Windows Server 2012 R2: Which version of the SMB protocol (SMB 1.0, SMB 2.0, SMB 2.1, SMB 3.0 or SMB 3.02) are you using?

1. Introduction

With the release of Windows 8.1 and Windows Server 2012 R2, I am frequently asked about how older versions of Windows will behave when connecting to or from these new versions. Upgrading to a new version of SMB is something that happened a few times over the years and we established a process in the protocol itself by which clients and servers negotiate the highest version that both support.

2. Versions

There are several different versions of SMB used by Windows operating systems:

• CIFS – The ancient version of SMB that was part of Microsoft Windows NT 4.0 in 1996. SMB1 supersedes this version.
• SMB 1.0 (or SMB1) – The version used in Windows 2000, Windows XP, Windows Server 2003 and Windows Server 2003 R2
• SMB 2.0 (or SMB2) – The version used in Windows Vista (SP1 or later) and Windows Server 2008
• SMB 2.1 (or SMB2.1) – The version used in Windows 7 and Windows Server 2008 R2
• SMB 3.0 (or SMB3) – The version used in Windows 8 and Windows Server 2012
• SMB 3.02 (or SMB3) – The version used in Windows 8.1 and Windows Server 2012 R2

Windows NT is no longer supported, so CIFS is definitely out. Windows Server 2003 R2 with a current service pack is under Extended Support, so SMB1 is still around for a little while. SMB 2.x in Windows Server 2008 and Windows Server 2008 R2 are under Mainstream Support until 2015. You can find the most current information on the support lifecycle page for Windows Server. The information is subject to the Microsoft Policy Disclaimer and Change Notice.  You can use the support pages to also find support policy information for Windows XP, Windows Vista, Windows 7 and Windows 8.

In Windows 8.1 and Windows Server 2012 R2, we introduced the option to completely disable CIFS//SMB1 support, including the actual removal of the related binaries. While this is not the default configuration, we recommend disabling this older version of the protocol in scenarios where it’s not useful, like Hyper-V over SMB. You can find details about this new option in item 7 of this blog post: What’s new in SMB PowerShell in Windows Server 2012 R2.

3. Negotiated Versions

Here’s a table to help you understand what version you will end up using, depending on what Windows version is running as the SMB client and what version of Windows is running as the SMB server:

* WS = Windows Server

4. Using PowerShell to check the SMB version

In Windows 8 or Windows Server 2012, there is a new PowerShell cmdlet that can easily tell you what version of SMB the client has negotiated with the File Server. You simply access a remote file server (or create a new mapping to it) and use Get-SmbConnection. Here’s an example:

PS C:\> Get-SmbConnection
 
ServerName   ShareName  UserName            Credential          Dialect   NumOpens
———-   ———  ——–            ———-          ——-   ——–
FileServer1  IPC$       DomainName\UserN… DomainName.Testi… 3.00      0
FileServer1  FileShare  DomainName\UserN… DomainName.Testi… 3.00      14
FileServ2    FS2        DomainName\UserN… DomainName.Testi… 3.02      3 
VNX3         Share1     DomainName\UserN… DomainName.Testi… 3.00      6
Filer2       Library    DomainName\UserN… DomainName.Testi… 3.00      8
DomainCtrl1  netlogon   DomainName\Compu… DomainName.Testi… 2.10      1

In the example above, a server called “FileServer1” was able to negotiate up to version 3.0. FileServ2 can use version 3.02. That means that both the client and the server support the latest version of the SMB protocol. You can also see that another server called “DomainCtrl1” was only able to negotiate up to version 2.1. You can probably guess that it’s a domain controller running Windows Server 2008 R2. Some of the servers on the list are not running Windows, showing the dialect that these non-Windows SMB implementations negotiated with this specific Windows client.

If you just want to find the version of SMB running on your own computer, you can use a loopback share combined with the Get-SmbConnection cmdlet. Here’s an example:

PS C:\> dir \\localhost\c$
 
Directory: \\localhost\c$
 
Mode                LastWriteTime     Length Name
—-                ————-     —— —-
d—-         5/19/2012   1:54 AM            PerfLogs
d-r–          6/1/2012  11:58 PM            Program Files
d-r–          6/1/2012  11:58 PM            Program Files (x86)
d-r–         5/24/2012   3:56 PM            Users
d—-          6/5/2012   3:00 PM            Windows
 
PS C:\> Get-SmbConnection -ServerName localhost
 
ServerName  ShareName  UserName            Credential          Dialect  NumOpens
———-  ———  ——–            ———-          ——-  ——–
localhost   c$         DomainName\UserN… DomainName.Testi… 3.02     0

You have about 10 seconds after you issue the “dir” command to run the “Get-SmbConnection” cmdlet. The SMB client will tear down the connections if there is no activity between the client and the server. It might help to know that you can use the alias “gsmbc” instead of the full cmdlet name.

