Confusing wording in the IPMI section of node power data

[Jeff Lane ]

New to the power management part of node info is this text:

"MAC address - the IP is looked up with ARP and is used if IP address is empty. This is better when the BMC uses DHCP."

What is better when the BMC uses DHCP? Does using DHCP make using ARP better? or more accurate?

I can't really seem to grok what this explanation of MAC Address actually means.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: maas 1.5+bzr2227-0ubuntu1
ProcVersionSignature: Ubuntu 3.13.0-23.45-generic 3.13.8
Uname: Linux 3.13.0-23-generic x86_64
ApportVersion: 2.14.1-0ubuntu1
Architecture: amd64
Date: Tue Apr 8 12:09:59 2014
InstallationDate: Installed on 2014-01-13 (84 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Alpha amd64 (20140113)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: maas
UpgradeStatus: No upgrade log present (probably fresh install)

[Julian Edwards (julian-edwards)]

Let me explain what it means and then maybe that will help me to understand which part is confusing you.

When a BMC is using DHCP, its address can change at any time at the whim of the DHCP server. It usually doesn't, which is why it normally works but on a busy network that is using all of its IPs that won't be the case.

To get around this, MAAS allows you to enter the BMCs MAC address instead and uses ARP to look up the IP for that MAC. This is a lot more reliable in the face of changing IPs, however it requires that the ARP table is populated so may not always work.

[Gavin Panella (allenap)]

Bug 1279460 is related to this. Though not directly relevant, it does add some context.

[Jeff Lane  (bladernr)]

Julian: THAT makes more sense... perhaps this would be less confusing, from a user standpoint:

MAC Address - Enter the BMC's MAC Address here if you are NOT using DHCP to assign BMC IP Addresses

[Rod Smith (rodsmith)]

I read Julian's comment as meaning that specifying the MAC address can be more reliable if DHCP *IS* used to assign BMC IP addresses on a crowded LAN. If this is correct, I recommend something more like the following:

MAC Address -- Enter the BMC's MAC address if its IP address is likely to change, as for instance if it's assigned via DHCP.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Gavin Panella (allenap)]

When a BMC uses DHCP we can't be sure of its IP address at any moment in time. Using a MAC address is better in this situation because the IP address can be discovered from that. If the BMC has a statically assigned IP address, or the DHCP server has been configured to assign it a stable address, then either the MAC or the IP addresses can be given.

[Julian Edwards (julian-edwards)]

How about:
"Use ARP on this MAC address to discover BMC's IP address if its IP is likely to change, e.g. if it's assigned via DHCP"

?

[Jeff Lane  (bladernr)]

Yeah, that could work.