Load Balancing 2 T1s with 2 routers

Discussion in 'Cisco' started by russianj, Apr 10, 2008.

  1. russianj

    russianj Guest

    I have two 3845 routers with IOS version 12.4(2)T1. The T1s are
    connected to a private MPLS cloud used by my company for remote sites.
    On the LAN side of the routers, HSRP is employed with one of the
    routers, called RTR01 used as primary, with the other, RTR02 as
    secondary for failover. On the WAN side, the routers broadcast EIGRP
    for LAN-connected subnets.
    Originally, all traffic flowed in and out of RTR01's T1 and RTR02 had
    no load. EIGRP was setup so that RTR01 had a better metric for Static
    (we use heavy weighted static routes to our dialup router when the
    MPLS connection goes down at a remote site) as follows:
    On RTR01
    router eigrp 100
    redistribute static 1500 10 255 1 1500
    On RTR02
    router eigrp 100
    redistribute static 1000 10 255 1 1500
    In an attempt to balance traffic across the two T1s and the two
    routers, I set the metric to "1500 10 255 1 1500". Now after the
    change, all incoming traffic flows through the T1 on RTR01 and all
    outbound traffic flows on the T1 out RTR02. Unfortunately, I am losing
    bandwidth by not having both incoming and outgoing traffic across the
    two T1s and routers.
    What is the next step? I am a little lost as to why the network
    would work this way when two routes are being given. Should I try it
    without any metrics and hope that it balances properly? Thanks.
    russianj, Apr 10, 2008
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  2. russianj

    Merv Guest

    start again ...

    For outbound, take a look at GLBP - Gateway Load Balancing Protocol

    For inbound, ask You provider if they can support EIBGP load
    balancing (note the EIBGP part - it is important)
    Merv, Apr 10, 2008
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  3. russianj

    russianj Guest

    The scenario that you are talking about, I believe, is to attempt to
    load balance the individual packets. That is not necessarily what I am
    going for. Currently, if I fill up either of the two T1s, the
    additional traffic that attempts to go across does not get balanced to
    the additional T1s. That is more specifically the problem. If I
    understand EIGRP correctly, then if metrics are not specified, then as
    connections use up bandwidth on one of the T1s, then the metric for
    the other T1 will be more favorable, and traffic will go through the
    second T1 accordingly. That is how EIGRP is designed to work, correct?
    russianj, Apr 11, 2008
  4. russianj

    Merv Guest


    the default value for the "k" variables are K1=1, K2 =0, K3=1,K4=0,

    so link load does not come into play

    the bandwidth referred to in metric calcluation is a fix value of the
    interface bandwidth - it is not dynamic link utilization
    Merv, Apr 11, 2008
  5. russianj

    Merv Guest

    Forgot to mention that K2, K4 and K5 were meaning for IGRP which used
    periodic updates

    They are not useful for EIGRP for which updates are event driven
    Merv, Apr 11, 2008
  6. russianj

    russianj Guest

    I would rather not change to BGP if at all possible. I will speak with
    our provider, but a change in routing protocol would necessitate
    changing every router in remote locations as well to speak BGP. CEF
    does load balancing across interfaces, so maybe that is more the
    scenario that I am thinking of in this case. Can CEF work across more
    than one router? Thanks for clearing this up.
    russianj, Apr 14, 2008
  7. russianj

    russianj Guest

    I just thought that CEF comment through. Please ignore that comment.
    russianj, Apr 14, 2008
  8. russianj

    Merv Guest

    Suggest starting with GLBP for outbound traffic and go from there
    Merv, Apr 14, 2008
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