From f2c2e5b0bf9def01b10651b9802fa38d07d9d265 Mon Sep 17 00:00:00 2001
From: Pouria Mousavizadeh Tehrani <pouria@FreeBSD.org>
Date: Fri, 13 Feb 2026 02:36:15 +0330
Subject: [PATCH] multicast.4: Fix disabling multicast forwarding

Reviewed by: markj, glebius
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D55266
---
 share/man/man4/multicast.4 | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/share/man/man4/multicast.4 b/share/man/man4/multicast.4
index aa3293e107e..84c6c5c4199 100644
--- a/share/man/man4/multicast.4
+++ b/share/man/man4/multicast.4
@@ -23,7 +23,7 @@
 .\" FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 .\" DEALINGS IN THE SOFTWARE.
 .\"
-.Dd May 27, 2009
+.Dd February 13, 2026
 .Dt MULTICAST 4
 .Os
 .\"
@@ -124,15 +124,15 @@ Therefore, for portability reason the multicast
 routing socket should be reused for IGMP and MLD messages as well.
 .Pp
 After the multicast routing socket is open, it can be used to enable
-or disable multicast forwarding in the kernel:
+multicast forwarding in the kernel:
 .Bd -literal
 /* IPv4 */
-int v = 1;        /* 1 to enable, or 0 to disable */
+int v = 1;
 setsockopt(mrouter_s4, IPPROTO_IP, MRT_INIT, (void *)&v, sizeof(v));
 .Ed
 .Bd -literal
 /* IPv6 */
-int v = 1;        /* 1 to enable, or 0 to disable */
+int v = 1;
 setsockopt(mrouter_s6, IPPROTO_IPV6, MRT6_INIT, (void *)&v, sizeof(v));
 \&...
 /* If necessary, filter all ICMPv6 messages */
@@ -142,6 +142,24 @@ setsockopt(mrouter_s6, IPPROTO_ICMPV6, ICMP6_FILTER, (void *)&filter,
            sizeof(filter));
 .Ed
 .Pp
+When applied to the multicast routing socket, the
+.Dv MRT_DONE
+and
+.Dv MRT6_DONE
+socket options disable multicast forwarding in the kernel:
+.Bd -literal
+/* IPv4 */
+int v = 1;
+setsockopt(mrouter_s4, IPPROTO_IP, MRT_DONE, (void *)&v, sizeof(v));
+.Ed
+.Bd -literal
+/* IPv6 */
+int v = 1;
+setsockopt(mrouter_s6, IPPROTO_IPV6, MRT6_DONE, (void *)&v, sizeof(v));
+.Ed
+.Pp
+Closing the socket has the same effect.
+.Pp
 After multicast forwarding is enabled, the multicast routing socket
 can be used to enable PIM processing in the kernel if we are running PIM-SM or
 PIM-DM