PVS Server StreamProcess Event ID 204: received invalid opcode
Article ID: CTX696925
Updated On:
Description
When the PVS server receives UDP packets on its Streaming Login port, which do not contain expected PVS headers, the PVS StreamProcess will log event ID 204 with a message "CSSInitialContact::DispatchPacket received invalid opcode" followed by some hexadecimal characters.
The hexadecimal characters are derived from the UDP payload.
To investigate further the Hexadecimal can be decoded to printable ASCII to help with investigation.
Example Hexadecimal string: 6C6C6548
- The string is split into pairs and then reversed for little-endian interpretation:
- 48,65,6C,6C decodes to H E L L
- Which was the initial part of a message "Hello from PowerShell" as could be observed in a network trace:
Network traces can be captured and viewed in Wireshark, with filters then applied to display only the packets containing this Hexadecimal:
- Using the same Hexadecimal string: 6C6C6548
- The string is split into pairs and then reversed and added to Wireshark filter data.data contains 48:65:6c:6c
The above two steps should enable PVS administrators to identify the source of the packets which result in the event ID 204 messages.
Cause
Non PVS packets arriving on the PVS login ports will cause PVS to generate these events.
PVS Login port monitoring is not possible via simple third-party network check, and attempting to do so by sending UDP packets to the PVS login port will result in these events being generated.
Resolution
In a customer case, it was identified that a network monitoring program was incorrectly attempting to monitor PVS UDP login ports.
Removing the network monitoring program configuration to check PVS login ports eliminated the events.
Issue/Introduction
A Citrix Provisioning (PVS) server may repeatedly log Event ID 204 messages ,in the application Event Log. similar to:
- Log Name: Application
- Source: StreamProcess
- Event ID: 204
- Content: CSSInitialContact::DispatchPacket received invalid opcode 6C6C6548
