route behavior in equal cost path EIGRP

Discussion in 'Cisco' started by Y0giBear, Feb 18, 2008.

  1. Y0giBear

    Y0giBear Guest

    Hi

    If there are 2 equal cost paths in the same EIGRP Process for the same
    destination, does it start load balancing straight away, if not which
    one will become the successor?

    Where can I find the default bandwidth and metric values for the known
    type of interfaces as those are used by EIGRP metric.

    Thanks in advance.
     
    Y0giBear, Feb 18, 2008
    #1
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  2. Y0giBear

    pk Guest

    Y0giBear wrote:

    > Hi
    >
    > If there are 2 equal cost paths in the same EIGRP Process for the same
    > destination, does it start load balancing straight away, if not which
    > one will become the successor?


    It starts balancing straight away (you can see by doing a "sh ip route").

    > Where can I find the default bandwidth and metric values for the known
    > type of interfaces as those are used by EIGRP metric.


    EIGRP uses this formula to calculate the metric:

    metric=256*[(K1*bw+((K2*bw)/(256-load))+K3*delay)]*[K5/(reliability+K4)]

    Where:

    bw=(10^7)/(bandwidth in kbs), taking the lowest bandwidth in the path

    delay=delay in tens of microseconds, sum of delays for all links in the path

    reliability=from 1 to 255, 255 means totally reliable

    by default, the values of the constants are K1=1,K2=0,K3=1,K4=0,K5=0, so the
    [K5/(reliability+K4)] term is ignored and the formula becomes

    metric = 256 * (bw + delay)

    where bw and delay are calculated as described above. The bandwidth of an
    interface is configured with the "bandwidth" command in interface
    configuration mode, or defaults to 1544Kbs for serial interfaces, and to
    the ethernet speed for ethernet interfaces.
     
    pk, Feb 18, 2008
    #2
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  3. Y0giBear

    Thrill5 Guest

    To see the EIGRP topology table, use the "show ip eigrp topology" command.
    The EIGRP topology table will show all the routes known by EIGRP, including
    feasible successors, and metrics. Routes from the topology table will be
    inserted into the routing table if the topology entry is a better or equal
    cost route than the one in the routing table.

    Load balancing is done in CEF on a per destination basis (as opposed to per
    packet), and can take from a few minutes to a few hours before you see the
    traffic load-balanced. Per destination load-balancing will never ever be
    50/50. Before you immediately say, I'll switch to per-packet
    load-balancing, make sure you understand the ramifications. Some platforms
    perform per packet load balancing in software, and if you are running
    multicast you will run into issues with that as well.


    "pk" <> wrote in message news:fpblmk$rhu$...
    > Y0giBear wrote:
    >
    >> Hi
    >>
    >> If there are 2 equal cost paths in the same EIGRP Process for the same
    >> destination, does it start load balancing straight away, if not which
    >> one will become the successor?

    >
    > It starts balancing straight away (you can see by doing a "sh ip route").
    >
    >> Where can I find the default bandwidth and metric values for the known
    >> type of interfaces as those are used by EIGRP metric.

    >
    > EIGRP uses this formula to calculate the metric:
    >
    > metric=256*[(K1*bw+((K2*bw)/(256-load))+K3*delay)]*[K5/(reliability+K4)]
    >
    > Where:
    >
    > bw=(10^7)/(bandwidth in kbs), taking the lowest bandwidth in the path
    >
    > delay=delay in tens of microseconds, sum of delays for all links in the
    > path
    >
    > reliability=from 1 to 255, 255 means totally reliable
    >
    > by default, the values of the constants are K1=1,K2=0,K3=1,K4=0,K5=0, so
    > the
    > [K5/(reliability+K4)] term is ignored and the formula becomes
    >
    > metric = 256 * (bw + delay)
    >
    > where bw and delay are calculated as described above. The bandwidth of an
    > interface is configured with the "bandwidth" command in interface
    > configuration mode, or defaults to 1544Kbs for serial interfaces, and to
    > the ethernet speed for ethernet interfaces.
    >
     
    Thrill5, Feb 18, 2008
    #3
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