diff --git a/tests/sys/net/Makefile b/tests/sys/net/Makefile
index 7340688286cc..ca50f6cbcd76 100644
--- a/tests/sys/net/Makefile
+++ b/tests/sys/net/Makefile
@@ -1,34 +1,35 @@
 # $FreeBSD$
 
 PACKAGE=	tests
 
 TESTSDIR=	${TESTSBASE}/sys/net
 BINDIR=		${TESTSDIR}
 
 ATF_TESTS_C+=	if_epair
 ATF_TESTS_SH+=	if_bridge_test
 ATF_TESTS_SH+=	if_clone_test
 ATF_TESTS_SH+=	if_gif
 ATF_TESTS_SH+=	if_lagg_test
+ATF_TESTS_SH+=	if_stf
 ATF_TESTS_SH+=	if_tun_test
 ATF_TESTS_SH+=	if_vlan
 
 # The tests are written to be run in parallel, but doing so leads to random
 # panics.  I think it's because the kernel's list of interfaces isn't properly
 # locked.
 TEST_METADATA+=	is_exclusive=true
 
 ${PACKAGE}FILES+=	\
 		dhclient_pcp.conf \
 		pcp.py \
 		stp.py
 
 ${PACKAGE}FILESMODE_pcp.py=		0555
 ${PACKAGE}FILESMODE_stp.py=		0555
 
 MAN=
 PROGS+=		randsleep
 
 WARNS?=		6
 
 .include <bsd.test.mk>
diff --git a/tests/sys/net/if_stf.sh b/tests/sys/net/if_stf.sh
new file mode 100644
index 000000000000..af53f7bdb5dd
--- /dev/null
+++ b/tests/sys/net/if_stf.sh
@@ -0,0 +1,84 @@
+# $FreeBSD$
+#
+# SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+#
+# Copyright (c) 2021 Rubicon Communications, LLC (Netgate)
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+
+. $(atf_get_srcdir)/../common/vnet.subr
+
+atf_test_case "6to4" "cleanup"
+6to4_head()
+{
+	atf_set descr 'Test 6to4'
+	atf_set require.user root
+}
+
+6to4_body()
+{
+	vnet_init
+	if ! kldstat -q -m if_stf; then
+		atf_skip "This test requires if_stf"
+	fi
+	if ! kldstat -q -m if_gif; then
+		atf_skip "This test requires if_stf"
+	fi
+
+	epair=$(vnet_mkepair)
+
+	vnet_mkjail relay ${epair}a
+	jexec relay ifconfig lo0 inet6 2001:db8::1/64 up
+	jexec relay ifconfig ${epair}a 192.0.2.1/24 up
+	# Simple gif to terminate 6to4
+	gif=$(jexec relay ifconfig gif create)
+	jexec relay ifconfig $gif inet6 2002:c000:0201::1/64 up no_dad
+	jexec relay ifconfig $gif tunnel 192.0.2.1 192.0.2.2
+	jexec relay route -6 add default -interface $gif
+
+	vnet_mkjail client ${epair}b
+	jexec client ifconfig ${epair}b 192.0.2.2/24 up
+	stf=$(jexec client ifconfig stf create)
+	jexec client ifconfig $stf inet6 2002:c000:0202::1/32 up no_dad
+	jexec client route -6 add default 2002:c000:0201::1
+
+	# Sanity check
+	atf_check -s exit:0 -o ignore \
+	    jexec client ping -c 1 192.0.2.1
+	# 6to4 direct
+	atf_check -s exit:0 -o ignore \
+	    jexec client ping6 -c 1 2002:c000:0201::1
+
+	# "Wider internet"
+	atf_check -s exit:0 -o ignore \
+	    jexec client ping6 -c 1 2001:db8::1
+}
+
+6to4_cleanup()
+{
+	vnet_cleanup
+}
+
+atf_init_test_cases()
+{
+	atf_add_test_case "6to4"
+}