Date: Sun, 28 Mar 1999 06:26:09 +0200 (CEST) From: perhov@phys.ntnu.no To: FreeBSD-gnats-submit@freebsd.org Cc: perhov@phys.ntnu.no Subject: kern/10826: TCP connection looped back to itself Message-ID: <199903280426.GAA95143@fimfpc19.math.ntnu.no>
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>Number: 10826 >Category: kern >Synopsis: TCP connection looped back to itself >Confidential: no >Severity: non-critical >Priority: low >Responsible: freebsd-bugs >State: open >Quarter: >Keywords: >Date-Required: >Class: sw-bug >Submitter-Id: current-users >Arrival-Date: Sat Mar 27 20:30:00 PST 1999 >Closed-Date: >Last-Modified: >Originator: Per Kristian Hove >Release: FreeBSD 3.1-STABLE i386 >Organization: Norwegian University of Science and Technology >Environment: FreeBSD 3.1-STABLE as of Mon Mar 15 13:47:02 CET 1999 >Description: On rare occations, a "telnet localhost N" (where N is an unused port number >1024) will succeed and result in a connection looped back to itself. >How-To-Repeat: Try hard enough, and you will get a connection. The connection seems to be looped back into itself (hey, isn't that WYSIWYG? "What You Send Is What You Get"?). The following example assumes your shell is bash: $ declare -i n=0 $ until telnet localhost 1234; do n=n+1; done; echo n=$n Trying 127.0.0.1... telnet: Unable to connect to remote host: Connection refused Trying 127.0.0.1... telnet: Unable to connect to remote host: Connection refused [...] Trying 127.0.0.1... telnet: Unable to connect to remote host: Connection refused Connected to localhost. Escape character is '^]'. hi, am I talking to myself? # I type this, hi, am I talking to myself? # this is the response I get ^] # quit telnet telnet> quit Connection closed. n=398 (Sometimes I have to wait until n=5000 before it occurs) A output of 'netstat' shows that the connection is indeed looped: # netstat Active Internet connections Proto Recv-Q Send-Q Local Address Foreign Address (state) tcp 0 0 localhost.1234 localhost.1234 ESTABLISHED Active UNIX domain sockets Address Type Recv-Q Send-Q Inode Conn Refs Nextref Addr [...] This behaviour also occurs when I try to telnet to an IP address assigned to another of the host's network interfaces (it doesn't have to be the loopback interface). I've never succeeded getting a connection to an unused port below 1024. >Fix: >Release-Note: >Audit-Trail: >Unformatted: To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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