Reserving ports in the Windows 10 Dynamic Port Range

Question

I want to set a Windows 10 dynamic port range between 20000 and 29999 (inclusively), so a range of 10000 ports.

To do this, I run the following commands:

netsh int ipv4 set dynamicport tcp start=20000 num=10000
netsh int ipv4 set dynamicport udp start=20000 num=10000
netsh int ipv6 set dynamicport tcp start=20000 num=10000
netsh int ipv6 set dynamicport udp start=20000 num=10000

Following this, querying the range using the following example command:

netsh int ipv4 show dynamicport tcp

...produces the following result:

Protocol tcp Dynamic Port Range
-------------------------------
Start Port      : 20000
Number of Ports : 10000

Which looks correct to me.

Now suppose I want to reserve certain ports within that Windows Dynamic Port Range, say 21000-21050, then I run the following command:

reg add HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\ /v ReservedPorts /t REG_MULTI_SZ /d 21000-21050 /f

Following this, requerying the Windows Dynamic Port range produces the following result:

Protocol tcp Dynamic Port Range
-------------------------------
Start Port      : 20000
Number of Ports : 10000

Is this expected behaviour? Or should the resultant table be fragmented somewhat to reflect the port reservations which fall within the middle of the dynamic range, e.g. something like:

Protocol tcp Dynamic Port Range
-------------------------------
Start Port      : 20000, 21051 
Number of Ports : 1000 , 8950

My port reservation command has updated the registry with the ReservedPorts setting so I assume this is all correct behaviour.

Are there any other ways to test this process prior to deployment in a system?

Thanks

Answer 1

Windows Vista and higher do not support the ReservedPorts registry value. (Source)

Instead, you can use the netsh utility to achieve the same effect:

netsh int <ipv4|ipv6> Add excludedportrange [protocol=]tcp|udp [startport=]<integer> [numberofports=]<integer> [[store=]active|persistent]

You can also remove entries:

netsh int <ipv4|ipv6> delete excludedportrange [protocol=]tcp|udp [startport=]<integer> [numberofports=]<integer> [[store=]active|persistent]

...or list them:

netsh int <ipv4|ipv6> show excludedportrange [protocol=]tcp|udp [[store=]active|persistent]

I doubt any of that would affect the output of netsh int <ipv4|ipv6> show dynamicport tcp.