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Hi all, One of the users on my server is unable to connect to pop3 on the server - everyone else can connect fine. Once I figured out his IP ...
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  1. #1
    Just Joined!
    Join Date
    Mar 2007
    Posts
    19

    Strange TCP problem for a particular user


    Hi all,

    One of the users on my server is unable to connect to pop3 on the server - everyone else can connect fine.

    Once I figured out his IP address, I ran tpcdump in an attempt to see what was going on. If I'm interpreting the output correctly, I see his SYNs, but the server sends no ACK back. After a few attempts the client sends an RST and gives in.

    Code:
    04:36:01.384945 IP client_ip.56299 > server_ip.pop3: S 591685373:591685373(0) win 64240 <mss 1360,sackOK,timestamp 12487 0,nop,wscale 1>
    04:36:04.308196 IP client_ip.56299 > server_ip.pop3: S 591685373:591685373(0) win 64240 <mss 1360,sackOK,timestamp 12787 0,nop,wscale 1>
    04:36:10.488605 IP client_ip.56299 > server_ip.pop3: S 591685373:591685373(0) win 64240 <mss 1360,sackOK,timestamp 13387 0,nop,wscale 1>
    04:36:13.292385 IP client_ip.56299 > server_ip.pop3: R 591685374:591685374(0) win 0
    04:36:17.249825 IP client_ip.57287 > server_ip.pop3: S 3711226351:3711226351(0) win 64240 <mss 1360,sackOK,timestamp 14079 0,nop,wscale 1>
    04:36:20.268227 IP client_ip.57287 > server_ip.pop3: S 3711226351:3711226351(0) win 64240 <mss 1360,sackOK,timestamp 14379 0,nop,wscale 1>
    04:36:26.328494 IP client_ip.57287 > server_ip.pop3: S 3711226351:3711226351(0) win 64240 <mss 1360,sackOK,timestamp 14979 0,nop,wscale 1>
    04:36:30.005021 IP client_ip.57287 > server_ip.pop3: R 3711226352:3711226352(0) win 0
    I can't figure out why this is happening. My hosts.allow and hosts.deny are empty, as is the iptables ruleset. I've tried telnetting in to pop from various other locations, and never have any problems.

    Any ideas please? I'm baffled

  2. #2
    Just Joined!
    Join Date
    Jul 2010
    Posts
    5
    hi.
    Client firewall issue ?
    happned to me once...
    regards

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