* For DHCP client there are several programs available. I don't know which one is used by your distro. Most common are 'pump' and 'dhcpcd' (dhcp client daemon). See which command is installed and try the man page for it (e.g. type "man pump"). There you will find the details, e.g. if you have pump, 'pump -R' should renew the leased IP. It's all in there.
* Viewing/Changing the current TCP/IP network config: "ifconfig" (network card settings); "route" (routing tables); "iptables" (firewalling); "ip" (can do a lot). They all have man pages too, explaining usage and options.
* About SSH... Maybe it's possible to restrict who can connect to your ssh server. I'm not sure though. Maybe check the manual page, too