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Multiple IP HELPER address (is this correct)

Hi,

Here is the scenario:-

I have 2 DHCP servers 192.168.1.1 (SERVER 1) & 192.168.1.2 (SERVER 2). Both are in Vlan 110 which is the server Farm.

Server One is setup to give out address that have been reserved by MAC address only. The other server will give out address to any client asking for a lease, but has MAC address filtering enabled.

All the clients live in VLAN 100, which have the two IP HELPER address associated with it.

Is the following correct?

When a client with a MAC address allowed to get an IP address from server 2 asks for an IP address the request gets sent to both servers. It wont get anything from server 1 because it only gives out address which have been reserved and that client MAC has not been reserved. It should get an address from server 2 because that is actively giving out address if the MAC address matches the allowed list, and it does match.

Does all this sound as though it will work?

Jamie

3 REPLIES

Re: Multiple IP HELPER address (is this correct)

Hi,

Here is the scenario:-

I have 2 DHCP servers 192.168.1.1 (SERVER 1) & 192.168.1.2 (SERVER 2). Both are in Vlan 110 which is the server Farm.

Server One is setup to give out address that have been reserved by MAC address only. The other server will give out address to any client asking for a lease, but has MAC address filtering enabled.

All the clients live in VLAN 100, which have the two IP HELPER address associated with it.

Is the following correct?

When a client with a MAC address allowed to get an IP address from server 2 asks for an IP address the request gets sent to both servers. It wont get anything from server 1 because it only gives out address which have been reserved and that client MAC has not been reserved. It should get an address from server 2 because that is actively giving out address if the MAC address matches the allowed list, and it does match.

Does all this sound as though it will work?

Jamie

Hi Jamie,

If you see the behaivior of DHCP client and server handshake, A DHCP client may receive offers from multiple DHCP Servers and can accept any one of the offers; however, the client usually accepts the first offer it receives. Additionally, the offer from the DHCP Server is not a guarantee that the IP address will be allocated to the client; however, the server usually reserves the address until the client has had a chance to formally request the address.The client returns a formal request for the offered IP address to the DHCP Server in a DHCPREQUEST broadcast message. The DHCP Server confirms that the IP address has been allocated to the client by returning a DHCPACK unicast message to the client.

So if you have configured a static mac binding for specific ip address then request will be served by that server too, i have not tested thos type of setup but as per the theory i suppose it should work.

Hope to help !!

Ganesh.H

New Member

Re: Multiple IP HELPER address (is this correct)

Thanks for your response Ganesh.

I will try it out int he lab and report back to the forum.

Kind regards,

Jamie

Hall of Fame Super Silver

Re: Multiple IP HELPER address (is this correct)

Hello Jamie,

>> When a client with a MAC address allowed to get an IP address from server 2 asks for an IP address the request gets sent to both servers.

this is correct, your lab tests should give good results

Hope to help

Giuseppe

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