Discovered a configuration error in our network and would like to double check if the conclusions I drew from it are correct.

Incorrect configuration:

  • dhcp helper set on VLAN xyz to point at DHCP01 in VLAN abc (this helper address should not have been set here)
  • DHCP01 does NOT have a DHCP range available for the subnet in VLAN xyz
  • in VLAN xyz was a DHCP02 server (VM) present for subnet VLAN xyz

Observed: When DHCP01 is running, clients in VLAN XYZ are handed an IP from DHCP02. When DHCP01 is dead, clients in VLAN XYZ don't receive an IP.

Question: Could it be that as long as DHCP01 is running, all broadcasts are captured by the switch, forwared to DHCP01 and when DHCP01 reports back it doesn't have an IP for the client, the broadcast is again send out on the network and DHCP02 picks it up and offers an IP?

And when DHCP01 is dead, the switch still sends the broadcast but as no response is received, it tells the client there is no address available?

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