diff --git a/tools/testing/selftests/net/forwarding/ip6gre_custom_multipath_hash.sh b/tools/testing/selftests/net/forwarding/ip6gre_custom_multipath_hash.sh
new file mode 100755
index 000000000000..8436f182d6a6
--- /dev/null
+++ b/tools/testing/selftests/net/forwarding/ip6gre_custom_multipath_hash.sh
@@ -0,0 +1,458 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Test traffic distribution when there are multiple paths between an IPv6 GRE
+# tunnel. The tunnel carries IPv4 and IPv6 traffic between multiple hosts.
+# Multiple routes are in the underlay network. With the default multipath
+# policy, SW2 will only look at the outer IP addresses, hence only a single
+# route would be used.
+#
+# +--------------------------------+
+# | H1                             |
+# |                     $h1 +      |
+# |   198.51.100.{2-253}/24 |      |
+# |   2001:db8:1::{2-fd}/64 |      |
+# +-------------------------|------+
+#                           |
+# +-------------------------|-------------------+
+# | SW1                     |                   |
+# |                    $ol1 +                   |
+# |         198.51.100.1/24                     |
+# |        2001:db8:1::1/64                     |
+# |                                             |
+# |+ g1 (ip6gre)                                |
+# |  loc=2001:db8:3::1                          |
+# |  rem=2001:db8:3::2 -.                       |
+# |     tos=inherit     |                       |
+# |                     v                       |
+# |                     + $ul1                  |
+# |                     | 2001:db8:10::1/64     |
+# +---------------------|-----------------------+
+#                       |
+# +---------------------|-----------------------+
+# | SW2                 |                       |
+# |               $ul21 +                       |
+# |   2001:db8:10::2/64 |                       |
+# |                     |                       |
+# !   __________________+___                    |
+# |  /                      \                   |
+# |  |                      |                   |
+# |  + $ul22.111 (vlan)     + $ul22.222 (vlan)  |
+# |  | 2001:db8:11::1/64    | 2001:db8:12::1/64 |
+# |  |                      |                   |
+# +--|----------------------|-------------------+
+#    |                      |
+# +--|----------------------|-------------------+
+# |  |                      |                   |
+# |  + $ul32.111 (vlan)     + $ul32.222 (vlan)  |
+# |  | 2001:db8:11::2/64    | 2001:db8:12::2/64 |
+# |  |                      |                   |
+# |  \__________________+___/                   |
+# |                     |                       |
+# |                     |                       |
+# |               $ul31 +                       |
+# |   2001:db8:13::1/64 |                   SW3 |
+# +---------------------|-----------------------+
+#                       |
+# +---------------------|-----------------------+
+# |                     + $ul4                  |
+# |                     ^ 2001:db8:13::2/64     |
+# |                     |                       |
+# |+ g2 (ip6gre)        |                       |
+# |  loc=2001:db8:3::2  |                       |
+# |  rem=2001:db8:3::1 -'                       |
+# |  tos=inherit                                |
+# |                                             |
+# |                    $ol4 +                   |
+# |          203.0.113.1/24 |                   |
