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

Simon Hobson dhcp1 at thehobsons.co.uk
Thu Oct 29 11:47:26 UTC 2015

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*.

As far as the DHCP server is concerned, it'll quite happily lease different addresses to the "same client" in different networks. You can see this if you (for example) plug a computer into one network, let it get an address, then pull the network cable (so it can't release the lease). When you plug it into another network, it'll get another address - but the first lease is still current.

* Amusing story.
Our local LUG used to meet in a university facility. They bought a truckload of new computers, and had "strange" network problems with a few computers. Eventually they pinned it down to MAC addresses - the manufacturer had a bug in their addressing code, and duplicated one address in every 257 machines ! This hadn't shown up before since it is only a problem if those 2 machines in each set of 257 are on the same network - and even buying 300+ machines wouldn't guarantee that you got consecutive MAC addresses.

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