Add support for IP_MULTICAST_ALL to EpollDatagramChannel and IOUringDatagramChannel (netty 4.2) by mahoestar · Pull Request #15755 · netty/netty

mahoestar · 2025-10-15T12:04:26Z

Motivation:

IP multicast behaviour varies between Windows and Linux.

On Windows, you only receive datagrams for the groups your socket has joined.

On Linux, by default, you receive datagrams for all groups joined by the host.

This behaviour can be controlled using the IP_MULTICAST_ALL (or IPV6_MULTICAST_ALL) socket option - it is set to 1 by default.

OpenJDK sets this to 0 on all NIO and Net multicast channels, it is not configurable.

This PR makes the option configurable for epoll socket channels, so that behaviour can be made consistent between NIO and native datagram channels.

Modification:

Add IP_MULTICAST_ALL and IPV6_MULTICAST_ALL options to native epoll transport and native io uring transport.

Set IP_MULTICAST_ALL to 0 when constructing epoll and io uring datagram channels.

Result:

Fixes #15753.

IP multicast behaviour varies between Windows and Linux. On Windows, you only receive datagrams for the groups your socket has joined. On Linux, by default, you receive datagrams for all groups joined by the host. This behaviour can be controlled using the IP_MULTICAST_ALL (or IPV6_MULTICAST_ALL) socket option - it is set to 1 by default. OpenJDK sets this to 0 on all NIO and Net multicast channels, it is not configurable. This PR makes the option configurable for epoll socket channels, so that behaviour can be made consistent between NIO and Epoll DatagramChannel.

normanmaurer · 2025-10-15T12:09:14Z

I think we also want to have this for IoUringDatagramChannel.

mahoestar · 2025-10-15T12:11:43Z

Agreed - will add that now.

normanmaurer · 2025-10-16T08:27:16Z

@mahoestar did you sign our ical ? https://netty.io/s/icla ?

normanmaurer · 2025-10-16T13:20:08Z

Let's merge this one and then do another PR for io_uring as well

mahoestar · 2025-10-21T14:40:02Z

Sorry for radio silence - needed to get the CLA signed.

Corporate CLA has been signed by my employer now.

I'll review all requested changes on this and the netty5 PR now.

mahoestar · 2025-10-21T15:37:04Z

This PR doesn't yet set the IP_MULTICAST_ALL automatically - I can port those changes across before you merge if you would like?

Then can raise io_uring support for 4.2 as a separate PR.

normanmaurer · 2025-10-27T08:58:55Z

@mahoestar can you just do the changes required here and we will port it to other branches later on ?

normanmaurer · 2025-10-29T09:37:41Z

@mahoestar also please sign our ICLA and let me know one done: https://netty.io/s/icla

normanmaurer · 2025-11-07T13:34:38Z

@mahoestar also please sign our ICLA and let me know one done: https://netty.io/s/icla

@mahoestar ping

mahoestar · 2025-11-07T13:43:39Z

Hi, sorry for the delay.

My employer has signed the CCLA - is that sufficient? I should be listed under approved contributors there.

I will make the following changes in this branch now:

Automatic setting of IP_MULTICAST_ALL
IO uring support

Is that OK?

normanmaurer · 2025-11-07T13:46:52Z

Hi, sorry for the delay.

My employer has signed the CCLA - is that sufficient? I should be listed under approved contributors there.

Yes!

I will make the following changes in this branch now:

Automatic setting of IP_MULTICAST_ALL

IO uring support

Is that OK?

Sounds good... feel free to close the other PR in the meantime.

Adds support for the IP_MULTICAST_ALL socket option for io uring.

…g and IoUringDatagramChannelConfig

…atagram channels

mahoestar · 2025-11-07T14:22:07Z

I've made the changes.

I'm not sure what behaviour would be best from the constructor of Epoll/IOUringDatagramChannel - whether we should throw a channel exception on failing to set IP_MULTICAST_ALL, or to log an internal error.

I suppose an error is possible if using an old kernel.

normanmaurer · 2025-11-07T14:37:13Z

I've made the changes.

I'm not sure what behaviour would be best from the constructor of Epoll/IOUringDatagramChannel - whether we should throw a channel exception on failing to set IP_MULTICAST_ALL, or to log an internal error.

I suppose an error is possible if using an old kernel.

Yeah I think logging might be the best bet for compat reasons.

normanmaurer · 2025-11-07T14:37:40Z

-import io.netty.channel.ChannelPipeline;
-import io.netty.channel.ChannelPromise;
-import io.netty.channel.DefaultAddressedEnvelope;
+import io.netty.channel.*;


Revert wildcard imports.

normanmaurer · 2025-11-07T14:38:01Z

 public final class EpollDatagramChannel extends AbstractEpollChannel implements DatagramChannel {
+    private static final InternalLogger logger = InternalLoggerFactory.getInstance(AbstractByteBuf.class);
+    private static final boolean IP_MULTICAST_ALL =
+            SystemPropertyUtil.getBoolean("io.netty5.transport.linux.ipMulticastAll", false);


Suggested change

SystemPropertyUtil.getBoolean("io.netty5.transport.linux.ipMulticastAll", false);

SystemPropertyUtil.getBoolean("io.netty.transport.linux.ipMulticastAll", false);

normanmaurer · 2025-11-07T14:38:34Z

+        try {
+            fd.setIpMulticastAll(IP_MULTICAST_ALL);
+        } catch (IOException e) {
+            throw new ChannelException(e);


