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We have recently set up a small cluster of GPU workstations and have recently got them networked together. Although connectivity looks fine for e.g. web browsers and SSH, pinging other addresses results in what looks like a duplicate packet (DUP!) with every ping it does. We have set everything up ourselves, so I wouldn't be surprised if it is an issue with settings... and while it could be a hardware issue, I doubt this somewhat.

Does anybody have any idea what's going on? I've looked this up online and it seems others have had this problem, but I didn't find any clear answers (I could have looked more, I suppose). Suggestions on how to get more information are also appreciated... maybe I should run a traceroute? I am utterly clueless.

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Could you check with Wireshark which packets actually get duplicated? Just ICMP echo replies, or everything? – grawity Sep 23 '11 at 14:35
@grawity: I think that's a great idea, and will try that out. However, I think I'll wait a bit and see if anybody swoops in with a "just edit line foo in /etc/bar.conf"-esque answer. – Patrick87 Sep 23 '11 at 14:43
Receiving duplicate packets from other machines is not something your /etc would handle... While you wait, why not install Wireshark? :) – grawity Sep 23 '11 at 14:53
Would tcpdump not be sufficient? That comes pre-loaded on the CentOS OS we have installed. In any event, I have been playing around with that, based on your suggestion. – Patrick87 Sep 23 '11 at 15:06
It would suffice, it's mostly a matter of preference. Both tcpdump and tshark/Wireshark have the same libpcap core functionality. – grawity Sep 23 '11 at 15:07

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