I'm guessing your neighbor may be blocking all MAC addresses..
I'm also guessing that you are trying to leech your neighbor's wireless internet.
I assume that they are using wireless routers, of course.
If he's blocking MAC addresses, except for his.. no way in hell you are going to get access, period.
(Unless of course, you change your MAC address to match one of his 'allowed' addresses.. but I doubt you understand that..)
Another possibility is that he is using encryption for his wireless network.
Meaning, you'll have to first crack the encryption before you can start using his internet.. and for the record, no I will NOT explain that.
(It is 'unethical' and illegal, if you aren't the network's owner..)
Finally.. the 'gateway' you encounter is actually his router. It allows you to connect to the router to change settings.. provided you know the router's admin password.
In fact.. I'd recommend either asking politely if he'd share the connection, that's about as much as you can legally do.
As such, I will not condone illegal activities at khi.
~~Azurith