ISP 5 Device Limit - double NAT the solution?

Question

I have asked this question in response to another question here ( 5 Max connections/devices to the internet? Is my ISP limiting me somehow? ), but thought I should start a thread to see if I can get wider more specific help:

I have a 5 device limit that I cannot seem to work around. I live in an apartment and the ISP's modem / router sits in a central locked room that I cannot access physically and is, of course, password protected.

I have a Time Capsule hard wired into the ISP modem / router operating in Bridge mode which is the only mode that I have been able to operate. I would like to use the full gambit of devices (2 iPhone / 2 iPad / iMac / 2 AppleTV / 2 Airport Express) and still have room on the network for guests. Currently, if my wife wants to get online I have to turn off the wifi on one of my devices. It would appear that both Time Capsule and Airport Express are using one of the 5 slots on the network.

A solution may be to 'double-NAT' but I do not know how to do that nor the pitfalls behind it. Is there anyone out there that can give me some basic guidance?

Answer 1

Pitfalls are it can be awkward to host things/do port forwarding well - but, for standard internet usage, it should work fine.

Simply purchase an ethernet (sometimes called cable) router (e.g. non modem/rj-11), and plug their uplink in to the router's wan port.

Next, I would recommend that you chose a different IP/subnet for the new router.. so, if its uplink to the internet network is 192.168.1.x with a subnet of 255.255.255.0, choose a network of 192.168.2.x with a subnet of 255.255.255.0 - or, there can be routing issues.

When you do this, you should be able to connect absolutely fine!

As for 5 device limit... I just got thinking... this seems like hell to enforce and I have only seen device limits on campus networks - Are these private or public IPs? If it is public, it could actually be that they are expecting you to use your own router and if they are private, maybe someone mis configured DHCP.... It may be worth trying to manually set ips and see if you can get anywhere before you purchase a router.

Answer 2

I have a feeling they are enforcing the five device limit by using dynamic layer 2 port security. Spoof a few MAC addresses and then try adding a new device. Report with results!

Double NAT would be a solution. It sounds like you aren't forwarding any ports so that could be the solution. What IP addresses are your devices receiving?