2 DHCP's on 1 Network

[Steven]

Hi All I have DHCP running on my server at my house and my neighbor is on the same network, We have 2 internet routers, and when he plugs a network cable in to his pc's etc he gets assigned an IP address from my server but it points his computers to my internet router is there anyway of having a DHCP at his house which assigns his computers with an IP address and then having all the computers talk to each other still? Thanks Steven.

[matt40k]

You can't have two DHCP on one network, ok there are ways round this, but it gets complex. I would just use static IPs.

 

Why may I ask are you on 1 network, but with two internet connections? Is that correct?

[FN-GM]

Why may I ask are you on 1 network, but with two internet connections? Is that correct?

 

He has a home setup and has a common network with his mate nextdoor. I presume this is so they can share resources and then play LAN games. He doesn't want his mates computers using his internet connection.

 

Im thinking use a linux firewall between the physical connection and block the DHCP port, Thats as far as my knowledge goes on that thought. Can someone recomend a product for this?

[kmount]

Without knowing more about the reasoning behind the set up it's difficult to advise but yes, a firewall could work, as could several other ideas.

[tmcd35]

If I understand what you want correctly, the answer is it can be done but you'll have to change your network setup.

 

The first step would be to split it into two separate networks. They will need to be totally separate, no cables directly between the two. Each would be set up to get DHCP addresses from their own router.

 

Make sure each router is on totally separate subnets. 192.168.1.x/255.255.255.0 and 192.168.2.x/255.255.255.0 will do fine.

 

Now the trickey part. You'll need a pc with two NIC's. This PC should have 1 NIC plugged into each network. You then basically need to bridge the NIC's. I'd prefer a standalone machine running Linux to do this personally.

 

Finally, you need to add a route rule to each PC on each network pointing to the bridging NIC on their side of the network.

 

So for the 192.168.2.x network (from memory):

 

route add -p 192.168.1.0 255.255.255.0 192.168.2.x

 

and for 192.168.1.x:

 

route add -p 192.168.2.0 255.255.255.0 192.168.1.x

 

replacing x with the IP of the appropriate NIC on the bridging server.

There is a place within the windows DHCP settings (can't remember of top of head where) where you can put this rather than go round each machine and adding it manually. Your neighbours router may or may not have the option to send this info out with DHCP rather than doing it on each machine manually.

[Heebeejeebee]

Now the trickey part. You'll need a pc with two NIC's. This PC should have 1 NIC plugged into each network. You then basically need to bridge the NIC's. I'd prefer a standalone machine running Linux to do this personally.

 

Just asking ... but could you not do this if you add a second IP address to a single NIC? I know they're pennies now but ....

 

HBJB

[ajbritton]

If the DHCP servers can be configured to only allocate addresses to known MAC addresses then reservations could be set up in each DHCP server.

[mac_shinobi]

If the DHCP servers can be configured to only allocate addresses to known MAC addresses then reservations could be set up in each DHCP server.

 

am presuming you mean you could do that from each of there routers but you would still need a firewall or something to stop dhcp on each of there networks from conflicting.

[tmcd35]

Just asking ... but could you not do this if you add a second IP address to a single NIC? I know they're pennies now but ....

 

HBJB

 

AFAIK, no. Pretty much as has been said before (by others) you don't want DHCP traffic from 1 network infiltrating the other, thus the use of a bridge/gateway machine between the two network.

 

The important bit is that the physical cabling for the two networks are kept totally separate.

[featured_spectre]

stick with single networks and use a program called HAMACHI. It opens up your network for your usage only so you can fileshare, play lan games and various other features that you would get on a network.

 

I use it and I am on a virtual network with my brother in glasgow and my father in law in America. Works fine for us.

[mac_shinobi]

stick with single networks and use a program called HAMACHI. It opens up your network for your usage only so you can fileshare, play lan games and various other features that you would get on a network.

 

I use it and I am on a virtual network with my brother in glasgow and my father in law in America. Works fine for us.

 

Is there something like that for os x ( 10.5 ) aka Leopard ?

[FN-GM]

stick with single networks and use a program called HAMACHI. It opens up your network for your usage only so you can fileshare, play lan games and various other features that you would get on a network.

 

I use it and I am on a virtual network with my brother in glasgow and my father in law in America. Works fine for us.

 

Basically its a VPN right?

[featured_spectre]

effectively it is an online virtual network. Much like a VPN but unlike a VPN, you can play LAN games.

 

And yes I believe there is a version for MAC OSX Leopard.

 

 

https://secure.logmein.com/products/hamachi/vpn.asp?lang=en < Download link to HAMACHI

[FN-GM]

Much like a VPN but unlike a VPN, you can play LAN games.

 

I didn't know that, why?

[featured_spectre]

a VPN like a Cisco VPN physically will not allow games to play due to the port restrictions that it has, but HAMACHI does not have port restrictions on games.

[matt40k]

I would have to agree with the HAMACHI idea. Unless you want to join both your internet connections into one big pipe.

[featured_spectre]

doing that is not a good idea, fine if you share the wireless between each other thats not much of a problem as if one goes down you have the other, but connecting the two and bridging them, the ISP's will clock on and fine you for it. I know as I bridged my Virgin Media, Orange and o2 connections together and got a £100 fine from each for doing so.

[matt40k]

doing that is not a good idea, fine if you share the wireless between each other thats not much of a problem as if one goes down you have the other, but connecting the two and bridging them, the ISP's will clock on and fine you for it. I know as I bridged my Virgin Media, Orange and o2 connections together and got a £100 fine from each for doing so.

 

Really? Why was that? Surely if you did it right they would never know. It's only if you try bonding them that problems would occur.

[featured_spectre]

when you bridge connections, it lets your ISP know what you are doing. For example if you bridge your wireless and your Ethernet card, the ISP will think you are just doing that to save mucking around with DHCP / IP addresses, but if you bridge connections from one ISP to another, it automatically notifies them, there isnt a way around it.

 

Bonding the connections is a whole different avenue which I havent tried.

[matt40k]

Mmm.... sounds like that was BGP\RIP\etc

 

I've always used OpenBSD and use PF. This allows you to load balance incoming\outgoing connections and it doesn't need\try to update with ISP with new routes.

[featured_spectre]

ahhh, that may well be an option for me!

[matt40k]

Two books I'll recommend

 

Secure Architectures: With OpenBSD by Brandon Palmerand it's come down alot in price too.

 

Absolute OpenBSD: UNIX for the Practical Paranoid by Michael Lucas

It's good, but really most of it in the man pages, which you can view for free on the Openbsd website.

 

There is an good example on how to create a firewall on Openbsd website and some others around the web about load balancing. It's pretty straight forward, SSL (anything staticful) and FTP create a bit of a problem, but you can over come it with a good pf config.

[ajbritton]

am presuming you mean you could do that from each of there routers but you would still need a firewall or something to stop dhcp on each of there networks from conflicting.

 

Multiple DHCP servers do not 'conflict' as such. Both servers will respond to the initial 'discover' broadcast request for IP address and client will choose whichever 'offer' it sees first.

 

I've set up networks with multiple DHCP servers where the address ranges are split across multiple servers. Microsoft recommends this approach in certain circumstances either splitting range 80/20 or 50/50 depending on what is required (resilience or complex subnetting).

 

In this instance though, my solution would only work if reservations were set up for ALL clients.