forwarding DHCP packets via a router.

Simon Hobson dhcp1 at
Mon Jul 13 19:37:21 UTC 2015

Rajeev Bansal <rajeev.bansal at> wrote:

>  I have a specific requirement, where I would like to forward a dhcp discover/request/renew/release packets from a client via a router to another subnet. I can't use a dhcrelay for this purpose, because in my scenario both interface of my router (client side and dhcp server side) will not have IPv4 address assigned. Yes that means, I am trying to forward the dhcp packets to different link without my client knowing that it is communicating over different Ethernet link.

Can you clarify things a bit more ? Is there IPv4 connectivity between client and server ? If not then it won't work.

A few details that come to mind ...

Firstly, the relay agent does *not* have to be in a router, it can be any device on the same network segment (broadcast domain) as the client. So you can put a relay agent on any convenient system.

Both client and relay agent must have IPv4 connectivity to the server. It doesn't matter how (could be VPN, 4 in 6 tunnel, ...), but they need to be able to exchange unicast packets.

For the ISC relay agent, there is a restriction (due to historical design decisions) that all interfaces used by the relay agent must be broadcast capable (in practical terms, look like an ethernet interface). This also applies to the server unless you compile without raw sockets support - which would mean it couldn't handle clients on the directly attached network.
I don't know if a 4 in 6 tunnel (with an endpoint on the relay agent/server machine) will work for this.

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