Duplicate icmp packet blues

Duplicate icmp packet blues

Post by Emmett Biffi » Tue, 27 Jul 1999 04:00:00

I have Linux 6.0 set up as a router passing packets between ethernet and
token-ring LANs. I'm using an Olicom PCI 16/4 and an 3Com Etherlink
combo 10Mb. When I ping a host across the router (either way) I get a
massive number of (DUP)!'s along with the original echo. This was
driving me crazy. I ran tcpdump on both interfaces and the duplicate
packets disappeared, but returned promptly when tcpdump was killed.
Obviously this isn't a viable solution.

Any suggestions?



1. Duplicate ICMP Packets?

I just added a Linux machine to our network.  (Red Hat 5.0, Linux
2.0.32). I have a 3Com 3509 card in there (, and it
sits on the the network with 5 Windows 95/NT machines.  We're hooked
to our ISP via a Cisco 1000 Lan Extender ( see the
output below).  

The problem is that when I ping any of the Windows machines from the
Linux machine, I get three duplicate packets back.  When I ping the
router, its own address or external addresses, everything is ok.
I can't reproduce the duplicate packets by pinging FROM the windows

It appears that the router has something to do with it, but our ISP
can't figure out what it is....  Below is the result of ping -R.  (I
can't reproduce this using traceroute)

Any help is very appreciated!

Very confused,

PING www.gsnet.com ( 56 data bytes
64 bytes from icmp_seq=0 ttl=128 time=0.8 ms
RR:     mu.gsnet.com (
        www.gsnet.com (
        mu.gsnet.com (
64 bytes from icmp_seq=0 ttl=128 time=40.8 ms (DUP!)
RR:     mu.gsnet.com (
        inet-gate (
        www.gsnet.com (
        mu.gsnet.com (
64 bytes from icmp_seq=0 ttl=127 time=49.8 ms (DUP!)
RR:     mu.gsnet.com (
        www.gsnet.com (
        inet-gate (
        mu.gsnet.com (
64 bytes from icmp_seq=0 ttl=127 time=73.2 ms (DUP!)
RR:     mu.gsnet.com (
        inet-gate (
        www.gsnet.com (
        inet-gate (
        mu.gsnet.com (

--- www.gsnet.com ping statistics ---
1 packets transmitted, 1 packets received, +3 duplicates, 0% packet
loss round-trip min/avg/max = 0.8/41.1/73.2 ms

Mike Bridge
Edmonton, Canada

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