Re: BSD doesn't track window size changes correctly.

To: Dennis Ferguson <dennis.c.ferguson%gmail.com@localhost>
Subject: Re: BSD doesn't track window size changes correctly.
From: Darren Reed <darrenr%netbsd.org@localhost>
Date: Tue, 03 Apr 2012 17:16:46 +1000

Dennis Ferguson wrote:

...

Notice there's another inconsistency, however.  While the zero window
packet NetBSD sends is carrying data which advances the (NetBSD) sequence
to 4438371, the FreeBSD packets are carrying an ack for 4441251.  FreeBSD
has seen NetBSD packets which are not in that trace, it is reasonable for
FreeBSD to ignore the zero window in those old packets, and there's no way
to tell whether what it is doing is reasonable without seeing the NetBSD
packet with a sequence of 4441251.

I think the only brokenness there is evidence for in that trace is the trace
itself.  There's not enough of the conversation to figure out what is going
on.

09:03:38.011416 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], ack 4436931,win 7520, options [nop,nop,TS val 1076481 ecr 249], length 009:03:38.019028 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], ack 4436931,win 8033, options [nop,nop,TS val 1076482 ecr 249], length 009:03:38.020855 IP NetBSD.ssh > FreeBSD.35421: Flags [.], ack 230249,win 295, options [nop,nop,TS val 249 ecr 1076458], length 009:03:38.053904 IP NetBSD.ssh > FreeBSD.35421: Flags [.], ack 232917,win 211, options [nop,nop,TS val 249 ecr 1076458], length 009:03:38.080020 IP NetBSD.ssh > FreeBSD.35421: Flags [.], ack 235568,win 128, options [nop,nop,TS val 249 ecr 1076463], length 009:03:38.112052 IP NetBSD.ssh > FreeBSD.35421: Flags [.], ack 238424,win 39, options [nop,nop,TS val 249 ecr 1076464], length 009:03:38.222896 IP NetBSD.ssh > FreeBSD.35421: Flags [.], seq4438371:4439811, ack 238424, win 39, options [nop,nop,TS val 249 ecr1076479], length 144009:03:38.223740 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq239664:239672, ack 4436931, win 8280, options [nop,nop,TS val 1076502ecr 249,nop,nop,sack 1 {4438371:4439811}], length 809:03:38.225524 IP NetBSD.ssh > FreeBSD.35421: Flags [.], seq4439811:4441251, ack 238424, win 39, options [nop,nop,TS val 249 ecr1076479], length 144009:03:38.226304 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], ack 4436931,win 8280, options [nop,nop,TS val 1076502 ecr 249,nop,nop,sack 1{4438371:4441251}], length 009:03:38.416891 IP NetBSD.ssh > FreeBSD.35421: Flags [.], ack 239664,win 0, options [nop,nop,TS val 249 ecr 1076479], length 009:03:38.437943 IP NetBSD.ssh > FreeBSD.35421: Flags [.], seq4436931:4438371, ack 239672, win 0, options [nop,nop,TS val 249 ecr1076502], length 144009:03:38.439168 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq239672:241112, ack 4441251, win 7740, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.439290 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq241112:242552, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.439412 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq242552:243992, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.439535 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq243992:245432, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.439657 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq245432:246872, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.439780 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq246872:248312, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.439902 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq248312:249752, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.440024 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq249752:251192, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.440147 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq251192:252632, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.440269 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq252632:254072, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.440393 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq254072:255512, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.440516 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq255512:256952, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.440638 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq256952:258392, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.440761 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq258392:259832, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.440885 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq259832:261272, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.441007 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq261272:262712, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.441143 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq262712:264152, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:38.441250 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq264152:265592, ack 4441251, win 8139, options [nop,nop,TS val 1076524ecr 249], length 144009:03:39.128537 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], seq239672:241112, ack 4441251, win 8280, options [nop,nop,TS val 1076593ecr 249], length 144009:03:39.720321 IP NetBSD.ssh > FreeBSD.35421: Flags [.], seq4436931:4438371, ack 239672, win 0, options [nop,nop,TS val 252 ecr1076502], length 144009:03:39.721146 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], ack 4441251,win 8280, options [nop,nop,TS val 1076652 ecr 249], length 009:03:39.932057 IP NetBSD.ssh > FreeBSD.35421: Flags [.], ack 239672,win 0, options [nop,nop,TS val 252 ecr 1076502], length 009:03:42.722687 IP NetBSD.ssh > FreeBSD.35421: Flags [.], seq4436931:4438371, ack 239672, win 0, options [nop,nop,TS val 258 ecr1076502], length 144009:03:42.723459 IP FreeBSD.35421 > NetBSD.ssh: Flags [.], ack 4441251,win 8280, options [nop,nop,TS val 1076952 ecr 252], length 009:03:42.937384 IP NetBSD.ssh > FreeBSD.35421: Flags [.], seq4441251:4442691, ack 239672, win 0, options [nop,nop,TS val 258 ecr1076952], length 1440


