DHCP Configuration in Core Switches

[ehsan12345]

Dear Professionals 

I have two locations and both locations have Core Switches installed. Location names are factory-1 and factory-2. Both locations have DHCP configured in their core switches and these two locations are connected with fiber. Access switches of the two locations are connected via fiber to their respective core switches. It means that users connected to access switches should take dynamic IP addresses from their respective core switches (dhcp server). I am facing one problem here which is as follow:

Users of factory-1 gets IP address from the factory-1 Core Switch , which is OK. The problem is that, users of factory-2 are also getting IP addresses from factory-1 core switch, even tough factory-2 core switch also has DHCP configured and enabled. what can be the reason? please help me to solve this issue. I want factory-2 users to take dynamic IP address from their factory-2 core switch, waiting for your response

Thank you

[Reza Sharifi]

Hi,

Can you make sure that factory-2 core switches DHCP scopes have the correct gateway?

It maybe that factory-2 switche scopes have the gateway from factory-1 switches.

HTH

[pwwiddicombe]

Is it a single layer-2 subnet for both core switches? 

Do you have IP helper-address on them (probably not necessary if they are all one subnet).

Remember that on the LOCAL subnet, a DHCP request is broadcast, and the FIRST DHCP response received by the workstation will be acknowleged and that address used.  You can sometimes tune this by having a duplicate check (or multiple pings) by the DHCP server; the server with the extra pings or duplicate checks will tend to farm out fewer addresses.

[Richard Burts · Accepted solution]

There are things about this environment that we do not know and which could change the answer that we give. Given the limited information that we have I believe that there are at least two potential explanations for the symptoms which are described.

1) It is possible that there is a flaw in the scope defined on the core switch for factory-2 and that all clients are receiving their IP address assignment from the factory-1 core.

2) It is possible that all clients are in the same vlan. In that case the DHCP request from the client is received by both DHCP servers and that both servers respond, and that the factory-1 core is responding more quickly than the factory-2 core.

Some clarification of the environment might help us to understand the issue more clearly.

HTH

Rick

[Richard Burts]

I am glad that my suggestions were helpful. Thank you for using the rating system to mark this question as answered. This will help other readers in the forum to identify discussions which have helpful information. These forums are an excellent place to learn about Cisco networking and I hope to see you continue to be active in the forum.

HTH

Rick