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I'm trying to understand what's needed to make Windows 7 combine two Ethernet ports into one virtual 2 gigabit port. I know I need 802.3ad compatible switch, my NAS also supports 802.3ad, but it's not sure what's needed on the desktop side.

I know I can buy an expensive 2-port server NIC, and Intel drivers have "teaming" support in them. However, my motherboard already has an integrated NIC. If I put a second, cheap regular network adapter, is there a way to enable 802.3ad over them in Windows?

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You need the proper hardware. Here is a good discussion on that topic. forums.smallnetbuilder.com/showthread.php?t=427 – Ramhound Mar 15 '13 at 17:31
up vote 3 down vote accepted

For NIC teaming or link aggregation support, you'll need to contact your network adaptor vendor or OEM (e.g. Dell offers a teaming driver). They will need to provide you a driver that enables NIC teaming, since Windows does not offer this functionality in the core OS.

Source: http://answers.microsoft.com/en-us/windows/forum/windows_other-networking/does-windows-natively-support-link-aggregation/81e647f9-d89e-4028-8370-7e8bb0e3dc2f?msgId=6ca73c70-5ea7-4054-a75a-1be66d545b8a

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Link aggregation will not provide any benefits using one computer connected to one NAS.

Link aggregation could not split a TCP/IP session on two links. Since one file transfer is one TCP session, it will use only one link.

Link aggregation is good for servers delivering files to several client simultaneously.

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It depends on usage patterns... If you, say, copy two files simultaneously it will be beneficial. Moreover, starting with Windows Server 2012 and Windows 8, SMB 3.0 supports multichannel: blogs.technet.com/b/josebda/archive/2012/06/28/… – haimg Oct 3 '13 at 20:05
    
@haimg : Coping two files does not work (or I have been very unluky). But thank you for pointing the new feature of SMB3 – bokan Oct 3 '13 at 21:52
    
802.3ad aggregation can split a TCP/IP session just fine, since it works at the Ethernet level rather than the IP level. You just need hardware at both ends of the link that supports it. – Mark Nov 22 '15 at 6:36
    
@Mark : could you please verify and give reference for this statement ? For me it does not work. The algorithm for choosing wich link will be used by a TCP session is fairly simple, it's something like : hash(SoucreMac + DestMac) mod number_of_links. I tested various configurations and I could never get more than gigabit transfer per TCP/IP session. If the file transfert is splited over 2 TCP sessions, like SMB3 does, it works. Why would Microsoft have developed multichannel if 802.3ad were able to do it ? – bokan Nov 23 '15 at 10:54
    
@bokan, 802.3ad requires that the entire path support it in order to benefit: if your client supports it, your server supports it, but the switch in between doesn't, you only get one cable's worth of bandwidth. SMB multichannel looks like it's mainly about dealing with inefficiencies at the TCP level, with a side benefit of permitting link aggregation even if the hardware in between doesn't support it, but can only divide bandwidth at the TCP stream level, not the Ethernet packet level. – Mark Nov 23 '15 at 19:46

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