Does the Windows Failover Cluster for a multi-subnet SQL Server
Availability Group require a static IP entry for each subnet?
The CNO will require an IP address for every subnet it could reside in.
I am running SQL Server 2012 on Windows Server 2012 Hyper V VMs in 2
separate subnets in the same domain. I understand that I will need an
IP from each subnet when I create the listener for my AAG. What I am
unclear on is the configuration of IPs on the underlying Windows
Failover Cluster.
For the underlying WSFC you'll need at a minimum:
Node1 - IP Address for each unique subnet for each network interface
Node2 - IP Address for each unique subnet for each network interface
CNO - IP Address for each unique subnet
EX: 2 nodes, 2 subnets, 1 interface per node, subnets 192.168.1.1/24 and 192.168.2.1/24
Node1: 192.168.1.10
Node2: 192.168.2.10
CNO: 192.168.1.20, 192.168.2.20
Also, if the server hosting the secondary replica does require its own
IP, does it also require its own unique cluster name (and can you
explain why this is necessary)?
I'm not sure I understand this part of the question. All of the resources can only belong to a single cluster - there is no cluster inside of a cluster thing.
Edit - I looked at the link that you posted and I'm not sure why the author stated "•Cluster name for each node". My only guess is they meant each node needs a name and IP (for the node). Otherwise it's not a correct statement, the author should probably be contacted.
Technically, yes, you should still be able to read from the DR instance assuming it is configured as a Read Only replica and you are connecting to it directly (As read only routing through the primary would not be working).
You should really be concerned in this case though about bringing the DR site online as the new primary replica. You would need to force quorum on the DR site, and manually failover (with possible data loss) so you can then accept reads and writes at the DR site.
Perform a Forced Manual Failover of an Availability Group (SQL Server)
Best Answer
Couple of points of clarification. Nodes and replicas are not the same thing. Nodes refer to the Windows Failover cluster and replicas to AvailabilityGroup instances. So assuming you are running a 2 node WSFC, each hosting a SQL instance in an AvailabilityGroup, then yes, you will need another server to achieve quorum and avoid split brain behavior. The easiest way to achieve this is simply set up a quorum file on another server outside of the cluster, known as Node and File Share majority. Read more on WSFC Quorum Modes.
You don't necessarily need to commission a new server for this. Any server outside of the server will work.