SMB Multichannel skips non-routable IP addresses of a network interface if routable IP addresses are also configured

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Article ID: 2777646 - View products that this article applies to.
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Symptoms

On a Windows Server 2012-based computer or a Windows 8-based computer that connects to a server message block (SMB) 3.0 file share, SMB Multichannel ignores non-routable IP addresses if the network interface has both routable and non-routable IP addresses configured. This behavior occurs even though SMB Multichannel typically tries to connect with additional interfaces if multiple network interfaces exist, and tries to establish multiple TCP/IP connections for a Receive-Side Scaling (RSS) capable network interface.

Note Non-routable IP addresses include IPv6 link-local addresses and Automatic Private IP Addressing (APIPA) IPv4 addresses.

Consider the following example scenario:
  • The SMB client has the following configuration:
    • Multiple network interfaces are available and enabled for both IPv4 and IPv6.
    • A static routable IPv4 address is configured for each network interface.
    • The only IPv6 address assigned to each network interface is a link-local address.
    • The network interfaces are RSS capable.
  • The SMB server has the following configuration:
    • A single network interface is available and is enabled for IPv6 only.
    • The only IPv6 address that is assigned to the network interface is a link-local address.
    • The network interface is RSS-capable.
In this scenario, only one SMB session is established, and the SMB client creates a single TCP/IP connection by using the IPv6 link-local address on only one of the network interfaces. Other network interfaces are not used. Additionally, multiple TCP/IP connections are not created, even though the network interface is RSS-capable.

Cause

This behavior is by design. SMB Multichannel uses non-routable IP addresses for a network interface only if no routable IP addresses are available for the interface. If a network interface has both non-routable and routable IP addresses configured, SMB Multichannel ignores the non-routable IP addresses.

In the example scenario, only one network interface (interface A) is used for the SMB session because the link-local addresses of the other interfaces are ignored by SMB Multichannel, and the client can connect only to the link-local address of the server. Additionally, only one TCP/IP connection is created for interface A because the link-local address of A is ignored by SMB Multichannel, and the client can connect only to the link-local address of the server.

Workaround

To work around this behavior, use one of the following methods to enable multiple connections for a network interface:
  • Configure routable IP addresses for network interfaces that must take advantage of SMB 3.0 Multichannel.
  • Configure only non-routable IP addresses (APIPA or link-local addresses) for network interfaces that must take advantage of SMB 3.0 Multichannel.

    Notes
    • The first method is the recommended workaround.
    • In the second method, both the SMB client and SMB server must be on the same network segment because the IP addresses are non-routable.

More information

For more information about SMB Multichannel, go to the following Microsoft Server and Management Blog article:
The basics of SMB Multichannel, a feature of Windows Server 2012 and SMB 3.0
APIPA IPv4 addresses use the 169.254.0.0/16 prefix. IPv6 link-local addresses use the FE80:: /64 prefix. For more information about APIPA IPv4 and IPv6 link-local addresses, go to the following Windows Server website:
Unicast IPv6 addresses
For more information about how SMB clients select network interfaces, go to the following MSDN website:
SMB tech document - Appendix A: Product Behavior

Properties

Article ID: 2777646 - Last Review: January 3, 2013 - Revision: 2.0
Applies to
  • Windows Server 2012 Datacenter
  • Windows Server 2012 Essentials
  • Microsoft Hyper-V Server 2012
  • Windows Server 2012 Standard
  • Windows 8
  • Windows 8 Enterprise
  • Windows 8 Pro
Keywords: 
kbtshoot kbexpertiseadvanced kbsmb KB2777646

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