dhcp server and vlans

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Mar 7th, 2008
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Hi all, If I have my network say on a 10.1.0.0/16 on vlan 1 and a dhcp server on that network also, and I have a scope on my dhcp server for this, say 10.1.0.1 to 10.1.1.254, If I create another scope on my dhcp server say 10.5.0.1 to 10.6.1.254 /24 will the hosts be able to see this scope on vlan 1 ?

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Yes. It is a broadcast remember.


If you want the DHCP server to give out specific IP addresses to specific workstations then I would not put the DHCP server in the same VLAN as all of the other hosts.

Consider creating 3 VLANs.


1 for your servers

1 for your workstations 10.1.0.0/16 (I would make this a smaller network)

1 for your workstations 10.5.0.0/15 (make this a smaller network also)


Then configure ip helper on your vlan interfaces. The DHCP server will get a relay message from the gateway of the respective network and it will understand to supply the IP address accordingly.


vlan 2

name server-net-10.7.1.0/24

vlan 3

name workstation-net-10.1.0.0/16

vlan 4

name workstation-net-10.5.0.0/15


interface vlan 2

ip address 10.7.1.254 255.255.255.0

no shut


interface vlan 3

ip address 10.1.x.x/16

no shut

ip helper-address


interface vlan 4

ip address 10.5.x.x/16

no shut

ip helper-address


Not sure if that is what you are looking to do but good luck.

carl_townshend Wed, 03/12/2008 - 08:01
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If the server is on say 10.112.0.0/16 network and there is a scope on the server for this same subnet and also a scaope of there for say 192.168.1.0/24 network, which scope would it give out? would it give the 10.112.0.0 scope out as the server has an interface on that subnet ?

amohabir1 Wed, 03/12/2008 - 08:17
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It will give out whatever the forwarding network is. 10.112.0.0 in this case. 192.168.1.0/24 will never be assigned, unless you specify another vlan that contains hosts that will potentially be on this network. You will then have to setup the ip helper-address to forward the dhcp requests to the dhcp server.

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