POP3 session hangs

I am experiencing a weird problem downloading mail from a Linux (
RedHat 6.2 , kernel 2.2.22-6.2.3 ) , from a Psion Epoq client through
PPP :

the connection after a while seems to hang, so i did a tcpdump and it
hangs right here :

....

270 145.209900 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327575601 Win=8192 Len=0
271 145.209937 SERVER CLIENT POP Continuation
272 145.469903 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327577061 Win=8192 Len=0
273 145.469918 SERVER CLIENT POP Continuation
274 145.999993 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327578521 Win=8192 Len=0
275 146.000011 SERVER CLIENT POP Continuation
276 146.265720 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327579981 Win=8192 Len=0
277 146.265734 SERVER CLIENT POP Continuation
278 146.795770 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327581441 Win=8192 Len=0
279 146.795788 SERVER CLIENT POP Continuation
280 147.065809 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327582901 Win=8192 Len=0
281 147.065848 SERVER CLIENT POP Continuation
282 147.595846 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327584361 Win=6732 Len=0
283 147.865890 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327585821 Win=5272 Len=0
284 148.395924 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327587281 Win=3812 Len=0
285 148.665953 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327588741 Win=2352 Len=0
286 148.918120 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327590201 Win=892 Len=0
287 151.758721 SERVER CLIENT POP Continuation
288 152.408379 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0
289 158.098716 SERVER CLIENT TCP pop3 > 2795
[ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
290 158.293192 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0
291 166.528715 SERVER CLIENT TCP pop3 > 2795
[ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
292 166.701317 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0
293 183.178717 SERVER CLIENT TCP pop3 > 2795
[ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
294 183.407362 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0
312 216.358713 SERVER CLIENT TCP pop3 > 2795
[ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
313 216.520005 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0
331 282.438712 SERVER CLIENT TCP pop3 > 2795
[ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0


And it goes on and on with this series of 2 packets :

444 763.058713 SERVER CLIENT TCP pop3 > 2795
[ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
445 763.212666 CLIENT SERVER TCP 2795 > pop3
[ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0


What could be the problem ?

Please let me know if you need more details and CC replies to my email
since i'm not subscribed to this list.

Thanks in advance,
Enrico


Enrico Demarin

I don't know a lot about TCP, but it looks like your Psion ran out of space

Enrico Demarin wrote:
> I am experiencing a weird problem downloading mail from a Linux (
> RedHat 6.2 , kernel 2.2.22-6.2.3 ) , from a Psion Epoq client through
> PPP :
>
> the connection after a while seems to hang, so i did a tcpdump and it
> hangs right here :
>
> ...
>
> 270 145.209900 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327575601 Win=8192 Len=0

Psion tells Linux that it has 8192 bytes left free in it's receive buffer

> 271 145.209937 SERVER CLIENT POP Continuation
> 272 145.469903 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327577061 Win=8192 Len=0
> 273 145.469918 SERVER CLIENT POP Continuation
> 274 145.999993 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327578521 Win=8192 Len=0
> 275 146.000011 SERVER CLIENT POP Continuation
> 276 146.265720 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327579981 Win=8192 Len=0
> 277 146.265734 SERVER CLIENT POP Continuation
> 278 146.795770 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327581441 Win=8192 Len=0
> 279 146.795788 SERVER CLIENT POP Continuation
> 280 147.065809 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327582901 Win=8192 Len=0
> 281 147.065848 SERVER CLIENT POP Continuation
> 282 147.595846 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327584361 Win=6732 Len=0

Psion now has 6732 bytes left free in it's receive buffer

> 283 147.865890 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327585821 Win=5272 Len=0

Now only 5272 bytes left as freespace in the Psion's buffer

> 284 148.395924 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327587281 Win=3812 Len=0

Down to 3812 bytes freespace in the Psion's buffer

> 285 148.665953 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327588741 Win=2352 Len=0

Down to 2352 bytes freespace in the Psion's buffer

> 286 148.918120 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327590201 Win=892 Len=0

Down to 892 bytes free in the Psion's buffer

> 287 151.758721 SERVER CLIENT POP Continuation
> 288 152.408379 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0

Psion says that it has no more room (0 bytes window) for data from Linux

> 289 158.098716 SERVER CLIENT TCP pop3 > 2795
> [ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0

Linux says that there's 32120 bytes freespace on the Linux side's buffer

> 290 158.293192 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0

But Psion still has no room in it's receive buffer for Linux's data

> 291 166.528715 SERVER CLIENT TCP pop3 > 2795
> [ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
> 292 166.701317 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0

And still no room

> 293 183.178717 SERVER CLIENT TCP pop3 > 2795
> [ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
> 294 183.407362 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0

And still no room

> 312 216.358713 SERVER CLIENT TCP pop3 > 2795
> [ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
> 313 216.520005 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0

And still no room

> 331 282.438712 SERVER CLIENT TCP pop3 > 2795
> [ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
>
>
> And it goes on and on with this series of 2 packets :
>
> 444 763.058713 SERVER CLIENT TCP pop3 > 2795
> [ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
> 445 763.212666 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0
>
>
> What could be the problem ?

