dhcrelay does not relay answers back to client

José Queiroz zekkerj at gmail.com
Fri Mar 11 21:26:19 UTC 2011


Hi Peter,

This "NAT" you're using... can you explain that?

Being more specific. Does this NAT affects the packets that cross the VPN?

2011/3/11 Peter Daum <gator_ml at yahoo.de>

> I spent many hours trying to get dhcp working over a VPN setup.
> It is "almost" working, but for some (at least to me) mysterious
> reason, dhcrelay does not send the dhcp server answers back to
> the original client.
>
> The setup looks about like this:
>
>
> DHCP          Gate    (vpn)  Gate   [eth0]
> Server <----> way1  <------> way2 <---> Client
>              (NAT)
>
> On Gateway2, there is a dhcrelay running:
>  dhcrelay [-i eth0] <dhcp server address)
> (I tried various additional options which did not seem to affect the
> result)
>
> The setup looks about like this:
>
>
> DHCP          Gate    (vpn)  Gate   [eth0]
> Server <----> way1  <------> way2 <---> Client
>              (NAT)
>
> On Gateway2, there is a dhcrelay running:
>  dhcrelay [-i eth0] <dhcp server address)
> (I tried various additional options which did not seem to affect the
> result)
>
> The DHCP queries are successfully forwarded to the dhcpserver, which
> sends it back to the address from the IP address of the relay agent.
> With tcpdump I can verify that the answer also arrives on Gateway2
> (via the interface "tun0", the VPN endpoint).
> Despite some address translations on the way, all fields in the answer
> have reasonable IP addresses, the destination address is the address
> of eth0 on GW2.
>

Did you checked that the answers from the dhcp server are coming from the
same source adress configured as the dhcp relay?
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