> All NICs on all machines involved report exactly the same: > > negotiated 100baseTx-FD flow-control, link ok > > We've also checked ifconfig on all interfaces, and no errors, dropped > packets, overruns, nor collisions have been recorded. Great! Is your upstream device also able to talk at 100 Mb/s? You might also try running some point to point bandwidth tests with iperf <http://dast.nlanr.net/Projects/Iperf/> to try and isolate which machine(s) are having issues. ntop <http://www.ntop.org> and iptraf (included in CentOS) can also be useful to monitor bandwidth/throughput as well. Barry