vpn with dhcp into a network with a dhcp?

March 16, 2010 at 09:11:41
Specs: Windows XP
hi, i setup a gateway type ipsec VPN between
two Netgear FVX538.

Network-1 has a DHCP for the local wireless
clients (a bunch of laptop users).
Network-2 has a DHCP i need in order for
Network-1 to have IP Phones (avaya) working.

the Avaya IP phones in Network-1 need a
DHCP address from Network-2 (where the
avaya phone system is) which gives it access
VOIP from Network-2.

but Network-1 still needs its local DHCP for its
regular laptop clients .

is there a way to make this work?

Network-1 is 192.168.4.x
Network-2 is 192.168.5.x


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#1
March 16, 2010 at 12:25:55
I'm not sure you can do this.

I know when crossing a boundary you would use a 'DHCP relay agent' to provide DHCP. Which is to say, you would need a relay agent for Network 2, located in Network 1.

But here's the problem, you also require a separate DHCP service in Network 1 that will be dishing out IP's in a completely different subnet. So the problem as I see it is, how would each DHCP (the server for Network 1, or the agent from Network 2) know which DHCP requests are for it?

If you have managed switches that are VLAN capable, no problem. You would have separate VLAN's for data and VoIP and the VoIP VLAN would be the same VLAN tag in Network 1 and 2 and DHCP requests for each subnet would never leave their VLAN and there would be no confusion. VoIP clients plugged into VoIP VLAN ports would get VoIP IP's. Data clients plugged into data ports would get data IP's.


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#2
March 16, 2010 at 15:17:56
I',m not sure if I understand correctly but if a packet is traveling let's say from 192.168.110.x/24 and you have a scope on your DHCP server for .110 it will know you are requesting an IP from .110 subnet and DHCP will give out an IP for that device. You still need to configure options for the VoIP Phones but it should work. Create a different scope.

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#3
March 17, 2010 at 06:05:04
mamut0o1

I',m not sure if I understand correctly

You don't.

if a packet is traveling let's say from 192.168.110.x/24 and you have a scope on your DHCP server for .110 it will know you are requesting an IP from .110 subnet and DHCP will give out an IP for that device.

The OP states they want both DHCP subnets on the same network segment. DHCP server has no way of knowing which subnet a request is coming from. You could configure two separate DHCP servers on the same segment each with it's own subnet. The problem is, there's no way for the DHCP servers to know which clients to respond to and which to ignore.

Besides which, in the real world, two DHCP servers in one network segment isn't going to work properly anyhow unless they're issuing settings within the same subnet and even then it can create problems unless they have separate scopes and there's just no point in doing something like that right....I mean, why would you want to configure two DHCP servers when one will do the job.


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