Forwarded to NANOG in the interests of wider awareness... having been there and torn out my already scarce hair, duplicate MAC addresses can really mess up your day... --- Just when you thought this couldn't happen any more... Copying from a different email list... mac address 04:4b:80:80:80:03, was showing up in multiple places across the network. I googled the mac address and discovered that other people are having the same issue with this mac address. Below are some links describing the problem: http://forums.nvidia.com/index.php?showtopic=22148 http://www.nvnews.net/vbulletin/archive/index.php/t-73469.html I just wanted everyone to know about this problem in case you run across similar slow "connectivity" issues. I believe the network card is made by NVIDIA.