diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 6e99eccdb837c..3616389c8c2df 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -131,6 +131,20 @@ fib_multipath_hash_fields - UNSIGNED INTEGER
 
 	Default: 0x0007 (source IP, destination IP and IP protocol)
 
+fib_multipath_hash_seed - UNSIGNED INTEGER
+	The seed value used when calculating hash for multipath routes. Applies
+	to both IPv4 and IPv6 datapath. Only present for kernels built with
+	CONFIG_IP_ROUTE_MULTIPATH enabled.
+
+	When set to 0, the seed value used for multipath routing defaults to an
+	internal random-generated one.
+
+	The actual hashing algorithm is not specified -- there is no guarantee
+	that a next hop distribution effected by a given seed will keep stable
+	across kernel versions.
+
+	Default: 0 (random)
+
 fib_sync_mem - UNSIGNED INTEGER
 	Amount of dirty memory from fib entries that can be backlogged before
 	synchronize_rcu is forced.
diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
index 40ba314fbc72a..800dfb64ec830 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
@@ -11450,12 +11450,16 @@ static int mlxsw_sp_mp_hash_init(struct mlxsw_sp *mlxsw_sp)
 {
 	bool old_inc_parsing_depth, new_inc_parsing_depth;
 	struct mlxsw_sp_mp_hash_config config = {};
+	struct net *net = mlxsw_sp_net(mlxsw_sp);
 	char recr2_pl[MLXSW_REG_RECR2_LEN];
 	unsigned long bit;
 	u32 seed;
 	int err;
 
-	seed = jhash(mlxsw_sp->base_mac, sizeof(mlxsw_sp->base_mac), 0);
+	seed = READ_ONCE(net->ipv4.sysctl_fib_multipath_hash_seed).user_seed;
+	if (!seed)
+		seed = jhash(mlxsw_sp->base_mac, sizeof(mlxsw_sp->base_mac), 0);
+
 	mlxsw_reg_recr2_pack(recr2_pl, seed);
 	mlxsw_sp_mp4_hash_init(mlxsw_sp, &config);
 	mlxsw_sp_mp6_hash_init(mlxsw_sp, &config);
diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
index 99626475c3f4a..3e47e123934d4 100644
--- a/include/net/flow_dissector.h
+++ b/include/net/flow_dissector.h
@@ -442,6 +442,8 @@ static inline bool flow_keys_have_l4(const struct flow_keys *keys)
 }
 
 u32 flow_hash_from_keys(struct flow_keys *keys);
+u32 flow_hash_from_keys_seed(struct flow_keys *keys,
+			     const siphash_key_t *keyval);
 void skb_flow_get_icmp_tci(const struct sk_buff *skb,
 			   struct flow_dissector_key_icmp *key_icmp,
 			   const void *data, int thoff, int hlen);
diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 9b2f69ba5e498..6e7984bfb986c 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -520,7 +520,35 @@ void fib_nhc_update_mtu(struct fib_nh_common *nhc, u32 new, u32 orig);
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 int fib_multipath_hash(const struct net *net, const struct flowi4 *fl4,
 		       const struct sk_buff *skb, struct flow_keys *flkeys);
+
+static void
+fib_multipath_hash_construct_key(siphash_key_t *key, u32 mp_seed)
+{
+	u64 mp_seed_64 = mp_seed;
+
+	key->key[0] = (mp_seed_64 << 32) | mp_seed_64;
+	key->key[1] = key->key[0];
+}
+
+static inline u32 fib_multipath_hash_from_keys(const struct net *net,
+					       struct flow_keys *keys)
+{
+	siphash_aligned_key_t hash_key;
+	u32 mp_seed;
+
+	mp_seed = READ_ONCE(net->ipv4.sysctl_fib_multipath_hash_seed).mp_seed;
+	fib_multipath_hash_construct_key(&hash_key, mp_seed);
+
+	return flow_hash_from_keys_seed(keys, &hash_key);
+}
+#else
+static inline u32 fib_multipath_hash_from_keys(const struct net *net,
+					       struct flow_keys *keys)
+{
+	return flow_hash_from_keys(keys);
+}
 #endif
+
 int fib_check_nh(struct net *net, struct fib_nh *nh, u32 table, u8 scope,
 		 struct netlink_ext_ack *extack);
 void fib_select_multipath(struct fib_result *res, int hash);
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index a91bb971f9015..5fcd61ada6228 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -40,6 +40,13 @@ struct inet_timewait_death_row {
 
 struct tcp_fastopen_context;
 
