Re: DHCP serving more than one subnet (longish)

From: John E. Malmberg (wb8tyw_at_qsl.network)
Date: 10/24/03 

Date: Fri, 24 Oct 2003 17:37:56 GMT

Michael T. Davis wrote:
> I probably should have including our routing information when I
> described our DHCP server's configuration:
>
> Type Destination Gateway
>
> AN 0.0.0.0 192.168.0.1
> AH 127.0.0.1 127.0.0.1
> AN 192.168.0.0/22 192.168.0.5
> AH 192.168.0.5 192.168.0.5
> AN 192.168.4.0/24 192.168.4.5
> AH 192.168.4.5 192.168.4.5
>
> The 0.0.0.0 is our "default" route to the Internet. Recall that WE0 is
> our server's physical intrface, bound to 192.168.0.5, and WEA1 is a
> pseudo-interface, bound to 192.168.4.5.
>
> The response from John E. Malmberg brought up an interesting point.
> The above routes don't seem to provide for a direct route for the pseudo-
> interface (WEA1, bound to 192.168.4.5) to get to the Internet. Might the
> functionality we're looking for be obtained by running two DHCP servers (on
> separate machines), each configured for a specific subnet?

All DHCP servers that can be reached by a client must be able to
properly service the request with the correct data.

So as long as you have two subnets on the same network segment, that
alone will not help.

As I have not done DHCP stuff for over 3 years, and even then nothing
that complex, I do not know what specific steps are needed to do what
you want.

When the DHCP request comes in for the first time, it is coming in as
0.0.0.0. as a broadcast request. No subnet information is present.

So I would configure the DHCP server to have a list of MAC addresses
that are fixed to specific I.P. addresses/subnet/default gateways for
the 192.168.0.0/22 subnet, and let the rest of the addresses get the
dyanmic information.

As long as the clients have a route to the DHCP server before and after
they have been assigned an address, this should work.

All it depends on is if your DHCP server can give out the specific
subnet and default gateway information for the fixed MAC addresses.

Again this is not something that I have ever done, so I do not know how
hard it would be to implement, if your DHCP server allows it.

Multiple DHCP servers that give out equivalent data are possible and
very useful, but they either have to know what addresses that the others
have given out, or they must not have any overlapping addresses.

-John
wb8tyw@qsl.network
Personal Opinion Only

Relevant Pages

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