intellij freezing on startup + putty routinely failing to bind to ports used for ssh tunneling

for the past few weeks i was plagued by putty randomly failing to bind to ports used for ssh tunneling giving me in its log “forwarding failed: Network error: Permission denied”

today my intellij failed to launch – it was freezing on the splash screen, C:\Users\xxxxxxxxxxxx\AppData\Local\JetBrains\IdeaIC2021.2\log\log.log had:

2021-10-20 11:32:47,562 [   9285]  ERROR - llij.ide.plugins.PluginManager - Address already in use: bind 
java.util.concurrent.CompletionException: Address already in use: bind
    at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(
    at java.base/java.util.concurrent.CompletableFuture.completeThrowable(
    at java.base/java.util.concurrent.CompletableFuture$
    at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.exec(
    at java.base/java.util.concurrent.ForkJoinTask.doExec(
    at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(
    at java.base/java.util.concurrent.ForkJoinPool.scan(
    at java.base/java.util.concurrent.ForkJoinPool.runWorker(
    at java.base/
Caused by: Address already in use: bind
    at java.base/ Method)
    at java.base/
    at java.base/
    at java.base/
    at io.netty.bootstrap.AbstractBootstrap$
    at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(
    at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(
    at io.netty.util.concurrent.SingleThreadEventExecutor$
    at io.netty.util.internal.ThreadExecutorMap$
    at java.base/

that brought me to and workaroudn described there:

netsh int ipv4 set dynamicport tcp start=49152 num=16383
netsh int ipv4 set dynamicport udp start=49152 num=16383

net stop winnat
net start winnat

that did the trick – problems with intellij and tunneling in putty are gone! indeed, few weeks earlier i was playing with NAT for Hyper-V. before the change this command indeed was showing wide ranges of ports being reserved:

netsh interface ipv4 show excludedportrange protocol=tcp

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