+#ifdef CONFIG_IP_ROUTE_MULTIPATH
+struct sysctl_fib_multipath_hash_seed {
+	u32 user_seed;
+	u32 mp_seed;
+};
+#endif
+
 struct netns_ipv4 {
 	/* Cacheline organization can be found documented in
 	 * Documentation/networking/net_cachelines/netns_ipv4_sysctl.rst.
@@ -246,6 +253,7 @@ struct netns_ipv4 {
 #endif
 #endif
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
+	struct sysctl_fib_multipath_hash_seed sysctl_fib_multipath_hash_seed;
 	u32 sysctl_fib_multipath_hash_fields;
 	u8 sysctl_fib_multipath_use_neigh;
 	u8 sysctl_fib_multipath_hash_policy;
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index e479790db0f72..e64a263798070 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1806,6 +1806,13 @@ u32 flow_hash_from_keys(struct flow_keys *keys)
 }
 EXPORT_SYMBOL(flow_hash_from_keys);
 
+u32 flow_hash_from_keys_seed(struct flow_keys *keys,
+			     const siphash_key_t *keyval)
+{
+	return __flow_hash_from_keys(keys, keyval);
+}
+EXPORT_SYMBOL(flow_hash_from_keys_seed);
+
 static inline u32 ___skb_get_hash(const struct sk_buff *skb,
 				  struct flow_keys *keys,
 				  const siphash_key_t *keyval)
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index cb0bdf34ed50c..54512acbead73 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1923,7 +1923,7 @@ static u32 fib_multipath_custom_hash_outer(const struct net *net,
 		hash_keys.ports.dst = keys.ports.dst;
 
 	*p_has_inner = !!(keys.control.flags & FLOW_DIS_ENCAPSULATION);
-	return flow_hash_from_keys(&hash_keys);
+	return fib_multipath_hash_from_keys(net, &hash_keys);
 }
 
 static u32 fib_multipath_custom_hash_inner(const struct net *net,
@@ -1972,7 +1972,7 @@ static u32 fib_multipath_custom_hash_inner(const struct net *net,
 	if (hash_fields & FIB_MULTIPATH_HASH_FIELD_INNER_DST_PORT)
 		hash_keys.ports.dst = keys.ports.dst;
 
-	return flow_hash_from_keys(&hash_keys);
+	return fib_multipath_hash_from_keys(net, &hash_keys);
 }
 
 static u32 fib_multipath_custom_hash_skb(const struct net *net,
@@ -2009,7 +2009,7 @@ static u32 fib_multipath_custom_hash_fl4(const struct net *net,
 	if (hash_fields & FIB_MULTIPATH_HASH_FIELD_DST_PORT)
 		hash_keys.ports.dst = fl4->fl4_dport;
 
-	return flow_hash_from_keys(&hash_keys);
+	return fib_multipath_hash_from_keys(net, &hash_keys);
 }
 
 /* if skb is set it will be used and fl4 can be NULL */
@@ -2030,7 +2030,7 @@ int fib_multipath_hash(const struct net *net, const struct flowi4 *fl4,
 			hash_keys.addrs.v4addrs.src = fl4->saddr;
 			hash_keys.addrs.v4addrs.dst = fl4->daddr;
 		}
-		mhash = flow_hash_from_keys(&hash_keys);
+		mhash = fib_multipath_hash_from_keys(net, &hash_keys);
 		break;
 	case 1:
 		/* skb is currently provided only when forwarding */
@@ -2064,7 +2064,7 @@ int fib_multipath_hash(const struct net *net, const struct flowi4 *fl4,
 			hash_keys.ports.dst = fl4->fl4_dport;
 			hash_keys.basic.ip_proto = fl4->flowi4_proto;
 		}
-		mhash = flow_hash_from_keys(&hash_keys);
+		mhash = fib_multipath_hash_from_keys(net, &hash_keys);
 		break;
 	case 2:
 		memset(&hash_keys, 0, sizeof(hash_keys));
@@ -2095,7 +2095,7 @@ int fib_multipath_hash(const struct net *net, const struct flowi4 *fl4,
 			hash_keys.addrs.v4addrs.src = fl4->saddr;
 			hash_keys.addrs.v4addrs.dst = fl4->daddr;
 		}
-		mhash = flow_hash_from_keys(&hash_keys);
+		mhash = fib_multipath_hash_from_keys(net, &hash_keys);
 		break;
 	case 3:
 		if (skb)
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index bb64c0ef092db..9140d20eb2d44 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -464,6 +464,61 @@ static int proc_fib_multipath_hash_fields(struct ctl_table *table, int write,
 
