netdev - [PATCH net 2/2] selftests: fib_nexthops: Add test case for ipv4 multi nexthops

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Message-ID: <20251213135849.2054677-2-vadim.fedorenko@linux.dev>
Date: Sat, 13 Dec 2025 13:58:49 +0000
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: "David S. Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Willem de Bruijn <willemb@...gle.com>,
	Jakub Kicinski <kuba@...nel.ord>
Cc: Shuah Khan <shuah@...nel.org>,
	Ido Schimmel <idosch@...dia.com>,
	netdev@...r.kernel.org,
	Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Subject: [PATCH net 2/2] selftests: fib_nexthops: Add test case for ipv4 multi nexthops

The test checks that with multi nexthops route the preferred route is the
one which matches source ip. In case when source ip is on loopback, it
checks that the routes are balanced.

Signed-off-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
---
 tools/testing/selftests/net/fib_nexthops.sh | 85 +++++++++++++++++++++
 1 file changed, 85 insertions(+)

diff --git a/tools/testing/selftests/net/fib_nexthops.sh b/tools/testing/selftests/net/fib_nexthops.sh
index 2b0a90581e2f..9d6f57399a73 100755
--- a/tools/testing/selftests/net/fib_nexthops.sh
+++ b/tools/testing/selftests/net/fib_nexthops.sh
@@ -31,6 +31,7 @@ IPV4_TESTS="
 	ipv4_compat_mode
 	ipv4_fdb_grp_fcnal
 	ipv4_mpath_select
+	ipv4_mpath_select_nogrp
 	ipv4_torture
 	ipv4_res_torture
 "
@@ -375,6 +376,17 @@ check_large_res_grp()
 	log_test $? 0 "Dump large (x$buckets) nexthop buckets"
 }
 
+get_route_dev_src()
+{
+	local pfx="$1"
+	local src="$2"
+	local out
+
+	if out=$($IP -j route get "$pfx" from "$src" | jq -re ".[0].dev"); then
+		echo "$out"
+	fi
+}
+
 get_route_dev()
 {
 	local pfx="$1"
@@ -641,6 +653,79 @@ ipv4_fdb_grp_fcnal()
 	$IP link del dev vx10
 }
 
+ipv4_mpath_select_nogrp()
+{
+	local rc dev match h addr
+
+	echo
+	echo "IPv4 multipath selection no group"
+	echo "------------------------"
+	if [ ! -x "$(command -v jq)" ]; then
+		echo "SKIP: Could not run test; need jq tool"
+		return $ksft_skip
+	fi
+
+	IP="ip -netns $peer"
+	# Use status of existing neighbor entry when determining nexthop for
+	# multipath routes.
+	local -A gws
+	gws=([veth2]=172.16.1.1 [veth4]=172.16.2.1)
+	local -A other_dev
+	other_dev=([veth2]=veth4 [veth4]=veth2)
+	local -A local_ips
+	local_ips=([veth2]=172.16.1.2 [veth4]=172.16.2.2 [veth5]=172.16.100.1)
+	local -A route_devs
+	route_devs=([veth2]=0 [veth4]=0)
+
+	run_cmd "$IP address add 172.16.100.1/32 dev lo"
+	run_cmd "$IP ro add 172.16.102.0/24 nexthop via ${gws['veth2']} dev veth2 nexthop via ${gws['veth4']} dev veth4"
+	rc=0
+	for dev in veth2 veth4; do
+		match=0
+		from_ip="${local_ips[$dev]}"
+		for h in {1..254}; do
+			addr="172.16.102.$h"
+			if [ "$(get_route_dev_src "$addr" "$from_ip")" = "$dev" ]; then
+				match=1
+				break
+			fi
+		done
+		if (( match == 0 )); then
+			echo "SKIP: Did not find a route using device $dev"
+			return $ksft_skip
+		fi
+		run_cmd "$IP neigh add ${gws[$dev]} dev $dev nud failed"
+		if ! check_route_dev "$addr" "${other_dev[$dev]}"; then
+			rc=1
+			break
+		fi
+		run_cmd "$IP neigh del ${gws[$dev]} dev $dev"
+	done
+
+	log_test $rc 0 "Use valid neighbor during multipath selection"
+
+	from_ip="${local_ips["veth5"]}"
+	for h in {1..254}; do
+		addr="172.16.102.$h"
+		route_dev=$(get_route_dev_src "$addr" "$from_ip")
+		route_devs[$route_dev]=1
+	done
+	for dev in veth2 veth4; do
+		if [ ${route_devs[$dev]} -eq 0 ]; then
+			rc=1
+			break;
+		fi
+	done
+
+	log_test $rc 0 "Use both neighbors during multipath selection"
+
+	run_cmd "$IP neigh add 172.16.1.2 dev veth1 nud incomplete"
+	run_cmd "$IP neigh add 172.16.2.2 dev veth3 nud incomplete"
+	run_cmd "$IP route get 172.16.101.1"
+	# if we did not crash, success
+	log_test $rc 0 "Multipath selection with no valid neighbor"
+}
+
 ipv4_mpath_select()
 {
 	local rc dev match h addr
-- 
2.47.3