Now when I modified FreeBSD's TCP to track all window changes (NetBSD
uses the same logic), not just those that increased the window, the
behaviour observed was this:

16:43:12.670784 IP FreeBSD.56171 > NetBSD.ssh: . 216603:217839(1236) ack4387088 win 8280 <nop,nop,timestamp 259836 269,nop,nop,sack 1{4388528:4391408}>16:43:12.672440 IP NetBSD.ssh > FreeBSD.56171: . 4387088:4388528(1440)ack 213747 win 157 <nop,nop,timestamp 269 259812>16:43:12.673315 IP FreeBSD.56171 > NetBSD.ssh: . ack 4391408 win 7740<nop,nop,timestamp 259836 269>16:43:12.675599 IP FreeBSD.56171 > NetBSD.ssh: . ack 4391408 win 8280<nop,nop,timestamp 259836 269>16:43:12.799261 IP NetBSD.ssh > FreeBSD.56171: . ack 216603 win 68<nop,nop,timestamp 270 259812>16:43:12.900628 IP NetBSD.ssh > FreeBSD.56171: . 4391408:4392848(1440)ack 217839 win 30 <nop,nop,timestamp 270 259836>16:43:12.903525 IP NetBSD.ssh > FreeBSD.56171: . 4392848:4394288(1440)ack 217839 win 30 <nop,nop,timestamp 270 259836>16:43:12.904630 IP FreeBSD.56171 > NetBSD.ssh: . 217839:218799(960) ack4394288 win 8100 <nop,nop,timestamp 259859 270>16:43:12.906231 IP NetBSD.ssh > FreeBSD.56171: . 4394288:4395728(1440)ack 217839 win 30 <nop,nop,timestamp 270 259836>16:43:12.907031 IP FreeBSD.56171 > NetBSD.ssh: . ack 4395728 win 8280<nop,nop,timestamp 259859 270>16:43:13.131700 IP NetBSD.ssh > FreeBSD.56171: . 4395728:4397168(1440)ack 218799 win 0 <nop,nop,timestamp 270 259859>16:43:13.134319 IP NetBSD.ssh > FreeBSD.56171: . 4397168:4398608(1440)ack 218799 win 0 <nop,nop,timestamp 270 259859>16:43:13.135221 IP FreeBSD.56171 > NetBSD.ssh: . ack 4398608 win 8100<nop,nop,timestamp 259882 270>16:43:13.136843 IP NetBSD.ssh > FreeBSD.56171: . 4398608:4400048(1440)ack 218799 win 0 <nop,nop,timestamp 270 259859>16:43:13.137692 IP FreeBSD.56171 > NetBSD.ssh: . ack 4400048 win 8280<nop,nop,timestamp 259882 270>16:43:13.139551 IP NetBSD.ssh > FreeBSD.56171: . 4400048:4401488(1440)ack 218799 win 0 <nop,nop,timestamp 270 259859>16:43:13.142504 IP NetBSD.ssh > FreeBSD.56171: . 4401488:4402928(1440)ack 218799 win 0 <nop,nop,timestamp 270 259859>16:43:13.143268 IP FreeBSD.56171 > NetBSD.ssh: . ack 4402928 win 7993<nop,nop,timestamp 259883 270>


