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SubjectRe: Turning off ARP in linux-2.4.0
> On Tue, Jan 23, 2001 at 03:50:36PM -0800, Pete Elton wrote:
> The snippet you posted doesn't describe what ClusterThingy exactly wants
> to do with ARPs.

Well I think the main difference in what you implemented and
what the cluster server thing is doing (I think) is it sounds
like you can arp on a specific interface, but for the cluster server
software to work, the node cannot arp at all since a separate machine
is acting as a redirector and all incoming request go to that server
first and are then pasted to a node. (how's that for a run on sentence)

Here is what their documentation says about that explicitly. It appears
just before the other section I quoted:
Creating an alias has one problem: when another system on the network
wants to send a packet to the IP address on the same subnet,
it sends an ARP broadcast to determine which computer has that IP address.
The machine with that IP address is supposed to answer back with its IP
address and corresponding MAC (hardware) address. But if all the nodes
in the cluster have the same IP address, they are all going to answer
this broadcast ARP message. So we have to tell all of the systems except
for the primary ATM not to reply to those ARP requests. We want all
traffic destined for the cluster to go through the primary ATM first.

Part of the solution to this is to create the alias on the loopback
interface instead of the Ethernet interface. The loopback interface
is a network interface that has no hardware or physical network
associated with it. So instead of creating the alias on eth0:1, you
would add the alias to the loopback interface (lo) using the following

# ifconfig lo:1 netmask up

So in the setup I have, we have an ATM which gets all incoming requests
for the web site. And then we have 7 other machines that get the
requests passed onto them by the ATM. So only the ATM can ARP for
the ip address of the web site. The 7 other servers cannot. So for
the 2.2.18 kernel, I have the ipaddress aliased to the lo interface
with the hidden sysctrl option set to 1 and everything works. When I
try and bring one of the nodes up on the 2.4.0 kernel, I cannot keep
it from ARPing so it fights with the ATM for all of the traffic and
that causes problems.

I hope that this makes more sense.

Any ideas on how I can turn off the arping? I guess the thing that I
am most curious about is how it ending up being removed from the kernel
in the first place. It must have been a decision that someone made.
Either, we don't need that any more since we can do it this way, or
we'll take it out since nobody uses it.


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