diff --git a/tools/testing/selftests/net/forwarding/lib.sh b/tools/testing/selftests/net/forwarding/lib.sh
index 736f56098cc7..9fe3004af6dc 100755
--- a/tools/testing/selftests/net/forwarding/lib.sh
+++ b/tools/testing/selftests/net/forwarding/lib.sh
@@ -1672,6 +1672,43 @@ hw_stats_monitor_test()
 	log_test "${type}_stats notifications"
 }
 
+ipv4_to_bytes()
+{
+	local IP=$1; shift
+
+	printf '%02x:' ${IP//./ } |
+	    sed 's/:$//'
+}
+
+# Convert a given IPv6 address, `IP' such that the :: token, if present, is
+# expanded, and each 16-bit group is padded with zeroes to be 4 hexadecimal
+# digits. An optional `BYTESEP' parameter can be given to further separate
+# individual bytes of each 16-bit group.
+expand_ipv6()
+{
+	local IP=$1; shift
+	local bytesep=$1; shift
+
+	local cvt_ip=${IP/::/_}
+	local colons=${cvt_ip//[^:]/}
+	local allcol=:::::::
+	# IP where :: -> the appropriate number of colons:
+	local allcol_ip=${cvt_ip/_/${allcol:${#colons}}}
+
+	echo $allcol_ip | tr : '\n' |
+	    sed s/^/0000/ |
+	    sed 's/.*\(..\)\(..\)/\1'"$bytesep"'\2/' |
+	    tr '\n' : |
+	    sed 's/:$//'
+}
+
+ipv6_to_bytes()
+{
+	local IP=$1; shift
+
+	expand_ipv6 "$IP" :
+}
+
 igmpv3_is_in_get()
 {
 	local igmpv3