However that was not a perfect change because the connection ends like this:

16:43:31.734465 IP FreeBSD.56171 > NetBSD.ssh: . 477711:479143(1432) ack5174804 win 7113 <nop,nop,timestamp 261742 308>16:43:31.739882 IP FreeBSD.56171 > NetBSD.ssh: . ack 5174804 win 7625<nop,nop,timestamp 261743 308>16:43:31.744796 IP FreeBSD.56171 > NetBSD.ssh: . ack 5174804 win 8157<nop,nop,timestamp 261743 308>16:43:31.905789 IP NetBSD.ssh > FreeBSD.56171: . ack 453231 win 0<nop,nop,timestamp 308 261704>16:43:31.956684 IP NetBSD.ssh > FreeBSD.56171: . 5176244:5177684(1440)ack 453231 win 0 <nop,nop,timestamp 308 261704>16:43:31.957530 IP FreeBSD.56171 > NetBSD.ssh: . ack 5174804 win 8280<nop,nop,timestamp 261765 308,nop,nop,sack 1 {5176244:5177684}>16:43:31.958955 IP NetBSD.ssh > FreeBSD.56171: . ack 453231 win 0<nop,nop,timestamp 308 261704>16:43:32.174523 IP NetBSD.ssh > FreeBSD.56171: . 5174804:5176244(1440)ack 453231 win 0 <nop,nop,timestamp 308 261765>16:43:32.175434 IP FreeBSD.56171 > NetBSD.ssh: . ack 5177684 win 7920<nop,nop,timestamp 261786 308>16:43:32.175500 IP FreeBSD.56171 > NetBSD.ssh: . ack 5177684 win 8280<nop,nop,timestamp 261786 308>16:43:32.177426 IP NetBSD.ssh > FreeBSD.56171: . 5177684:5179124(1440)ack 453231 win 0 <nop,nop,timestamp 308 261765>16:43:32.185135 IP NetBSD.ssh > FreeBSD.56171: . ack 453231 win 128<nop,nop,timestamp 308 261765>16:43:32.186063 IP FreeBSD.56171 > NetBSD.ssh: . 453231:454671(1440) ack5179124 win 8280 <nop,nop,timestamp 261787 308>16:43:32.186184 IP FreeBSD.56171 > NetBSD.ssh: . 454671:456111(1440) ack5179124 win 8280 <nop,nop,timestamp 261787 308>16:43:32.186289 IP FreeBSD.56171 > NetBSD.ssh: . 456111:457327(1216) ack5179124 win 8280 <nop,nop,timestamp 261787 308>16:43:32.392350 IP NetBSD.ssh > FreeBSD.56171: . 5179124:5180564(1440)ack 453231 win 128 <nop,nop,timestamp 309 261786>16:43:32.394970 IP NetBSD.ssh > FreeBSD.56171: . 5180564:5182004(1440)ack 453231 win 128 <nop,nop,timestamp 309 261786>16:43:32.395842 IP FreeBSD.56171 > NetBSD.ssh: . ack 5182004 win 8100<nop,nop,timestamp 261808 309>16:43:32.397691 IP NetBSD.ssh > FreeBSD.56171: . 5182004:5183444(1440)ack 453231 win 128 <nop,nop,timestamp 309 261786>16:43:32.408085 IP FreeBSD.56171 > NetBSD.ssh: . ack 5183444 win 8280<nop,nop,timestamp 261810 309>16:43:32.416708 IP NetBSD.ssh > FreeBSD.56171: . 5183444:5184884(1440)ack 454671 win 83 <nop,nop,timestamp 309 261787>16:43:32.419593 IP NetBSD.ssh > FreeBSD.56171: . 