David Curry wrote: | Andy Green wrote: | |> |> But I am still bemused by the two listening sockets on the same port |> being possible. Maybe it is some kind of cool load balancing feature I |> never heard of. Can anyone else here explain how it can be? |> |> - -Andy | | | | May be this is a dumb question from a clueless neophyte, but does the | phenomenon constitute a security problem that needs to be addressed?
Probably not, because I'm pretty sure it will only allow it if the two listens are coming from inside the same process ID.
For example in one window
[root@server root]# nc -l -p 1234
works and is listening
[root@server root]# netstat -plutn | grep 1234 tcp 0 0 0.0.0.0:1234 0.0.0.0:* ~ LISTEN 19055/nc
If you try to start a second nc to the same port in another window...
[root@server root]# nc -l -p 1234 Can't grab 0.0.0.0:1234 with bind
So it seems that maybe it's just a (little-known?) feature for a single process rather than a bug?
No, you've been setting up TCP sockets. If you do it with UDP sockets (nc -l -u -p 1234) you can have multiple listeners, and they don't have to be the same process or even started by the same user.
Paul.
