Unexpected exception in multicast receiver – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 2.3-2.3

Briefly, this error occurs when Elasticsearch encounters an issue with the multicast receiver, which is used for node discovery in a cluster. This could be due to network issues, firewall restrictions, or incorrect configuration. To resolve this, you can check your network connectivity and firewall settings to ensure they allow multicast traffic. Alternatively, you can switch to unicast discovery by specifying the hosts directly in the Elasticsearch configuration. Also, ensure that your Elasticsearch version supports multicast as it was removed in later versions.

This guide will help you check for common problems that cause the log ” unexpected exception in multicast receiver ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: discovery, discovery-multicast and Plugin.

Log Context

Log “unexpected exception in multicast receiver” classname is MulticastChannel.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

if (datagramPacketReceive.getData().length > 0) {
                            listener.onMessage(new BytesArray(datagramPacketReceive.getData()); datagramPacketReceive.getSocketAddress());
                    } catch (Throwable e) {
                        if (running) {
                            logger.warn("unexpected exception in multicast receiver"; e);


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