BGP and load balancing two routers

Discussion in 'Cisco' started by Matt, Oct 17, 2005.

  1. Matt

    Matt Guest

    Hi,
    Our network is setup as such:

    SPRINT (45Meg) -----> ROUTER A

    QWEST (10Meg) ------> ROUTER B

    Router A and B, then interconnect with a patch cable.

    We are currently running BGP between the routers, as well as with our
    peers (SPRINT/QWEST). As Qwest is only a 10Meg pipe I would like to
    reduce the amount of traffic that is going out. I have tried
    weighting, localpref, (for outbound traffic) and as-prepend (for inbound
    traffic) but have not been able to get anything to work. I have issued
    "clear ip bgp *" after each command, but still no go. Below are the
    commands I've issued.. any thoughts?

    ROUTER A:
    neighbor 160.81.248.77 remote-as 1239
    neighbor 160.81.248.77 description ebgp link to sprint
    neighbor 160.81.248.77 version 4
    neighbor 160.81.248.77 weight 150
    neighbor 160.81.248.77 soft-reconfiguration inbound
    neighbor 160.81.248.77 filter-list 2 out

    ROUTER B:
    bgp default local-preference 75
    neighbor 65.123.21.137 remote-as 209
    neighbor 65.123.21.137 description ebgp link to qwest
    neighbor 65.123.21.137 version 4
    neighbor 65.123.21.137 soft-reconfiguration inbound
    neighbor 65.123.21.137 route-map filter out


    route-map filter permit 10
    set as-path prepend 26383 26383 26383


    on ROUTER A, a sh ip bgp shows that localpref and weight are going in:
    *> 8.2.64.0/23 160.81.248.77 29 150 1239 7132
    16803 16803 16803 i
    *> 8.3.41.0/24 160.81.248.77 29 150 1239 7911
    7911 7911 30033 30033 i
    *> 8.3.43.0/24 160.81.248.77 29 150 1239 7911
    7911 7911 30033 30033 i
    *> 8.6.240.0/24 160.81.248.77 29 150 1239 7911
    7911 7911 31846 31846 31846 31846 31846 i
    *> 8.7.83.0/24 160.81.248.77 29 150 1239 5650
    5650 12284 ?
    *> 8.8.9.0/24 160.81.248.77 610 150 1239 27646 ?
    *>i8.10.50.0/24 65.123.21.137 8937 75 0 209 32760 i
    *> 8.10.119.0/24 160.81.248.77 190 150 1239 4323
    25642 ?
    *> 8.10.128.0/24 160.81.248.77 190 150 1239 4323
    25642 i
    *> 8.10.241.0/24 160.81.248.77 29 150 1239 6395
    22324 22324 22324 22324 i
    *> 8.15.2.0/24 160.81.248.77 29 150 1239 6395
    26049 26049 26049 26049 i
    *> 8.15.5.0/24 160.81.248.77 29 150 1239 6395
    26049 26049 26049 26049 i
    *> 8.15.6.0/24 160.81.248.77 29 150 1239 6395
    26049 26049 26049 26049 i
    *> 12.0.18.0/24 160.81.248.77 50 150 1239 27585 i
    *>i12.0.48.0/20 65.123.21.137 8710 75 0 209 1742 i

    But a traceroute from me to a site hosted on the qwest network goes out
    my qwest router, rather then going out my Sprint router.
    1 faste-2-0-medusa (63.174.244.17) 0.482 ms 32.847 ms 9.912 ms
    2 faste-2-0-hydra (65.165.94.77) 2.403 ms 12.238 ms 9.897 ms
    3 pa1-edge-03.inet.qwest.net (65.123.21.137) 9.949 ms 11.850 ms
    8.757 ms
    4 aggr-01.ewr.qwest.net (205.171.17.169) 10.402 ms 10.607 ms 11.627 ms
    5 jfk-core-02.inet.qwest.net (205.171.8.246) 10.982 ms 10.742 ms
    11.421 ms
    6 jfk-edge-01.inet.qwest.net (205.171.30.86) 10.839 ms 11.201 ms
    10.759 ms
    7 65.116.172.98 (65.116.172.98) 42.611 ms 42.381 ms 42.830 ms
    8 suscomweb.synacor.com (208.197.227.23) 41.574 ms 41.672 ms 41.730 ms

    Any thoughts?
     
    Matt, Oct 17, 2005
    #1
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  2. With a four to one bandwidth ratio, load balancing with BGP
    is going to be an exercise in futility unless your traffic is
    very predictable. My general rule of thumb is that if you need
    to balance BGP links to closer than +/- 50%, you either need a
    load balancing appliance or re-examination of your load balancing
    requirements. In your case, I would suggest reconsidering whether
    the complexity added by trying to move 20% of your Sprint traffic
    to Qwest would compensate for the miniscule (and possibly negative)
    performance improvement at any traffic loads under 35 Mbps total.

    If your traffic loads routinely exceed 35 Mbps, you need to consider
    the performance hit when your Sprint link fails and all your traffic
    goes over the Qwest link. Bottom line: my thoughts are that you
    should either bump up the Qwest link to 45 Mbps or configure your
    BGP so Sprint is primary and the Qwest link is only used for backup
    (and maybe local Qwest destinations).

    Good luck and have fun!
     
    Vincent C Jones, Oct 17, 2005
    #2
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