I ran into an interesting issue today. We use a dedicated port range for RPC connections through firewall per this Microsoft article. Doing so allows RPC to work through dedicated hardware firewalls. We also enable the local Windows firewall on several boxes as this provides a firewall for any systems not using a dedicated piece of hardware or from other systems behind dedicated firewalls.
While using Shavlik NetChk Configure to scan systems for compliance, I noticed some inconsistencies which I traced back to a firewall issue on the server being scanned. The scans perform some of the checks over RPC. I confirmed that Remote Administration had been enabled using this command:
netsh firewall set service REMOTEADMIN enable
However, netstat would show the connection in a SYN_SENT state on a port in the dedicated RPC range. Buried in this technet article, I found the reason:
|Remote Administration||Adds TCP ports 135 and 445 to the exceptions list. Also adds Svchost.exe and Lsass.exe to the exceptions list to allow hosted services to open additional, dynamically-assigned ports, typically in the range of 1024 to 1034. This setting allows a computer to be remotely managed with administrative tools, such as the Microsoft Management Console (MMC) and Windows Management Instrumentation (WMI). It also allows a computer to receive unsolicited incoming Distributed Component Object Model (DCOM) and remote procedure call (RPC) traffic.|
It seems that when setting a custom range of ports for RPC via the HKLM\Software\Microsoft\RPC\Internet key, it “breaks” the Remote Administration firewall rule in the Windows Firewall. This was tested on a Server 2003 R2 SP2 system, but I suspect similar issues would apply to Server 2008.