diff --git a/tools/testing/selftests/net/forwarding/ip6gre_flat.sh b/tools/testing/selftests/net/forwarding/ip6gre_flat.sh
new file mode 100755
index 000000000000..96c97064f2d3
--- /dev/null
+++ b/tools/testing/selftests/net/forwarding/ip6gre_flat.sh
@@ -0,0 +1,65 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# Test IP-in-IP GRE tunnel without key.
+# This test uses flat topology for IP tunneling tests. See ip6gre_lib.sh for
+# more details.
+
+ALL_TESTS="
+	gre_flat
+	gre_mtu_change
+"
+
+NUM_NETIFS=6
+source lib.sh
+source ip6gre_lib.sh
+
+setup_prepare()
+{
+	h1=${NETIFS[p1]}
+	ol1=${NETIFS[p2]}
+
+	ul1=${NETIFS[p3]}
+	ul2=${NETIFS[p4]}
+
+	ol2=${NETIFS[p5]}
+	h2=${NETIFS[p6]}
+
+	forwarding_enable
+	vrf_prepare
+	h1_create
+	h2_create
+	sw1_flat_create $ol1 $ul1
+	sw2_flat_create $ol2 $ul2
+}
+
+gre_flat()
+{
+	test_traffic_ip4ip6 "GRE flat IPv4-in-IPv6"
+	test_traffic_ip6ip6 "GRE flat IPv6-in-IPv6"
+}
+
+gre_mtu_change()
+{
+	test_mtu_change
+}
+
+cleanup()
+{
+	pre_cleanup
+
+	sw2_flat_destroy $ol2 $ul2
+	sw1_flat_destroy $ol1 $ul1
+	h2_destroy
+	h1_destroy
+	vrf_cleanup
+	forwarding_restore
+}
+
+trap cleanup EXIT
+
+setup_prepare
+setup_wait
+tests_run
+
+exit $EXIT_STATUS
diff --git a/tools/testing/selftests/net/forwarding/ip6gre_flat_key.sh b/tools/testing/selftests/net/forwarding/ip6gre_flat_key.sh
new file mode 100755
index 000000000000..ff9fb0db9bd1
--- /dev/null
+++ b/tools/testing/selftests/net/forwarding/ip6gre_flat_key.sh
@@ -0,0 +1,65 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# Test IP-in-IP GRE tunnel with key.
+# This test uses flat topology for IP tunneling tests. See ip6gre_lib.sh for
+# more details.
+
+ALL_TESTS="
+	gre_flat
+	gre_mtu_change
+"
+
+NUM_NETIFS=6
+source lib.sh
+source ip6gre_lib.sh
+
+setup_prepare()
+{
+	h1=${NETIFS[p1]}
+	ol1=${NETIFS[p2]}
+
+	ul1=${NETIFS[p3]}
+	ul2=${NETIFS[p4]}
+
+	ol2=${NETIFS[p5]}
+	h2=${NETIFS[p6]}
+
+	forwarding_enable
+	vrf_prepare
+	h1_create
+	h2_create
+	sw1_flat_create $ol1 $ul1 key 233
+	sw2_flat_create $ol2 $ul2 key 233
+}
+
+gre_flat()
+{
+	test_traffic_ip4ip6 "GRE flat IPv4-in-IPv6 with key"
+	test_traffic_ip6ip6 "GRE flat IPv6-in-IPv6 with key"
+}
+
+gre_mtu_change()
+{
+	test_mtu_change
+}
+
+cleanup()
+{
+	pre_cleanup
+
+	sw2_flat_destroy $ol2 $ul2
+	sw1_flat_destroy $ol1 $ul1
+	h2_destroy
+	h1_destroy
+	vrf_cleanup
+	forwarding_restore
+}
+
+trap cleanup EXIT
+
+setup_prepare
+setup_wait
+tests_run
+
+exit $EXIT_STATUS
diff --git a/tools/testing/selftests/net/forwarding/ip6gre_flat_keys.sh b/tools/testing/selftests/net/forwarding/ip6gre_flat_keys.sh
new file mode 100755
index 000000000000..12c138785242
--- /dev/null
+++ b/tools/testing/selftests/net/forwarding/ip6gre_flat_keys.sh
@@ -0,0 +1,65 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# Test IP-in-IP GRE tunnel with keys.
