Jonathan S. Abrams wrote:
Hello,
I am trying to troubleshoot an issue with connecting to an FTP server,
and have captured some packets that match a theory I have that the issue
is related to a timeout. I am hoping that someone can either explain to
me what this data means or point me in the right direction towards
interpreting it.
When I initiated a connection to the FTP server in question, the
following packets caught my attention.
No. Time Source Destination Protocol
Info
23 10.212754 SERVER ME TCP ftp > 49497 [ACK]
Seq=336 Ack=33 Win=524280 Len=0 TSV=113977199 TSER=777016821
No. Time Source Destination Protocol
Info
24 11.057690 SERVER ME TCP 57314 > ident
[SYN] Seq=0 Win=65535 Len=0 MSS=1460
No. Time Source Destination Protocol
Info
25 19.073737 SERVER ME TCP 57314 > ident
[SYN] Seq=0 Win=65535 Len=0 MSS=1460
No. Time Source Destination Protocol
Info
26 35.105752 SERVER ME TCP 57314 > ident
[SYN] Seq=0 Win=65535 Len=0 MSS=1460
No. Time Source Destination Protocol
Info
27 40.232279 SERVER ME FTP-DATA FTP Data: 85 bytes
No. Time Source Destination Protocol
Info
28 40.232321 ME SERVER TCP 49497 > ftp [ACK]
Seq=33 Ack=421 Win=524280 Len=0 TSV=777017121 TSER=113977499
Here is why I think it is a timeout issue. I am using Mac OS X, and
when I use Transmit to connect to this server, it takes about 31 seconds
to connect, but it does connect. Transmit does not have a timeout
preference that I can find, so as long as I wait patiently, it
connects. If I use Cyberduck, with its defaults, it will not connect.
If I change the Cyberduck timeout preference to 31 seconds, it does
connect. If you look at the times on the packets above, you will see
the first packet I pasted here has a time of 10.212754. The next packet
coming from ME going to the SERVER occurs at 40.232321, which is more
than 30 seconds after the first server packet. As such, if I don't
adjust Cyberduck's default timeout preference to a higher value,
Cyberduck does not connect. This packet capture was done using
Cyberduck, with its timeout preference set to 31 seconds, so I was able
to connect successfully.
Ultimately what I would like to do is get the time between packet 23 and
packet 28 to be less than 30 seconds. This way nobody will have to
adjust their timeout preference if they are using Cyberduck to connect
to this server. Does any of the packet data here suggest what I might
be able to do to achieve that? Any insights are appreciated.
The timeout occurs because the FTP server is sending "IDENT" requests
to your system and getting no reply.
In the above the server tried 3 times with no response before finally
proceeding with the connection.
Google something like "FTP Server" "Ident" and you'll find lot's of info.
I'm not at all familiar with MAC OS X (and using FTP clients on same); I
suspect you may need to somehow have the OS send a "reject" reply when
the IDENT request is received (rather than ignoring the request).
