Delays etc.: ping,
OWAMP, GPS
Bandwidth: iperf,
pathload, pipechar, netest, ABwE
Utilization: SNMP
Topology/tomography:
traceroute, skitter, INCITE
Routing: RIPE,
routeviews
Traffic
characterization: netflow, NeTraMet, tcpdump, coralreef
Visualization: MRTG,
RRD, netgeo, geoplot, tcptrace, xplot