DHCP and 2 subnets

Glenn Satchell Glenn.Satchell at uniq.com.au
Sat Apr 12 15:05:10 UTC 2008

>Date: Fri, 11 Apr 2008 21:02:13 -0400 (EDT)
>From: Chris Arnold <carnold at electrichendrix.com>
>To: dhcp-users at isc.org
>Subject: Re: DHCP and 2 subnets
>>Notice that the last two clients have 7 octets in their hardware
>>address? That 1 at the beginning is a media type, 1 is ethernet, 4
>>token ring I think, and there are others for FDDI, etc.
>>You need to list subclasses like this:
>>       subclass "123 DHCP Clients" 1:00:0B:DB:C8:B1:71;
>>Well, this is getting away from your original issue but you probably
>>want to add router (aka default gateway) specifications to your two
>>subnet stanzas; so your hosts will know how to reach the other IP subnet.
>>Otherwise it looks good. 
>Well, it is with much thanks to you all on the dhcp list that i energetically 
tell you that this works now :))
>The only thing i have noticed is on clients on the 123 network, it takes a long 
time to get an IP (like minutes); longer than clients on the 124 network. Is 
there any reason you can think of when looking at the config:
> authoritative;
> option domain-name "domain here";
> option domain-name-servers 192.168.123.x;
> option ntp-servers 192.168.123.x;
> ddns-update-style interim;
> default-lease-time 14400;
> max-lease-time 172800;
> Class "123 DHCP Clients" {
>     match hardware;
> }
> subclass "123 DHCP Clients" 1:00:0B:DB:C8:F1:71;
> Shared-network EH {
>        subnet netmask {
>          option routers 192.168.123.x;
>          pool {
> 	     range;
>            allow members of "123 DHCP Clients";
>          }
>       }
>        subnet netmask {
>           option routers 192.168.124.x;
>          pool {
>   	     range;
>            deny members of "123 DHCP Clients";
>          }
>        }
> }
>On the dns updating side----i have searched the archives of the list and read 
the man pages and see where there is only 2 ways and 1 does not work (ad-hock). 
So you can see from the config file i have interim; but i still am unable to 
ping a dhcp client. Any ideas on this?
>Thanks again for all your help.
Read a bit further down the dhcpd.conf man page to the section titles
"DYNAMIC DNS UPDATES" and follow the configuration suggestions there.
There are sample file entries for both dhcpd.conf and named.conf that
do work. Specifically note the use of quotes and zone names, one file
requires quotes, the other doesn't.

If it doesn't work after that post the dhcpd conf, named.conf and any
log entries for dhcpd and named. The most common problem is incorrect
access control in named.conf that does not allow the dhcp server to
dynamically update the dns zone data. This shows up as a dns server
timedout in dhcpd, and if logging is enabled on the dns server you'll
get a missage like update ignored.


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