 	return ret;
 }
+
+static u32 proc_fib_multipath_hash_rand_seed __ro_after_init;
+
+static void proc_fib_multipath_hash_init_rand_seed(void)
+{
+	get_random_bytes(&proc_fib_multipath_hash_rand_seed,
+			 sizeof(proc_fib_multipath_hash_rand_seed));
+}
+
+static void proc_fib_multipath_hash_set_seed(struct net *net, u32 user_seed)
+{
+	struct sysctl_fib_multipath_hash_seed new = {
+		.user_seed = user_seed,
+		.mp_seed = (user_seed ? user_seed :
+			    proc_fib_multipath_hash_rand_seed),
+	};
+
+	WRITE_ONCE(net->ipv4.sysctl_fib_multipath_hash_seed, new);
+}
+
+static int proc_fib_multipath_hash_seed(struct ctl_table *table, int write,
+					void *buffer, size_t *lenp,
+					loff_t *ppos)
+{
+	struct sysctl_fib_multipath_hash_seed *mphs;
+	struct net *net = table->data;
+	struct ctl_table tmp;
+	u32 user_seed;
+	int ret;
+
+	mphs = &net->ipv4.sysctl_fib_multipath_hash_seed;
+	user_seed = mphs->user_seed;
+
+	tmp = *table;
+	tmp.data = &user_seed;
+
+	ret = proc_douintvec_minmax(&tmp, write, buffer, lenp, ppos);
+
+	if (write && ret == 0) {
+		proc_fib_multipath_hash_set_seed(net, user_seed);
+		call_netevent_notifiers(NETEVENT_IPV4_MPATH_HASH_UPDATE, net);
+	}
+
+	return ret;
+}
+#else
+
+static void proc_fib_multipath_hash_init_rand_seed(void)
+{
+}
+
+static void proc_fib_multipath_hash_set_seed(struct net *net, u32 user_seed)
+{
+}
+
 #endif
 
 static struct ctl_table ipv4_table[] = {
@@ -1072,6 +1127,13 @@ static struct ctl_table ipv4_net_table[] = {
 		.extra1		= SYSCTL_ONE,
 		.extra2		= &fib_multipath_hash_fields_all_mask,
 	},
+	{
+		.procname	= "fib_multipath_hash_seed",
+		.data		= &init_net,
+		.maxlen		= sizeof(u32),
+		.mode		= 0644,
+		.proc_handler	= proc_fib_multipath_hash_seed,
+	},
 #endif
 	{
 		.procname	= "ip_unprivileged_port_start",
@@ -1550,6 +1612,8 @@ static __net_init int ipv4_sysctl_init_net(struct net *net)
 	if (!net->ipv4.sysctl_local_reserved_ports)
 		goto err_ports;
 
+	proc_fib_multipath_hash_set_seed(net, 0);
+
 	return 0;
 
 err_ports:
@@ -1584,6 +1648,8 @@ static __init int sysctl_ipv4_init(void)
 	if (!hdr)
 		return -ENOMEM;
 
+	proc_fib_multipath_hash_init_rand_seed();
+
 	if (register_pernet_subsys(&ipv4_sysctl_ops)) {
 		unregister_net_sysctl_table(hdr);
 		return -ENOMEM;
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index ad5fff5a210c0..1916de6153981 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2372,7 +2372,7 @@ static u32 rt6_multipath_custom_hash_outer(const struct net *net,
 		hash_keys.ports.dst = keys.ports.dst;
 
