Double NAT and ip addresses allocation

[Devdeep60]

I am confused by who allocates isp addresses. Connection is: ONT--> isp router--> my router ("X")

Isp router does not alllow DHCP switch off and is necessary to connect my phone to it.

1. If I let the isp router handle ip addressing, to avoid resetting all devices on my current router (X), can I give the isp router the same SSID as X? X has ethernet wired switches - will the same name cause issues?

2. If I turn off WiFi in the isp router, presumably X will provide the ip addresses (as it is now). I can ignore other ethernet ports in the isp router so only address given by it is the X ip address.

3. In 2 above, any other double net issues I need to consider?

[jamesn123]

@Devdeep60 

When you say 'ISP router' do you mean Sky router? If so it does allow you to switch of DHCP. 

[Devdeep60]

@jamesn123 

Yes. I meant Sky Router when I said isp router.

[jamesn123]

@Devdeep60 

Okay so yeah you can switch DHCP off on the Sky hub. You have two setup options really...

1. Leave DHCP ON for the Sky hub and let it handle IP addressing. In this case you'd need to put your own router in 'Access Point' mode to avoid having two DHCP servers on your network and creating double NAT

2. Turn DHCP OFF for the Sky hub and let your own router handle IP addressing. In this case you'd put your own router into 'Router' mode and take advantage of all its features that wouldn't all be available in 'Access Point' mode. The downside to this approach is that the Sky hub doesnt have modem mode so you'd have double NAT. 

[Devdeep60]

@jamesn123 

Thanks. I am thinking of the 2nd option. When you say "switch off Sky DHCP", is that an option in the Sky menu? I was thinking of switching off WiFi and not use the Sky eathernet ports (except one that goes to my Router).

I may not need the phone line - inthat case I can connect my router directly to the ONT (my router has IPV6 and DHCP 61.

[jamesn123]

@Devdeep60 

Yes its under LAN IP setup. You need to uncheck the DHCP box.

[Devdeep60]

@jamesn123 

Thanks a lot. If I turn off the DHCP, will my Router be able to connect to Sky Hub via ethernet(will the Sky Hub still provide an Ip address to the router?. My newbie thinking is that by turning off the DHCP in Sky hub, it cannot provide any Ip addresses.

[Chrisee]

@Devdeep60 you could assign a fixed IP,address to the WAN interface on your second router such as 192.168.0.2 which will connect. If  the two hubs are in a double NAT set up you could indeed leave the Sky hub's DHCP server on. Loads of possibilities like putting the second hub in the Sky's DMZ so by passing the Sky hubs firewall. Read up on the implications of doing things like that as you will be relying on the second routers protection. The set up you need will depend on the apps you run to a large extent. Found this item which tomquick glance loks accurate https://dongknows.com/double-nat-vs-single-nat/

I assume you are using a different IP address range for your second router if such as 192.168.0.2 to .254? its not strictly necessary but it means you can see what is connected to what easily.

[Devdeep60]

@Chrisee 

I assume you are using a different IP address range for your second router if such as 192.168.0.2 to .254? its not strictly necessary but it means you can see what is connected to what easily.

For the second router, can I use 192.168.1.1 range and 192.168.2.1 for the Sky hub?

[Chrisee]

@Devdeep60 yup any private range will work.

[jamesn123]

@Devdeep60 

Yes it means your other router wont get an IP from the Sky hub but you can just assign any fixed IP to it since it will be the only thing connected to the Sky hub.

[Devdeep60]

@jamesn123 

you can just assign any fixed IP to it since it will be the only thing connected to the Sky hub.

Thanks a lot. Just so that I understand this clearly, by assigning a fixed ip in Sky router for my Router, Sky router will still provide this fixed ip address although the DHCP is turned off in Sky? 

So, if I then connect a device to another Sky  give another fixed ip in Sky, that will also be available?

[jamesn123]

@Devdeep60 

Yes exactly. 

You dont even really need to reserve an IP in the Sky router, you can just assign your router any IP within the Sky hubs IP address space (192.168.0.2 - 192.168.0.253) and it'll work. 

[Devdeep60]

Sure. Appreciated. I want to assign 193.168.1.1 to my Router otherwise I will need to reset quite a few devices.

Is this possible? If so, solves my  major problem.

[jamesn123 · Accepted solution]

@Devdeep60 

So you'd need to assign an IP in the address space of 192.168.0.xxx to your router so that it can communicate with your Sky hub. But then on the other side of the personal router you can tell it to hand out IPs on the 192.168.1.xxx address space.