I get flooded with ACKs under 2.1.36 when I connect to certain FTP sites.
Here is a section of tcpdump output under 2.1.36 during an ftp session to
a particular server:
12:27:38.494757 140.142.3.227.ftp-data > 194.222.36.72.1525: S 1096000000:1096000000(0) win 16384
12:27:38.494757 194.222.36.72.1525 > 140.142.3.227.ftp-data: S 1818665878:1818665878(0) ack 1096000001 win 8192 <mss 0>
*** (notice <mss 0>)
12:27:38.544757 140.142.3.227.ftp > 194.222.36.72.1491: . ack 62 win 16384
12:27:38.934754 140.142.3.227.ftp-data > 194.222.36.72.1525: . ack 1 win 16384
12:27:38.994754 140.142.3.227.ftp > 194.222.36.72.1491: P 1493:1566(73) ack 62 win 16384
12:27:39.004754 194.222.36.72.1491 > 140.142.3.227.ftp: . ack 1566 win 2144 [tos 0x10]
12:27:39.014754 140.142.3.227.ftp-data > 194.222.36.72.1525: . ack 1 win 16384
12:27:39.034754 140.142.3.227.ftp-data > 194.222.36.72.1525: . ack 1 win 16384
12:27:39.054754 140.142.3.227.ftp-data > 194.222.36.72.1525: . ack 1 win 16384
*** (and MUCH more of this. The other end doesn't stop for half an hour.)
A little later, under 2.1.29, the remote host hasn't given up:
12:34:41.522079 140.142.3.227.ftp-data > 194.222.36.72.1525: . ack 1818665879 win 16384
12:34:41.522079 194.222.36.72.1525 > 140.142.3.227.ftp-data: R 1818665879:1818665879(0) win 0
12:34:41.542079 140.142.3.227.ftp-data > 194.222.36.72.1525: . ack 1 win 16384
12:34:41.542079 194.222.36.72.1525 > 140.142.3.227.ftp-data: R 1818665879:1818665879(0) win 0
*** (continues)
(The resets weren't being sent under 2.1.36)
After the remote end has settled down, I tried ftping again (still under
2.1.29), and the handshake looks like this:
13:21:20.532336 140.142.4.227.ftp-data > 194.222.36.72.1714: S 310592001:310592001(0) win 16384
13:21:20.532336 194.222.36.72.1714 > 140.142.4.227.ftp-data: S 3102652652:3102652652(0) ack 310592002 win 8192 <mss 536>
*** (this time, notice <mss 536>)
13:21:20.652336 140.142.4.227.ftp > 194.222.36.72.1650: . ack 62 win 16384
13:21:20.972336 140.142.4.227.ftp-data > 194.222.36.72.1714: . ack 1 win 16384
13:21:21.032336 140.142.4.227.ftp > 194.222.36.72.1650: P 1493:1566(73) ack 62 win 16384
13:21:21.042336 194.222.36.72.1650 > 140.142.4.227.ftp: . ack 1566 win 2144 [tos 0x10]
13:21:21.312332 140.142.4.227.ftp-data > 194.222.36.72.1714: . 1:513(512) ack 1 win 16384
*** (continues normally)
Tim.
*/