 	*p_has_inner = !!(keys.control.flags & FLOW_DIS_ENCAPSULATION);
-	return flow_hash_from_keys(&hash_keys);
+	return fib_multipath_hash_from_keys(net, &hash_keys);
 }
 
 static u32 rt6_multipath_custom_hash_inner(const struct net *net,
@@ -2421,7 +2421,7 @@ static u32 rt6_multipath_custom_hash_inner(const struct net *net,
 	if (hash_fields & FIB_MULTIPATH_HASH_FIELD_INNER_DST_PORT)
 		hash_keys.ports.dst = keys.ports.dst;
 
-	return flow_hash_from_keys(&hash_keys);
+	return fib_multipath_hash_from_keys(net, &hash_keys);
 }
 
 static u32 rt6_multipath_custom_hash_skb(const struct net *net,
@@ -2460,7 +2460,7 @@ static u32 rt6_multipath_custom_hash_fl6(const struct net *net,
 	if (hash_fields & FIB_MULTIPATH_HASH_FIELD_DST_PORT)
 		hash_keys.ports.dst = fl6->fl6_dport;
 
-	return flow_hash_from_keys(&hash_keys);
+	return fib_multipath_hash_from_keys(net, &hash_keys);
 }
 
 /* if skb is set it will be used and fl6 can be NULL */
@@ -2482,7 +2482,7 @@ u32 rt6_multipath_hash(const struct net *net, const struct flowi6 *fl6,
 			hash_keys.tags.flow_label = (__force u32)flowi6_get_flowlabel(fl6);
 			hash_keys.basic.ip_proto = fl6->flowi6_proto;
 		}
-		mhash = flow_hash_from_keys(&hash_keys);
+		mhash = fib_multipath_hash_from_keys(net, &hash_keys);
 		break;
 	case 1:
 		if (skb) {
@@ -2514,7 +2514,7 @@ u32 rt6_multipath_hash(const struct net *net, const struct flowi6 *fl6,
 			hash_keys.ports.dst = fl6->fl6_dport;
 			hash_keys.basic.ip_proto = fl6->flowi6_proto;
 		}
-		mhash = flow_hash_from_keys(&hash_keys);
+		mhash = fib_multipath_hash_from_keys(net, &hash_keys);
 		break;
 	case 2:
 		memset(&hash_keys, 0, sizeof(hash_keys));
@@ -2551,7 +2551,7 @@ u32 rt6_multipath_hash(const struct net *net, const struct flowi6 *fl6,
 			hash_keys.tags.flow_label = (__force u32)flowi6_get_flowlabel(fl6);
 			hash_keys.basic.ip_proto = fl6->flowi6_proto;
 		}
-		mhash = flow_hash_from_keys(&hash_keys);
+		mhash = fib_multipath_hash_from_keys(net, &hash_keys);
 		break;
 	case 3:
 		if (skb)
diff --git a/tools/testing/selftests/net/forwarding/Makefile b/tools/testing/selftests/net/forwarding/Makefile
index fa7b59ff40295..99576d7ecbf63 100644
--- a/tools/testing/selftests/net/forwarding/Makefile
+++ b/tools/testing/selftests/net/forwarding/Makefile
@@ -70,6 +70,7 @@ TEST_PROGS = bridge_fdb_learning_limit.sh \
 	router_broadcast.sh \
 	router_mpath_nh_res.sh \
 	router_mpath_nh.sh \
+	router_mpath_seed.sh \
 	router_multicast.sh \
 	router_multipath.sh \
 	router_nh.sh \
diff --git a/tools/testing/selftests/net/forwarding/lib.sh b/tools/testing/selftests/net/forwarding/lib.sh
index eabbdf00d8ca2..9086d2015296f 100644
--- a/tools/testing/selftests/net/forwarding/lib.sh
+++ b/tools/testing/selftests/net/forwarding/lib.sh
@@ -1134,12 +1134,19 @@ bridge_ageing_time_get()
 }
 
 declare -A SYSCTL_ORIG
+sysctl_save()
+{
+	local key=$1; shift
+
+	SYSCTL_ORIG[$key]=$(sysctl -n $key)
+}
+
 sysctl_set()
 {
 	local key=$1; shift
 	local value=$1; shift
 
