[Bug Report] key conflict message for create host by Omapi

John Wobus jw354 at cornell.edu
Fri Oct 30 20:05:32 UTC 2015

On Oct 29, 2015, at 7:47 AM, Simon Hobson <dhcp1 at thehobsons.co.uk> wrote:

> Muhammad Faisal <faisalusuf at yahoo.com> wrote:
>> The DHCP experts might explain this but what about arp resolution within the server ? The MAC address is a unique identifier so if your deployment is getting two IP for the same MAC how the conflict will resolve?
> The assumption is that the client won't be in two places at once - so wherever it is located at any point in time, ARP will work fine and there's no conflict.
> However, a device with a single MAC address can have two IP addresses - and that'll work fine. Also, though I *REALLY* do not recommend this, you can have two clients with the same MAC address in different networks (in different collision domains) and IP addressing will work fine - ARP resolution within each network will work fine, the MAC address only needs to be unique within one collision domain*.

And if the DHCP protocol or server were not to handle this, a client could DOS another
client using the same DHCP server, even on a separate subnet, simply by using the victim's
MAC address.

As far as I know, ISC dhcpd serves DHCP for identical MAC addresses on different subnets,
except for configuring it via the OMAPI interface.  It seems reasonable that dhcpd support
such configuration but I don’t know where that potential enhancement falls on ISC’s priority list.

John Wobus
Cornell U IT 

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