more than one ip range
dhcp1 at thehobsons.co.uk
Wed Apr 27 07:02:01 UTC 2011
Usuário do Sistema wrote:
>hi everyone, I'm in an project of network segmentation in some VLANS.
>so...I need set my DHCP server distribute more than one IP range.
>for exemplo, currently my server DHCP is inside to VLAN what is VLAN 1
>( 172.18.0.0/16 ) it's distributes only on this VLAN 1.
>I wish that it distributes other ip ranges for other VLANs but on same
>NIC ( Interface 172.18.0.1/16 - VLAN 1 )
>for exemplo, Users from VLAN 2 ( network 10.10.10.0/24 ) will be ask
>IP on server DHCP interface that has IP 172.18.0.1
>in my switch structure all it's ready....I have switch Cisco and I've
>configuration ip helper address in my vlan 1.
>how can I reach this scenery....more than one ip range on my server DHCP ??
This is very basis DHCP stuff.
You need three things for this to work :
1) On the "remote" network you need a relay agent
- this picks up the local broadcasts, fills in a
field to identify the network to the DHCP server,
and forwards it. It sounds like you already have
this in your switch.
2) You configure each subnet in the server, like this :
subnet 172.18.0.0 ...
subnet 10.10.10.0 ...
That's all there is to it - it doesn't matter
which subnets are locally attached and which are
remote, the server will work that out.
3) You need appropriate router(s) and link(s)
that will allow unicast traffic between the
clients on the remote networks and the server -
this is needed to allow the clients to renew
leases which is done by unicast rather than
With these in place you'll find that it all happens automagically.
In a bit more detail, the key is that in the DHCP
discovery and request packets there is a field
called GI Addr (Gateway Interface Address). In
requests from clients on a local network this
will be blank and the server detects the correct
subnet according to the interface the packet was
received on. For remote networks, the relay agent
fills in it's local IP address on the remote
network and the server uses that both to
determine the right subnet, and to return the
packet to the gateway so it can broadcast it to
It is well worth getting hold of the book "The
DHCP Handboook" by Ralph Droms and Ted Lemon.
It's very well written and explains all the
details clearly - including some historical stuff
that explains why it's done the way it is.
Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.
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