Louise Addis of SLAC reported that the SLAC library folks could not use ssh
to execute commands at usparc.ihep.su. The packet loss was measured to be over 80%:
--- usparc.ihep.su ping statistics ---
103 packets transmitted, 12 packets received, 88% packet loss
round-trip min/avg/max/mdev = 213.072/219.313/234.612/5.784 ms
ksa@osiris $
Packet losses of this magnitude (in fact losses over 10-12% make it difficult to
maintain a connection) will quickly lead to the TCP connection being broken.
Measurements
The traceroute indicates that the route is via
ESnet to Internet 2 to NorduNet to various Russian networks.
Pipechar indicates that the path is OC3 through
NorduNet and then drops to T3.
Pingroute indicates that the losses start to occur between
St Petersburg and rbnet.RUN.Net, and gets really bad (90%) on the last hop to
usparc.ihep.su.
Looking at the PingER plots from SLAC to www.ihep.su for 1000 Byte
and
100 Byte pings
shows that this route has heavy loss, and that it has got worse somewhere around
September 18th.
The tabular output for
www.ihep.su from PingER indicates that the median daily losses have increased from about 8%
to about 12% on September 18th. This is way below the over 80% reported by
Louise to usparc.ihep.su. Looking at the hourly losses for September 18th, 2001, it appears
that they are varying between 0 and 20%, again way below the ~80% reported by Louise.
Pings measured around 8:40pm 9/19/01 PDT
from pharlap.slac.stanford.edu to usparc.ihep.su show losses of 90% for 105 packets.
The losses appear quite bursty, e.g. most of
the packets will be lost (not respond in 1 second)
but then a burst of 4 or 5 consective pings respond.
---- usparc.ihep.su (194.190.161.54) PING Statistics ----
105 packets transmitted, 10 packets received, 90% packet loss
round-trip (ms) min/avg/max = 212/216/223 (std = 3.48)
4cottrell@pharlap:~>nping www.ihep.su
Pings to www.ihep.su measured around the same time on the other hand
show much lower packet losses of less than 10%:
---- altair.ihep.su (194.190.161.18) PING Statistics ----
107 packets transmitted, 102 packets received, 4.7% packet loss
round-trip (ms) min/avg/max = 211/215/241 (std = 5.37)
Thus it appears that the major part of the problem
is in the IHEP LAN, or the machine usparc itself.
Comparing the pingroute from SLAC to
www.ihep.su witrh the pingroute above from SLAC to usparc.ihep.su
confirms the above conclusions.
Page owner: Les Cottrell