The Psion's inbound buffer is full, and the Psion app that's reading it has
stopped emptying the buffer. You have a problem with the mail client on the
Psion; it doesn't like big emails, apparently. Otherwise, the psion mail
client would suck some data out of the Psion's TCP receive buffer, and the
Psion's receive window would go back into positive numbers.

So long as the email client refuses to read data from the Psion TCP stack, the
Psion TCP receive buffer will remain full, and the Psion will advertise a 0
byte window. Linux won't try to send data when it knows that the Psion won't
receive it into it's buffer; that's what the "Win=" value is all about. It
lets the other guy know how much data it can send before it has to stop
because of full buffers.

> Please let me know if you need more details and CC replies to my email
> since i'm not subscribed to this list.

Sorry, but no. You post here, you read here. I'm not set up to post a reply
here /and/ email you.

> Thanks in advance,
> Enrico


--
Lew Pitcher

Master Codewright and JOAT-in-training
Registered Linux User #112576 (http://counter.li.org/)
Slackware - Because I know what I'm doing.

On Thu, 23 Oct 2003 23:22:06 -0400, Lew Pitcher <(E-Mail Removed)> wrote:
>
>
>

<snip>

> Sorry, but no. You post here, you read here. I'm not set up to post a reply
> here /and/ email you.

Yep.

>
>> Thanks in advance,
>> Enrico
>
>
> --
> Lew Pitcher
>
> Master Codewright and JOAT-in-training
> Registered Linux User #112576 (http://counter.li.org/)
> Slackware - Because I know what I'm doing.
>

Very informative post, Lew. Thanks for the lesson. Saved with annotations
to my TCP docs dir.

--
Alan C
Post validation at http://tinyurl.com/rv0y

Questo succede perché sei uno sbifidone acido. Se + acido di una
spremuta di limoni verdi.

Ahhhhaahhhaa.

Fabio.


(E-Mail Removed) (Enrico Demarin) wrote in message news:<(E-Mail Removed). com>...
> I am experiencing a weird problem downloading mail from a Linux (
> RedHat 6.2 , kernel 2.2.22-6.2.3 ) , from a Psion Epoq client through
> PPP :
>
> the connection after a while seems to hang, so i did a tcpdump and it
> hangs right here :
>
> ...
>
> 270 145.209900 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327575601 Win=8192 Len=0
> 271 145.209937 SERVER CLIENT POP Continuation
> 272 145.469903 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327577061 Win=8192 Len=0
> 273 145.469918 SERVER CLIENT POP Continuation
> 274 145.999993 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327578521 Win=8192 Len=0
> 275 146.000011 SERVER CLIENT POP Continuation
> 276 146.265720 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327579981 Win=8192 Len=0
> 277 146.265734 SERVER CLIENT POP Continuation
> 278 146.795770 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327581441 Win=8192 Len=0
> 279 146.795788 SERVER CLIENT POP Continuation
> 280 147.065809 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327582901 Win=8192 Len=0
> 281 147.065848 SERVER CLIENT POP Continuation
> 282 147.595846 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327584361 Win=6732 Len=0
> 283 147.865890 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327585821 Win=5272 Len=0
> 284 148.395924 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327587281 Win=3812 Len=0
> 285 148.665953 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327588741 Win=2352 Len=0
> 286 148.918120 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327590201 Win=892 Len=0
> 287 151.758721 SERVER CLIENT POP Continuation
> 288 152.408379 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0
> 289 158.098716 SERVER CLIENT TCP pop3 > 2795
> [ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
> 290 158.293192 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0
> 291 166.528715 SERVER CLIENT TCP pop3 > 2795
> [ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
> 292 166.701317 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0
> 293 183.178717 SERVER CLIENT TCP pop3 > 2795
> [ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
> 294 183.407362 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0
> 312 216.358713 SERVER CLIENT TCP pop3 > 2795
> [ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
> 313 216.520005 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0
> 331 282.438712 SERVER CLIENT TCP pop3 > 2795
> [ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
>
>
> And it goes on and on with this series of 2 packets :
>
> 444 763.058713 SERVER CLIENT TCP pop3 > 2795
> [ACK] Seq=3327591092 Ack=1637462565 Win=32120 Len=0
> 445 763.212666 CLIENT SERVER TCP 2795 > pop3
> [ACK] Seq=1637462565 Ack=3327591093 Win=0 Len=0
>
>
> What could be the problem ?
>
> Please let me know if you need more details and CC replies to my email
> since i'm not subscribed to this list.
>
> Thanks in advance,
> Enrico