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

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

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.

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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.

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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.

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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

(http://blogs.technet.com/b/josebda/archive/2012/06/28/the-basics-of-smb-multichannel-a-feature-of-windows-server-2012-and-smb-3-0.aspx)

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

(http://technet.microsoft.com/en-us/library/cc759208(v=WS.10).aspx)

For more information about how SMB clients select network interfaces, go to the following MSDN website:

SMB tech document - Appendix A: Product Behavior

(http://msdn.microsoft.com/en-us/library/a64e55aa-1152-48e4-8206-edd96444e7f7#id136)

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