5184884:5186324(1440)ack 454671 win 83 <nop,nop,timestamp 309 261787>16:43:32.420415 IP FreeBSD.56171 > NetBSD.ssh: . ack 5186324 win 8100<nop,nop,timestamp 261811 309>16:43:32.439702 IP NetBSD.ssh > FreeBSD.56171: . ack 457327 win 0<nop,nop,timestamp 309 261787>16:43:32.610095 IP NetBSD.ssh > FreeBSD.56171: . ack 457327 win 0<nop,nop,timestamp 309 261787>16:43:32.622473 IP NetBSD.ssh > FreeBSD.56171: . ack 457327 win 0<nop,nop,timestamp 309 261787>16:43:32.634325 IP NetBSD.ssh > FreeBSD.56171: . ack 457327 win 0<nop,nop,timestamp 309 261787>16:43:33.446151 IP FreeBSD.56171 > NetBSD.ssh: . ack 5186324 win 8280<nop,nop,timestamp 261914 309>16:43:33.660807 IP NetBSD.ssh > FreeBSD.56171: . ack 457327 win 0<nop,nop,timestamp 311 261787>16:43:34.410749 IP NetBSD.ssh > FreeBSD.56171: . 5179124:5180564(1440)ack 457327 win 0 <nop,nop,timestamp 313 261787>16:43:34.411650 IP FreeBSD.56171 > NetBSD.ssh: . ack 5186324 win 8280<nop,nop,timestamp 262010 311>16:43:34.625870 IP NetBSD.ssh > FreeBSD.56171: . ack 457327 win 0<nop,nop,timestamp 313 261787>16:43:37.412651 IP NetBSD.ssh > FreeBSD.56171: . 5179124:5180564(1440)ack 457327 win 0 <nop,nop,timestamp 319 261787>16:43:37.413365 IP FreeBSD.56171 > NetBSD.ssh: . ack 5186324 win 8280<nop,nop,timestamp 262310 313>16:43:37.628045 IP NetBSD.ssh > FreeBSD.56171: . ack 457327 win 0<nop,nop,timestamp 319 261787>16:43:43.414789 IP NetBSD.ssh > FreeBSD.56171: . 5179124:5179648(524)ack 457327 win 0 <nop,nop,timestamp 331 261787>16:43:43.415237 IP FreeBSD.56171 > NetBSD.ssh: . ack 5186324 win 8280<nop,nop,timestamp 262911 319>16:43:43.629769 IP NetBSD.ssh > FreeBSD.56171: . ack 457327 win 0<nop,nop,timestamp 331 261787>16:43:55.423047 IP NetBSD.ssh > FreeBSD.56171: . 5179124:5179648(524)ack 457327 win 0 <nop,nop,timestamp 355 261787>16:43:55.423645 IP FreeBSD.56171 > NetBSD.ssh: . ack 5186324 win 8280<nop,nop,timestamp 264112 331>16:43:55.637501 IP NetBSD.ssh > FreeBSD.56171: . ack 457327 win 0<nop,nop,timestamp 355 261787>


and eventually is reset after a couple of minutes of those last three
packets being replayed.

Darren

Follow-Ups:
- Re: BSD doesn't track window size changes correctly.
  - From: Dennis Ferguson

References:
- Re: BSD doesn't track window size changes correctly.
  - From: Dennis Ferguson
- BSD doesn't track window size changes correctly.
  - From: Darren Reed
- Re: BSD doesn't track window size changes correctly.
  - From: Robert Elz
- Re: BSD doesn't track window size changes correctly.
  - From: Darren Reed
- Re: BSD doesn't track window size changes correctly.
  - From: Darren Reed
- Re: BSD doesn't track window size changes correctly.
  - From: Robert Elz
- Re: BSD doesn't track window size changes correctly.
  - From: Dennis Ferguson

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