DHCP & multiple interfaces

DHCP & multiple interfaces

Post by Artur Bartnick » Wed, 12 Mar 1997 04:00:00



Does anyone a know working solution for DHCP server on Linux box
serving two subnets (and having two eth interfaces)? All tricks
with static host 255.255.255.255 routes unfortunately don't apply
here.

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    Artur "Archie" Bartnicki              work: (0-71) 48 81 93

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DHCP & multiple interfaces

Post by Jeremy Fisch » Thu, 13 Mar 1997 04:00:00



>Does anyone a know working solution for DHCP server on Linux box
>serving two subnets (and having two eth interfaces)? All tricks
>with static host 255.255.255.255 routes unfortunately don't apply
>here.

>--

For the ISC's implemtation, this is a known problem. It's explained
in the Readme on their web site or in the DHCP docs you get with
the distribution. Here's the key to it, though:

---from ftp://ftp.vix.com/pub/dhcp/DHCPD-BETA-5-README ---

Even if you only need dhcpd to work on systems with a single
interface, there can still be problems.  Of all the systems dhcpd
currently works on, only one (Solaris) has an IP stack that allows the
all-ones broadcast address (255.255.255.255) to go out onto the
network unchanged.  Other systems insist on changing 255.255.255.255
into the local subnet broadcast address (here, that's
204.254.239.255).  This results in a protocol violation, and while
many DHCP clients don't notice the problem, some (e.g., all Microsoft
DHCP clients) do.  Clients that have this problem will appear not to
see DHCOPFFER responses from the server.

It is possible to work around this problem on most such systems by
creating a host route from your network interface address to
255.255.255.255.   On most systems, you do this with:

        route add 255.255.255.255 <your-interface-address> 0

or

        route add -host 255.255.255.255 <your-interface-address>

Some Linux systems work better with:

        route add -host 255.255.255.255 dev <your-interface-name>

On some systems, you will get error messages if you use the route
command, but may succeed if you write a small program to do the system
calls.   It would be nice if dhcpd were to do this automatically.
If you have a patch to do this, send it in!   :')
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Good luck,
Jeremy