MAC to IP assignment not working - dhcprelay
Glenn Satchell
Glenn.Satchell at uniq.com.au
Wed Apr 25 12:41:48 UTC 2007
Yes, the deny known-clients just reinforces the default behaviour and
forces it to use fixed-address only. A fixed-address will be preferred
if it is valid in that subnet or shared-network. Sounds like you don't
need the deny in your case.
regards,
-glenn
>Date: Wed, 25 Apr 2007 08:06:14 -0400
>From: Edwin Whitelaw <Edwin.Whitelaw at nrvunwired.net>
>To: dhcp-users at isc.org
>Subject: Re: MAC to IP assignment not working - dhcprelay
>
>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
>
>
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