335 Chapter 10: Windows DNS, BitLocker Drive Encryption, and Itanium Support
Windows Link-Local Multicast Name Resolution
Microsoft Windows link-local multicast name resolution (LLMNR) might sound complicated,
but it??™s simply the way Windows Server 2008 (and even Windows Vista) can resolve hosts
local to their network segment without the use of DNS. In the past, this feature was facilitated
by WINS or NetBIOS, but WINS and NetBIOS support only IPv4. Now that Windows
Server 2008 supports IPv6, a different way to resolve names without DNS is needed. Why
would you ever need LLMNR? Suppose you??™re on a small network running a workgroup
rather than a domain. Your client??™s DNS server addresses may be pointing to a DNS server
out there on the Internet; how are you supposed to resolve names of hosts in your own
network? LLMNR is the answer.
For example, suppose you wanted to ping a host called WIN2K8TEST from your
server. Your server first queries its configured DNS server. If a DNS server is found, it
attempts to query the server for that hostname. If that server cannot resolve the hostname
??”and assuming your DNS server is pointing to a host out on the Internet, then it
won??™t??”it sends a multicast query over UDP for that hostname. Each host on your network
that supports LLMNR checks to see if the hostname matches its own hostname. If
it doesn??™t, it discards the packet.
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