dhcrelay and ipip tunnels
dhcp1 at thehobsons.co.uk
Sat Sep 8 07:31:30 UTC 2012
Homer Wilson Smith wrote:
> Apparently dhcrelay-3.03 will not run properly across an ipip or
>gre tunnel, because the tunnel interface will not properly pick up and
>send the return answer from dhcdp.
> Notes on the net claim this is because dhcrelay is using LPF rather
>than sockets, but turning on sockets in site.h causes dhcrelay to send
>all answers as broadcasts which causes everyone to get all dhcp
>responses all the time, including ACKS.
I don't know the details, but the ISC code was written (or at least
the design philosophy laid down) back in the days when networks were
almost all either a) ethernet like, or b) SLIP or PPP like.
For what were good reasons then, the design was done such that it
only works properly on networks that are ethernet like - in
particular having ethernet like broadcast mechanisms. Thus PPP (and I
assume GRE) interfaces don't work and aren't supported.
For the server, and simply going from previous threads (I'm not
really a programmer), the server can be compiled to use sockets - at
which point it can handle non-ethernet networks but cannot handle
clients on the local network. I suspect the same applies to the relay
agent - and making it not handle local clients would rather defeat
What I can suggest is :
Run the relay agent on any other host on the network(s) rather than
the gateway running the tunnel interfaces. For the server(s), either
do the same, or compile them to use sockets (assuming you don't need
local client support. If your relay agent is on a different device to
the gateway, then communications between it and the server are just
unicast packets - and the tunnel is not visible to it.
It may even be possible to run the relay agent on the gateway if you
can set it up in some sort of partitioned environment with it's own
ethernet interface such that it uses one interface and it's server
traffic goes via the local wire and back in on the main ethernet
interface (and vice-versa for return packets).
Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.
More information about the dhcp-users