dhcrelay does not relay answers back to client

Simon Hobson dhcp1 at thehobsons.co.uk
Sat Mar 12 11:09:22 UTC 2011

Peter Daum wrote:

>  > dhcrelay (and dhcpd) use raw sockets, and only work with broadcast
>>  capable interfaces like ethernet, token rign and fddi. You could try
>>  hacking around in the source to make it work on the tunnel devices.
>I started trying this, but then I discovered in the release notes, that
>using point-to-point interfaces has been "fixed" at some point in time.
>Now I managed to build a "dhcrelay" program that runs on my box from
>the ISC DHCP 2.0 sources, which seems to work fine for my purposes :-)

Just for completeness should anyone be reading this thread in the 
future. The alternative already suggested by Glenn of running a 
separate system on the remote LAN does not need huge resources. You 
could just get a cheap consumer grade router/wireless access 
point/whatever and stick something like Open-WRT or DD-WRT on it. It 
needn't be expensive either in purchase cost or power consumption - 
and may also be useful for other uses such as a local DNS cache etc.

>P.S.: A little suggestion to the maintainers:
>   While it certainly makes sense to skip non-broadcast devices when
>   auto-discovering interfaces, I think it would be good if "dhcrelay"
>   actually used all interfaces that have been explicitly listed on the
>   command line. Right now, in my situation it will (in debug mode)
>   still say "Listening on Socket/tun0" even though this is obviously
>   not the case ...

As read various messages, I think the ISC would like to revisit 
several aspects of the design since the world has moved on and some 
of the original assumptions are no longer valid. However, some of 
these architectural choices (such as using non-broadcast interfaces 
on a relay agent) probably aren't trivial to change.
Ultimately, like the original DHCP server, I believe it comes down to 
having a sponsor who will pay the wages of whoever does the work.

Simon Hobson

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.

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