--- /dev/null
+# 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"
+}