One DHCP Server, Multiple Subnets

[Simon Hobson]

Shaun R wrote:
>I have a network (VLAN) that has many /26 subnets attached to it.  I 
>am trying to run a DHCP server that will awnser dhcp requests for 
>all subnets on this network.  I dont have a free ip pool in my dhcp 
>config, i assign each server it's IP using it's mac address.  The 
>problem i'm seeing is that if a machine in a different subnet from 
>the subnet the dhcp server is running on asks for a ip it shoes the 
>following.
>
>Feb  4 09:35:21 host dhcpd: DHCPREQUEST for 10.82.117.197 from 
>fe:fd:d0:52:75:c5 via eth0: wrong network.
>Feb  4 09:35:21 host dhcpd: DHCPNAK on 10.82.117.197 to 
>fe:fd:d0:52:75:c5 via eth0
>Feb  4 09:35:27 host dhcpd: DHCPDISCOVER from fe:fd:d0:52:75:c5 via 
>eth0: network 10.10.37.64/26: no free leases
>
>
>Here's a snip from my config.
>
>subnet 10.82.117.64 netmask 255.255.255.192 {
>         option routers 10.82.117.67;
>         option subnet-mask 255.255.255.192;
>         authoritative;
>
>         host D0527545 {
>                 hardware ethernet FE:FD:D0:52:75:45;
>                 fixed-address 10.82.117.69;
>         }
>
><<many more of the above for each ip>>
>}
>
>subnet 10.10.37.64 netmask 255.255.255.192 {
>         option routers 10.10.37.65;
>         option subnet-mask 255.255.255.192;
>         authoritative;
>
>         host CC0A2543 {
>                 hardware ethernet FE:FD:CC:0A:25:43;
>                 fixed-address 10.10.37.67;
>         }
>
><<many more of the above for each ip>>
>}
>
>
>Where am i going wrong here?

Several places !

As Maurice Massar says, it looks more like you have a flat network 
there, the "via eth0" is a bit of a giveaway that the client is on 
the same broadcast domain as the server. Clearly 10.82.117.197 is not 
in the subnet which eth0 is a member of, yet the device is directly 
attached.

You need a shared network like this :
shared network vlan_something {
   subnet ...
   subnet ...
   subnet ...
}
where vlan_something is an arbitrary text label you assign. If you do 
actually have more than one physical network or VLAN (ie broadcast 
domain), then you need a shared network for each of them, and of 
course, a relay agent in any the server is not directly attached to.


The other thing is that HOST STATEMENTS ARE GLOBAL IN SCOPE, and you 
will have had a warning about this when starting the DHCP server. 
Except for some very odd setups, the inheritance effects you would 
get due to putting host statements inside a subnet declaration are 
not what you want - put them in the global scope. As it happens, the 
fixed address statements will prevent such strange effects, but you 
shouldn't rely on that to keep you out of trouble.


-- 
Simon Hobson

WANTED: "Software CD ROM Kit" for Canon CLBP 360-PS printer (Canon 
part no RH6-3612, or possibly RH6-3810, or RH6-3610 might do). I've a 
dead HD and need this CD so I can replace the disk and re-install the 
printer OS on it. If anyone knows where I might get hold of one I'd 
be grateful - requests to Canon drew a blank, it's been out of 
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Alternatively, if anyone has one of these and would let me image 
their hard disk ...

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