I think it might be better to just log

normanmaurer · 2025-11-07T14:38:53Z

-import io.netty.channel.ChannelPromise;
-import io.netty.channel.DefaultAddressedEnvelope;
-import io.netty.channel.IoRegistration;
+import io.netty.channel.*;


revert wildcard support

normanmaurer · 2025-11-07T14:39:12Z

 public final class IoUringDatagramChannel extends AbstractIoUringChannel implements DatagramChannel {
+    private static final InternalLogger logger = InternalLoggerFactory.getInstance(AbstractByteBuf.class);
+    private static final boolean IP_MULTICAST_ALL =
+            SystemPropertyUtil.getBoolean("io.netty5.transport.linux.ipMulticastAll", false);


Suggested change

SystemPropertyUtil.getBoolean("io.netty5.transport.linux.ipMulticastAll", false);

SystemPropertyUtil.getBoolean("io.netty.transport.linux.ipMulticastAll", false);

normanmaurer · 2025-11-07T14:39:22Z

+        try {
+            fd.setIpMulticastAll(IP_MULTICAST_ALL);
+        } catch (IOException e) {
+            throw new ChannelException(e);


- Revert wildcard imports - Correct system property names (not netty5) - Log on failure to set IP_MULTICAST_ALL when constructing datagram channels.

…pollDatagramChannel.java

…g/IoUringDatagramChannel.java

normanmaurer · 2025-11-13T16:12:42Z

@mahoestar thanks a lot!

mahoestar changed the title ~~feat: support for IP_MULTICAST_ALL for epoll (netty 4.2)~~ Add support for IP_MULTICAST_ALL to EpollDatagramChannel (netty 4.2) Oct 15, 2025

normanmaurer requested changes Oct 15, 2025

View reviewed changes

fix: correct netty prefix for epoll_linuxsocket multicast all methods

0381148

normanmaurer added this to the 4.2.8.Final milestone Oct 16, 2025

mahoestar added 3 commits November 7, 2025 14:02

feat: add IP_MULTICAST_ALL support for io uring

a444c66

Adds support for the IP_MULTICAST_ALL socket option for io uring.

fix: add IP_MULTICAST_ALL to getOptions for EpollDatagramChannelConfi…

05478ef

…g and IoUringDatagramChannelConfig

feat: automatically disable IP_MULTICAST_ALL for epoll and io uring d…

52f4f7c

…atagram channels

mahoestar changed the title ~~Add support for IP_MULTICAST_ALL to EpollDatagramChannel (netty 4.2)~~ Add support for IP_MULTICAST_ALL to EpollDatagramChannel and IOUringDatagramChannel (netty 4.2) Nov 7, 2025

mahoestar requested a review from normanmaurer November 7, 2025 14:26

normanmaurer reviewed Nov 7, 2025

View reviewed changes

normanmaurer requested changes Nov 7, 2025

View reviewed changes

fix: address IP_MULTICAST_ALL review comments

ec9b42a

- Revert wildcard imports - Correct system property names (not netty5) - Log on failure to set IP_MULTICAST_ALL when constructing datagram channels.

normanmaurer requested changes Nov 10, 2025

View reviewed changes

Comment thread transport-classes-epoll/src/main/java/io/netty/channel/epoll/EpollDatagramChannel.java Outdated

Comment thread transport-classes-io_uring/src/main/java/io/netty/channel/uring/IoUringDatagramChannel.java Outdated

Apply suggestions from code review

821796c

normanmaurer reviewed Nov 13, 2025

View reviewed changes

Comment thread transport-classes-epoll/src/main/java/io/netty/channel/epoll/EpollDatagramChannel.java Outdated

Comment thread transport-classes-io_uring/src/main/java/io/netty/channel/uring/IoUringDatagramChannel.java Outdated

Apply suggestion from @normanmaurer

18605c9

Apply suggestion from @normanmaurer

1e9856b

normanmaurer requested changes Nov 13, 2025

View reviewed changes

normanmaurer added 6 commits November 13, 2025 13:59

Update transport-classes-epoll/src/main/java/io/netty/channel/epoll/E…

6ae4338

…pollDatagramChannel.java

Update transport-classes-epoll/src/main/java/io/netty/channel/epoll/E…

9b4d336

…pollDatagramChannel.java

Update transport-classes-epoll/src/main/java/io/netty/channel/epoll/E…

17ab172

…pollDatagramChannel.java

Update transport-classes-io_uring/src/main/java/io/netty/channel/urin…

cbe3366

…g/IoUringDatagramChannel.java

Update transport-classes-io_uring/src/main/java/io/netty/channel/urin…

d8b71f7

…g/IoUringDatagramChannel.java

Update transport-classes-io_uring/src/main/java/io/netty/channel/urin…

f2e3f95

…g/IoUringDatagramChannel.java

normanmaurer merged commit 7759a07 into netty:4.2 Nov 13, 2025
16 of 19 checks passed

mahoestar deleted the feat-IP_MULTICAST_ALL branch November 21, 2025 15:53

tomdcc mentioned this pull request Feb 4, 2026

Attempting to set IPV6_MULTICAST_ALL socket option on older linux kernels breaks IPV6 support #16225

Closed

	SystemPropertyUtil.getBoolean("io.netty5.transport.linux.ipMulticastAll", false);
	SystemPropertyUtil.getBoolean("io.netty.transport.linux.ipMulticastAll", false);

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