net: sockets: IPv6_MULTICAST_LOOP Support

Add support for the IPV6_MULTICAST_LOOP socket option.
This option allows enabling or disabling the consumption of multicast
packets by the sender. By default, the socket option will be enabled.

Co-authored-by: Pieter De Gendt <pieter.degendt@gmail.com>

Signed-off-by: Sayooj K Karun <sayooj@aerlync.com>

Author: sayoojkkarun

include/zephyr/net/net_context.h

@@ -7,6 +7,7 @@
 /*
  * Copyright (c) 2016 Intel Corporation
  * Copyright (c) 2021 Nordic Semiconductor
+ * Copyright (c) 2025 Aerlync Labs Inc.
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -390,6 +391,10 @@ __net_socket struct net_context {
 			 */
 			uint8_t ipv4_mcast_ifindex;
 		};
+		/** Flag to enable/disable multicast loop */
+		union {
+			bool ipv6_mcast_loop;  /**< IPv6 multicast loop */
+		};
 #endif /* CONFIG_NET_IPV6 || CONFIG_NET_IPV4 */
 
 #if defined(CONFIG_NET_CONTEXT_TIMESTAMPING)
@@ -897,6 +902,40 @@ static inline void net_context_set_ipv6_mcast_hop_limit(struct net_context *cont
 	context->ipv6_mcast_hop_limit = hop_limit;
 }
 
+#if defined(CONFIG_NET_IPV6)
+
+/**
+ * @brief Get IPv6 multicast loop value for this context.
+ *
+ * @details This function returns the IPv6 multicast loop value
+ *          that is set to this context.
+ *
+ * @param context Network context.
+ *
+ * @return IPv6 multicast loop value
+ */
+static inline bool net_context_get_ipv6_mcast_loop(struct net_context *context)
+{
+	return context->options.ipv6_mcast_loop;
+}
+
+/**
+ * @brief Set IPv6 multicast loop value for this context.
+ *
+ * @details This function sets the IPv6 multicast loop value for
+ *          this context.
+ *
+ * @param context Network context.
+ * @param ipv6_mcast_loop IPv6 multicast loop value.
+ */
+static inline void net_context_set_ipv6_mcast_loop(struct net_context *context,
+						   bool ipv6_mcast_loop)
+{
+	context->options.ipv6_mcast_loop = ipv6_mcast_loop;
+}
+
+#endif
+
 /**
  * @brief Enable or disable socks proxy support for this context.
  *
@@ -1325,6 +1364,7 @@ enum net_context_option {
 	NET_OPT_MCAST_IFINDEX     = 19, /**< IPv6 multicast output network interface index */
 	NET_OPT_MTU               = 20, /**< IPv4 socket path MTU */
 	NET_OPT_LOCAL_PORT_RANGE  = 21, /**< Clamp local port range */
+	NET_OPT_IPV6_MCAST_LOOP	  = 22, /**< IPV6 multicast loop */
 };
 
 /**

include/zephyr/net/socket.h

@@ -8,6 +8,7 @@
 /*
  * Copyright (c) 2017-2018 Linaro Limited
  * Copyright (c) 2021 Nordic Semiconductor
+ * Copyright (c) 2025 Aerlync Labs Inc.
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -1005,6 +1006,9 @@ struct ip_mreq  {
 /** Set the multicast hop limit for the socket. */
 #define IPV6_MULTICAST_HOPS 18
 
+/** Set the multicast loop bit for the socket. */
+#define IPV6_MULTICAST_LOOP 19
+
 /** Join IPv6 multicast group. */
 #define IPV6_ADD_MEMBERSHIP 20
 

subsys/net/ip/Kconfig.ipv6

@@ -1,6 +1,7 @@
 # IPv6 Options
 
 # Copyright (c) 2016 Intel Corporation.
+# Copyright (c) 2025 Aerlync Labs Inc.
 # SPDX-License-Identifier: Apache-2.0
 
 menuconfig NET_IPV6
@@ -81,6 +82,13 @@ config NET_INITIAL_MCAST_HOP_LIMIT
 	  don't leave the local network unless the application explicitly
 	  requests it.
 
+config NET_INITIAL_IPV6_MCAST_LOOP
+	bool "Control whether the socket sees multicast packets sent by itself"
+	default y
+	help
+	  Assign initial value to IPV6_MULTICAST_LOOP in socket options,
+	  if not set by the user using setsockopt().
+
 config NET_IPV6_MAX_NEIGHBORS
 	int "How many IPv6 neighbors are supported"
 	default 8

subsys/net/ip/net_context.c

@@ -7,6 +7,7 @@
 /*
  * Copyright (c) 2016 Intel Corporation
  * Copyright (c) 2021 Nordic Semiconductor
+ * Copyright (c) 2025 Aerlync Labs Inc.
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -583,6 +584,10 @@ int net_context_get(sa_family_t family, enum net_sock_type type, uint16_t proto,
 
 				contexts[i].ipv6_hop_limit = INITIAL_HOP_LIMIT;
 				contexts[i].ipv6_mcast_hop_limit = INITIAL_MCAST_HOP_LIMIT;
+#if defined(CONFIG_NET_IPV6)
+				contexts[i].options.ipv6_mcast_loop =
+					IS_ENABLED(CONFIG_NET_INITIAL_IPV6_MCAST_LOOP);
+#endif
 			}
 			if (IS_ENABLED(CONFIG_NET_IPV4) && family == AF_INET) {
 				struct sockaddr_in *addr = (struct sockaddr_in *)&contexts[i].local;
@@ -2033,6 +2038,20 @@ static int get_context_local_port_range(struct net_context *context,
 #endif
 }
 
