tcp: set net.inet.tcp.nolocaltimewait to 0 and deprecate it

Set the default value of the sysctl-variable
net.inet.tcp.nolocaltimewait to 0. This will make the behavior
compliant with RFC 9293.
Furthermore document that using the sysctl-variable is deprecated
and will be removed in FreeBSD 16.

Reviewed by:		glebius, Peter Lei
Relnotes:		yes
Sponsored by:		Netflix, Inc.
Differential Revision:	https://reviews.freebsd.org/D5106

2 files changed, 31 insertions, 7 deletions

diff --git a/share/man/man4/tcp.4 b/share/man/man4/tcp.4
index f19b6cb2ae14..fcfda42908d8 100644
--- a/share/man/man4/tcp.4
+++ b/share/man/man4/tcp.4
@@ -31,7 +31,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd June 26, 2025
+.Dd June 27, 2025
 .Dt TCP 4
 .Os
 .Sh NAME
@@ -785,8 +785,8 @@ The Maximum Segment Lifetime, in milliseconds, for a packet when both endpoints
 are local.
 .Va msl_local
 is only used if
-.Va nolocaltimewait
-is zero.
+.Va nolocaltimewait ,
+which is deprecated, is zero.
 .It Va mssdflt
 The default value used for the TCP Maximum Segment Size
 .Pq Dq MSS
@@ -798,10 +798,16 @@ application limited and the network bandwidth is not utilized completely.
 That prevents self-inflicted packet losses once the application starts to
 transmit data at a higher speed.
 .It Va nolocaltimewait
-Suppress creation of TCP
+Suppress the creation of TCP
 .Dv TIME_WAIT
 states for connections in
 which both endpoints are local.
+The default is 0.
+.Va nolocaltimewait
+is deprecated and will be removed in
+.Fx 16 .
+.Va msl_local
+can be used instead.
 .It Va path_mtu_discovery
 Enable Path MTU Discovery.
 .It Va pcbcount
diff --git a/sys/netinet/tcp_timewait.c b/sys/netinet/tcp_timewait.c
index 08673ddd1152..7c6c55909215 100644
--- a/sys/netinet/tcp_timewait.c
+++ b/sys/netinet/tcp_timewait.c
@@ -87,10 +87,28 @@
 
 #include <security/mac/mac_framework.h>
 
-VNET_DEFINE_STATIC(bool, nolocaltimewait) = true;
+VNET_DEFINE_STATIC(bool, nolocaltimewait) = false;
 #define	V_nolocaltimewait	VNET(nolocaltimewait)
-SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, nolocaltimewait,
-    CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(nolocaltimewait), 0,
+
+static int
+sysctl_net_inet_tcp_nolocaltimewait(SYSCTL_HANDLER_ARGS)
+{
+	int error;
+	bool new;
+
+	new = V_nolocaltimewait;
+	error = sysctl_handle_bool(oidp, &new, 0, req);
+	if (error == 0 && req->newptr) {
+		V_nolocaltimewait = new;
+		gone_in(16, "net.inet.tcp.nolocaltimewait is obsolete."
+		    " Use net.inet.tcp.local_msl instead.\n");
+	}
+	return (error);
+}
+
+SYSCTL_PROC(_net_inet_tcp, OID_AUTO, nolocaltimewait,
+    CTLFLAG_VNET | CTLFLAG_RW | CTLTYPE_U8,
+    &VNET_NAME(nolocaltimewait), 0, sysctl_net_inet_tcp_nolocaltimewait, "CU",
     "Do not create TCP TIME_WAIT state for local connections");
 
 static u_int