+# This test uses flat topology for IP tunneling tests. See ip6gre_lib.sh for
+# more details.
+
+ALL_TESTS="
+	gre_flat
+	gre_mtu_change
+"
+
+NUM_NETIFS=6
+source lib.sh
+source ip6gre_lib.sh
+
+setup_prepare()
+{
+	h1=${NETIFS[p1]}
+	ol1=${NETIFS[p2]}
+
+	ul1=${NETIFS[p3]}
+	ul2=${NETIFS[p4]}
+
+	ol2=${NETIFS[p5]}
+	h2=${NETIFS[p6]}
+
+	forwarding_enable
+	vrf_prepare
+	h1_create
+	h2_create
+	sw1_flat_create $ol1 $ul1 ikey 111 okey 222
+	sw2_flat_create $ol2 $ul2 ikey 222 okey 111
+}
+
+gre_flat()
+{
+	test_traffic_ip4ip6 "GRE flat IPv4-in-IPv6 with ikey/okey"
+	test_traffic_ip6ip6 "GRE flat IPv6-in-IPv6 with ikey/okey"
+}
+
+gre_mtu_change()
+{
+	test_mtu_change	gre
+}
+
+cleanup()
+{
+	pre_cleanup
+
+	sw2_flat_destroy $ol2 $ul2
+	sw1_flat_destroy $ol1 $ul1
+	h2_destroy
+	h1_destroy
+	vrf_cleanup
+	forwarding_restore
+}
+
+trap cleanup EXIT
+
+setup_prepare
+setup_wait
+tests_run
+
+exit $EXIT_STATUS
diff --git a/tools/testing/selftests/net/forwarding/ip6gre_lib.sh b/tools/testing/selftests/net/forwarding/ip6gre_lib.sh
new file mode 100644
index 000000000000..2a5b2126b674
--- /dev/null
+++ b/tools/testing/selftests/net/forwarding/ip6gre_lib.sh
@@ -0,0 +1,270 @@
+# SPDX-License-Identifier: GPL-2.0
+#!/bin/bash
+
+# Handles creation and destruction of IP-in-IP or GRE tunnels over the given
+# topology.
+#
+# Flat Model:
+# Overlay and underlay share the same VRF.
+# SW1 uses default VRF so tunnel has no bound dev.
+# SW2 uses non-default VRF tunnel has a bound dev.
+# +--------------------------------+
+# | H1                             |
+# |                     $h1 +      |
+# |        198.51.100.1/24  |      |
+# |        2001:db8:1::1/64 |      |
+# +-------------------------|------+
+#                           |
+# +-------------------------|-------------------+
+# | SW1                     |                   |
+# |                    $ol1 +                   |
+# |        198.51.100.2/24                      |
+# |        2001:db8:1::2/64                     |
+# |                                             |
+# |      + g1a (ip6gre)                         |
+# |        loc=2001:db8:3::1                    |
+# |        rem=2001:db8:3::2 --.                |
+# |        tos=inherit         |                |
+# |                            .                |
+# |      .---------------------                 |
+# |      |                                      |
+# |      v                                      |
+# |      + $ul1.111 (vlan)                      |
+# |      | 2001:db8:10::1/64                    |
+# |       \                                     |
+# |        \____________                        |
+# |                     |                       |
+# | VRF default         + $ul1                  |
+# +---------------------|-----------------------+
+#                       |
+# +---------------------|-----------------------+
+# | SW2                 |                       |
+# |                $ul2 +                       |
+# |          ___________|                       |
+# |         /                                   |
+# |        /                                    |
+# |       + $ul2.111 (vlan)                     |
+# |       ^ 2001:db8:10::2/64                   |
+# |       |                                     |
+# |       |                                     |
+# |       '----------------------.              |
+# |       + g2a (ip6gre)         |              |
+# |         loc=2001:db8:3::2    |              |
+# |         rem=2001:db8:3::1  --'              |
+# |         tos=inherit                         |
+# |                                             |
+# |                     + $ol2                  |
