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IP helper address and Server config

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Roger Richards
Occasional Advisor

IP helper address and Server config

I understand that the IP helper will point to a server IP from that vlan. How do I get other clients to point to another scope using ip helper from another vlan. Lets say vlan 1 has the IP helper command pointing to 10.150.40.1 and vlan 2 10.150.40.1 and on the server I have two scopes. How will the server know which scope address will be forwarded to those client on vlan 1 or vlan 2.
6 REPLIES
Mohieddin Kharnoub
Honored Contributor
Solution

Re: IP helper address and Server config

Hi

Its an easy thing to do.
Say you have a switch with 3 Vlans,
Vlan1: IP 192.168.1.0/24
Vlan2: IP 192.168.2.0/24
VLan3: IP 192.168.3.0/24

You untag some ports on that switch for clients in different Vlan, and in the Vlan you configure the IP Helper-Address pointing to your DHCP server.
Your Switch configuration will be something like this:

Switch(config)#vlan 1 ip add 192.168.1.1/24
Switch(config)#vlan 1 ip helper-address 192.168.1.2 (DHCP server IP)
Switch(config)#vlan 2 ip add 192.168.2.1/24
Switch(config)#vlan 2 ip helper-address 192.168.1.2
Switch(config)#vlan 3 ip add 192.168.3.1/24
Switch(config)#vlan 3 ip helper-address 192.168.1.2

Now on the DHCP server, create 3 Scopes,

1st: Network 192.168.1.0 mask 255.255.255.0 and specify the range (keep some IPs for static assignment) , and the router attribute is 192.168.1.1 (default gateway for Vlan1)

2dn: Network 192.168.2.0 mask 255.255.255.0 and specify the range and the router attribute is 192.168.2.1 (default gateway for Vlan2)

3rd: Network 192.168.3.0 mask 255.255.255.0 and specify the range and the router attribute is 192.168.3.1 (default gateway for Vlan2)

Now any DHCP request will come from any Vlan, the DHCP will give the proper IP based on the Vlan that DHCP request came from.

Good Luck !!!
Science for Everyone
Roger Richards
Occasional Advisor

Re: IP helper address and Server config

Did not work.

Here is my actual setup.

# ip address 10.150.48.1 255.255.240.0
# ip helper-address 192.168.2.2
# untagged B7

On server

Scope

10.150.48.2 - 10.150.48.7
router 10.150.48.1

Whats wrong here?
Roger Richards
Occasional Advisor

Re: IP helper address and Server config

Did not work.

Here is my actual setup.

(vlan-7)# ip address 10.150.48.1 255.255.240.0
(vlan-7)# ip helper-address 192.168.2.2
(vlan-7)# untagged B7

On server

Scope

10.150.48.2 - 10.150.48.7
router 10.150.48.1

Whats wrong here?
Shayne Heidemann
Regular Advisor

Re: IP helper address and Server config

Is this a IP helper address issue, or a routing issue?

Could be that that segment does not have a route to that vlan?
Mohieddin Kharnoub
Honored Contributor

Re: IP helper address and Server config

Hi

Your setup os fine from the switch side and server side also.

What yo ucan do is, assign a static route to one host on Vlan7 with the same parameters you posted in the scope like:

IP: 10.150.48.5
Mask: 255.255.240.0
Gateway: 10.150.48.1

And now try to pinig your gateway, your DHCP server, and do some test and i think you will find out whats the problem.

Otherwise i can ask you to attach the config of your switch here.

Good Luck !!!
Science for Everyone
Roger Richards
Occasional Advisor

Re: IP helper address and Server config

I got it to work, it was how the DCHP server is setup. It's on a different switch, which is in the DMZ. I tried it at another site and it worked. Now the only problem is getting the clients for that new vlan to get out on the internet?

Scenario:
The 5300 default gateway is the vlan 1 ip, we have a vlan 11 with a 172.16.2.156 for the backbone address.

DCHP server has the ip 10.128.144.7 which is also the gateway or router address for the clients. Ayudar por favor..