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Forum Replies

  1. Hey rene.
    Could you explain, why would you use offset-list in a working network?

  2. Hi Don,

    The main reason to use it is for path control of distance vector routing protocols (RIP or EIGRP). If you have two links between routers then you could use an offset-list to increase the metric of 1 prefix, making it prefer the other link.

    For outbound traffic I wouldn't use the offset-list, you can use policy based routing for this (it has more options). An offset-list might be useful for inbound traffic perhaps...for example, let's say that you have a router with two links connected to another router that is out of your control. You could use an offset-list to increase the metric for 1 prefix so that the router on the other side prefers the other link for this particular prefix. This allows you to have "path control" even without access to the other router.

    Rene

  3. Hi Jason,

    That's correct. R1 is advertising these networks with a certain hop count to R2 so that's what R2 is installing in its routing table.

    When it's advertising these prefixes to R3, it will advertise the metric that it has stored for these networks.

    Rene

  4. How would the offset work for eigrp since it doesnt use hopcount.

  5. Abdool,
    Good question! If you lab up offset lists with EIGRP you will discover that whatever value you enter as the offset will be added to the composite metric of EIGRP. As you may know, the composite metric of EIGRP is the result of a complex formula, but by default, it is a result of Bandwidth and Delay values. Fortunately, Cisco is smart enough to know that it is best not to mess with bandwidth values for the purpose of EIGRP traffic engineering (because this can mess up things like QoS).

    So what you will see is that the Delay used to calculate the Composite Metric will be manipulated such that the final Composite Metric will increase to include your offset list value.

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