socket programming and port scans

[rbt]

I don't fully understand sockets, I just know enough to be dangerous.
The below is not detected by nmap, but is affected by iptables or ipsec.
Can anyone explain why that is?

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((ip_param, port_param))
while 1:
s.listen(5)

I can connect to the socket server and even transmit data so I know it's
there.

Thanks,
rbt

 

[millerch]

Are you explicitly referencing the port for nmap, or is it a general
port scan?

The version of nmap I run only checks common ports unless a port range
is specified.

 

[rbt]

Are you explicitly referencing the port for nmap, or is it a general
port scan?

The version of nmap I run only checks common ports unless a port range
is specified.

I did not know that. It works as expected now. Thanks!

 

[Peter Hansen]

I don't fully understand sockets, I just know enough to be dangerous.
The below is not detected by nmap, but is affected by iptables or ipsec.
Can anyone explain why that is?

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((ip_param, port_param))
while 1:
s.listen(5)

This, by the way, is wrong. s.listen(5) just tells the stack that you
would like to allow a backlog of up to 5 waiting-to-be-connected
connection attempts while you are accepting another. The call doesn't
block and needn't be called repeatedly. You could just as well do the
call to listen first, then have an empty "while 1: pass" loop (but note
that in either case it is a "busy wait", consuming 100% CPU while it runs).

What you are looking for is more like this:

s.listen(5)
while 1:
s.accept() # wait for connection, and ignore it


If you want to simulate a little server to allow multiple connections,
you would of course need to use the value returned by accept() and
probably call close() on the client socket right away.

-Peter