Mac Binding in Dhcp server in another subnet

Unanswered Question
Dec 27th, 2007
User Badges:

Dear all,

I have many DHCP servers in different subnets. They provide ip using mac-bindness. I wanted to centralize my DHCP servers. I configured router to be a DHCP relay agent using cisco 3750 layer 3 using " ip helper-address <dhcp address> " stuff. Now I am not being able to mac-bind the ips of another subnet, because the dhcp server in the another end is receving only the router's interface as source mac id. How to infiltrate the mac-addresses of one subnet into another so that i can mac bind the ips in my DHCP server located in another subnet ???

Thanks in advance,

Basanta Karki

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Edison Ortiz Thu, 12/27/2007 - 07:44
User Badges:
  • Super Bronze, 10000 points or more
  • Hall of Fame,

    Founding Member

I'm sorry but that's not the way DHCP Relay Agent really works.

The DHCP client broadcasts a request for an IP address and additional configuration parameters on its local LAN.

The Switch, acting as a DHCP relay agent, picks up the broadcast and generates a new DHCP message to send out on another interface. As part of this DHCP message, the relay agent inserts the IP address of the interface containing the ip helper-address command into the gateway IP address (giaddr) field of the DHCP packet.

This IP address enables the DHCP server to determine which subnet should receive the offer and identify the appropriate IP address range to offer.

The MAC Address from the DHCP Client is never modified.

Can you post 'debug' information from the switch on DHCP packets ?


This Discussion