EIGRP slowness and backup

Discussion in 'Cisco' started by jmiklo, Nov 22, 2004.

  1. jmiklo

    jmiklo Guest

    Hi,
    I have a bunch of location connected to regional office. Regional office
    summarize all routes to a central location. On central location there is
    dialin router that handles location when they loose primary link and connect
    to a that router on central location.
    When location goes on backup, it sends its eigrp route son there is
    summarized route from regional office and a specific one sent by location on
    backup so traffic for that location is routed ok.
    When primary of that location goes up, location starts to send packets thru
    primary link. As isdn link is still up (because of delay timer) specific
    eigrp route is still sent to a central location so during a transition time
    we have asymetric routing - location sends packet trhu primary link, and
    traffic is sent from central location thru isdn because of more specific
    route.
    Since traffic is not sent outside isdn interface on location (only received)
    eventually location shuts down isdn interface.
    But although isdn is down, eigrp neighborship between dialin router and
    location via isdn is not immediately broken, so when traffic is sent from
    central location to a remote location, specific route is still active in
    dialin backup router. Immediately when packet enters that router, backup
    router calls remote router and isdn connection is restored.
    If there was no traffic during isdn going down and neighborship breaking,
    route would dissapear and it would be fine. This way ISDN is very often up.
    Solution: I could remove summarization done on regional office toward
    central location so all specific routes would be visible on central
    location. But design studies always recommend summarization in direction to
    central location.
     
    jmiklo, Nov 22, 2004
    #1
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  2. jmiklo

    Scooby Guest

    "jmiklo" <> wrote in message
    news:cntlqj$84t$...
    > Hi,
    > I have a bunch of location connected to regional office. Regional office
    > summarize all routes to a central location. On central location there is
    > dialin router that handles location when they loose primary link and

    connect
    > to a that router on central location.
    > When location goes on backup, it sends its eigrp route son there is
    > summarized route from regional office and a specific one sent by location

    on
    > backup so traffic for that location is routed ok.
    > When primary of that location goes up, location starts to send packets

    thru
    > primary link. As isdn link is still up (because of delay timer) specific
    > eigrp route is still sent to a central location so during a transition

    time
    > we have asymetric routing - location sends packet trhu primary link, and
    > traffic is sent from central location thru isdn because of more specific
    > route.
    > Since traffic is not sent outside isdn interface on location (only

    received)
    > eventually location shuts down isdn interface.
    > But although isdn is down, eigrp neighborship between dialin router and
    > location via isdn is not immediately broken, so when traffic is sent from
    > central location to a remote location, specific route is still active in
    > dialin backup router. Immediately when packet enters that router, backup
    > router calls remote router and isdn connection is restored.
    > If there was no traffic during isdn going down and neighborship breaking,
    > route would dissapear and it would be fine. This way ISDN is very often

    up.
    > Solution: I could remove summarization done on regional office toward
    > central location so all specific routes would be visible on central
    > location. But design studies always recommend summarization in direction

    to
    > central location.
    >
    >


    I've encountered a similar problem. I have designed backup connections
    through broadband vpn. These connections are always up. Therefore, summary
    routes don't work for me. You really can't summarize when you have
    different entry points into the same network. That totally defeats the
    whole purpose of summarization.

    Here is a solution that may work for you... Start by removing the
    summarization and just letting the whole route tables come to each location.
    This will get you working right. Then, add an incoming distribute-list to
    eigrp at the remote sites to just allow a default route. That way, you
    don't have to worry about having large route tables at the remotes, but you
    still will have a default route back to the main site. Your switchover
    should be almost immediate when the sites come back up.

    ex:
    access-list 5 permit 0.0.0.0
    access-list 5 deny any

    router eigrp 100
    distribute-list 5 in

    Hope that helps,

    Jim
     
    Scooby, Nov 23, 2004
    #2
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  3. jmiklo

    jmiklo Guest

    > I've encountered a similar problem. I have designed backup connections
    > through broadband vpn. These connections are always up. Therefore,

    summary
    > routes don't work for me. You really can't summarize when you have
    > different entry points into the same network. That totally defeats the
    > whole purpose of summarization.
    >
    > Here is a solution that may work for you... Start by removing the
    > summarization and just letting the whole route tables come to each

    location.
    > This will get you working right. Then, add an incoming distribute-list to
    > eigrp at the remote sites to just allow a default route. That way, you
    > don't have to worry about having large route tables at the remotes, but

    you
    > still will have a default route back to the main site. Your switchover
    > should be almost immediate when the sites come back up.
    >
    > ex:
    > access-list 5 permit 0.0.0.0
    > access-list 5 deny any
    >
    > router eigrp 100
    > distribute-list 5 in
    >
    > Hope that helps,
    >
    > Jim
    >

    Thanks for sharing your experience. That way was also my idea (which I
    didn't elaborate in details but goes with removing summarization toward
    core). Central location (core) would have all specific location routes, but
    would summarize back to regional offices and to end locations.
    But I was wondering because summarization to the core is always recommended
    in order to avoid route recalculation in core when some end locations goes
    down.
    Mostly all networks have centralized backup so all locations dials to the
    same dialin routers so similar problem always exists.

    thanks
    j
     
    jmiklo, Nov 23, 2004
    #3
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