+# |        2001:db8:2::1/64 |               SW4 |
+# +-------------------------|-------------------+
+#                           |
+# +-------------------------|------+
+# |                         |      |
+# |                     $h2 +      |
+# |    203.0.113.{2-253}/24        |
+# |   2001:db8:2::{2-fd}/64     H2 |
+# +--------------------------------+
+
+ALL_TESTS="
+	ping_ipv4
+	ping_ipv6
+	custom_hash
+"
+
+NUM_NETIFS=10
+source lib.sh
+
+h1_create()
+{
+	simple_if_init $h1 198.51.100.2/24 2001:db8:1::2/64
+	ip route add vrf v$h1 default via 198.51.100.1 dev $h1
+	ip -6 route add vrf v$h1 default via 2001:db8:1::1 dev $h1
+}
+
+h1_destroy()
+{
+	ip -6 route del vrf v$h1 default
+	ip route del vrf v$h1 default
+	simple_if_fini $h1 198.51.100.2/24 2001:db8:1::2/64
+}
+
+sw1_create()
+{
+	simple_if_init $ol1 198.51.100.1/24 2001:db8:1::1/64
+	__simple_if_init $ul1 v$ol1 2001:db8:10::1/64
+
+	tunnel_create g1 ip6gre 2001:db8:3::1 2001:db8:3::2 tos inherit \
+		dev v$ol1
+	__simple_if_init g1 v$ol1 2001:db8:3::1/128
+	ip route add vrf v$ol1 2001:db8:3::2/128 via 2001:db8:10::2
+
+	ip route add vrf v$ol1 203.0.113.0/24 dev g1
+	ip -6 route add vrf v$ol1 2001:db8:2::/64 dev g1
+}
+
+sw1_destroy()
+{
+	ip -6 route del vrf v$ol1 2001:db8:2::/64
+	ip route del vrf v$ol1 203.0.113.0/24
+
+	ip route del vrf v$ol1 2001:db8:3::2/128
+	__simple_if_fini g1 2001:db8:3::1/128
+	tunnel_destroy g1
+
+	__simple_if_fini $ul1 2001:db8:10::1/64
+	simple_if_fini $ol1 198.51.100.1/24 2001:db8:1::1/64
+}
+
+sw2_create()
+{
+	simple_if_init $ul21 2001:db8:10::2/64
+	__simple_if_init $ul22 v$ul21
+	vlan_create $ul22 111 v$ul21 2001:db8:11::1/64
+	vlan_create $ul22 222 v$ul21 2001:db8:12::1/64
+
+	ip -6 route add vrf v$ul21 2001:db8:3::1/128 via 2001:db8:10::1
+	ip -6 route add vrf v$ul21 2001:db8:3::2/128 \
+	   nexthop via 2001:db8:11::2 \
+	   nexthop via 2001:db8:12::2
+}
+
+sw2_destroy()
+{
+	ip -6 route del vrf v$ul21 2001:db8:3::2/128
+	ip -6 route del vrf v$ul21 2001:db8:3::1/128
+
+	vlan_destroy $ul22 222
+	vlan_destroy $ul22 111
+	__simple_if_fini $ul22
+	simple_if_fini $ul21 2001:db8:10::2/64
+}
+
+sw3_create()
+{
+	simple_if_init $ul31 2001:db8:13::1/64
+	__simple_if_init $ul32 v$ul31
+	vlan_create $ul32 111 v$ul31 2001:db8:11::2/64
+	vlan_create $ul32 222 v$ul31 2001:db8:12::2/64
+
+	ip -6 route add vrf v$ul31 2001:db8:3::2/128 via 2001:db8:13::2
+	ip -6 route add vrf v$ul31 2001:db8:3::1/128 \
+	   nexthop via 2001:db8:11::1 \
+	   nexthop via 2001:db8:12::1
+
+	tc qdisc add dev $ul32 clsact
+	tc filter add dev $ul32 ingress pref 111 prot 802.1Q \
+	   flower vlan_id 111 action pass
+	tc filter add dev $ul32 ingress pref 222 prot 802.1Q \
+	   flower vlan_id 222 action pass
+}
+
+sw3_destroy()
+{
+	tc qdisc del dev $ul32 clsact
+
+	ip -6 route del vrf v$ul31 2001:db8:3::1/128
+	ip -6 route del vrf v$ul31 2001:db8:3::2/128
+
+	vlan_destroy $ul32 222
+	vlan_destroy $ul32 111
+	__simple_if_fini $ul32
+	simple_if_fini $ul31 2001:db8:13::1/64
+}
+
+sw4_create()
+{
+	simple_if_init $ol4 203.0.113.1/24 2001:db8:2::1/64
+	__simple_if_init $ul4 v$ol4 2001:db8:13::2/64
+
+	tunnel_create g2 ip6gre 2001:db8:3::2 2001:db8:3::1 tos inherit \
+		dev v$ol4
+	__simple_if_init g2 v$ol4 2001:db8:3::2/128
+	ip -6 route add vrf v$ol4 2001:db8:3::1/128 via 2001:db8:13::1
+
+	ip route add vrf v$ol4 198.51.100.0/24 dev g2
+	ip -6 route add vrf v$ol4 2001:db8:1::/64 dev g2
+}
+
+sw4_destroy()
+{
+	ip -6 route del vrf v$ol4 2001:db8:1::/64
+	ip route del vrf v$ol4 198.51.100.0/24
+
