Pool selection based on Giaddr of different subnet
Simon Hobson
dhcp1 at thehobsons.co.uk
Tue Mar 17 17:34:32 UTC 2009
Dario Aguilar wrote:
>---------------
>But here it´s saying another thing...
>---------------
> Note that, in some network architectures (e.g., internets with more
> than one IP subnet assigned to a physical network segment), it may be
> the case that the DHCP client should be assigned an address from a
> different subnet than the address recorded in 'giaddr'. Thus, DHCP
> does not require that the client be assigned as address from the
> subnet in 'giaddr'. A server is free to choose some other subnet,
> and it is beyond the scope of the DHCP specification to describe ways
> in which the assigned IP address might be chosen.
>.....
It's describing a shared network - the address
used by the gateway is still the address of an
interface on the same physical network as the
client, and the dhcp server must be configured
with a shared network declaration.
Eg, suppose the relay agent is a Linux box, and
eth0 is the interface the client is connected to.
Lets also assume it's a shared network, so you
might see :
eth0 192.168.1.1/24
eth0:0 172.16.1.1/24
eth0:1 10.0.1.1/24
The GI Addr used by the relay agent can be any of
: 192.168.1.1, 172.16.1.1, or 10.0.1.1
The DHCP server MUST be configured like this :
shared-network big-net {
subnet 192.168.1.0 netmask 255.255.255.0 {
...
}
subnet 172.16.1.0 netmask 255.255.255.0 {
...
}
subnet 10.0.1.0 netmask 255.255.255.0 {
...
}
}
As far as teh DHCP server is concerned, all ip
addresses in these subnets are equivalent - ie if
you define a range in two or three subnets, then
the server will NOT assign IPs from a specific
range to a specific client without some mechanism
(such as classes) to do it. So in that case, you
CAN use a class to assign IPs from a specific
range, but the IP must still be valid for a
subnet in the shared network determined from the
GI Addr.
--
Simon Hobson
Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
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