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DHCP and IP Helper

I have sliced up my new subnet as follows

Datacenter - 10.10.1.x/24
Everything in the data center will be static from this subnet

Outside the data center - 10.10.2.x/23

This will include switches, printers and users

Now the DHCP server is obviously going to be sitting on 10.10.1.x/24 but will need to hand out 10.10.2.x/23 addresses.

On my layer 2/3 switch I have multiple interfaces on VLAN1 and I believe all I need to do is on the VLAN1 interface

ip helper-address 10.10.1.253 (this is the IP of the DHCP server)

And that should be that yes?
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Les MooreSr. Systems Engineer
Top Expert 2008

Commented:
Assuming that your 10.10.1.x network is VLAN1
and the 10.10.2.x/23 network will be VLAN2

interface vlan 1
 ip address 10.10.1.1 255.255.255.0
interface vlan 2
 ip address 10.10.3.254 255.255.254.0
 ip helper-address 10.10.1.253

The server will have to have its default gateway point to this switch vlan interface IP

Commented:
You got it almost right ;-)

It's the machines in 10.10.2.x/23 segment that need to find the DHCP server that's in the 10.10.1.x/24 segment. So you have to put the "ip helper-address 10.10.1.253" in the other VLAN.

Author

Commented:
There is only one VLAN - VLAN1 which houses secondary IP's for the other subnet
Commented:
Then the switch wil automaticly route the traffic between the 2 segments. But DHCP requests won't be routed. You need the ip helper-address command for that.

And the ip helper-address works only if you put it in the segment that can't find the DHCP server now. And you can only put it in that segment if it has a VLAN.

So I think you need to create a VLAN for your 10.10.2.x/23 segment, so you can put the ip helper-address command in that segment to point the direction to the DHCP server.
Since you have 2 different subnets, you need to route packet between them.
On a layer 3 switch this is accomplished by setting several VLans and enabling inter VLan routing.

If you have a router between your 2 subnets, the ip helper setting must be set there.

Maybe check this page:
http://allaboutmylife.wordpress.com/2007/10/17/ip-helper-addresses-for-dhcp/

Author

Commented:
I am going to be performing this after this first of the year. I'll add VLAN2 and then assign the new IP and IP Helper address to that interface.