Incorrect packet ACK during FTP transfers

Incorrect packet ACK during FTP transfers

Post by Mark Pilan » Sun, 23 May 2004 08:44:29



Greetings.

I've for a network problem that has me stumped.

My configuration is:

   - A Linux (DHCP, DNS, NAT/firewall & NTP) server running Redhat 7.1.
   - A Windows 2000 Workstation.
   - A Windows 2000 Advanced (terminal) Server.
   - A linux workstation running Redhat 9.0.

I have everything networked together through two 10/100 hubs, and have
no problems connecting to the internet using the Linux server and surfing
to my hearts content.

I can download fine from the W2K boxes, but when I try and download large
files from my Linux workstation, I will usually get about a meg transferred
at check point the transfer just "stops".  I will add this is all over a
56k dialup up connection.

I finally got around to running snort/tcpdump to log the activity and got
a few strange things.  First was a "sudden" increase in the connection
window size:

20:47:57.546507 linuxws1.sambelkee.net.34136 > updates.redhat.com.http: . ack 45652 win 5520 (DF)
20:47:57.612321 updates.redhat.com.http > linuxws1.sambelkee.net.34136: . 145652:147032(1380) ack 520 win 6432 (DF)
20:47:57.902329 updates.redhat.com.http > linuxws1.sambelkee.net.34136: . 147032:148412(1380) ack 520 win 6432 (DF)
20:47:58.106512 linuxws1.sambelkee.net.34136 > updates.redhat.com.http: . ack 148412 win 2760 (DF)
20:47:58.182307 updates.redhat.com.http > linuxws1.sambelkee.net.34136: . 148412:149792(1380) ack 520 win 6432 (DF)
20:47:58.452324 updates.redhat.com.http > linuxws1.sambelkee.net.34136: . 149792:151172(1380) ack 520 win 6432 (DF)
20:47:58.676534 linuxws1.sambelkee.net.34136 > updates.redhat.com.http: . ack 151172 win 0 (DF)
20:47:58.777052 linuxws1.sambelkee.net.34136 > updates.redhat.com.http: . ack 151172 win 4140 (DF)
20:47:58.777380 linuxws1.sambelkee.net.34136 > updates.redhat.com.http: . ack 151172 win 8280 (DF)
20:47:58.777881 linuxws1.sambelkee.net.34136 > updates.redhat.com.http: . ack 151172 win 16560 (DF)
20:47:58.778387 linuxws1.sambelkee.net.34136 > updates.redhat.com.http: . ack 151172 win 33120 (DF)
20:47:59.302324 updates.redhat.com.http > linuxws1.sambelkee.net.34136: . 151172:152552(1380) ack 520 win 6432 (DF)
20:47:59.302546 linuxws1.sambelkee.net.34136 > updates.redhat.com.http: . ack 152552 win 63480 (DF)
20:47:59.592364 updates.redhat.com.http > linuxws1.sambelkee.net.34136: . 152552:153932(1380) ack 520 win 6432 (DF)

Then, a bit later, the workstation appears to get confused somehow, and
keeps sending the same ACK (243632) in response.

20:48:17.432218 linuxws1.sambelkee.net.34136 > updates.redhat.com.http: . ack 240872 win 63480 (DF)
20:48:17.712226 updates.redhat.com.http > linuxws1.sambelkee.net.34136: . 240872:242252(1380) ack 520 win 6432 (DF)
20:48:17.992187 updates.redhat.com.http > linuxws1.sambelkee.net.34136: . 242252:243632(1380) ack 520 win 6432 (DF)
20:48:17.992210 linuxws1.sambelkee.net.34136 > updates.redhat.com.http: . ack 243632 win 63480 (DF)
20:48:18.272178 updates.redhat.com.http > linuxws1.sambelkee.net.34136: . 246392:247772(1380) ack 520 win 6432 (DF)
20:48:18.272222 linuxws1.sambelkee.net.34136 > updates.redhat.com.http: . ack 243632 win 63480 (DF)
20:48:18.552194 updates.redhat.com.http > linuxws1.sambelkee.net.34136: . 247772:249152(1380) ack 520 win 6432 (DF)

Eventually, the FTP server gets fed up and goes away :-)

The really strange part is the transfers works fine from W2K.  I'm
wondering what Ive missed or what serring I have ser incorrectly.

Thanks in advance.

- Mark

 
 
 

1. Login incorrect during ftp

I am running Linux 1.1.0 on my 486 DX2/66 with an Allied 1700 ethernet
card.  I can telnet out/in from/to another host.  I can even ftp to
another host but when I try to ftp from another host to my machine, I
can't get past the login procedure.  I supplied the correct id/password
which would work in a telnet session but not for the ftp session.
I keep getting 530 Login incorrect when I know the id/password pair is
correct.  Any ideas?

Thanks!
Benjamin Yu

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