Network connectivity between SLAC and Platform Computing January 2001Les Cottrell. Page created: January 12, 2001.
Central Computer Access | Computer Networking | Network Group | ICFA-NTF Monitoring
For the last two days [at least] slow response to Platform Computing seems to be hung on this Teleglobe.net stuff. Do we have any way to improve the performance there or bypass it?
----greyowl.platform.com PING Statistics---- 202 packets transmitted, 168 packets received, 16% packet loss round-trip (ms) min/avg/max = 122/172/284We also tried traceroutes from Stanford University and that showed a different route (as would be expected). Note that there are 2 traceroutes, the first was done from a Windows NT machine that does not use ICMP for the traceroute probes but rather uses UDP. The second was done from a Sun Solaris machine. Again the Solaris traceroute does not detect the ftp.platform.com machine. It is possible that the ftp.platform.com is blocked from receiving the ICMP probes. Note that Also the packet loss from Stanford University to Platform was lower (< 10%) than from SLAC.
---- greyowl.platform.com (126.96.36.199) PING Statistics ---- 202 packets transmitted, 186 packets received, 7.9% packet loss round-trip (ms) min/avg/max = 105/164/331 (std = 39.3)The path characterization from SLAC indicates congestion in the Teleglobe.net network.
We used pingroute to see if we could see where the pings start to be lost. It also indicates that from SLAC the losses start either at the border with ESnet or in the Teleglobe network. However, for the pingroute from Stanford there does not appear to be much loss in the Teleglobe network. From this we may deduce that the problem may be at the Esnet Teleglobe border.
We also used synack to see whethere there was any ICMP rate limiting between SLAC and ftp.platform.com but both syn/acks and pings were being lost at roughly the same rate (see Ping vs. Synack for plots of the data and ICMP Rate Limiting for a description of the methodology).
----greyowl.platform.com PING Statistics---- 360 packets transmitted, 266 packets received, 26% packet loss round-trip (ms) min/avg/max = 136/143/306We confirmed that the routefrom SLAC to Platform was now via Alternet. We also noted that the route from Stanford University to Platform was still via Teleglobe and had low (<1%) packet loss. We ran pingroute again from flora.slac.stanford.edu to ftp.platform.com to see if we could observe where the losses on this route started. Losses appear to start at hop 9. Note that hop 8 at 188.8.131.52 is reported by nslookup to be part of Alternet (br2.tco1.alter.net) and located near Washington according to the Hostname to Lat/Long service. The packet loss gets really bad between hops 14 and 15. We are unable to find any information on 184.108.40.206 or 220.127.116.11.
At the same time the route from Platform to SLAC was still using Teleglobe, thus the routing had become asymmetric.
We therefore used Sting to see whether the one way packet losses were also asymmetric. The results indicate that the losses are much higher (almost a factor of 10) higher in the route from Platform to SLAC.