-	SYSCTL_ORIG[$key]=$(sysctl -n $key)
+	sysctl_save "$key"
 	sysctl -qw $key="$value"
 }
 
diff --git a/tools/testing/selftests/net/forwarding/router_mpath_seed.sh b/tools/testing/selftests/net/forwarding/router_mpath_seed.sh
new file mode 100755
index 0000000000000..314cb906c1eb2
--- /dev/null
+++ b/tools/testing/selftests/net/forwarding/router_mpath_seed.sh
@@ -0,0 +1,333 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# +-------------------------+  +-------------------------+
+# |  H1                     |  |                      H2 |
+# |               $h1 +     |  | + $h2                   |
+# |      192.0.2.1/28 |     |  | | 192.0.2.34/28         |
+# |  2001:db8:1::1/64 |     |  | | 2001:db8:3::2/64      |
+# +-------------------|-----+  +-|-----------------------+
+#                     |          |
+# +-------------------|-----+  +-|-----------------------+
+# |  R1               |     |  | |                    R2 |
+# |             $rp11 +     |  | + $rp21                 |
+# |      192.0.2.2/28       |  |   192.0.2.33/28         |
+# |  2001:db8:1::2/64       |  |   2001:db8:3::1/64      |
+# |                         |  |                         |
+# |             $rp12 +     |  | + $rp22                 |
+# |     192.0.2.17/28 |     |  | | 192.0.2.18..27/28     |
+# | 2001:db8:2::17/64 |     |  | | 2001:db8:2::18..27/64 |
+# +-------------------|-----+  +-|-----------------------+
+#                     |          |
+#                     `----------'
+
+ALL_TESTS="
+	ping_ipv4
+	ping_ipv6
+	test_mpath_seed_stability_ipv4
+	test_mpath_seed_stability_ipv6
+	test_mpath_seed_get
+	test_mpath_seed_ipv4
+	test_mpath_seed_ipv6
+"
+NUM_NETIFS=6
+source lib.sh
+
+h1_create()
+{
+	simple_if_init $h1 192.0.2.1/28 2001:db8:1::1/64
+	ip -4 route add 192.0.2.32/28 vrf v$h1 nexthop via 192.0.2.2
+	ip -6 route add 2001:db8:3::/64 vrf v$h1 nexthop via 2001:db8:1::2
+}
+
+h1_destroy()
+{
+	ip -6 route del 2001:db8:3::/64 vrf v$h1 nexthop via 2001:db8:1::2
+	ip -4 route del 192.0.2.32/28 vrf v$h1 nexthop via 192.0.2.2
+	simple_if_fini $h1 192.0.2.1/28 2001:db8:1::1/64
+}
+
+h2_create()
+{
+	simple_if_init $h2 192.0.2.34/28 2001:db8:3::2/64
+	ip -4 route add 192.0.2.0/28 vrf v$h2 nexthop via 192.0.2.33
+	ip -6 route add 2001:db8:1::/64 vrf v$h2 nexthop via 2001:db8:3::1
+}
+
+h2_destroy()
+{
+	ip -6 route del 2001:db8:1::/64 vrf v$h2 nexthop via 2001:db8:3::1
+	ip -4 route del 192.0.2.0/28 vrf v$h2 nexthop via 192.0.2.33
+	simple_if_fini $h2 192.0.2.34/28 2001:db8:3::2/64
+}
+
+router1_create()
+{
+	simple_if_init $rp11 192.0.2.2/28 2001:db8:1::2/64
+	__simple_if_init $rp12 v$rp11 192.0.2.17/28 2001:db8:2::17/64
+}
+
+router1_destroy()
+{
+	__simple_if_fini $rp12 192.0.2.17/28 2001:db8:2::17/64
