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On Tue, Jun 15, 2004 at 10:18:42AM -0400, Joseph Mack wrote:
> Shinichi Kido wrote:
> >
> > Dear all,
> >
> > If anyone may give some advice to my concerns, it would be very helpful
> > and would like to appreciate.
> >
> > 1) Gratuitous ARP interval
> >
> > I'm setting two nodes cluster with heartbeat and checked the timing
> > when the gratuitous arp broadcast, using tcpdump.
> > I found the packet broadcasted when the fail over occurs, but it
> > looks likes never be broadcasted at regular intervals.
>
> yes, normal arp takes over after that
>
> > If so, when the router facing to WAN, missed to receive the arp, due
> > to network congestion, etc, the service would be unavailable till
> > the arp cash expires.
>
> yes, but since your network is congested, it doesn't matter, since nothing
> is getting through.
Several gratuitous ARP packets are sent so if the first one doesn't make
it hopefully the next one will. You can configure both the number of ARP
packets that are sent, and the time between sending them.
> > Is it possible to set to broadcast gratuitous arp constantly from
> > active server, regardless of the failover?
>
> yes, but I would kick you off the network if I was running it.
> Your problem is with congestion not with arp.
Actually that was my original design. I did that to gaurd against the
situation where some half-dead node can respond to ARP. The overhead
of sending a gratuitous ARP every second or so is pretty low. But
it is probably more trouble than it is worth. Particularly in the
situation where the node sending the gratuitous ARP packets
malfunctions.
To answer your question, yes this would be possible.
If you really want to do this I would suggest grabbing my original
IP Address Takover tool, fake, which does this. It can be used
as a resource to heartbeat (though I have not tested that extensively).
http://www.vergenet.net/linux/fake/
--
Horms
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