Setup: I have two data centers. In site1, my primary site, I'd like to deploy an AlwaysOn Failover Cluster Instance (FCI). In site2, my data recovery site, I'd like to deploy a single-node instance of SQL. I'd then like to use AlwaysOn Availability Groups (AG) to replicate data between site1 and site2.

I've read a lot of blog posts and TechNet articles. It's clear to me that automatic fail over is not supported for AGs with FCI members [1]. It's also clear that FCIs support nodes on multiple subnets [2]. Apparently this is achieved by updating the Virtual Network Name (VNN) in DNS.

Question: Do AGs support multiple subnets, or do I need a spanned subnet between site1 and site2? I haven't been able to find any sources that explicitly make that clear.


[1] Failover Clustering and AlwaysOn Availability Groups (SQL Server) http://msdn.microsoft.com/en-us/library/ff929171.aspx

[2] AlwaysOn Failover Cluster Instances (SQL Server) http://msdn.microsoft.com/en-us/library/ms189134.aspx

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    Yes AG support multiple subnets ... blogs.msdn.com/b/saponsqlserver/archive/2012/04/24/… ... Also make sure that your data provider supports MultiSubnetFailover .. .NET Framework 4 supports it.
    – Kin Shah
    Apr 16, 2013 at 14:13
  • Ah very helpful, you should post this as an answer so that I can accept it. But this does lead to a qualifying question. If my provider does not support MultiSubnetFailover then a spanned subnet is on only/best option, right? This new setup is expected to be used by dozens on random applications, some quite old... Apr 16, 2013 at 14:46
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    @ElijahW.Gagne No that's not correct. If your driver doesn't support MultiSubnetFailover then you just need to set RegisterAllProvidersIP to 0 in your cluster so that only the online IP address is registered to prevent connection latency/timeouts. Apr 16, 2013 at 15:01
  • I was just reading about that at: support.microsoft.com/kb/947048. My understanding is that the fail-over would be delayed by clients caching the old address... So even with a manual planned fail-over, there would be a potential outage until client s updated their cache? Apr 16, 2013 at 15:08
  • @ElijahW.Gagne I have added my comment as an answer and have reference to msdn link as well.
    – Kin Shah
    Apr 16, 2013 at 15:08

1 Answer 1


Yes AG support multiple subnets as described here. Also make sure that your data provider supports MultiSubnetFailover .. .NET Framework 4 supports it.

To answer your question ...

IF you use .NET framework 4 or 3.5 then the provider will support it as described here.

Also, a good reference to SQL Server Multi-Subnet Clustering is well documented.

With legacy client libraries or third party data providers, you cannot use the MultiSubnetFailover parameter in your connection string. To help ensure that your client application works optimally with multi-subnet FCI in SQL Server 2012, try to adjust the connection timeout in the client connection string by 21 seconds for each additional IP address. This ensures that the client’s reconnection attempt does not timeout before it is able to cycle through all IP addresses in your multi-subnet FCI.

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