dhcp relay from multiple switches

Mark Starling Mark.Starling at oa.com.au
Tue Jul 11 00:14:07 UTC 2017

I have dhcp server to use option 82 fields from procurve switches to assign IP addresses based on switch port. This works fine, however there are multiple switches in the same VLAN which are all relaying to the same DHCP server. The dhcp server receives dhcp request from the switch device attaches to, but also from the second switch with trunk port in circuit.id
The exchange goes like this for device connected to switch 1:

1.       DHCPDISCOVER via switch 1

2.       DHCPOFFER via switch 1

3.       DHCPDISCOVER via switch 2 (same transaction, circuit.id is trunk port) No free leases

4.       DHCPREQUEST via switch 1

5.       DHCPACK via switch 1

6.       DHCPREQUEST via switch 2 (repeat of  step 4)

7.       DHCPNAK via switch 2 because the lease is not associated with this switch as agent.

Depending on the device the NAK will cause it to begin a new DISCOVER and network will never stabilise.

I need to stop the NAK. From the procurve switches the dhcp relay is set per vlan so as far as I can see I can't prevent them from forwarding requests received on the trunk ports.
I'm at a loss as to how to get around this short of running a separate DHCP server per switch.
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