multiple subnets

Simon Hobson dhcp1 at
Wed Apr 2 15:10:16 UTC 2008

M U wrote:

>>>I'm using the ISC DHCP server V3.0.5 on Linux.
>>>I want to make the DHCP server work like below.
>>>1. One client(it behaves like a proxy) of acess the 
>>>DHCP server(,ETH0)
>>>2.This client wants to get the ipaddress from DHCP server from the 
>>>following range( to provide/distribute the 
>>>ipaddress for the PC under this client.
>>>PC---+( client ----> DHCP ser( ETH0)
>>>    <--------------------------------
>>>Firstly, technically, is it possible to implement on the DHCP 
>>>server like the above ?
>>>If possible, would you teach me how to configure or let me know 
>>>the good free document or so ASAP ?

>>You need to make your proxy client a dhcp relay.
>>To  do  this,  execute dhcrelay -i <interface facing clients> -i 
>><interface facing server> <ip address of the dchp server>

>How should I configure the DHCP server ?

Step 1 - RTFM ! Start with the man pages for dhcpd, dhcpd-conf, and dhrelay.

Step 2 - if you still don't know, perhaps you could explain what you 
want to achieve, because it's not clear from your question. The 
reason for asking what you want to achieve, is that often people will 
ask how to do a certain thing - when actually what they want isn't to 
do that.

But a few pointers to get started with :

The simplest approach is that the relay agent should have an address 
in the subnet. It will probably work if it doesn't (ie 
it only has an address in the subnet), but then you 
will need a shared network declaration.

You declare the subnet, declare any subnet specific 
options, and define a range of addresses to be given to clients. NB - to is not a practical range to be given out 
(assuming a 16bit netmask as it leaves no usable address for a router.

Any ranges defined MUST contain only addresses which may be given out 
to clients - ie addresses used by routers, statically defined clients 
etc must NOT be included. This is different to the usual methodology 
used when administering Windows DHCP servers.

You MUST declare a subnet for the subnet but you do 
not need to have any dynamically assigned ranges. The DHCP server 
won't start otherwise.

You MUST have full routing between the subnet and subnet or the clients won't be able to renew their 

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