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2394 Views 4 Replies Latest reply: Aug 1, 2011 10:49 AM by Gabriel RSS

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static routes main and backup explanation

Aug 1, 2011 12:42 AM

Gabriel 21 posts since
Jul 13, 2011

Hello,

 

I have a question which runs in my head for a while so,  if i have 2 static routes, lets` supose like this:

 

ip route 0.0.0.0 0.0.0.0 1.1.1.1

ip route 0.0.0.0 0.0.0.0 1.1.1.2 250

 

Can you explain me in details why the second route will never work as a backup? i know the fact that first route if it fails will become unreachable (interface down for example).

 

Solutions for this are: using a protocol, HSRP, etc.

 

But i want to know why the router doesnt use the second route.

 

Thank you for any respond,

Gabriel

  • Ryan Schuett 421 posts since
    Sep 29, 2008
    Currently Being Moderated
    1. Aug 1, 2011 7:45 AM (in response to Gabriel)
    Re: static routes main and backup explanation

    Hi Gabriel,

     

    The first line has an AD of 1 so it will of course be used instead of the default route with the AD of 250. As long as the interface to which the default gateway is connected is up, the route with the AD of 1 will always stay as the default route in the routing table. You need a way to remove this route if 1.1.1.1 is unavailable so that is gets removed from the routing table and the default route with the AD of 250 will then be inserted into the routing table and used. To do this, you can setup SLA(s) and tracking and apply the tracked object(s) to the default route pointing to 1.1.1.1.

     

    In essence, you need a way to remove the default route to 1.1.1.1 so the next route with a higher AD will really be a backup. This is true with routes tied to routers on the same subnet.

     

    HTH,

     

    Ryan

  • Conwyn 7,914 posts since
    Sep 10, 2008
    Currently Being Moderated
    3. Aug 1, 2011 10:30 AM (in response to Gabriel)
    Re: static routes main and backup explanation

    Hi Gabriel

     

    ip route 0.0.0.0 0.0.0.0 1.1.1.1

    ip route 0.0.0.0 0.0.0.0 1.1.1.2 250

     

    It is likely that 1.1.1.1 and 1.1.1.2 will use the same interface so

     

    ip route 0.0.0.0 0.0.0.0 fa0/0 1.1.1.1

    ip route 0.0.0.0 0.0.0.0 fa0/0 1.1.1.2 250

     

    would not help.

     

    One solution would be to verify 1.1.1.1 responds to a ping. You can then create a SLA and add the track keyword to the first route statement.

    If the SLA fails the route is removed and the second one takes effect.

     

    Regards Conwyn

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