5. Features and Capabilities

Here’s a very short summary of what changed with each version of SMB:

• From SMB 1.0 to SMB 2.0 – The first major redesign of SMB
  • Increased file sharing scalability
  • Improved performance
    • Request compounding
    • Asynchronous operations
    • Larger reads/writes
  • More secure and robust
    • Small command set
    • Signing now uses HMAC SHA-256 instead of MD5
    • SMB2 durability
• From SMB 2.0 to SMB 2.1
  • File leasing improvements
  • Large MTU support
  • BranchCache
• From SMB 2.1 to SMB 3.0
  • Availability
    • SMB Transparent Failover
    • SMB Witness
    • SMB Multichannel
  • Performance
    • SMB Scale-Out
    • SMB Direct (SMB 3.0 over RDMA)
    • SMB Multichannel
    • Directory Leasing
    • BranchCache V2
  • Backup
    • VSS for Remote File Shares
  • Security
    • SMB Encryption using AES-CCM (Optional)
    • Signing now uses AES-CMAC
  • Management
    • SMB PowerShell
    • Improved Performance Counters
    • Improved Eventing
• From SMB 3.0 to SMB 3.02
  • Automatic rebalancing of Scale-Out File Server clients
  • Improved performance of SMB Direct (SMB over RDMA)
  • Support for multiple SMB instances on a Scale-Out File Server

You can get additional details on the SMB 2.0 improvements listed above at
http://blogs.technet.com/b/josebda/archive/2008/12/09/smb2-a-complete-redesign-of-the-main-remote-file-protocol-for-windows.aspx

You can get additional details on the SMB 3.0 improvements listed above at
http://blogs.technet.com/b/josebda/archive/2012/05/03/updated-links-on-windows-server-2012-file-server-and-smb-3-0.aspx

You can get additional details on the SMB 3.02 improvements in Windows Server 2012 R2 at
http://technet.microsoft.com/en-us/library/hh831474.aspx

6. Recommendation

We strongly encourage you to update to the latest version of SMB, which will give you the most scalability, the best performance, the highest availability and the most secure SMB implementation.

Keep in mind that Windows Server 2012 Hyper-V and Windows Server 2012 R2 Hyper-V only support SMB 3.0 for remote file storage. This is due mainly to the availability features (SMB Transparent Failover, SMB Witness and SMB Multichannel), which did not exist in previous versions of SMB. The additional scalability and performance is also very welcome in this virtualization scenario. The Hyper-V Best Practices Analyzer (BPA) will warn you if an older version is detected.

7. Conclusion

We’re excited about SMB3, but we are also always concerned about keeping as much backwards compatibility as possible. Both SMB 3.0 and SMB 3.02 bring several key new capabilities and we encourage you to learn more about them. We hope you will be convinced to start planning your upgrades as early as possible.

Note 1: Protocol Documentation

If you consider yourself an SMB geek and you actually want to understand the SMB NEGOTIATE command in greater detail, you can read the [MS-SMB2-Preview] protocol documentation (which covers SMB 2.0, 2.1, 3.0 and 3.02), currently available from http://msdn.microsoft.com/en-us/library/ee941641.aspx. In regards to protocol version negotiation, you should pay attention to the following sections of the document:

• 1.7: Versioning and Capability Negotiation
• 2.2.3: SMB2 Negotiate Request
• 2.2.4: SMB2 Negotiate Response

Section 1.7 includes this nice state diagram describing the inner workings of protocol negotiation:

Note 2: Third-party implementations

There are several implementations of the SMB protocol from someone other than Microsoft. If you use one of those implementations of SMB, you should ask whoever is providing the implementation which version of SMB they implement for each version of their product. Here are a few of these implementations of SMB:

• Apple – Up to SMB2 implemented in OS X 10 Mavericks – http://images.apple.com/osx/preview/docs/OSX_Mavericks_Core_Technology_Overview.pdf
• EMC – Up to SMB3 implemented in VNX – http://www.emc.com/collateral/white-papers/h11427-vnx-introduction-smb-30-support-wp.pdf
• Linux (Client) – SMB 2.1 and SMB 3.0 (even minimum SMB 3.02 support) implemented in the Linux kernel 3.11 or higher – http://www.snia.org/sites/default/files2/SDC2013/presentations/Revisions/StevenFrench_SMB3_Meets_Linux_ver3_revision.pdf
• NetApp – Up to SMB3 implemented in Data ONTAP 8.2 – https://communities.netapp.com/community/netapp-blogs/cloud/blog/2013/06/11/clustered-ontap-82-with-windows-server-2012-r2-and-system-center-2012-r2-innovation-in-storage-and-the-cloud
• Samba (Server) – Up to SMB3 implemented in Samba 4.1 – http://www.samba.org/samba/history/samba-4.1.0.html

Please note that is not a complete list of implementations and the list is bound to become obsolete the minute I post it. Please refer to the specific implementers for up-to-date information on their specific implementations and which version and optional portions of the protocol they offer.

You also want to review the SNIA Tutorial SMB Remote File Protocol (including SMB 3.0). The SNIA Data Storage Innovation Conference (DSI’14) in April 22-24 2014 is offering an updated version of this tutorial. Tags HistoryHyper-VInteroperabilityRDMASMBSMB2SMB3StorageWindows ServerWindows Server 2008Windows Server 2008 R2Windows Server 2012Windows Server 2012 R2