Cannot listen on the lo interface

[Seraina Steiner]

Hi list

I need my DHCPD listen to both eth0 and lo interfaces. When I start dhcpd with with eth0 and lo (/usr/local/sbin/dhcpd eth0 lo), I get the following error message:

No subnet declaration for lo (127.0.0.1).
** Ignoring requests on lo. If this is not what
you want, please write a subnet declaration
in your dhcpd.conf file for the network segment
to which interface lo is attached. **

Well, that one is clear, so I've added the following network declaration to /etc/dhcpd.conf:

subnet 127.0.0.0 netmask 255.0.0.0 { }

But then I get this error:

Unsupported device type 772 for "lo"

I've no idea what is wrong, and I haven't found any more information about that.

Thank you for helping me

PS: The reason why I want DHCPD to listen on the lo device is that I query DHCP from the same host, and the packets go to the lo device.

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[Simon Hobson]

Post by Seraina Steiner
I need my DHCPD listen to both eth0 and lo interfaces. When I start
dhcpd with with eth0 and lo (/usr/local/sbin/dhcpd eth0 lo),

It won't do it. The ISC server only supports certain types of
interface (those supporting broadcast facilities I believe). In a
thread that came up last week, it was suggested that if you compile
with an option to use sockets, then you can run it on non-broadcast
interfaces - but it then won't support local clients.

Post by Seraina Steiner
PS: The reason why I want DHCPD to listen on the lo device is that I
query DHCP from the same host, and the packets go to the lo device.

Try addressing it by it's IP address ?

[Seraina Steiner]

Hi Simon

Post by Simon Hobson
It won't do it. The ISC server only supports certain types of
interface (those supporting broadcast facilities I believe). In a
thread that came up last week, it was suggested that if you compile
with an option to use sockets, then you can run it on non-broadcast
interfaces - but it then won't support local clients.

Okay. Well, I don't need broadcast anyway. The DHCP server sits behind a DHCP relay, and the communication between the DHCP server and relay is _always_ unicast. Furthermore, there are no "local" clients behind the relay, so my DHCPD doesn't need to understand broadcast at all.

So source code hacking would be an option, I think...

Post by Simon Hobson
Try addressing it by it's IP address ?

Yes, that was my first idea. Unfortunately, the operation system (Debian GNU/Linux) still routes the request to the lo interface. I also added a route that says each packet to the server's own IP address should go to eth0, but this does not work either.

When I sniff network traffic using tcpdump I see the packets on lo, but nothing on eth0.

What would you recommend?

Thank you
Seraina Steiner

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