GemFire "received unknown communication mode" exception.

Products

• VMware Tanzu Gemfire

Issue/Introduction

Symptoms:

This article discusses the GemFire exception message "received unknown communication mode"; its meaning and common causes.

The GemFire logs contain warning messages about receiving an "unknown communication mode", similar to the following:

[warning 2016/03/22 01:02:25.418 PDT cache  tid=0x294d] Bridge server: failed accepting client connection  {0}
java.io.IOException: Acceptor received unknown communication mode: 0
  at com.gemstone.gemfire.internal.cache.tier.sockets.AcceptorImpl.handleNewClientConnection(AcceptorImpl.java:1593)
  at com.gemstone.gemfire.internal.cache.tier.sockets.AcceptorImpl$5.run(AcceptorImpl.java:1369)
  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
  at java.lang.Thread.run(Thread.java:745)

Environment

Cause

The first byte of a GemFire message encodes the message type. When GemFire receives a message, or any connection, with an unknown value in this first header byte, it logs a warning similar to the one shown.

Resolution

These messages are often harmless as they are causes by unexpected message headers that are most often indicators of non-GemFire applications attempting to connect to a GemFire host and port. This could be a misconfigured application, a network security scan, or user error. In any case, GemFire logs a message and quickly terminates the connection, so it would take an overwhelming flood of such incorrect connections to cause any real harm and they should be noted but can generally be ignored.