Do you have 'no ip directed broadcast' configured
on the Ethernet interface of the router to which
the replying nodes are connected ?
> -----Original Message-----
> From: Jim Warner [mailto:warner@cats.UCSC.EDU]
> Sent: Sunday, December 02, 2001 03:22
> To: cisco-nsp@puck.nether.net
> Subject: packet duplication
>
>
> When I ping to a particular router my reply packets are
> getting duplicated. It looks like:
>
> bash-2.03$ ping 137.164.12.33
> PING 137.164.12.33 (137.164.12.33): 56 data bytes
> 64 bytes from 137.164.12.33: icmp_seq=0 ttl=250 time=24.924 ms
> 64 bytes from 137.164.12.33: icmp_seq=0 ttl=250 time=25.013 ms (DUP!)
> 64 bytes from 137.164.12.33: icmp_seq=0 ttl=248 time=25.247 ms (DUP!)
> 64 bytes from 137.164.12.33: icmp_seq=0 ttl=248 time=25.698 ms (DUP!)
> 64 bytes from 137.164.12.33: icmp_seq=1 ttl=250 time=24.084 ms
> 64 bytes from 137.164.12.33: icmp_seq=1 ttl=250 time=24.594 ms (DUP!)
> 64 bytes from 137.164.12.33: icmp_seq=1 ttl=248 time=24.825 ms (DUP!)
> 64 bytes from 137.164.12.33: icmp_seq=1 ttl=248 time=25.030 ms (DUP!)
> 64 bytes from 137.164.12.33: icmp_seq=2 ttl=250 time=24.330 ms
> 64 bytes from 137.164.12.33: icmp_seq=2 ttl=250 time=24.544 ms (DUP!)
> 64 bytes from 137.164.12.33: icmp_seq=2 ttl=248 time=24.750 ms (DUP!)
> 64 bytes from 137.164.12.33: icmp_seq=2 ttl=248 time=25.173 ms (DUP!)
>
> Not shown here, but this effect happens when I pass through this
> router. Anything beyond it is replicated.
>
> I have seen routing loops cause things that are similar, but
> not the same as this. But here the duplication is always the
> same. I think that my packets to the router are being replicated,
> and then each of the replies is getting replicated -- which is
> why I see four responses to everything I send.
>
> I am curious to hear what sorts of pathologies might result in
> this kind of packet copying. There is ATM in the path. Could
> it be the culprit? I am pretty sure that the equipment doing the
> packet copying is made by Cisco. The same way that I can't imagine
> that a bad packet would cause a fan to fail, I can't imagine how a
> packet could be copied a fixed number of times.
>
> I know this would be easier if there was a map of the topology.
> Is anyone willing to speculate without one?
>
> Thanks. -jim warner, UC santa cruz
>
>
>
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