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I am trying to make an SQL Server 2012 failover cluster. I have two DB machines. I understand that both machines need 2 NICs each. In my organization the IP scheme assigned is something like 192.168.1.X.

So I want to know if I assign 1 IP to each NIC, will that be enough? Like assigning 192.168.1.50, 192.168.1.51, 192.168.1.52 and 192.168.1.53?

Or two of the NICs in each machine have to have some private network scheme which will allow them to communicate directly?

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Or two of the NICs in each machine have to have some private network scheme which will allow them to communicate directly?

You need 2 NICs as

  • One NIC is connected to the public network --> This is where your client applications will connect using clustered IP address and clustered SQL Server name. A recommended practice is to have 2 teamed NICs for public network. This will provide you with availability and redundancy, incase one of them dies.

  • And the other NIC will be connected to a private cluster network which is nothing but a heartbeat connection checking the cluster for LooksAlive (every 5 seconds by default) and IsAlive (runs SELECT @@SERVERNAME against the instance).

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    No, actually, that's not correct. As of Win2008, separate network cards and IP addresses for the heartbeat are no longer required. (You can read my answer for more details.) – Brent Ozar Sep 18 '13 at 18:18
  • @BrentOzar Your point is valid that as of Win 2008, seperate NICs for heartbeat is not required. The Cluster Heartbeat can be configured to use any NIC presented to the OS. But as an old practice, I tend to use Dedicated NIC for it. Just for my knowledge, is it OK to use dedicated NIC or not ? – Kin Shah Sep 18 '13 at 18:54
  • I've seen more problems with separate NICs. At StackOverflow in particular, we had to get down to a single IP address per SQL Server in order to work around problems with clustering bugs in Win2012. – Brent Ozar Sep 18 '13 at 22:52
  • @BrentOzar Interesting case. Probably a blog post from Brent Ozar PLF .. will be a good knowledge base ? Personally, I have deployed it on win2008R2 and works perfectly fine. Thanks for the insight ! – Kin Shah Sep 19 '13 at 0:55
  • The couple of these I have set up both had 2 NICs in each server: one NIC for client access; the other NIC for the iSCSI network and for cluster heartbeat (the cluster heartbeat can use the public NIC but I prefer to get it off the public VLAN). – Greenstone Walker Sep 19 '13 at 2:21
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First, there's no SQL Server 2013, but the good news is that the version number of SQL Server doesn't matter. It's more based on Windows failover cluster networking, which is explained here in a 3-part series by the Microsoft folks:

http://blogs.technet.com/b/askcore/archive/2010/02/12/windows-server-2008-failover-clusters-networking-part-1.aspx

And then additional info in part 4:

http://blogs.technet.com/b/askcore/archive/2010/04/15/windows-server-2008-failover-clusters-networking-part-4.aspx

Short story - you need some network redundancy, but you don't have to get it with multiple IP addresses. Instead, you get it with network teaming software.

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I see lots of old school cluster guys still build MSCS or AOAG clusters with a heartbeat NIC - but there really is no point anymore. If you're virtualizing there is even less point, you're most likely using the same LACP load balanced pNICs on the host to create your private heartbeat VLAN. One a side note, you guys realize you're arguing with Brent Ozar, right?

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