+	ip -6 route del vrf v$ol4 2001:db8:3::1/128
+	__simple_if_fini g2 2001:db8:3::2/128
+	tunnel_destroy g2
+
+	__simple_if_fini $ul4 2001:db8:13::2/64
+	simple_if_fini $ol4 203.0.113.1/24 2001:db8:2::1/64
+}
+
+h2_create()
+{
+	simple_if_init $h2 203.0.113.2/24 2001:db8:2::2/64
+	ip route add vrf v$h2 default via 203.0.113.1 dev $h2
+	ip -6 route add vrf v$h2 default via 2001:db8:2::1 dev $h2
+}
+
+h2_destroy()
+{
+	ip -6 route del vrf v$h2 default
+	ip route del vrf v$h2 default
+	simple_if_fini $h2 203.0.113.2/24 2001:db8:2::2/64
+}
+
+setup_prepare()
+{
+	h1=${NETIFS[p1]}
+
+	ol1=${NETIFS[p2]}
+	ul1=${NETIFS[p3]}
+
+	ul21=${NETIFS[p4]}
+	ul22=${NETIFS[p5]}
+
+	ul32=${NETIFS[p6]}
+	ul31=${NETIFS[p7]}
+
+	ul4=${NETIFS[p8]}
+	ol4=${NETIFS[p9]}
+
+	h2=${NETIFS[p10]}
+
+	vrf_prepare
+	h1_create
+	sw1_create
+	sw2_create
+	sw3_create
+	sw4_create
+	h2_create
+
+	forwarding_enable
+}
+
+cleanup()
+{
+	pre_cleanup
+
+	forwarding_restore
+
+	h2_destroy
+	sw4_destroy
+	sw3_destroy
+	sw2_destroy
+	sw1_destroy
+	h1_destroy
+	vrf_cleanup
+}
+
+ping_ipv4()
+{
+	ping_test $h1 203.0.113.2
+}
+
+ping_ipv6()
+{
+	ping6_test $h1 2001:db8:2::2
+}
+
+send_src_ipv4()
+{
+	$MZ $h1 -q -p 64 -A "198.51.100.2-198.51.100.253" -B 203.0.113.2 \
+		-d 1msec -c 50 -t udp "sp=20000,dp=30000"
+}
+
+send_dst_ipv4()
+{
+	$MZ $h1 -q -p 64 -A 198.51.100.2 -B "203.0.113.2-203.0.113.253" \
+		-d 1msec -c 50 -t udp "sp=20000,dp=30000"
+}
+
+send_src_udp4()
+{
+	$MZ $h1 -q -p 64 -A 198.51.100.2 -B 203.0.113.2 \
+		-d 1msec -t udp "sp=0-32768,dp=30000"
+}
+
+send_dst_udp4()
+{
+	$MZ $h1 -q -p 64 -A 198.51.100.2 -B 203.0.113.2 \
+		-d 1msec -t udp "sp=20000,dp=0-32768"
+}
+
+send_src_ipv6()
+{
+	$MZ -6 $h1 -q -p 64 -A "2001:db8:1::2-2001:db8:1::fd" -B 2001:db8:2::2 \
+		-d 1msec -c 50 -t udp "sp=20000,dp=30000"
+}
+
+send_dst_ipv6()
+{
+	$MZ -6 $h1 -q -p 64 -A 2001:db8:1::2 -B "2001:db8:2::2-2001:db8:2::fd" \
+		-d 1msec -c 50 -t udp "sp=20000,dp=30000"
+}
+
+send_flowlabel()
+{
+	# Generate 16384 echo requests, each with a random flow label.
+	for _ in $(seq 1 16384); do
+		ip vrf exec v$h1 \
+			$PING6 2001:db8:2::2 -F 0 -c 1 -q >/dev/null 2>&1
+	done
+}
+
+send_src_udp6()
+{
+	$MZ -6 $h1 -q -p 64 -A 2001:db8:1::2 -B 2001:db8:2::2 \
+		-d 1msec -t udp "sp=0-32768,dp=30000"
+}
+
+send_dst_udp6()
+{
+	$MZ -6 $h1 -q -p 64 -A 2001:db8:1::2 -B 2001:db8:2::2 \
+		-d 1msec -t udp "sp=20000,dp=0-32768"
+}
+
+custom_hash_test()
+{
+	local field="$1"; shift
+	local balanced="$1"; shift
+	local send_flows="$@"
+
+	RET=0
+
+	local t0_111=$(tc_rule_stats_get $ul32 111 ingress)
+	local t0_222=$(tc_rule_stats_get $ul32 222 ingress)
+
+	$send_flows
+
+	local t1_111=$(tc_rule_stats_get $ul32 111 ingress)
+	local t1_222=$(tc_rule_stats_get $ul32 222 ingress)
+
+	local d111=$((t1_111 - t0_111))
+	local d222=$((t1_222 - t0_222))
+
+	local diff=$((d222 - d111))
+	local sum=$((d111 + d222))
+
+	local pct=$(echo "$diff / $sum * 100" | bc -l)
+	local is_balanced=$(echo "-20 <= $pct && $pct <= 20" | bc)
+
+	[[ ( $is_balanced -eq 1 && $balanced == "balanced" ) ||
+	   ( $is_balanced -eq 0 && $balanced == "unbalanced" ) ]]
+	check_err $? "Expected traffic to be $balanced, but it is not"
+
+	log_test "Multipath hash field: $field ($balanced)"
+	log_info "Packets sent on path1 / path2: $d111 / $d222"
+}
+
+custom_hash_v4()
+{
+	log_info "Running IPv4 overlay custom multipath hash tests"
+
+	# Prevent the neighbour table from overflowing, as different neighbour
+	# entries will be created on $ol4 when using different destination IPs.
