Re: Port 7070

Doug Hardie <bc979@xxxxxxxx> writes:

I just ran a netcat (nc -z) on my production servers and found an
unusual response:

Connection to xxxx 7070 port [tcp/arcp] succeeded!

I checked on all my production and test servers (7.0 stable as of
quite some time ago) and got the same response. I can't figure out
why that port is open. It always returns a reset when a connection is
opened. netstat -an does not return any 7070 entries. sockstat does
not show any 7070 entries. There is no 7070 entry in /etc/services.
ktrace of inetd shows nothing. tcpdump on the server shows the SYN
and RST packets only. tcpdump on the client machine shows a complete
TCP negotiation completion followed by a termination. The client is
going across the internet.

Running the client on a machine on the servers LAN shows that the port
is not open. And tcpdump from both shows only a SYN followed by a
RST. This indicates that some router between the original client and
the servers is accepting the connection and then forwarding it on.
This doesn't happen on other ports (although there may be a couple
others I haven't chased down yet though). The only router we have in
the path is a Cisco 2501 running a 2000 vintage IOS with nothing like
that in its configuration. Its a simple pass everything through
setup. Any ideas what is happening here?

Sounds like the router is blocking most incoming connections, but not
7070. 7070 is sometimes used for RSTP, which makes some sense to let
through. Nothing is actually listening on that port on the server,
though, which is why you don't see anything in sockstat et. al.

--
Lowell Gilbert, embedded/networking software engineer, Boston area
http://be-well.ilk.org/~lowell/
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