I''ve started programming the server part of a startegy game I''m working on, and have run into some problems. (Probably) not programming related, but maybe someone can help me anyway. I open a socket on port 4242 (with socket(), bind(), listen() and accept() ) and wait for conneciton. When a connection is established, it fork()s and wait for a new connection, with the child process handligh the connected socket. Anyway, it works fine and I can try it with chaos@ryush: ~> telnet localhost 4242 and connect (the server prints out some info about the connected socket and stuff). But if I try to connect from another computer on the network (a windows machine with IP 10.1.1.1, the server machine "ryush" has IP 10.1.1.3) C:\> telnet 10.1.1.3 4242 it doesn''t connect and telnet terminates with the error "Connection to host lost". ''Normal'' telnet works fine C:\> telnet 10.1.1.3 Connected to .... (and so on) How do i configure my linux machine to accept incoming connections from other machines on the network on this port? I thought ports > 1024 was free-to-use and you simply had to call bind() on them.

Ah, nevermind. I fooled around with the /etc/hosts , /etc/hosts.allow and /etc/hosts.deny files and it now works. The strange thing is that it accepted normal telnet and ftp connection, but not to the port I opened in my server app.... well, doesn''t matter now.

Just in case anyone makes the same mistake as I did, I now post the reason to why things blew up in my face like that


In the server code, I used gethostbyaddr() to get the hostname of the connected client. The problem is that I forgot to check the returned pointer. I happily used it right away. BUT, since gethostbyaddr() returns a null-pointer if it can''t resolve the ip address to a hostname, the process segfault:ed on me.

So, when fork():ing and then called gethostbyaddr() with the child process, the child process immediately segfault:ed without printing out the info about a client connecting -> I thought it hadn''t got any connection at all... *bangs head repeatedly against the wall*

This is the reason I got "connection to host lost" with the client, since it DID get a connection, but lost it right away when the socket was closed when the server child process crashed and burned.

And when I added the entry to /etc/hosts , gethostbyaddr() was able to get the hostname and therefor return a valid pointer -> all was good.

Note to self: ALWAYS check a returned pointer before using it. It''s as simple as that