[refshal]

I think this is what you need:

pawn Code:

public OnPlayerConnect(playerid)
{
new ip[20];
GetPlayerIp(playerid, ip, sizeof(ip));
if(strcmp(ip, "TypeInTheIPHere", true)) 
{
SendClientMessage(playerid, 0xFFFFFFFF, "You've been banned");
Ban(playerid);
return 1;
}
return 1;
}