router behind another router

[unclebob1]

I've picked up a THG3000 router, which I want to use BEHIND my existing router.

Router A for example has 192.168.1.1 as its internal ip, with a dhcp range 2-10 

It is connected to the internet directly.

I want to connect Router B such that it picks up a WAN ip from the dhcp pool from Router A, and then has its own internal LAN IP of say 192.168.2.1 with its own DHCP range of 192.168.2.2-10

Is this possible with the THG3000 running as router B? I tried to connect a cable between LAN port on Router A to WAN port on router B, but the THG3000 interface couldn't figure out that it had a connection to the internet - but the port was showing as active - so it knew there was a connection.

The aim for this setup in case anyone will ask why is that I want to separate the kids devices directly to router A and then have a second network for my devices. Happy for my devices to connect to devices on kids network, but dont want kids devices connecting to my devices.

I understand the double Nat problem etc, but this doesn't concern me as I don't do any port forwarding in my use.

[Cynric]

I had the following setup with VF:

BT Green Cabinet -> THG3000 (192.168.1.1) -> Netgear Router (192.168.0.1) -> LAN

This was the easiest and kept the VF (un)helpdesk happy because as far as they knew/cared the THG3000 was connected to them. The nice thing for me was that I could do my own WiFi settings as I required, run my own DNS and DHCP servers and effectively ignore VF entirely. Well entirely except for the awful line speeds.

[unclebob1]

Any ideas on doing it the other way around with the Vodafone thg as the second?

[Apollo37]

I think I have managed it. I managed to enable the IP4 CPE address.

under settings, Public Subnet, to enable the WAN address, it asks to enable the IP4 CPE, (Customer Premises Equipment) address. If your upstream router has address 192.168.2.1 for instance, enable CPE WAN address as 192.168.2.2, subnet mask, 255.255.255.0, Subnet 192.168.2.0. 

You should now be able to communicate with the upstream router and see statistics for ‘Fibre Status’ under, Status and Support. 

ensure you have DHCP reservations under Settings - Local Network. Make sure you can interrogate Overview for the MAC addresses of your devices. 
i found my devices jumping IP networks and obtaining reservations on the upstream router network and wondering why my previous devices that worked and connected to the internet were no longer responding until I checked on the upstream router. Obviously ignored the DHCP server on the downstream router or used NAT to request IP Addresses from the upstream router 

m you may need to switch off the upstream router once you have written down the MAC addresses and their names as I’m sure the devices will just request the same IP. 

you may need to enable DNS on the downstream router as the address of the Upstream router as a path to request internet access as I believe router 1 will use recursive DNS to contact the DSL router address. 

[Apollo37]

I think I have managed it. I managed to enable the IP4 CPE address.

under settings, Public Subnet, to enable the WAN address, it asks to enable the IP4 CPE, (Customer Premises Equipment) address. If your upstream router has address 192.168.2.1 for instance, enable CPE WAN address as 192.168.2.2, subnet mask, 255.255.255.0, Subnet 192.168.2.0. 

You should now be able to communicate with the upstream router and see statistics for ‘Fibre Status’ under, Status and Support. 

ensure you have DHCP reservations under Settings - Local Network. Make sure you can interrogate Overview for the MAC addresses of your devices. 
i found my devices jumping IP networks and obtaining reservations on the upstream router network and wondering why my previous devices that worked and connected to the internet were no longer responding until I checked on the upstream router. Obviously ignored the DHCP server on the downstream router or used NAT to request IP Addresses from the upstream router 

m you may need to switch off the upstream router once you have written down the MAC addresses and their names as I’m sure the devices will just request the same IP. 

you may need to enable DNS on the downstream router as the address of the Upstream router as a path to request internet access as I believe router 1 will use recursive DNS to contact the DSL router address. 

[Anonymous]

NAT is Network Address Translation, and it does have the potential to cause you problems since you are using a network router (which is performing NAT) and not a network switch.

Your downstream router B will be appearing to the upstream router A as having a single local IP address from it's WAN port.  In many cases, this is good enough that clients on the downstream router can access basic internet services - though there can still be problems caused by data lost from packet headers sent from B to A to the internet, and the addition of VLAN IDs and tags already added when the downstream router sends data through the upstream router (along with password verification and other protocols that will go nowhere).  Using a non-ISP locked router, even in a double NAT environment is going to be less problematic (and non-problematic if you just set it up as an access point)!

So a bit more info on why this won't work:

The A subnet will see all traffic originating from the B subnet as originating at router B, and the firewall on router B is quite capable of discarding data packets that appear to be unsolicited (they never get to their destination).

Many of the problems that are seen when you have double NAT will just look like (incredibly) annoying quirks, and people just think this is the way that it is, when it absolutely doesn't need to be!

[Cynric]

.@unclebob1 In fairness to .@KeithAlger did say "potential" but I have been fortunate with double-NAT. I can even connect to my work VPN and do my 9-to-5 stuff without problems. I think the only answer may be to try it and see what happens for you. One thing is that if you don't have the THG3000 connecting to VF then they are not going to help you with any issue as they will not support other modems.

[unclebob1]

Thanks for the info guys.

So I connected the Lan from my existing suppliers router to the wan on the thg3000, but it looks like the thg doesn't know there is a route to the internet there, but does acknowledge that the connection is active! 

I then connect via WiFi to the thg but it doesn't connect out, keeps telling me to login and check connection to internet.

I'm not on Vodafone at present (actually looking to sign up tonight/tomorrow!) But I'm guessing their support won't help with this regardless!

The only other way I can think of doing this is via dedicated hardware and separate vlans right from the main modem? Any recommendations for the modem? I have a couple of Netgear switches which allow vlan segregation etc but have no DHCP servers to serve each vlan

[Cynric]

THG3000 only works with VF as far as I know.

[unclebob1]

So if I go with voda, I'd have two, the second would still be in the same position or will it recognise that the outer one is voda and allow connectivity via wan?