Messages in this thread | | | Subject | Re: Turning off ARP in linux-2.4.0 | Date | Tue, 23 Jan 2001 16:27:21 -0800 | From | Pete Elton <> |
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> 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 10.0.0.99 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 command:
# ifconfig lo:1 10.0.0.99 netmask 255.255.255.255 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.
Pete
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