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List:       dhcp-users
Subject:    Re: [Bug Report] key conflict message for create host by Omapi
From:       John Wobus <jw354 () cornell ! edu>
Date:       2015-10-30 20:05:32
Message-ID: B185591F-2293-47F0-A8FF-F5BB31305B21 () cornell ! edu
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On Oct 29, 2015, at 7:47 AM, Simon Hobson <dhcp1@thehobsons.co.uk> wrote:

> Muhammad Faisal <faisalusuf@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 whe=
rever 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 - a=
nd that'll work fine. Also, though I *REALLY* do not recommend this, you ca=
n have two clients with the same MAC address in different networks (in diff=
erent 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 usi=
ng the victim's
MAC address.

As far as I know, ISC dhcpd serves DHCP for identical MAC addresses on diff=
erent subnets,
except for configuring it via the OMAPI interface.  It seems reasonable tha=
t dhcpd support
such configuration but I don=92t know where that potential enhancement fall=
s on ISC=92s priority list.

John Wobus
Cornell U IT =

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