[e2e] What's wrong with this picture?
David P. Reed
dpreed at reed.com
Sun Sep 6 18:00:16 PDT 2009
For those who have some idea of how TCP does congestion control, I ask
"what's wrong with this picture?" And perhaps those who know someone
responsible at the Internet Access Provider involved, perhaps we could
organize some consulting help...
(Hint: the problem relates to a question, "why are there no lost IP
datagrams?", and a second hint is that the ping time this morning was
about 193 milliseconds.)
Van Jacobsen, Scott Shenker, and Sally Floyd are not allowed to answer
the question. (they used to get funding from the IAP involved, but
apparently that company does not listen to them).
$ ping lcs.mit.edu
PING lcs.mit.edu (128.30.2.121) 56(84) bytes of data.
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=1 ttl=44
time=6330 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=2 ttl=44
time=6005 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=3 ttl=44
time=8509 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=4 ttl=44
time=9310 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=5 ttl=44
time=8586 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=6 ttl=44
time=7765 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=7 ttl=44
time=7168 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=8 ttl=44
time=10261 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=9 ttl=44
time=10624 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=10 ttl=44
time=9625 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=11 ttl=44
time=9725 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=12 ttl=44
time=8725 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=13 ttl=44
time=9306 ms
64 bytes from zermatt.csail.mit.edu (128.30.2.121): icmp_seq=14 ttl=44
time=8306 ms
^C
--- lcs.mit.edu ping statistics ---
24 packets transmitted, 14 received, 41% packet loss, time 33174ms
rtt min/avg/max/mdev = 6005.237/8589.365/10624.776/1334.140 ms, pipe 11
$ traceroute lcs.mit.edu
traceroute to lcs.mit.edu (128.30.2.121), 30 hops max, 60 byte packets
1 * * *
2 172.26.248.2 (172.26.248.2) 693.585 ms 693.415 ms 712.282 ms
3 * * *
4 172.16.192.18 (172.16.192.18) 712.700 ms 1356.680 ms 1359.469 ms
5 12.88.7.205 (12.88.7.205) 1361.306 ms 673.642 ms 673.541 ms
6 cr84.cgcil.ip.att.net (12.122.152.134) 673.442 ms 673.371 ms
673.742 ms
7 cr2.cgcil.ip.att.net (12.123.7.250) 655.126 ms 654.186 ms 554.690 ms
8 * * ggr2.cgcil.ip.att.net (12.122.132.133) 912.385 ms
9 192.205.33.210 (192.205.33.210) 909.925 ms 911.335 ms 911.204 ms
10 ae-31-53.ebr1.Chicago1.Level3.net (4.68.101.94) 569.740 ms 569.605
ms 907.409 ms
11 ae-1-5.bar1.Boston1.Level3.net (4.69.140.93) 369.680 ms 344.495
ms 345.252 ms
12 ae-7-7.car1.Boston1.Level3.net (4.69.132.241) 355.645 ms 641.866
ms 641.367 ms
13 MASSACHUSET.car1.Boston1.Level3.net (4.53.48.98) 636.598 ms
636.797 ms 635.755 ms
14 B24-RTR-2-BACKBONE-2.MIT.EDU (18.168.1.23) 635.766 ms 634.794 ms
866.430 ms
15 MITNET.TRANTOR.CSAIL.MIT.EDU (18.4.7.65) 758.305 ms 822.244 ms
821.202 ms
16 trantor.kalgan.csail.mit.edu (128.30.0.246) 833.699 ms 1055.548
ms 1116.813 ms
17 zermatt.csail.mit.edu (128.30.2.121) 1114.838 ms 539.951 ms
620.681 ms
[david at whimsy ~]$ ping 172.26.248.2
PING 172.26.248.2 (172.26.248.2) 56(84) bytes of data.
64 bytes from 172.26.248.2: icmp_seq=1 ttl=254 time=1859 ms
64 bytes from 172.26.248.2: icmp_seq=2 ttl=254 time=1363 ms
64 bytes from 172.26.248.2: icmp_seq=3 ttl=254 time=1322 ms
64 bytes from 172.26.248.2: icmp_seq=4 ttl=254 time=1657 ms
64 bytes from 172.26.248.2: icmp_seq=5 ttl=254 time=1725 ms
64 bytes from 172.26.248.2: icmp_seq=6 ttl=254 time=1740 ms
64 bytes from 172.26.248.2: icmp_seq=7 ttl=254 time=1838 ms
64 bytes from 172.26.248.2: icmp_seq=8 ttl=254 time=1738 ms
64 bytes from 172.26.248.2: icmp_seq=9 ttl=254 time=1517 ms
64 bytes from 172.26.248.2: icmp_seq=10 ttl=254 time=978 ms
64 bytes from 172.26.248.2: icmp_seq=11 ttl=254 time=715 ms
64 bytes from 172.26.248.2: icmp_seq=12 ttl=254 time=678 ms
64 bytes from 172.26.248.2: icmp_seq=13 ttl=254 time=638 ms
64 bytes from 172.26.248.2: icmp_seq=14 ttl=254 time=761 ms
^C
--- 172.26.248.2 ping statistics ---
15 packets transmitted, 14 received, 6% packet loss, time 14322ms
rtt min/avg/max/mdev = 638.651/1324.002/1859.725/455.200 ms, pipe 2
$
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