+	simple_if_fini $rp11 192.0.2.2/28 2001:db8:1::2/64
+}
+
+router2_create()
+{
+	simple_if_init $rp21 192.0.2.33/28 2001:db8:3::1/64
+	__simple_if_init $rp22 v$rp21 192.0.2.18/28 2001:db8:2::18/64
+	ip -4 route add 192.0.2.0/28 vrf v$rp21 nexthop via 192.0.2.17
+	ip -6 route add 2001:db8:1::/64 vrf v$rp21 nexthop via 2001:db8:2::17
+}
+
+router2_destroy()
+{
+	ip -6 route del 2001:db8:1::/64 vrf v$rp21 nexthop via 2001:db8:2::17
+	ip -4 route del 192.0.2.0/28 vrf v$rp21 nexthop via 192.0.2.17
+	__simple_if_fini $rp22 192.0.2.18/28 2001:db8:2::18/64
+	simple_if_fini $rp21 192.0.2.33/28 2001:db8:3::1/64
+}
+
+nexthops_create()
+{
+	local i
+	for i in $(seq 10); do
+		ip nexthop add id $((1000 + i)) via 192.0.2.18 dev $rp12
+		ip nexthop add id $((2000 + i)) via 2001:db8:2::18 dev $rp12
+	done
+
+	ip nexthop add id 1000 group $(seq -s / 1001 1010) hw_stats on
+	ip nexthop add id 2000 group $(seq -s / 2001 2010) hw_stats on
+	ip -4 route add 192.0.2.32/28 vrf v$rp11 nhid 1000
+	ip -6 route add 2001:db8:3::/64 vrf v$rp11 nhid 2000
+}
+
+nexthops_destroy()
+{
+	local i
+
+	ip -6 route del 2001:db8:3::/64 vrf v$rp11 nhid 2000
+	ip -4 route del 192.0.2.32/28 vrf v$rp11 nhid 1000
+	ip nexthop del id 2000
+	ip nexthop del id 1000
+
+	for i in $(seq 10 -1 1); do
+		ip nexthop del id $((2000 + i))
+		ip nexthop del id $((1000 + i))
+	done
+}
+
+setup_prepare()
+{
+	h1=${NETIFS[p1]}
+	rp11=${NETIFS[p2]}
+
+	rp12=${NETIFS[p3]}
+	rp22=${NETIFS[p4]}
+
+	rp21=${NETIFS[p5]}
+	h2=${NETIFS[p6]}
+
+	sysctl_save net.ipv4.fib_multipath_hash_seed
+
+	vrf_prepare
+
+	h1_create
+	h2_create
+	router1_create
+	router2_create
+
+	forwarding_enable
+}
+
+cleanup()
+{
+	pre_cleanup
+
+	forwarding_restore
+
+	nexthops_destroy
+	router2_destroy
+	router1_destroy
+	h2_destroy
+	h1_destroy
+
+	vrf_cleanup
+
+	sysctl_restore net.ipv4.fib_multipath_hash_seed
+}
+
+ping_ipv4()
+{
+	ping_test $h1 192.0.2.34
+}
+
+ping_ipv6()
+{
+	ping6_test $h1 2001:db8:3::2
+}
+
+test_mpath_seed_get()
+{
+	RET=0
+
+	local i
+	for ((i = 0; i < 100; i++)); do
+		local seed_w=$((999331 * i))
+		sysctl -qw net.ipv4.fib_multipath_hash_seed=$seed_w
+		local seed_r=$(sysctl -n net.ipv4.fib_multipath_hash_seed)
+		((seed_r == seed_w))
+		check_err $? "mpath seed written as $seed_w, but read as $seed_r"
+	done
+
+	log_test "mpath seed set/get"
+}
+
+nh_stats_snapshot()
+{
+	local group_id=$1; shift
+
+	ip -j -s -s nexthop show id $group_id |
+	    jq -c '[.[].group_stats | sort_by(.id) | .[].packets]'
+}
+
+get_active_nh()
+{
+	local s0=$1; shift
+	local s1=$1; shift
+
+	jq -n --argjson s0 "$s0" --argjson s1 "$s1" -f /dev/stdin <<-"EOF"
+		[range($s0 | length)] |
+		map($s1[.] - $s0[.]) |
+		map(if . > 8 then 1 else 0 end) |
+		index(1)
+	EOF
+}
+
+probe_nh()
+{
