Loopback behaviour on Windows Server 2008

Enable Loopback adapter on Windows Server 2008

netsh int ipv4 set int “Loopback Adapter” weakhostreceive=enabled weakhostsend=enabled

netsh int ipv4 set int “Local Area Connection” weakhostreceive=enabled weakhostsend=enabled

via Enable Loopback adapter on Windows Server 2008 – Steve Schofield Weblog.

Those two lines will save you lots of headaches: in Windows 2008 the network behaviour has changed in a subtle and tricky way. Packets coming in from a NIC will not go out from another one, by default.

If, like me, you were using the loopback trick to publish machines on the internet via ARP Proxying your win2k8 machines will NOT reply correctly by default. Use the settings above and you’re good to go: packets coming in from the loopback (with the internet address) will be sent back through the DMZ nic and will be routed normally.

Author: renatoram

sysadmin, rpg player, gunpla modeler, avid reader... yeah, your average geek :)

8 thoughts on “Loopback behaviour on Windows Server 2008”

  1. netsh int ipv4 set int “Loopback Adapter” weakhostreceive=enabled weakhostsend=enabled
    The filename, directory name, or volume label syntax is incorrect.

    1. It is because of the quotes “ ”. Change these with regular quotes ” ” and it should go well.

  2. Thanks very much. Spent long time wondering why DSR style load balancing wasnt working. thanks very much.

    1. My pleasure, really: I published this post because when I had this problem I had to hunt here and there to find the solution… it’s one of the most hit posts on this blog, historically, so I know I’ve been of service 🙂

    1. As far as I can tell/recall, yes it does. I don’t think I ever needed to do this again and the machine has been restarted many times.

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