In addition to many commercial tools such as EtherPeek Network Analyzer, WildPackets has provided some of the best free tools. I've always been a fan of IP Subnet Calculator™ myself. Check out some of their other free tools:
My favorite is netdoppler. Great tool to measure throughput, latency etc., really comfortable. pathchar for Linux/Unix offers roughly the same functionality but is somewhat outdated and difficult to understand as there is no real documentation.
Registered users: No registered users In total there are 77 users online :: 0 registered, 4 hidden and 73 guests (based on users active over the past 5 minutes) Most users ever online was 1535 on Fri Feb 01, 2008 4:38 pm Legend: Administrators, Global moderators