Windows Server: an Update causes iSCSI connection issues

[German]It seems, that an Update is causing iSCSI connection issues on Windows (Server) systems and causing event entries with ID 4231. In some cases, this error is causing a server to stall.


Stefan F., a reader of my German blog, send me an e-mail notifying me about an issue, he run into. He wrote:

… if an iSCSI connections stand at „try to connect", the server refuses any connection after a while. Microsoft has confirmed, that a fix isn't available and will take time. Also some of my colleagues are struggling with this error.

Stefan tried to connect iSCSI devices unter Windows Server, but this connection stalls multiple times a day. And it seems that this isn't a single observation. Also Microsoft is aware of this issue, because they noted for Update KB4025336 for instance:

If an iSCSI target becomes unavailable, attempts to reconnect will cause a leak. Initiating a new connection to an available target will work as expected. Microsoft is working on a resolution and will provide an update in an upcoming release.

More error details

Stefan pointed me to this Technet forum post, dealing with Ephemeral port exhaustion – Event ID 4231. A user describes the error causing an event with ID 4231 on Windows Server 2012 R2.

"A request to allocate an ephemeral port number from the global TCP port space has failed due to all such ports being in use."

The user reported, that Veeam Backup failed to work, because the device can't reached. Also printer doesn't work due to a connection failure on Windows Server 2012 R2, and RDP sessions to Windows Server wasn't possible. Rebooting the Server solves the issue for a couple of hours.

Emmanuel Paré mentioned within this thread the reason for this issue: When the server try to reconnect it will use ephemeral ports to try to reconnect (multiple time) until it use all portsl.  The issue was discovered in our lab and we are holding the patch for production until Microsoft release a fix.

Emmanuel Parè could reproduce this issue within labs. He mentioned, that Microsoft is aware of the issue and is working on a fix. It seems, that an 'April 2017 update' has caused this behavior.


Waiting for a Fix and a nasty workaround

Dave Hallwas mentioned within the Technet forum, that Microsoft is working on a fix, but won't release that before July Update Preview (3rd July week). And he mentioned a 'workaround': Just uninstalling all cumulative updates and rollup updates backward till March 2017.

Dave wrote, that he identified for his Windows Server 2016 Cluster Update KB4022715 as an issue. But uninstalling this update is causing a blue screen. So we have to wait for a fix released from Microsoft.

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