+	local group_id=$1; shift
+	local -a mz=("$@")
+
+	local s0=$(nh_stats_snapshot $group_id)
+	"${mz[@]}"
+	local s1=$(nh_stats_snapshot $group_id)
+
+	get_active_nh "$s0" "$s1"
+}
+
+probe_seed()
+{
+	local group_id=$1; shift
+	local seed=$1; shift
+	local -a mz=("$@")
+
+	sysctl -qw net.ipv4.fib_multipath_hash_seed=$seed
+	probe_nh "$group_id" "${mz[@]}"
+}
+
+test_mpath_seed()
+{
+	local group_id=$1; shift
+	local what=$1; shift
+	local -a mz=("$@")
+	local ii
+
+	RET=0
+
+	local -a tally=(0 0 0 0 0 0 0 0 0 0)
+	for ((ii = 0; ii < 100; ii++)); do
+		local act=$(probe_seed $group_id $((999331 * ii)) "${mz[@]}")
+		((tally[act]++))
+	done
+
+	local tally_str="${tally[@]}"
+	for ((ii = 0; ii < ${#tally[@]}; ii++)); do
+		((tally[ii] > 0))
+		check_err $? "NH #$ii not hit, tally='$tally_str'"
+	done
+
+	log_test "mpath seed $what"
+	sysctl -qw net.ipv4.fib_multipath_hash_seed=0
+}
+
+test_mpath_seed_ipv4()
+{
+	test_mpath_seed 1000 IPv4 \
+		$MZ $h1 -A 192.0.2.1 -B 192.0.2.34 -q \
+			-p 64 -d 0 -c 10 -t udp
+}
+
+test_mpath_seed_ipv6()
+{
+	test_mpath_seed 2000 IPv6 \
+		$MZ -6 $h1 -A 2001:db8:1::1 -B 2001:db8:3::2 -q \
+			-p 64 -d 0 -c 10 -t udp
+}
+
+check_mpath_seed_stability()
+{
+	local seed=$1; shift
+	local act_0=$1; shift
+	local act_1=$1; shift
+
+	((act_0 == act_1))
+	check_err $? "seed $seed: active NH moved from $act_0 to $act_1 after seed change"
+}
+
+test_mpath_seed_stability()
+{
+	local group_id=$1; shift
+	local what=$1; shift
+	local -a mz=("$@")
+
+	RET=0
+
+	local seed_0=0
+	local seed_1=3221338814
+	local seed_2=3735928559
+
+	# Initial active NH before touching the seed at all.
+	local act_ini=$(probe_nh $group_id "${mz[@]}")
+
+	local act_0_0=$(probe_seed $group_id $seed_0 "${mz[@]}")
+	local act_1_0=$(probe_seed $group_id $seed_1 "${mz[@]}")
+	local act_2_0=$(probe_seed $group_id $seed_2 "${mz[@]}")
+
+	local act_0_1=$(probe_seed $group_id $seed_0 "${mz[@]}")
+	local act_1_1=$(probe_seed $group_id $seed_1 "${mz[@]}")
+	local act_2_1=$(probe_seed $group_id $seed_2 "${mz[@]}")
+
+	check_mpath_seed_stability initial $act_ini $act_0_0
+	check_mpath_seed_stability $seed_0 $act_0_0 $act_0_1
+	check_mpath_seed_stability $seed_1 $act_1_0 $act_1_1
+	check_mpath_seed_stability $seed_2 $act_2_0 $act_2_1
+
+	log_test "mpath seed stability $what"
+	sysctl -qw net.ipv4.fib_multipath_hash_seed=0
+}
+
+test_mpath_seed_stability_ipv4()
+{
+	test_mpath_seed_stability 1000 IPv4 \
+		$MZ $h1 -A 192.0.2.1 -B 192.0.2.34 -q \
+			-p 64 -d 0 -c 10 -t udp
+}
+
+test_mpath_seed_stability_ipv6()
+{
+	test_mpath_seed_stability 2000 IPv6 \
+		$MZ -6 $h1 -A 2001:db8:1::1 -B 2001:db8:3::2 -q \
+			-p 64 -d 0 -c 10 -t udp
+}
+
+trap cleanup EXIT
+
+setup_prepare
+setup_wait
+nexthops_create
+
+tests_run
+
+exit $EXIT_STATUS