Four T1s - 2 ISPs - One 7200 - Solution?

Discussion in 'Cisco' started by SJ, May 13, 2004.

  1. SJ

    SJ Guest

    I have just been given the task of combining Four T1s (3 from ISP A and
    1 from ISP B) into a Cisco 7200.
    (Lines were inherited from merger and are under we cant get
    rid of them)
    I am assuming that running BGP to load balance among them is the way to go.
    Is it?

    And how difficult of a project is this since my BGP skills are in the
    novice-intermediate range.
    (My routing skills are pretty good however. I just have really never had the
    need for BGP in my past)

    I am also wondering how much help/info you get from the ISP to set this up.

    Any advice would be extremely helpful.
    Thank you!
    SJ, May 13, 2004
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  2. SJ

    mh Guest

    The load balancing can be broken down into two parts:

    a) load balancing the traffic over the 3 T1 between your network and
    ISP #1

    b) load balaning the traffic between ISP #1 and ISP#2 on a 3:1 ratio

    The easiest way to handle a is to configure the EBGP neighbors using
    loopback address and static routes see Cisco document
    Do not use the BGP weight attribute; use local preference sttribute

    The second part is a little trickier. One of the ways to do this is to
    set local preference for a set of major upstream AS numbers on the BGP
    routes received from a particular ISP. So for example set local
    preference for all UUNET routes to be routed over the three links to
    ISP #1. Thus manipulating local preference affects OUTBOUND traffic.

    Use AS path prepend for a subset of you address space for routes that
    you advertise. Rember that a lot os ISP we not accept BGP routes
    advertises for prefixes greater than /24s. If you have a small
    address space this will be problematic.
    mh, May 13, 2004
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