Realm IP is not constant; it WILL vary. Realm address is a range, it is randomly selected on login. I had this issue myself. Just port block it anyway (you'll DC obviously), next unblock it and relog. Your realm IP should change (say from xxx.xxx.xxx.123 to xxx.xxx.xxx.122) and now it's not the same IP as Storm Peaks or any other zone. Reblock the zone.