Anyone tried TCP over loopback?

Phil Torre ptorre at
Sat Sep 10 02:03:27 UTC 2005

I'm porting some code that uses TCP over loopback as an IPC mechanism.
I'm running into trouble where the connect() is refused even though
the matching listen() has already happened.

After debugging a bit, it turns out that the SYN packet is making it
through the loopback device and on to tcp_input(), which is responding
with a RST because it can't find the matching inpcb struct.  It almost
finds it, but the foreign and local port numbers are swapped, so the
comparison in in_pcblookuphash() fails. 

Does this ring any bells with anyone?



Phil Torre                               phone: 425-820-6363 x234
Design Engineer                          email: ptorre at
Switching Systems Group                    fax: 425-820-7031
Zetron, Inc.                               web:


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