ISP problem

[soke]

ok guys ... i have a wee problem!
iam on a Lan wirless broadband network.
i have internal and external ip......
i gave my mate my external ip so he could join my server for gaming, it worked well for a week.
then it stopped, my ip is the same, could my isp stop certain ips getting onto his LAN network?
(i live in a small village, i know the guy who set up network, he is a right twat with a massive chip on his shoulder, and he hates me). so on this basis can he stop certain IPs from entering his network? and if he can? how can i get round it, and it it leagal?
thanks soke

[oilman]

it is entirely possible that your friend's IP has been blocked. It's very easy to do. A quick way to check would be to see if your friend can ping your IP address and get a positive response. If he can then his IP is not blocked. If it is blocked then he will have to setup and connect to your computer via a proxy.

[soke]

ok. thanks....
but his ip changes everytime he conects!
can he block his MAC address?
and how do you set up a proxy?