? Is there a best practice associated with this? As far as I can tell, the advertisement of 0.0.0.0/0 seems to be the best as it is not reliant on a Classful address, nor does it produce an AD of 170 when redistributed.
  2. Is there any particular reason that a loopback interface,by default, has a delay of 50us when created? Is this the same for all IOS versions? It caught me out the other night and was wondering if there are any other caveats with this.
  3. With EIGRP, is it always best practice to turn off auto-summary? I know it is with RIP but i know that it works quite differently than EIGRP as it always uses classful advertisement when advertised to the same major network?

Thanks and I hope you can help.

James

 

Comments

  • 1. Yes - it is either redistribution of static or network command approach. You do not run across default-network becuase of the issues you described.

    2. I have never seen anything documented regarding the delay value of loopback - very interesting.

    3. Yes - auto-summarization is always turned off in production and the certification environments as a "default" action.

  • Hi James,

    See answers inline. 



    On Sep 3, 2010, at 1:58 PM, "jdunn" <[email protected]> wrote:

    Hi All,

    I bought the CCNP module a few weeks back and am so far very impressed with the quality of the videos and content of the site - well done!

    I have some questions around EIGRP which maybe you can help me with.

    1. Regarding default routes with EIGRP, which is the most commonly used way of injecting a default route into EIGRP? I know you can either redistribute, use the 'default-network' command or advertise a static of 0.0.0.0/0 using the 'network' command, but which do you use in a production environment and why? Is there a best practice associated with this? As far as I can tell, the advertisement of 0.0.0.0/0 seems to be the best as it is not reliant on a Classful address, nor does it produce an AD of 170 when redistributed.
    In a real world design it depends if you have multiple exit points out of the network. In the ace that you do, you might want to prefer one over the other, or remove one default route if an sit point goes down. If there's only one path and one default, it doesn't really matter how you advertise it.  

    1. Is there any particular reason that a loopback interface,by default, has a delay of 50us when created? Is this the same for all IOS versions? It caught me out the other night and was wondering if there are any other caveats with this.
    It's pretty much an arbitrary value. You can change it if you want to but there's usually no reason to. 
    1. With EIGRP, is it always best practice to turn off auto-summary? I know it is with RIP but i know that it works quite differently than EIGRP as it always uses classful advertisement when advertised to the same major network?
    Generally yes you want to turn it off. This way if you want to summarize you have full control by using the interface summary command. 

    HTH,

    Brian McGahan, CCIE #8593 (R&S/SP/Security)
     
    Internetwork Expert, Inc.
    Toll Free: 877-224-8987 x 705
    Outside US: 775-826-4344 x 705
    Online Community: http://www.IEOC.com

    Thanks and I hope you can help.

    James

     




    Internetwork Expert - The Industry Leader in CCIE Preparation

    http://www.internetworkexpert.com


  • Thanks both, that answers it - much appreciated.

    Keep up the good work.

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