Duplicate packets on every packet

Duplicate packets on every packet

Post by Alan Mus » Thu, 14 Aug 1997 04:00:00



With Linux 2.0.30-3 from Redhat, I am getting a duplicate of every packet.  
Ping, etc.  tcpdump from another system on the ether shows me that there are
two requests going to the machine, and naturally two replies:

host names removed, but they were legit.  ping from Win95 to linux
16:08:39.459721 m: icmp: echo request
16:08:39.459721: icmp: echo request
16:08:39.459721: icmp: echo reply
16:08:39.459721: icmp: echo reply
16:08:40.459721: icmp: echo request
16:08:40.459721 icmp: echo request
16:08:40.459721: icmp: echo reply
16:08:40.459721 : icmp: echo reply

Ping from good linux to bad linux:

64 bytes from: icmp_seq=0 ttl=64 time=1.1 ms
64 bytes from : icmp_seq=0 ttl=63 time=1.6 ms (DUP!)
64 bytes from : icmp_seq=1 ttl=64 time=1.1 ms
64 bytes from: icmp_seq=1 ttl=63 time=1.7 ms (DUP!)
64 bytes from : icmp_seq=2 ttl=64 time=1.1 ms
64 bytes from : icmp_seq=2 ttl=63 time=1.7 ms (DUP!)
64 bytes from  icmp_seq=3 ttl=64 time=1.1 ms
64 bytes from : icmp_seq=3 ttl=63 time=1.6 ms (DUP!)

I have swapped out ether cards (different types), cables, everything.

Although the duplicate seems to be coming from the source, it only happens
when the source is sending to the bad linux machine.

Does anyone have ideas on what would cause this?  It is annoying, but not show
stopping.

Alan Musha

 
 
 

Duplicate packets on every packet

Post by Peter van der Land » Fri, 15 Aug 1997 04:00:00



>With Linux 2.0.30-3 from Redhat, I am getting a duplicate of every packet.  
>Ping, etc.  tcpdump from another system on the ether shows me that there are
>two requests going to the machine, and naturally two replies:

I've seen that too. I've always thought it had something to do with
using tcpdump. Which is interesting, cause you mention using it too...

Anybody really know?

Regards,

Peter van der Landen

-----------------------------------------------------------------------------
       Law Faculty, L4-45, Erasmus University, Rotterdam, Holland
          Tel +31-10-4082237 (home 2800956) Fax +31-10-2800957


 
 
 

Duplicate packets on every packet

Post by Douglas A. Salzman » Fri, 15 Aug 1997 04:00:00



> >With Linux 2.0.30-3 from Redhat, I am getting a duplicate of every packet.
> >Ping, etc.  


Quote:

> I've seen that too. I've always thought it had something to do with
> using tcpdump. Which is interesting, cause you mention using it too...

Same thing is happening on my box, consistently.

2.0.30 kernel (Slackware).

Does *not* happen when pinging localhost.

Any answers?

        -Doug

 
 
 

Duplicate packets on every packet

Post by Michael Bole » Fri, 15 Aug 1997 04:00:00



> With Linux 2.0.30-3 from Redhat, I am getting a duplicate of every
> packet.
> Ping, etc.  tcpdump from another system on the ether shows me that
> there are
> two requests going to the machine, and naturally two replies:

Hi,

what sort of switch/machines/hubs do have between the two clients? Have
you checked everything about that? Is there a machine with two
ethernetcards and a switch between them? Is it possible that the machine
gets in the packets about two cards and answers ower both?

Michael

 
 
 

Duplicate packets on every packet

Post by Alan Mus » Sun, 17 Aug 1997 04:00:00


I found the problem/solution.

The 'bad linux' machine was on a different class-C than the other machines on
the ethernet.  Therefore, everything between those machines went towards the
Cisco, who had IP addresses on both 'networks.'

Adding a respective routes to each machines fixed it.  I don't know why dual
packets showed up though.  The best I can figure is that the packet got sent
addressed to the Cisco (which routed it), *and* possibly again to the bad
machine because of an ICMP redirect from the Cisco.

So, was this a stupid error on my part, or a sign of a bug somewhere?

Alan Musha




>>With Linux 2.0.30-3 from Redhat, I am getting a duplicate of every packet.  
>>Ping, etc.  tcpdump from another system on the ether shows me that there are
>>two requests going to the machine, and naturally two replies:

>I've seen that too. I've always thought it had something to do with
>using tcpdump. Which is interesting, cause you mention using it too...

>Anybody really know?

>Regards,

>Peter van der Landen

>-----------------------------------------------------------------------------
>       Law Faculty, L4-45, Erasmus University, Rotterdam, Holland
>          Tel +31-10-4082237 (home 2800956) Fax +31-10-2800957


 
 
 

Duplicate packets on every packet

Post by Diamo » Wed, 20 Aug 1997 04:00:00


: With Linux 2.0.30-3 from Redhat, I am getting a duplicate of every packet.  
: Ping, etc.  tcpdump from another system on the ether shows me that there are
: host names removed, but they were legit.  ping from Win95 to linux

: Does anyone have ideas on what would cause this?  It is annoying, but not show
: stopping.

        Had that problem, my netmask was set wrong.  If your broadcast
address=your IP that'll happen, but the system will still talk.  You'll
get 1 dup packet for every online linux system on your local net.  I was
getting 4 packets for every one to the bad machine, but not *FROM* that
machine, just every system responded to that packet.  Make sure you have
reserved <from your IP block> the top address as your network address and
the bottom one as the broadcast address.  Hope this helps!

: Alan Musha

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