+	sysctl_set net.ipv4.neigh.default.gc_thresh1 1024
+	sysctl_set net.ipv4.neigh.default.gc_thresh2 1024
+	sysctl_set net.ipv4.neigh.default.gc_thresh3 1024
+
+	sysctl_set net.ipv6.fib_multipath_hash_fields 6
+	custom_hash_test "Inner source IP" "balanced" send_src_ipv4
+	custom_hash_test "Inner source IP" "unbalanced" send_dst_ipv4
+
+	sysctl_set net.ipv6.fib_multipath_hash_fields 7
+	custom_hash_test "Inner destination IP" "balanced" send_dst_ipv4
+	custom_hash_test "Inner destination IP" "unbalanced" send_src_ipv4
+
+	sysctl_set net.ipv6.fib_multipath_hash_fields 10
+	custom_hash_test "Inner source port" "balanced" send_src_udp4
+	custom_hash_test "Inner source port" "unbalanced" send_dst_udp4
+
+	sysctl_set net.ipv6.fib_multipath_hash_fields 11
+	custom_hash_test "Inner destination port" "balanced" send_dst_udp4
+	custom_hash_test "Inner destination port" "unbalanced" send_src_udp4
+
+	sysctl_restore net.ipv4.neigh.default.gc_thresh3
+	sysctl_restore net.ipv4.neigh.default.gc_thresh2
+	sysctl_restore net.ipv4.neigh.default.gc_thresh1
+}
+
+custom_hash_v6()
+{
+	log_info "Running IPv6 overlay custom multipath hash tests"
+
+	# Prevent the neighbour table from overflowing, as different neighbour
+	# entries will be created on $ol4 when using different destination IPs.
+	sysctl_set net.ipv6.neigh.default.gc_thresh1 1024
+	sysctl_set net.ipv6.neigh.default.gc_thresh2 1024
+	sysctl_set net.ipv6.neigh.default.gc_thresh3 1024
+
+	sysctl_set net.ipv6.fib_multipath_hash_fields 6
+	custom_hash_test "Inner source IP" "balanced" send_src_ipv6
+	custom_hash_test "Inner source IP" "unbalanced" send_dst_ipv6
+
+	sysctl_set net.ipv6.fib_multipath_hash_fields 7
+	custom_hash_test "Inner destination IP" "balanced" send_dst_ipv6
+	custom_hash_test "Inner destination IP" "unbalanced" send_src_ipv6
+
+	sysctl_set net.ipv6.fib_multipath_hash_fields 9
+	custom_hash_test "Inner flowlabel" "balanced" send_flowlabel
+	custom_hash_test "Inner flowlabel" "unbalanced" send_src_ipv6
+
+	sysctl_set net.ipv6.fib_multipath_hash_fields 10
+	custom_hash_test "Inner source port" "balanced" send_src_udp6
+	custom_hash_test "Inner source port" "unbalanced" send_dst_udp6
+
+	sysctl_set net.ipv6.fib_multipath_hash_fields 11
+	custom_hash_test "Inner destination port" "balanced" send_dst_udp6
+	custom_hash_test "Inner destination port" "unbalanced" send_src_udp6
+
+	sysctl_restore net.ipv6.neigh.default.gc_thresh3
+	sysctl_restore net.ipv6.neigh.default.gc_thresh2
+	sysctl_restore net.ipv6.neigh.default.gc_thresh1
+}
+
+custom_hash()
+{
+	# Test that when the hash policy is set to custom, traffic is
+	# distributed only according to the fields set in the
+	# fib_multipath_hash_fields sysctl.
+	#
+	# Each time set a different field and make sure traffic is only
+	# distributed when the field is changed in the packet stream.
+
+	sysctl_set net.ipv6.fib_multipath_hash_policy 3
+
+	custom_hash_v4
+	custom_hash_v6
+
+	sysctl_restore net.ipv6.fib_multipath_hash_policy
+}
+
+trap cleanup EXIT
+
+setup_prepare
+setup_wait
+tests_run
+
+exit $EXIT_STATUS
