Management of a DHCP client in a remote unknown network

[Jean-Yves ANDREOLETTI]

Dear all,

Here is my problem :

I have the network A with a DHCP Server.

Network A knows the network B only with its NATed addresses

In DHCP Server (which is on a Solaris machine) the remote client is configured with NATed informations.

In network B I have a client.

Network B knows the network A only with its NATed addresses

The ip helper-adress is set to NATed address of the DHCP Server.

At the client power up, all works fine but the client receive all its NATed informations so it's IP, netmask and gateway addresses are wrong.

I would like to know if the DHCP relay can modify some information in the DHCP-OFFER packets.

Thanks for your help.

Br,

Jean-Yves ANDREOLETTI

[Peter Paluch]

Hi Jean-Yves,

To my best knowledge, a DHCP relay agent is not capable of modifying the information in the relayed DHCP messages.

Having a NAT between DHCP clients and servers is, from a design standpoint, wrong. The DHCP server needs to know the clients or at least their relay agents individually by their true addresses, because they are what allows the DHCP server to select the correct pool to offer IP addresses from. Your situation of having the DHCP clients and servers separated by a NAT device is, sadly, quite unfortunate. Is there an option of removing the NAT for DHCP communication, or moving the DHCP server closer to clients?

Best regards,

Peter

[Jean-Yves ANDREOLETTI]

Thanks Peter for this answer,

I think I will configure a DHCP server on a router but it remains a question, can I add some options on my clients from the DHCP master server.

Br,

Jean-Yves

[Peter Paluch]

Hi Jean-Yves,

can I add some options on my clients from the DHCP master server.

This is, in general, impossible. DHCP protocol essentially lacks any features in which DHCP servers can cooperate, share the address leases or synchronize the configuration options handed out to clients. Indeed, the entire DHCP protocol focuses exclusively on the client-server communication, and there are no provisions for server-server information exchange.

If your router was obtaining an IP address from the DHCP server itself (i.e. if one of its interface was configured with ip address dhcp) then you could use the import all command in the DHCP pool on the router, causing the router to obtain all DHCP options not explicitly specified in the pool from the DHCP server. However, this scenario is more applicable to dialout solutions, and I do not think it is suited to your network.

Apart from this, I am not aware of any method that would allow you to merge a selected set of settings on a local DHCP server with another settings from a master DHCP server. I am sorry to disappoint you.

Best regards,

Peter