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I have a Windows Server 2008 machine with dual NICs. Both are plugged into the same switch in a typical one-switch, one-gateway home network.

This server is used almost exclusively for inbound connections. It hosts a web server (IIS 6), SQL server, and file server (via LAN UNC paths and mapped drives).

How do I make best use of inbound bandwidth across both NICs? For example, if I connect to it by hostname and one of the interfaces has high traffic, I'd like the new connection to use the other interface.

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3 Answers

up vote 2 down vote accepted

Transmit load-balancing is quite simple, you just enable it on the NIC and it should send traffic out through both ports.

However receive load-balancing is a bit more involved. In short:

  • Configure both connected ports on the switch for etherchannel
  • Team the NICs and set the load balancing policy to 802.3ad Dynamic with Fault Tolerance
  • Ensure your traffic is hitting the web server on at least 2 unique IP addresses (inside the network)

You must ensure your traffic is coming in on multiple IPs because load balancing is achieved on a per-connection basis. I don't know a way to load balance a single connection across 2 NICs.

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Using certain bonding modes under Linux you can kind of get receive load balancing. This is achieved by the Linux box by responding ARP requests using a different MAC address from the bonded interfaces each time. This is only useful on a LAN though. If all the traffic is coming through a single router, this method of receive load balancing would be worthless. –  Zoredache Feb 1 '11 at 22:14
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You could use Windows bonding to bond the NICs together. But the amount of bandwidth between one NIC and the public Internet is minimal. The odds of you seeing much of a slowdown over that NIC is minimal.

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Adapter teaming doesn't really work that way, certainly in general Windows use anyway. its handled at the driver level so the operating system just sees 1x2Gb connection, for example, instead of 2x1Gb connections and a choice of which one to use.

How intelligently this is handled is a function of the NIC, switch and their associated software/drivers rather than the OS.

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