Backup route with better eigrp metric

Discussion in 'Cisco' started by Daniel Eyholzer, Dec 3, 2004.

  1. Hi there


    We have several routers which are distributing routes with EIGRP. There is
    a subnet that needs to be routed over a serial link. The router on both
    sides of this link does not talk EIGRP or any other routing protocol with
    each other, so I have defined a static route (ip route 192.168.33.48
    255.255.255.248 s1) This route is redistributed to the other routers in the
    network. Then we have a backup link to the same subnet (subnet from above
    behinde the serial link). This backup link is only available if the serial
    link goes down. On the router providing the backup link I have defined a
    route with an administrative distance of 250. (ip route 192.168.33.48
    255.255.255.248 192.168.56.1 250)

    This all works fine. If the serial link goes down, the traffic is routed
    over the backup link but if the serial link comes up again the route over
    the serial link is not choosen by EIGRP because the metric of this link is
    higher. I need to delete and reinsert the backup route to get rid of the
    backup route.

    Any idea how I could solve this problem?


    Daniel
     
    Daniel Eyholzer, Dec 3, 2004
    #1
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  2. In article <>,
    Daniel Eyholzer <> wrote:
    >Hi there
    >
    >
    >We have several routers which are distributing routes with EIGRP. There is
    >a subnet that needs to be routed over a serial link. The router on both
    >sides of this link does not talk EIGRP or any other routing protocol with
    >each other, so I have defined a static route (ip route 192.168.33.48
    >255.255.255.248 s1) This route is redistributed to the other routers in the
    >network. Then we have a backup link to the same subnet (subnet from above
    >behinde the serial link). This backup link is only available if the serial
    >link goes down. On the router providing the backup link I have defined a
    >route with an administrative distance of 250. (ip route 192.168.33.48
    >255.255.255.248 192.168.56.1 250)
    >
    >This all works fine. If the serial link goes down, the traffic is routed
    >over the backup link but if the serial link comes up again the route over
    >the serial link is not choosen by EIGRP because the metric of this link is
    >higher. I need to delete and reinsert the backup route to get rid of the
    >backup route.
    >
    >Any idea how I could solve this problem?
    >
    >
    >Daniel


    Two ways to get around it (nasty little feature, isn't it :)

    1 - If the subnet below is not in use, make the backup route with a
    shorter prefix (ip route 192.168.33.32 255.255.255.240 ...) That way,
    when the real route is available it will ALWAYS win because longer
    prefix (more specific route) always wins regardless of any metrics.

    2 - Redistribute the static routes with explicit rather than default
    EIGRP metrics. Adjust so the preferred route will have a better metric
    even at the routers with the backup link. Route maps make it very easy
    to precisely control what static routes get distributed with what
    metrics.

    Good luck and have fun!
    --
    Vincent C Jones, Consultant Expert advice and a helping hand
    Networking Unlimited, Inc. for those who want to manage and
    Tenafly, NJ Phone: 201 568-7810 control their networking destiny
    http://www.networkingunlimited.com
     
    Vincent C Jones, Dec 4, 2004
    #2
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  3. (Vincent C Jones) wrote:
    > 1 - If the subnet below is not in use, make the backup route with a
    > shorter prefix (ip route 192.168.33.32 255.255.255.240 ...) That
    > way, when the real route is available it will ALWAYS win because
    > longer prefix (more specific route) always wins regardless of any
    > metrics.


    Okay this is not an option for my case, because the subnet below is in
    use.


    > 2 - Redistribute the static routes with explicit rather than default
    > EIGRP metrics. Adjust so the preferred route will have a better
    > metric even at the routers with the backup link. Route maps make it
    > very easy to precisely control what static routes get distributed
    > with what metrics.


    I will have a look at route maps and check out how I can redistribute
    static routes with an explicit EIGRP metric. Are there any good docs
    about how to do that?


    > Good luck and have fun!


    Thanks! ;-)
     
    Daniel Eyholzer, Dec 5, 2004
    #3
  4. Daniel Eyholzer

    Hansang Bae Guest

    In article <>,
    says...
    [snip]
    > I will have a look at route maps and check out how I can redistribute
    > static routes with an explicit EIGRP metric. Are there any good docs
    > about how to do that?


    CCO has good examples. Other good references are "Slattery/Burton's
    Advanced IP Routing" book and of course, Doyle's VOL I.

    --

    hsb

    "Somehow I imagined this experience would be more rewarding" Calvin
    *************** USE ROT13 TO SEE MY EMAIL ADDRESS ****************
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    Hansang Bae, Dec 6, 2004
    #4
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