Clustering

Tarrith Do’Urden writes:

“Love your page as it is very informative; just
wondering if you could touch on a subject that is driving me a
little batty at the moment.

“I have downloaded a copy of Clustermatic (I’m trying out
clustering). It boots from the CD-ROM, but… at a particular
point, it waits for a RARP request. I think I have an idea what a
RARP is, but wouldn’t have a clue how to get it working. Just
thought you might.”

Dee-Ann responds:

Ah, clustering. That’s what I was teaching in California! To start
with, type /sbin/arp at a
command line. You’ll get a response similar to:


ARP (Address Resolution Protocol) maps IP addresses to MAC
addresses. A MAC address is a unique series of hexadecimal numbers
that specifically identifies only one Ethernet card on the planet.
This helps to make sure that the Internet doesn’t descend into new
levels of chaos where packets are bouncing around every which way
trying to find where they belong.

Now, your problem is with RARP. That’s just the reverse, where
MACs are mapped to IPs. Most cluster installers at some point
either need to be able to automatically learn what the MAC address
is for each node using a network boot (something that isn’t
supported still in many modern BIOS’s), or need you to tell them
what MACs it’s trying to talk to so it can use DHCP to then assign
IP addresses to each node’s Ethernet card.

You can find out if your nodes support network booting by
rebooting them and seeing if you’re offered more than one pre-BIOS
option. For example, you might be told to press Del to enter
Setup, or F12 to network boot. When a machine is network booted,
it broadcasts its MAC among other things out onto the network. If
your BIOS doesn’t support network booting, then the most painful
way to set up for netbooting is to place the netboot code onto a
computer chip and then solder that chip onto your Ethernet cards.
Frankly, that sounds like something to avoid when all possible.

Some cluster installers offer an option for creating a netboot
floppy disk instead. However, these require you to first learn the
MACs for each of your Ethernet cards and, typically, enter those
into a file that you can then have the cluster installation
routine load. You can use a lot of different techniques to, one by
one, learn those MACs. A simple one is to use either a bootable
Linux distribution such as Knoppix, or a rescue disk from a full
Linux distribution such as Red Hat, in order to boot and access a
shell where you can type /sbin/ifconfig -a and copy out the resulting MAC.

Hope this helps!

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