From f28c804969c91e572249211c9f0e9239c777f4f2 Mon Sep 17 00:00:00 2001
From: matt7aylor <matt+github@dingus.me.uk>
Date: Fri, 28 Nov 2025 05:14:35 +0000
Subject: [PATCH] Fixed ipv6 destination port and multicast interface issues.
 (#1161)

---
 apps/router-ipv6/main.c |  5 +++--
 ports/linux/bip6.c      | 12 ++++++++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/apps/router-ipv6/main.c b/apps/router-ipv6/main.c
index 0ef3b854..6d764951 100644
--- a/apps/router-ipv6/main.c
+++ b/apps/router-ipv6/main.c
@@ -1037,10 +1037,11 @@ static void datalink_init(void)
     }
     pEnv = getenv("BACNET_BIP6_BROADCAST");
     if (pEnv) {
-        BACNET_IP6_ADDRESS addr;
+        BACNET_IP6_ADDRESS addr = { 0 };
         bvlc6_address_set(
-            &addr, (uint16_t)strtol(pEnv, NULL, 0), 0, 0, 0, 0, 0, 0,
+            &addr, (uint16_t)strtol(pEnv, NULL, 16), 0, 0, 0, 0, 0, 0,
             BIP6_MULTICAST_GROUP_ID);
+        addr.port = bip6_get_port();
         bip6_set_broadcast_addr(&addr);
     }
     if (!bip6_init(getenv("BACNET_BIP6_IFACE"))) {
diff --git a/ports/linux/bip6.c b/ports/linux/bip6.c
index c13b3b6b..e6f9faf9 100644
--- a/ports/linux/bip6.c
+++ b/ports/linux/bip6.c
@@ -484,12 +484,24 @@ bool bip6_init(char *ifname)
         bvlc6_address_set(
             &BIP6_Broadcast_Addr, BIP6_MULTICAST_SITE_LOCAL, 0, 0, 0, 0, 0, 0,
             BIP6_MULTICAST_GROUP_ID);
+        BIP6_Broadcast_Addr.port = BIP6_Addr.port;
     }
     /* assumes that the driver has already been initialized */
     BIP6_Socket = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);
     if (BIP6_Socket < 0) {
         return false;
     }
+
+    if (BIP6_Socket_Scope_Id > 0) {
+        unsigned int idx = BIP6_Socket_Scope_Id;
+        /* Explicitly set the interface for OUTGOING multicast packets */
+        status = setsockopt(
+            BIP6_Socket, IPPROTO_IPV6, IPV6_MULTICAST_IF, &idx, sizeof(idx));
+        if (status < 0) {
+            debug_perror("BIP6: setsockopt(IPV6_MULTICAST_IF)");
+        }
+    }
+
     /* Allow us to use the same socket for sending and receiving */
     /* This makes sure that the src port is correct when sending */
     sockopt = 1;