one DHCPD server multi subnets
Simon Hobson
dhcp1 at thehobsons.co.uk
Thu Nov 1 07:04:49 UTC 2007
tangaish.en wrote:
>now my conf file look like this:
>
>ddns-update-style interim;
>ignore client-updates;
>
>subnet 172.16.0.0 netmask 255.255.0.0 {
>
># --- default gateway
>
> option domain-name "guest.XXX.com";
> option domain-name-servers 172.16.1.2,172.16.1.4;
>
> option netbios-name-servers 172.16.1.4;
> default-lease-time 21600;
> max-lease-time 43200;
>
>pool {
> range 172.16.5.210 172.16.5.220;
> option routers 172.16.5.1; option
>subnet-mask 255.255.255.0;
> }
>
>pool {
> range 172.16.4.210 172.16.4.220;
> option routers 172.16.4.1; option
>subnet-mask 255.255.255.0;
> }
>}
>
>I can't test it because of the 3-layer switch offer dhpc function
>and PCs need it every work day, I must wait weekend to try isc dhcp
>and switch relay.
>
>I think this conf file don't work.
Correct, it won't work. You need a subnet declaration for each
subnet, and inside that a pool declaration for the addresses in that
subnet which are to be dynamically assigned. Every subnet declaration
must match exactly (address & mask) the real subnets. Something like
this, note global options at the start which are outside the subnet
declaration.
option domain-name "guest.XXX.com";
option domain-name-servers 172.16.1.2,172.16.1.4;
option netbios-name-servers 172.16.1.4;
default-lease-time 21600;
max-lease-time 43200;
subnet 172.16.1.0 netmask 255.255.255.0 {
option routers 172.16.1.1;
option subnet-mask 255.255.255.0;
pool {
range 172.16.1.210 172.16.1.220;
}
}
subnet 172.16.2.0 netmask 255.255.255.0 {
option routers 172.16.2.1;
option subnet-mask 255.255.255.0;
pool {
range 172.16.2.210 172.16.2.220;
}
}
...
subnet 172.16.5.0 netmask 255.255.255.0 {
option routers 172.16.5.1;
option subnet-mask 255.255.255.0;
pool {
range 172.16.5.210 172.16.5.220;
}
}
>I want to know dhcpd run with this conf file can do it or not? if
>yes I'm intersting in figure out how isc dhcpd know which
>dhcprequest is coming from that net, is there a relay address in
>dhcprequest package and dhcpd assign address base on that address?
Once you configure DHCP to match teh subnets available, the server
automatically works out which subnet a client belongs to. For clients
on a local network, it is done simply by which physical interface the
request arrives on.
For clients on remote subnets, the bootp-helper is the key - it
receives the broadcast from the client, fills in it's own address on
that network (in the GIAddr (Gateway Interface Address) field), and
then forwards it to the server. The server then uses the GIAddr to
figure out the correct subnet.
So you as the admin need do nothing (apart from correctly defining
the subnets) to make this work - it's just happens automagically.
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