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Cluster failover - network level

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Cluster failover - network level

Postby guest » Fri Dec 05, 2008 11:54 pm

That conversion will actually be pretty quick.

What happens when it fails over
1) group goes offline on Node 1 (at this point the IP address is not bound
to the MAC address anymore, and clients already get timeouts/discards, so
the ARP cache will start refreshing here)
2) the group ownership moves and starts onlining the group, including the IP
address which now binds to a new MAC on the Node 2

as all of this is still taking a couple of seconds at least, the IP is down
long enought for ARP to refresh its cycle.

Never seen this being a real problem

Rgds,
Edwin.

> Correct, but the clients have an ARP cache. So when they try to use
Outlook
> to connect, won't they include the MAC information from the ARP cache into
> the packet which then the switch shouuld see that the MAC address was sent
> to an old port. But then the old active isn't listening on that port
> anymore. That's what I'm curious about.
>

> >> Just curious how clustering takes care of things on the network level.
I
> >> know that the failover node will take over the Cluster Group which
takes
> >> care of the Network Name and Network IP resources. But the switch has
a
> > map
> >> of IPs to MACs.
> >
> > Switches do not store IP addresses at all, as typically you are talking
> > about a "Layer-2 switch" and IP is "layer-3"
> > Switches are mainatining a "dynamic" table of MAC's per switch port
> >
> > the IP to MAC conversion is done by (R)ARP protocol which is a
> > "broadcasting" protocol which will get the MAC of the second node of the
> > cluster after failover.
> >
> > So, this is taken care of by the IP and Ethernet network stacks &
> > protocols,
> > not cluster.
> >
> > Rgds,
> > Edwin.
> >
Just curious how clustering takes care of things on the network level. I
know that the failover node will take over the Cluster Group which takes
care of the Network Name and Network IP resources. But the switch has a map
of IPs to MACs. So wouldn't the switch still be trying to send to the old
port of the downed server? Or does the Cluster send out some type of
agnostic notification to the switch so it knows to rebuild or switch the new
IP to MAC association with the new port for the failover cluster node that
comes online after old active fails?
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Postby guest » Fri Dec 05, 2008 11:54 pm

this behavior is controlled by relying on gratuitous ARP. Your network
devices should be able to handle it properly if you need to use them in
clustered environment. For more info, refer to
http://support.microsoft.com/kb/244331
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