+# |                     | 203.0.113.2/24        |
+# | VRF v$ol2           | 2001:db8:2::2/64      |
+# +---------------------|-----------------------+
+# +---------------------|----------+
+# | H2                  |          |
+# |                 $h2 +          |
+# |    203.0.113.1/24              |
+# |    2001:db8:2::1/64            |
+# +--------------------------------+
+
+source lib.sh
+source tc_common.sh
+
+h1_create()
+{
+	simple_if_init $h1 198.51.100.1/24 2001:db8:1::1/64
+	ip route add vrf v$h1 203.0.113.0/24 via 198.51.100.2
+	ip -6 route add vrf v$h1 2001:db8:2::/64 via 2001:db8:1::2
+}
+
+h1_destroy()
+{
+	ip -6 route del vrf v$h1 2001:db8:2::/64 via 2001:db8:1::2
+	ip route del vrf v$h1 203.0.113.0/24 via 198.51.100.2
+	simple_if_fini $h1 198.51.100.1/24 2001:db8:1::1/64
+}
+
+h2_create()
+{
+	simple_if_init $h2 203.0.113.1/24 2001:db8:2::1/64
+	ip route add vrf v$h2 198.51.100.0/24 via 203.0.113.2
+	ip -6 route add vrf v$h2 2001:db8:1::/64 via 2001:db8:2::2
+}
+
+h2_destroy()
+{
+	ip -6 route del vrf v$h2 2001:db8:1::/64 via 2001:db8:2::2
+	ip route del vrf v$h2 198.51.100.0/24 via 203.0.113.2
+	simple_if_fini $h2 203.0.113.1/24 2001:db8:2::1/64
+}
+
+sw1_flat_create()
+{
+	local ol1=$1; shift
+	local ul1=$1; shift
+
+	ip link set dev $ol1 up
+        __addr_add_del $ol1 add 198.51.100.2/24 2001:db8:1::2/64
+
+	ip link set dev $ul1 up
+	vlan_create $ul1 111 "" 2001:db8:10::1/64
+
+	tunnel_create g1a ip6gre 2001:db8:3::1 2001:db8:3::2 tos inherit \
+		ttl inherit "$@"
+	ip link set dev g1a up
+        __addr_add_del g1a add "2001:db8:3::1/128"
+
+	ip -6 route add 2001:db8:3::2/128 via 2001:db8:10::2
+	ip route add 203.0.113.0/24 dev g1a
+	ip -6 route add 2001:db8:2::/64 dev g1a
+}
+
+sw1_flat_destroy()
+{
+	local ol1=$1; shift
+	local ul1=$1; shift
+
+	ip -6 route del 2001:db8:2::/64
+	ip route del 203.0.113.0/24
+	ip -6 route del 2001:db8:3::2/128 via 2001:db8:10::2
+
+	__simple_if_fini g1a 2001:db8:3::1/128
+	tunnel_destroy g1a
+
+	vlan_destroy $ul1 111
+	__simple_if_fini $ul1
+	__simple_if_fini $ol1 198.51.100.2/24 2001:db8:1::2/64
+}
+
+sw2_flat_create()
+{
+	local ol2=$1; shift
+	local ul2=$1; shift
+
+	simple_if_init $ol2 203.0.113.2/24 2001:db8:2::2/64
+	__simple_if_init $ul2 v$ol2
+	vlan_create $ul2 111 v$ol2 2001:db8:10::2/64
+
+	tunnel_create g2a ip6gre 2001:db8:3::2 2001:db8:3::1 tos inherit \
+		ttl inherit dev v$ol2 "$@"
+	__simple_if_init g2a v$ol2 2001:db8:3::2/128
+
+	# Replace neighbor to avoid 1 dropped packet due to "unresolved neigh"
+	ip neigh replace dev $ol2 203.0.113.1 lladdr $(mac_get $h2)
+	ip -6 neigh replace dev $ol2 2001:db8:2::1 lladdr $(mac_get $h2)
+
+	ip -6 route add vrf v$ol2 2001:db8:3::1/128 via 2001:db8:10::1
+	ip route add vrf v$ol2 198.51.100.0/24 dev g2a
+	ip -6 route add vrf v$ol2 2001:db8:1::/64 dev g2a
+}
+
+sw2_flat_destroy()
+{
+	local ol2=$1; shift
+	local ul2=$1; shift
+
+	ip -6 route del vrf v$ol2 2001:db8:2::/64
+	ip route del vrf v$ol2 198.51.100.0/24
+	ip -6 route del vrf v$ol2 2001:db8:3::1/128 via 2001:db8:10::1
+
+	__simple_if_fini g2a 2001:db8:3::2/128
+	tunnel_destroy g2a
+
+	vlan_destroy $ul2 111
+	__simple_if_fini $ul2
+	simple_if_fini $ol2 203.0.113.2/24 2001:db8:2::2/64
+}
+
+test_traffic_ip4ip6()
+{
+	RET=0
+
+	h1mac=$(mac_get $h1)
+	ol1mac=$(mac_get $ol1)
+
+	tc qdisc add dev $ul1 clsact
+	tc filter add dev $ul1 egress proto all pref 1 handle 101 \
+		flower $TC_FLAG action pass
+
+	tc qdisc add dev $ol2 clsact
+	tc filter add dev $ol2 egress protocol ipv4 pref 1 handle 101 \
+		flower $TC_FLAG dst_ip 203.0.113.1 action pass
+
+	$MZ $h1 -c 1000 -p 64 -a $h1mac -b $ol1mac -A 198.51.100.1 \
+		-B 203.0.113.1 -t ip -q -d 1msec
+
+	# Check ports after encap and after decap.
