Techniques for providing two LANs on a BT router

At present my information is very limited, since I am not even sure whether I will be dealing with a BT "smart" Hub!

The aim will be for one ethernet port to be on one subnet (say 10.20.30.nnn)
and all other ethernet ports to be on a second subnet (say 192.168.1.nnn).
(Apologies if this does not make good networking sense.)
The first subnet will have a dumb 5-port ethernet switch connected to the single ethernet port.
If DHCP could operate somehow over both LANs that would be ideal.

There are probably a number of methods by which this result can be achieved, so please could someone suggest a simple method. Can it be done purely by router configuring? Will any further equipment (say a second router) be required?

TIA!

BT hub won't do that. You could plug another router in that deals with the second subnet. The BT hubs (and pretty much any ISP supplied router) can only provide for one local network.

What is it you are trying to achieve by having a separate subnet? If you explain the why then perhaps other suggestions might be possible for a solution.

The reason is to separate the IT equipment for two different organisations,
one is small with just three PCs off a single switch;
the other is considerably larger with lots of PCs, and wireless hubs throughout a building.
Getting a second broadband line would solve the problem, but at disproportionate expense!

Previously they used a Draytek 2830, wherein up to four LANs could be configured. I don't know why they didn't keep it, or, if too old, get a Draytek 2862 instead.

I'd definitely recommend the DrayTek for having more than one LAN subnet.
If you only have one internet connection and only need two subnets the 2762 as it would be cheaper.

Thanks
Dan

Perhaps adding a Ubiquity Edgerouter X @£50 could do what you need which can be set with firewall rules to completely segregate the subnets.

What your after is a router which will do Multi-Nat, I dont want to recommend one though.

Do you have more than 1 public IP?

Edited by rowter (Mon 11-Nov-19 15:41:41)

Depends what you are trying to separate...and why.
and do the 2 LAN's need to be able to see each other - or not.

the BT buisness Smart Hub can do a form of Multi-NAT
If you take the block of 8 (5 usable) Static IP option.

You can do one of two things.
a) NAT on each of the Static IP's
and Assign any PC/Device to that 'NAT'
-> curiously though, the NAT IP range is the same - just selecting which Static IP that host's NAT ends up on.

b) Select a specific Static IP (of the 5) to a specific Device (no NAT)
so you could then put a simple (cable WAN) NAT router on that IP (by assigning it in the BT router), and do that 2 times (or 5..)...

in all of the above, the default NAT would be still NAT the routing IP (that the Block of static IP's is routed on - same as if you did nothing / had no Static IP range)

The BT business Smart hub has some curious features not usually expected... there again why you would not be able to set 5 separate NAT ranges is a wee bit puzzeling.

A second router between the 10.20.30.nnn and 192.168.1.nnn LANs. Run more sophisticated software like openwrt on the second router with firewall rules to keep the subnets traffic separated and a masquarade rule to do source NAT translation for the LAN not directly connected to the Internet router (to avoid the need for additional static routes). The second router can do the additional DHCP for the second LAN.

Thanks for all the suggestions above!

The incoming line is VDSL2 with a single external IP address, and the intention is to prevent the two LANs from being able to see each other (different companies).

The BT Business 'smart' Hub 2 appears to be one of the least technically-documented pieces of IT equipment, with BT apparently trying to avoid anyone messing with its configuration.

It seems to me that the most straightfoward solution will be to use a DrayTek 2862/2762 souter to provide two separate LANs/subnets, albeit at a price of £200/£150 or so.
The actual decision is out of my hands.

The thing is, the scenario desired is a "Business type" requirement, hence Andy's post about the BT Business Hub. Is the BT Hub that is in use one of those, or BT's bog standard domestic one? (Ah - you said at the start you don't know what router it is).

Would simply setting up a Guest network suffice?

Do you need any arrangements for Wifi?

The guest network on the BT Business "smart" Hub 2 is being used for WiFi already, unfortunately.

So you want three separate services, not two?

The BT Business 'smart' Hub 2 appears to be one of the least technically-documented pieces of IT equipment, with BT apparently trying to avoid anyone messing with its configuration.

indeed,When i bumped into one
I could not believe the features it had.. and completely undocumented.
and IPv6 support
BT hiding their light under a bushel...

including that (on the Business hub) you can define your Custom Branded Guest wifi, not simply take the BT Wifi option. or just turn it off completely (something not possible on the Home version without a call to customer services to disable it remotely), else it can suck all your bandwidth unknowingly.


That said, for 2 companies, needing complete isolation,
Simpler would surely be 2 contracts, 2 routers. etc.
Or as you suggest a Draytek or similar that can NAT into two separate subnets and set it to NOT route between them.