DHCP Relay forwarded to Secondary when Scope is not available in Primaray

Answered Question
Oct 19th, 2009
User Badges:

Two ip helper-addresses (let suppose DHCPServer1 and DHCPServer2) are defined on each of the branch router, and customer want to divide the load of DHCP request on two different DHCP Servers. The propose solution by customer is to disable some scope from one DHCP Server (DHCPServer1) and define the similar scope in second DHCP Server (DHCPServer2). Does the DHCP Relay request would be forwarded to secondary server (DHCPServer2), if the scope is disabled on first DHCP Server (DHCPServer1)?

Correct Answer by Jon Marshall about 7 years 6 months ago

Shouldn't matter because the 2nd DHCP server will still respond with an offer and then the client can use that one. Remember that the router simply forwards the responses on to the client so as long as the client receives an offer you should be fine.


Jon

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (2 ratings)
Loading.
Jon Marshall Mon, 10/19/2009 - 23:13
User Badges:
  • Super Blue, 32500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

The DHCP request is forwarded to all the addresses defined with the ip helper-address command.


So if you have 2 ip helper-addresses then the DHCP request is sent to both at the same time by the router. First one to respond is usually the one accepted by the client.


Jon

Ahmed Shahzad Tue, 10/20/2009 - 14:20
User Badges:

What if the first DHCP, having no scope for the subnet, would respond first with failure message like scope does not exist?

Correct Answer
Jon Marshall Tue, 10/20/2009 - 16:47
User Badges:
  • Super Blue, 32500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

Shouldn't matter because the 2nd DHCP server will still respond with an offer and then the client can use that one. Remember that the router simply forwards the responses on to the client so as long as the client receives an offer you should be fine.


Jon

Actions

This Discussion