DNS.EXE allocates 5000+ ports immediately

Solution 1:

This is a well-known side effect of the hotfix distributed to address MS08-037, since the hotfix is intended to decrease the predictability of ports used for DNS responses.

You can restrict the amount of ports used by defining a lower Socket Pool Size, as described in this article:

Using dnscmd.exe

• Open an elevated Command Prompt (Run as Administrator...)
• Issue dnscmd /Config /SocketPoolSize <value> where <value> is a number between 0 and 10000

Using regedit.exe

• Open regedit.exe and expand the HKLM hive
• Navigate to SYSTEM\CurrentControlSet\services\DNS\Parameters
• If not already present, create a new DWORD value named SocketPoolSize
• Set a decimal value between 0 and 10000
• Restart the DNS Server service: net stop dns && net start dns

Be aware that setting the value too low, effectively defeats the purpose of MS08-037

If you're on Windows Server 2008 R2 and just want to make sure that a number of individual UDP endpoints are not used by DNS, you can also specify a list of port ranges to be excluded from use by DNS:

dnscmd /Config /SocketPoolExcludedPortRanges <start>-<end>