Router Flooding Interface

Discussion in 'Cisco' started by Matt, Jul 10, 2003.

  1. Matt

    Matt Guest

    Is it normal for this to happen?

    Upstream provider routs IPs to me.
    I don't put a route in my router for those IPs.
    My pipe gets flooded by traffic going around in circles between my
    upstream and me.

    Is that normal? Shouldn't my router just drop and ignore the traffic
    if there is no default rout in for it and it's INCOMING?
    Matt, Jul 10, 2003
    #1
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  2. In article <3f0dc6e4$>, Matt <> wrote:
    >Is it normal for this to happen?
    >
    >Upstream provider routs IPs to me.
    >I don't put a route in my router for those IPs.


    Why not? Add a null0 route if you don't have a place to send them at the
    moment.

    >My pipe gets flooded by traffic going around in circles between my
    >upstream and me.
    >
    >Is that normal? Shouldn't my router just drop and ignore the traffic
    >if there is no default rout in for it and it's INCOMING?


    No. Sometimes it's correct for packets to go back out the same interface
    they came in on. Most of these cases happen on LANs rather than serial
    interfaces, but the forwarding decisions are made without taking into
    account the type of interface.

    --
    Barry Margolin,
    Level(3), Woburn, MA
    *** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
    Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.
    Barry Margolin, Jul 10, 2003
    #2
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  3. With few exceptions, perimeter routers should always have a static route to
    null0 for the set of all IP addresses under private control. Set the static
    route to a high administrative distance, which will cause the route to serve
    as a safety net. So, if one of your internal routes disappears from the
    perimeter routing table, packets will drop. Otherwise, internal traffic can
    cause congestion on your outside link (exactly like you're describing).

    Michael


    "Barry Margolin" <> wrote in message
    news:pUjPa.88$3.com...
    > In article <3f0dc6e4$>, Matt <> wrote:
    > >Is it normal for this to happen?
    > >
    > >Upstream provider routs IPs to me.
    > >I don't put a route in my router for those IPs.

    >
    > Why not? Add a null0 route if you don't have a place to send them at the
    > moment.
    >
    > >My pipe gets flooded by traffic going around in circles between my
    > >upstream and me.
    > >
    > >Is that normal? Shouldn't my router just drop and ignore the traffic
    > >if there is no default rout in for it and it's INCOMING?

    >
    > No. Sometimes it's correct for packets to go back out the same interface
    > they came in on. Most of these cases happen on LANs rather than serial
    > interfaces, but the forwarding decisions are made without taking into
    > account the type of interface.
    >
    > --
    > Barry Margolin,
    > Level(3), Woburn, MA
    > *** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to

    newsgroups.
    > Please DON'T copy followups to me -- I'll assume it wasn't posted to the

    group.
    Michael T. Hall, Jul 11, 2003
    #3
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