Monday, September 28, 2009

LLMNR and IPv6 file sharing

The accountants were having trouble accessing an IPv6 file share on their Vista machines, but their 2003 server and my Ubuntu Linux box could access it just fine: this condition developed over the weekend. The DNS functionality on the 2003 box is suspect, and we're looking to replace the box: in the meanwhile, I did some digging to figure out what was going on. A run of Wireshark yielded that when you plugin a network cable into a Vista/7 box, you generate LLMNR broadcasts on UDP port 5355. I set the firewall on the server to unblock that port on the local subnets and rebooted it: the Vista clients were able to access the share afterwards. Coincidence perhaps, but definitely something to keep in mind when managing DNS-based stuff.

Microsoft documentation on LLMNR

btw, if you want to route an IPv6 share to an XP or 2003 box, you can setup a portproxy to map port 445 of the target server to any unused local port. Example...

netsh int portproxy add v4tov6 listenport=2000 connectaddress=servername connectport=445

As long as the servername has an AAAA DNS record and accessible over IPv6, it should work.


  1. Interesting ... Does this mean that in a real production environment, IPv6-shares are used?
    And: does the Ubuntu understand the LLMNR stuff too?

  2. Sorry for late reply, been quite busy this month. Yes we're using IPv6 shares in production: using Vista/7 to access Server 2008 & Samba 3.4 shares. Ubuntu doesn't understand LLMNR, but there are some Linux builds of source code out there for it (Microsoft Rally). Also look at my following post to this regarding 2008's new DNS functionality.

  3. Michael,

    Can you explain *why* you use IPv6 shares? Which add-on functionality does the IPv6 offer?


  4. I need to find some email notification for comments. I use IPv6 as a VPN for my work sites: each site using a private IPv4 subnet, but each element accessible globally with IPv6 addresses. Its a rather clean mix of old and new tech.

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