+static int get_context_ipv6_mcast_loop(struct net_context *context,
+				       void *value, size_t *len)
+{
+#if defined(CONFIG_NET_IPV6)
+	return get_bool_option(context->options.ipv6_mcast_loop, value, len);
+#else
+	ARG_UNUSED(context);
+	ARG_UNUSED(value);
+	ARG_UNUSED(len);
+
+	return -ENOTSUP;
+#endif
+}
+
 /* If buf is not NULL, then use it. Otherwise read the data to be written
  * to net_pkt from msghdr.
  */
@@ -3329,6 +3348,20 @@ static int set_context_unicast_hop_limit(struct net_context *context,
 #endif
 }
 
+static int set_context_ipv6_mcast_loop(struct net_context *context,
+				       const void *value, size_t len)
+{
+#if defined(CONFIG_NET_IPV6)
+	return set_bool_option(&context->options.ipv6_mcast_loop, value, len);
+#else
+	ARG_UNUSED(context);
+	ARG_UNUSED(value);
+	ARG_UNUSED(len);
+
+	return -ENOTSUP;
+#endif
+}
+
 static int set_context_reuseaddr(struct net_context *context,
 				 const void *value, size_t len)
 {
@@ -3652,6 +3685,9 @@ int net_context_set_option(struct net_context *context,
 	case NET_OPT_LOCAL_PORT_RANGE:
 		ret = set_context_local_port_range(context, value, len);
 		break;
+	case NET_OPT_IPV6_MCAST_LOOP:
+		ret = set_context_ipv6_mcast_loop(context, value, len);
+		break;
 	}
 
 	k_mutex_unlock(&context->lock);
@@ -3737,6 +3773,9 @@ int net_context_get_option(struct net_context *context,
 	case NET_OPT_LOCAL_PORT_RANGE:
 		ret = get_context_local_port_range(context, value, len);
 		break;
+	case NET_OPT_IPV6_MCAST_LOOP:
+		ret = get_context_ipv6_mcast_loop(context, value, len);
+		break;
 	}
 
 	k_mutex_unlock(&context->lock);

subsys/net/ip/net_core.c

@@ -7,6 +7,7 @@
 
 /*
  * Copyright (c) 2016 Intel Corporation
+ * Copyright (c) 2025 Aerlync Labs Inc.
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -409,6 +410,30 @@ int net_try_send_data(struct net_pkt *pkt, k_timeout_t timeout)
 		goto err;
 	}
 
+#if defined(CONFIG_NET_IPV6)
+	if (net_pkt_family(pkt) == AF_INET6) {
+		const struct in6_addr *dest = (const struct in6_addr *)&NET_IPV6_HDR(pkt)->dst;
+		struct net_context *ctx = net_pkt_context(pkt);
+
+		if (net_ipv6_is_addr_mcast(dest) && ctx != NULL &&
+		    net_context_get_ipv6_mcast_loop(ctx)) {
+			struct net_pkt *clone = net_pkt_clone(pkt, K_NO_WAIT);
+
+			if (clone != NULL) {
+				net_pkt_set_iface(clone, net_pkt_iface(pkt));
+				if (net_recv_data(net_pkt_iface(clone), clone) < 0) {
+					if (IS_ENABLED(CONFIG_NET_STATISTICS)) {
+						net_stats_update_ipv6_drop(net_pkt_iface(pkt));
+					}
+					net_pkt_unref(clone);
+				}
+			} else {
+				NET_DBG("Failed to clone multicast packet");
+			}
+		}
+	}
+#endif
+
 	if (net_if_try_send_data(net_pkt_iface(pkt), pkt, timeout) == NET_DROP) {
 		ret = -EIO;
 		goto err;

subsys/net/lib/sockets/sockets_inet.c

@@ -2,6 +2,7 @@
  * Copyright (c) 2017 Linaro Limited
  * Copyright (c) 2021 Nordic Semiconductor
  * Copyright (c) 2023 Arm Limited (or its affiliates). All rights reserved.
+ * Copyright (c) 2025 Aerlync Labs Inc.
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -2080,6 +2081,18 @@ int zsock_getsockopt_ctx(struct net_context *ctx, int level, int optname,
 			}
 
 			return 0;
+
+		case IPV6_MULTICAST_LOOP:
+			ret = net_context_get_option(ctx,
+						     NET_OPT_IPV6_MCAST_LOOP,
+						     optval, optlen);
+			if (ret < 0) {
+				errno = -ret;
+				return -1;
+			}
+
+			return 0;
+
 		}
 
 		break;
@@ -2722,6 +2735,17 @@ int zsock_setsockopt_ctx(struct net_context *ctx, int level, int optname,
 			}
 
 			break;
+
+		case IPV6_MULTICAST_LOOP:
+			ret = net_context_set_option(ctx,
+						     NET_OPT_IPV6_MCAST_LOOP,
+						     optval, optlen);
+			if (ret < 0) {
+				errno = -ret;
+				return -1;
+			}
+
+			return 0;
 		}
 
 		break;