MAC to IP assignment not working - dhcprelay
Edwin Whitelaw
Edwin.Whitelaw at nrvunwired.net
Wed Apr 25 12:06:14 UTC 2007
Glenn,
The shared-subnet comment was the key. I'm a wireless ISP and each
remote access point (Voyage Linux on a single board computer) has two
nets per system, one NATed, for customers' routers and the other a
non-NATed, IP for internal network devices. This being my first attempt
to use the relay approach, I'd failed to realize I still needed the
shared-network statement back on the central DHCP server.
The small range declared allows both client routers and network bridges
to acquire a NATed IP automagically with a short lease pending their
addition to the include file for a fixed MAC-IP relationship. It's
worked well in practice but needed to be consolidated via relay.
Assuming my other configuration is correct, I've not had a problem with
clients getting range addresses if they have an entry in the included
host assignment file. I assume the deny known-clients declaration
simply reinforces the default behavior of use the fixed assignment
before referring to the range? I'd rather have the client get some
address, even from the range, rather than none at all. Periodic review
of the leases file lets me see where I've overlooked a fixed assignment
since my client radios have known MAC ranges.
Thanks for the insightful comments.
Regards,
Edwin
> Hi Edwin
>
> You said the include file was copied directly from the standalone dhcp
> server. Were the subnet definitions also copied exactly?
>
> The dhcp server will ignore a fixed-address statement if that address
> is not valid for the subnet where the request came from. So your hosts
> with 172.17.20.x address will get an address from 172.16.20.20x if the
> relay forwards a request stating that they are coming from 172.16.20.0
> network.
>
> Perhaps you need a shared-network statement around the two subnet
> definitions if both are valid in the remote location?
>
> You may also want to change the dynamic subnet defintion to explicitly
> exclude the fixed hosts, eg:
>
> subnet 172.17.20.0 netmask 255.255.255.0 {
> pool {
> deny known-clients;
> range 172.17.20.201 172.17.20.250;
> }
> default-lease-time 3600;
> max-lease-time 3600;
> option routers 172.17.20.1;
> option broadcast-address 172.17.20.255;
> option subnet-mask 255.255.255.0;
> } # End of subnet 172.17.20.0
>
> regards,
> -glenn
>
--
<=+=+=+==+=+=+==+=+=+=+=+=+=+=+=>
Edwin Whitelaw, P.E.
New River Valley Unwired, LLC
2200 Lonesome Dove Dr
Christiansburg, VA 24073
540-239-0318
More information about the dhcp-users
mailing list