+	tc_check_at_least_x_packets "dev $ul1 egress" 101 1000
+	check_err $? "Packets did not go through $ul1, tc_flag = $TC_FLAG"
+
+	tc_check_at_least_x_packets "dev $ol2 egress" 101 1000
+	check_err $? "Packets did not go through $ol2, tc_flag = $TC_FLAG"
+
+	log_test "$@"
+
+	tc filter del dev $ol2 egress protocol ipv4 pref 1 handle 101 flower
+	tc qdisc del dev $ol2 clsact
+	tc filter del dev $ul1 egress proto all pref 1 handle 101 flower
+	tc qdisc del dev $ul1 clsact
+}
+
+test_traffic_ip6ip6()
+{
+	RET=0
+
+	h1mac=$(mac_get $h1)
+	ol1mac=$(mac_get $ol1)
+
+	tc qdisc add dev $ul1 clsact
+	tc filter add dev $ul1 egress proto all pref 1 handle 101 \
+		flower $TC_FLAG action pass
+
+	tc qdisc add dev $ol2 clsact
+	tc filter add dev $ol2 egress protocol ipv6 pref 1 handle 101 \
+		flower $TC_FLAG dst_ip 2001:db8:2::1 action pass
+
+	$MZ -6 $h1 -c 1000 -p 64 -a $h1mac -b $ol1mac -A 2001:db8:1::1 \
+		-B 2001:db8:2::1 -t ip -q -d 1msec
+
+	# Check ports after encap and after decap.
+	tc_check_at_least_x_packets "dev $ul1 egress" 101 1000
+	check_err $? "Packets did not go through $ul1, tc_flag = $TC_FLAG"
+
+	tc_check_at_least_x_packets "dev $ol2 egress" 101 1000
+	check_err $? "Packets did not go through $ol2, tc_flag = $TC_FLAG"
+
+	log_test "$@"
+
+	tc filter del dev $ol2 egress protocol ipv6 pref 1 handle 101 flower
+	tc qdisc del dev $ol2 clsact
+	tc filter del dev $ul1 egress proto all pref 1 handle 101 flower
+	tc qdisc del dev $ul1 clsact
+}
+
+topo_mtu_change()
+{
+	local mtu=$1
+
+	ip link set mtu $mtu dev $h1
+	ip link set mtu $mtu dev $ol1
+	ip link set mtu $mtu dev g1a
+	ip link set mtu $mtu dev $ul1
+	ip link set mtu $mtu dev $ul1.111
+	ip link set mtu $mtu dev $h2
+	ip link set mtu $mtu dev $ol2
+	ip link set mtu $mtu dev g2a
+	ip link set mtu $mtu dev $ul2
+	ip link set mtu $mtu dev $ul2.111
+}
+
+test_mtu_change()
+{
+	RET=0
+
+	ping6_do $h1 2001:db8:2::1 "-s 1800 -w 3"
+	check_fail $? "ping GRE IPv6 should not pass with packet size 1800"
+
+	RET=0
+
+	topo_mtu_change	2000
+	ping6_do $h1 2001:db8:2::1 "-s 1800 -w 3"
+	check_err $?
+	log_test "ping GRE IPv6, packet size 1800 after MTU change"
+}