This Airport is the NAT what I mentioned before. Note the cable modem should work in bridge mode rather than a modem router. Or you will need to bypass two NAT devices

As far as I know, it is impossible to implement what you want to do. Even if you get another AP, you just can't decide which DHCP to use, never talk about the guests network. If you want two DHCP in...

On site A, remote subnet should be 0.0.0.0/32, when the connection built up, route table in site B will looks like [dst:0.0.0.0 nexthop:site A] I'm not sure will it work for you. I never tried, This...

I also have this firmware, it work fine for me. remember one port on NAT can only be mapped to one host.

Brian, you should consider if there is any NAT between the iPad and your VPN server. If yes, the NAT should support VPN passthrough. I think the most popular client to server mode VPN is PPTP. And it...