We did a "traceroute" end-to-end routing measurement in 2004 and found about 5-10% of measuremnts exhibiting rapidly-variable routing on the time scale of a single traceroute (seconds to minutes). In other words, the packets belonging to a single traceroute took multiple paths. Vern Paxson mentioned in 1997 one mechanism that can lead to this "route fluttering" behavior as "route splitting", which is explicity allowed in RFC1812 - Requirements for IP version 4 Routers. Route change in such a short scale for packets in the same flow could be troublesome. But the occurrence of such behavior does not seem to have reduced over the past years at least from our measurements. Does anyone know how to explain this behavior? Thanks! An example traceroute record containing the fluttering is shown below (see the 5th hop) Fri Apr 09 09:35:35 2004 1 cisfhfb.fh-friedberg.de (212.201.24.1) 1.095 ms 0.402 ms 0.321 ms 2 ar-frankfurt2.g-win.dfn.de (188.1.42.9) 120.105 ms 198.766 ms 200.040 ms 3 cr-frankfurt1-ge5-0.g-win.dfn.de (188.1.80.1) 2.093 ms 2.142 ms 2.087 ms 4 so-6-0-0.ar2.FRA2.gblx.net (208.48.23.141) 2.461 ms 2.349 ms 2.333 ms 5 pos5-0-2488M.cr2.FRA2.gblx.net (67.17.65.53) 2.448 ms pos6-0-2488M.cr1.FRA2.gblx.net (67.17.65.77) 2.368 ms 2.281 ms 6 so3-0-0-2488M.ar2.FRA3.gblx.net (67.17.65.82) 2.676 ms 2.750 ms so2-0-0-2488M.ar2.FRA3.gblx.net (67.17.65.58) 2.569 ms 7 ge-7-2.Frankfurt1.Level3.net (195.122.136.245) 10.971 ms 10.967 ms 10.882 ms 8 ae-0-55.mp1.Frankfurt1.Level3.net (195.122.136.97) 11.488 ms 11.417 ms 11.353 ms 9 so-0-0-0.mp1.London2.Level3.net (212.187.128.61) 27.203 ms 27.042 ms 27.048 ms 10 so-1-0-0.bbr1.Washington1.Level3.net (212.187.128.138) 91.004 ms 91.006 ms 90.977 ms 11 ge-0-0-0.mpls1.Honolulu2.Level3.net (4.68.128.13) 212.254 ms 212.321 ms 212.351 ms 12 so-7-0.hsa1.Honolulu2.Level3.net (4.68.112.90) 212.407 ms 212.250 ms 212.365 ms 13 s1.lavanet.bbnplanet.net (4.24.134.18) 212.609 ms 212.372 ms 213.270 ms 14 malasada.lava.net (64.65.64.17) 212.260 ms 212.460 ms 212.226 ms Best regards, Charles