Dear People;
I was experiencing a lot of 'hung' connections when downloading files
from web servers; the application just stopped receiving data and sat
there. Usually, the second shot worked, or occasionally it would hang up
at a different spot, so I just blamed it on my network connection. Then
I came across a file on THEM (sunsite) that I could not download no mater
how many times I tried, though it hung at different points.
I used tcpdump, and its edited output is included below.
I would like to know if the problem is ME, THEM, or what? Why do I see packets
cross only at long intervals after ME sets his SACK option? Why dont I see
this problem if I ftp files? (luck?) If I waited long enough, would
THEM eventually fill in the hole I have in my sequence? I would think
that eventually ME would do something to force retransmission starting at
the last contiguous sequence it recieved....
I am using 2.2.10int, ppp2.3.6, and lynx as the browser. Turning off
tcp_sack prevents this from happening, so I think its definitely related
to SACK.
I would like to understand what is going on, so any comments are appreciated.
If anyone wants more info, Ill be happy to provide it.
Paul
[EMAIL PROTECTED]
( I dont think my tcpdump3.4 is correctly interpreting the SACK option,
as I looked at the rfc, and it should be pairs of 32bit values, not 16bit
values...? So, I havent verified the sanity of the SACK options passed yet.)
.... First, we both agree to SACK,
17:51:29.260000 ME.2899 > THEM.www: S 2855793436:2855793436(0) win 32472 <mss
984,sackOK,timestamp 243242035 0,nop,wscale 0> (DF)
17:51:29.460000 THEM.www > ME.2899: S 4166595690:4166595690(0) ack 2855793437 win 9720
<nop,nop,timestamp 37620505 243242035,nop,wscale 0,nop,nop,sackOK,mss 984> (DF)
.... now we start to download....
17:51:37.060000 THEM.www > ME.2900: . 1:973(972) ack 625 win 9720 <nop,nop,timestamp
37621229 243242736> (DF)
17:51:37.060000 ME.2900 > THEM.www: . ack 973 win 31500 <nop,nop,timestamp 243242815
37621229> (DF)
17:51:37.410000 THEM.www > ME.2900: P 973:1945(972) ack 625 win 9720
<nop,nop,timestamp 37621229 243242736> (DF)
17:51:37.410000 ME.2900 > THEM.www: . ack 1945 win 31104 <nop,nop,timestamp 243242850
37621229> (DF)
.... working fine so far....
17:52:08.550000 THEM.www > ME.2900: . 87230:88202(972) ack 625 win 9720
<nop,nop,timestamp 37623320 243244852> (DF)
17:52:08.550000 ME.2900 > THEM.www: . ack 88202 win 31104 <nop,nop,timestamp 243245964
37623320> (DF)
17:52:08.920000 THEM.www > ME.2900: . 88202:89174(972) ack 625 win 9720
<nop,nop,timestamp 37623391 243244922> (DF)
17:52:09.260000 THEM.www > ME.2900: . 89174:90146(972) ack 625 win 9720
<nop,nop,timestamp 37623391 243244922> (DF)
17:52:09.260000 ME.2900 > THEM.www: . ack 90146 win 31104 <nop,nop,timestamp 243246035
37623391> (DF)
17:52:09.620000 THEM.www > ME.2900: . 92090:93062(972) ack 625 win 9720
<nop,nop,timestamp 37623529 243245061> (DF)
.... after this, the application doesnt receive any more data....
.... packets come from the sender every minute or so hearafter....
17:52:09.620000 ME.2900 > THEM.www: . ack 90146 win 31104 <nop,nop,timestamp 243246071
37623529,nop,nop,sack 26369@63727 27341@63727> (DF)
17:52:09.960000 THEM.www > ME.2900: . 93062:94034(972) ack 625 win 9720
<nop,nop,timestamp 37623529 243245061> (DF)
17:52:09.960000 ME.2900 > THEM.www: . ack 90146 win 31104 <nop,nop,timestamp 243246105
37623529,nop,nop,sack 26369@63727 28313@63727> (DF)
17:52:10.320000 THEM.www > ME.2900: . 94034:95006(972) ack 625 win 9720
<nop,nop,timestamp 37623600 243245132> (DF)
17:52:10.320000 ME.2900 > THEM.www: . ack 90146 win 31104 <nop,nop,timestamp 243246141
37623600,nop,nop,sack 26369@63727 29285@63727> (DF)
17:52:10.660000 THEM.www > ME.2900: . 95006:95978(972) ack 625 win 9720
<nop,nop,timestamp 37623600 243245132> (DF)
17:52:10.660000 ME.2900 > THEM.www: . ack 90146 win 31104 <nop,nop,timestamp 243246175
37623600,nop,nop,sack 26369@63727 30257@63727> (DF)
17:52:11.020000 THEM.www > ME.2900: . 95978:96950(972) ack 625 win 9720
<nop,nop,timestamp 37623674 243245206> (DF)
17:52:11.020000 ME.2900 > THEM.www: . ack 90146 win 31104 <nop,nop,timestamp 243246211
37623674,nop,nop,sack 26369@63727 31229@63727> (DF)
17:52:11.360000 THEM.www > ME.2900: . 96950:97922(972) ack 625 win 9720
<nop,nop,timestamp 37623674 243245206> (DF)
....
.... It goes on like this until the download is canceled...
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