BGP default routes

Discussion in 'Cisco' started by srp336@getcoactive.com, Jun 23, 2005.

  1. Guest

    I've got a router with 2 T1s going to different ISPs. Each ISP
    advertises a default route to this router with the same weight via BGP.


    What is the normal behavior in this situation? I was hoping to get the
    router load sharing the outbound traffic equally between the 2 T1s.
    What I get is all outbound traffic going out the T1 where the
    destination IP address is the lowest. How can I equalize the outgoing
    traffic?
     
    , Jun 23, 2005
    #1
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  2. In article <>,
    wrote:

    > I've got a router with 2 T1s going to different ISPs. Each ISP
    > advertises a default route to this router with the same weight via BGP.
    >
    >
    > What is the normal behavior in this situation? I was hoping to get the
    > router load sharing the outbound traffic equally between the 2 T1s.
    > What I get is all outbound traffic going out the T1 where the
    > destination IP address is the lowest. How can I equalize the outgoing
    > traffic?


    Default routes are processed the same way any other routes are, by
    comparing attributes like AS path length, weight, local preference, etc.
    If all the BGP attributes are the same, the final tie-breaker is the age
    of the route (older routes are preferred).

    BGP is very poor at load balancing. Search the newsgroup archive for
    "bgp load balance" to find past discussions and suggestions.

    --
    Barry Margolin,
    Arlington, MA
    *** PLEASE post questions in newsgroups, not directly to me ***
     
    Barry Margolin, Jun 24, 2005
    #2
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  3. Igor Mamuzic Guest

    Try with bgp multipath...
    http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml


    B.R.
    Igor


    <> wrote in message
    news:...
    > I've got a router with 2 T1s going to different ISPs. Each ISP
    > advertises a default route to this router with the same weight via BGP.
    >
    >
    > What is the normal behavior in this situation? I was hoping to get the
    > router load sharing the outbound traffic equally between the 2 T1s.
    > What I get is all outbound traffic going out the T1 where the
    > destination IP address is the lowest. How can I equalize the outgoing
    > traffic?
    >
     
    Igor Mamuzic, Jun 24, 2005
    #3
  4. Guest

    I thought , it was the lowest "router-id". Is it the oldest route in
    age ?
     
    , Jun 24, 2005
    #4
  5. Guest

    I've added 'maximum-paths 2' to my bgp stanza. I can't seem to tell any
    difference. What's the point of bgp multipath?

    I'm just trying to setup more equal utilization for our 2 T1s. Can BGP
    not really get close to that? What's our alternatives?
     
    , Jun 24, 2005
    #5
  6. In article <>,
    <> wrote:
    >
    >I'm just trying to setup more equal utilization for our 2 T1s. Can BGP
    >not really get close to that? What's our alternatives?


    Generally speaking, load balancing using BGP in a dual ISP setup is
    considered "good" if you can get within a two-to-one ratio between
    the two links, and that assumes significant numbers of internal
    users and external destinations. Typically, a single user with a
    single TCP connection to a single Internet server will see higher
    performance if all the traffic goes over a single T1, and typical
    load sharing set ups are configured to ensure that that is the case.

    As Barry stated in his reply, Google Groups is your friend, as this
    topic has been hashed to death multiple times over the past few
    years, making old timers (the ones who actually know the answers)
    reluctant to waste their time doing it yet again.

    --
    Vincent C Jones, Consultant Expert advice and a helping hand
    Networking Unlimited, Inc. for those who want to manage and
    Tenafly, NJ Phone: 201 568-7810 control their networking destiny
    http://www.networkingunlimited.com
     
    Vincent C Jones, Jun 25, 2005
    #6
  7. In article <>,
    "" <> wrote:

    > I thought , it was the lowest "router-id". Is it the oldest route in
    > age ?


    The tie-breaker used to be lowest router-id. Several years ago Cisco
    changed it to age.

    --
    Barry Margolin,
    Arlington, MA
    *** PLEASE post questions in newsgroups, not directly to me ***
     
    Barry Margolin, Jun 25, 2005
    #7
  8. In article <>,
    wrote:

    > I've added 'maximum-paths 2' to my bgp stanza. I can't seem to tell any
    > difference. What's the point of bgp multipath?


    I think maximum-paths will only insert multiple routes learned from the
    same ASN. So the point of it is when you have multiple T1's to the same
    ISP.

    > I'm just trying to setup more equal utilization for our 2 T1s. Can BGP
    > not really get close to that? What's our alternatives?


    There are some tricks you can play with route-maps that set weights
    based on as-path access lists. Like I said before, search the archives.

    --
    Barry Margolin,
    Arlington, MA
    *** PLEASE post questions in newsgroups, not directly to me ***
     
    Barry Margolin, Jun 25, 2005
    #8
  9. Guest

    Thanks Barry
     
    , Jun 27, 2005
    #9
  10. Igor Mamuzic Guest

    I'm not quiet experienced in BGP, but If you can get two routes to the same
    destination learned from BGP in your IP routing table, then try to play
    around with cef load balancing. It requires two or more prefixes to the same
    destination in it's FIB to do proper load balancing (CEF load balancing is
    not, AFAIK, enabled by default).

    B.R.
    Igor

    <> wrote in message
    news:...
    > I've added 'maximum-paths 2' to my bgp stanza. I can't seem to tell any
    > difference. What's the point of bgp multipath?
    >
    > I'm just trying to setup more equal utilization for our 2 T1s. Can BGP
    > not really get close to that? What's our alternatives?
    >
     
    Igor Mamuzic, Jun 27, 2005
    #10
  11. theapplebee

    Joined:
    Jun 19, 2009
    Messages:
    67
    Location:
    USA
    BGP will pick only one best path, unless multi path commands. Load sharing won't happening.
     
    theapplebee, Jun 20, 2009
    #11
  12. theapplebee

    Joined:
    Jun 19, 2009
    Messages:
    67
    Location:
    USA
    Also, it should apply on both peers
     
    theapplebee, Jul 24, 2009
    #12
  13. theapplebee

    Joined:
    Jun 19, 2009
    Messages:
    67
    Location:
    USA
    The best practice about load-sharing as outbound as concern would be using default route on both upstream links. It would make about 50/50 traffic balancing.
    Seems like above case, cx was getting default route and some of route from ISP... then it won't make 50/50 load balancing.
     
    theapplebee, Sep 8, 2009
    #13
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