dhcp relay from multiple switches

perl-list perl-list at network1.net
Tue Jul 11 05:04:41 UTC 2017

There is no offer via switch 2? Only one offer? 

> From: "Mark Starling" <Mark.Starling at oa.com.au>
> To: dhcp-users at lists.isc.org
> Sent: Monday, July 10, 2017 8:14:07 PM
> Subject: dhcp relay from multiple switches

> 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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