Walter Hofmann wrote:
> I have the following set up at home:
>
> desktop (gimli) <--wlan--> access point <--ether--> desktop (gandalf) <--PPPoE--> DSL modem
>
> When I download a certain file from ftp.de.debian.org (with aptitude,
> http protocol) than the connection hangs. Network traces (below) show
> that a certain packet from ftp.de.debian.org arrives on gandalf and is
> sent on to gimli, but never arrives. The segment that causes the problem
> is 271051:272491.
>
> Here is the trace from gandalf:
>
> 13:39:53.944390 IP (tos 0x0, ttl 64, id 30737, offset 0, flags [DF], length: 64) gimli.local.33601 > ftp.de.debian.org.www: . [tcp sum ok] 1753:1753(0) ack 271051 win 31680 <nop,nop,timestamp 66121693 1647346510,nop,nop,sack sack 1 {272491:393451} >
> 13:39:53.951311 IP (tos 0x0, ttl 51, id 21284, offset 0, flags [DF], length: 1492) ftp.de.debian.org.www > gimli.local.33601: . 393451:394891(1440) ack 1753 win 723 <nop,nop,timestamp 1647347327 66120629>
> 13:39:53.959175 IP (tos 0x0, ttl 64, id 30739, offset 0, flags [DF], length: 64) gimli.local.33601 > ftp.de.debian.org.www: . [tcp sum ok] 1753:1753(0) ack 271051 win 31680 <nop,nop,timestamp 66121707 1647346510,nop,nop,sack sack 1 {272491:394891} >
> 13:39:53.960009 IP (tos 0x0, ttl 51, id 21286, offset 0, flags [DF], length: 1492) ftp.de.debian.org.www > gimli.local.33601: . 394891:396331(1440) ack 1753 win 723 <nop,nop,timestamp 1647347351 66120653>
> 13:39:53.966442 IP (tos 0x0, ttl 64, id 30741, offset 0, flags [DF], length: 64) gimli.local.33601 > ftp.de..debian.org.www: . [tcp sum ok] 1753:1753(0) ack 271051 win 31680 <nop,nop,timestamp 66121715 1647346510,nop,nop,sack sack 1 {272491:396331} >
> 13:39:53.973187 IP (tos 0x0, ttl 51, id 21288, offset 0, flags [DF], length: 1492) ftp.de.debian.org.www > gimli.local.33601: . 396331:397771(1440) ack 1753 win 723 <nop,nop,timestamp 1647347351 66120653>
> 13:39:53.979677 IP (tos 0x0, ttl 64, id 30743, offset 0, flags [DF], length: 64) gimli.local.33601 > ftp.de.debian.org.www: . [tcp sum ok] 1753:1753(0) ack 271051 win 31680 <nop,nop,timestamp 66121728 1647346510,nop,nop,sack sack 1 {272491:397771} >
> 13:39:53.986257 IP (tos 0x0, ttl 51, id 21290, offset 0, flags [DF], length: 1492) ftp.de.debian.org.www > gimli.local.33601: . 271051:272491(1440) ack 1753 win 723 <nop,nop,timestamp 1647347406 66120703>
> 13:39:54.119443 IP (tos 0x0, ttl 51, id 21292, offset 0, flags [DF], length: 1492) ftp.de.debian.org.www > gimli.local.33601: . 271051:272491(1440) ack 1753 win 723 <nop,nop,timestamp 1647348512 66121728>
> 13:39:56.330501 IP (tos 0x0, ttl 51, id 21294, offset 0, flags [DF], length: 1492) ftp.de.debian.org.www > gimli.local.33601: . 271051:272491(1440) ack 1753 win 723 <nop,nop,timestamp 1647350724 66121728>
> 13:40:00.753346 IP (tos 0x0, ttl 51, id 21296, offset 0, flags [DF], length: 1492) ftp.de.debian.org.www > gimli.local.33601: . 271051:272491(1440) ack 1753 win 723 <nop,nop,timestamp 1647355148 66121728>
> 13:40:09.598006 IP (tos 0x0, ttl 51, id 21298, offset 0, flags [DF], length: 1492) ftp.de.debian.org.www > gimli.local.33601: . 271051:272491(1440) ack 1753 win 723 <nop,nop,timestamp 1647363996 66121728>
>
> And from gimli it looks like this:
>
> 13:40:17.120971 IP gimli.local.33601 > ftp.de.debian.org.www: . ack 271051 win 31680 <nop,nop,timestamp 66121693 1647346510,nop,nop,sack 1 {272491:393451}>
> 13:40:17.134568 IP ftp.de.debian.org.www > gimli.local.33601: . 393451:394891(1440) ack 1753 win 723 <nop,nop,timestamp 1647347327 66120629>
> 13:40:17.134600 IP gimli.local.33601 > ftp.de.debian.org.www: . ack 271051 win 31680 <nop,nop,timestamp 66121707 1647346510,nop,nop,sack 1 {272491:394891}>
> 13:40:17.142867 IP ftp.de.debian.org.www > gimli.local.33601: . 394891:396331(1440) ack 1753 win 723 <nop,nop,timestamp 1647347351 66120653>
> 13:40:17.142897 IP gimli.local.33601 > ftp.de.debian.org.www: . ack 271051 win 31680 <nop,nop,timestamp 66121715 1647346510,nop,nop,sack 1 {272491:396331}>
> 13:40:17.156203 IP ftp.de.debian.org.www > gimli.local.33601: . 396331:397771(1440) ack 1753 win 723 <nop,nop,timestamp 1647347351 66120653>
> 13:40:17.156245 IP gimli.local.33601 > ftp.de.debian.org.www: . ack 271051 win 31680 <nop,nop,timestamp 66121728 1647346510,nop,nop,sack 1 {272491:397771}>
> [nothing more]
>
> Note that the packet is question is 1492 bytes long, and that other
> packets from ftp.de.debian.org that are also 1492 bytes long get
> through: e.g. 394891:396331. They are ack'ed by gimli with the tcp sack
> option. This rules out MTU problems.
>
> Speaking of MTU, the one on
> gimli/wlan0 is 1500,
> gandalf/eth0 is 1500,
> gandalf/ppp0 is 1492.
>
> gimli is Linux 2.6.11.3, gandalf is Linux 2.4.22.
>
> I already tried to set the MTU on gimli to 400. Then ftp.de.debian.org
> sends much smaller packets, but the connection still hangs with a trace
> similar to the one above.
> I also made pppd negotiate a smaller mtu on the ppp link, to no avail.
>
> There are firewalls on both machines, but I already tried with them
> switched off -- no change.
>
> Everything is reproducable every time.
>
> What could be wrong? Any help is much appreciated!
>
> Walter
>
FTP is flaky as hell. I have some files that just wont go over FTP from
certain clients and whatnot. Just yesterday I could not sftp a file,
but once renamed it went just fine. FTP is rediculous. or maybe its the
clients or servers..Are you positive its using http protocol? I would
verify that first.
--
Respectfully,
CL Gilbert
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