Tcpdump says I'm getting incomplete packets; how to find the culprit?

[Doug Lee]

On Mon, Dec 27, 2004 at 07:30:41PM -0600, Dan Nelson wrote:
In the last episode (Dec 27), Doug Lee said:
> I use FreeBSD 4.10-STABLE as a nat/firewall box.  When connected to
> DSL, I got fast web surfing but many gaps in incoming audio traffic
> using some audio software.  I switched to cable, and now audio works
> great, but at least when I pop open pages in Lynx right on the
> FreeBSD box, I often experience five-second delays--one at "202 OK"
> and one or more during the loading of the page.  Tcpdump reports that
> I'm receiving incomplete packets, so I assume the five-second delays
> are timeouts on my box before a request for packet resends.

What is tcpdump printing that makes you think that packets are
incomplete?   If you are manually decoding packets by looking at
tcpdump -X output, make sure you also use -s 0 to grab the entire
packet.

This is from a "tcpdump -s 0 -w tco -i ed0 port 80" run.  Line 12
shows a truncation but no delay, interestingly enough; but I believe
line 17 is the one that occurred when I saw "202 OK" and a five-second
delay.  Actually, I guess it's a seven-second delay after all. :-)  I
replaced my ip with <me> here.

05:20:02.131687 <me>.4891 > 12.129.203.38.http: S 1518360911:1518360911(0) win 65535 <mss 1460,nop,wscale 1,nop,nop,timestamp 449963838 0> (DF)
05:20:02.211922 12.129.203.38.http > <me>.4891: S 1407738134:1407738134(0) ack 1518360912 win 10136 <nop,nop,timestamp 164687034 449963838,nop,wscale 0,mss 1460> (DF)
05:20:02.212540 <me>.4891 > 12.129.203.38.http: . ack 1 win 33304 <nop,nop,timestamp 449963919 164687034> (DF)
05:20:02.221406 <me>.4891 > 12.129.203.38.http: . 1:1449(1448) ack 1 win 33304 <nop,nop,timestamp 449963928 164687034> (DF)
05:20:02.311500 12.129.203.38.http > <me>.4891: . ack 1449 win 10136 <nop,nop,timestamp 164687044 449963928> (DF)
05:20:02.312173 <me>.4891 > 12.129.203.38.http: P 1449:1615(166) ack 1 win 33304 <nop,nop,timestamp 449964019 164687044> (DF)
05:20:02.397972 12.129.203.38.http > <me>.4891: . 1:1449(1448) ack 1615 win 10136 <nop,nop,timestamp 164687052 449964019> (DF)
05:20:02.399266 12.129.203.38.http > <me>.4891: P 1449:2897(1448) ack 1615 win 10136 <nop,nop,timestamp 164687052 449964019> (DF)
05:20:02.402194 <me>.4891 > 12.129.203.38.http: . ack 2897 win 32580 <nop,nop,timestamp 449964109 164687052> (DF)
05:20:02.485577 12.129.203.38.http > <me>.4891: . 2897:4345(1448) ack 1615 win 10136 <nop,nop,timestamp 164687061 449964109> (DF)
05:20:02.486357 <me>.4891 > 12.129.203.38.http: . ack 4345 win 33304 <nop,nop,timestamp 449964193 164687061> (DF)
05:20:02.486606 truncated-ip - 276 bytes missing! 12.129.203.38.http > <me>.4891: . 4345:5793(1448) ack 1615 win 10136 <nop,nop,timestamp 164687061 449964109> (DF)
05:20:02.487904 12.129.203.38.http > <me>.4891: P 5793:7241(1448) ack 1615 win 10136 <nop,nop,timestamp 164687061 449964109> (DF)
05:20:02.491372 <me>.4891 > 12.129.203.38.http: . ack 4345 win 33304 <nop,nop,timestamp 449964198 164687061> (DF)
05:20:02.580962 12.129.203.38.http > <me>.4891: . 7241:8689(1448) ack 1615 win 10136 <nop,nop,timestamp 164687071 449964198> (DF)
05:20:02.581628 <me>.4891 > 12.129.203.38.http: . ack 4345 win 33304 <nop,nop,timestamp 449964288 164687061> (DF)
05:20:02.581839 truncated-ip - 434 bytes missing! 12.129.203.38.http > <me>.4891: P 8689:10137(1448) ack 1615 win 10136 <nop,nop,timestamp 164687071 449964198> (DF)
05:20:07.060856 12.129.203.38.http > <me>.4891: . 4345:5793(1448) ack 1615 win 10136 <nop,nop,timestamp 164687519 449964198> (DF)
05:20:07.061557 <me>.4891 > 12.129.203.38.http: . ack 8689 win 31132 <nop,nop,timestamp 449968770 164687519> (DF)
05:20:07.061997 <me>.4891 > 12.129.203.38.http: . ack 8689 win 33180 <nop,nop,timestamp 449968770 164687519> (DF)
05:20:07.144915 12.129.203.38.http > <me>.4891: . 8689:10137(1448) ack 1615 win 10136 <nop,nop,timestamp 164687527 449968770> (DF)
05:20:07.146198 12.129.203.38.http > <me>.4891: . 10137:11585(1448) ack 1615 win 10136 <nop,nop,timestamp 164687527 449968770> (DF)
05:20:07.159433 <me>.4891 > 12.129.203.38.http: . ack 11585 win 32580 <nop,nop,timestamp 449968867 164687527> (DF)


-- 
Doug Lee           dgl at dlee.org        http://www.dlee.org
Bartimaeus Group   doug at bartsite.com   http://www.bartsite.com
"Never does the human soul appear so strong as when it foregoes
revenge, and dares forgive an injury." --E. H. Chapin