diff --git a/tools/testing/selftests/net/forwarding/lib.sh b/tools/testing/selftests/net/forwarding/lib.sh
old mode 100644
new mode 100755
index e3b3cdef317085f28ba259cd5d325dc0b013e5d8..de10451d767164f05f05ae25b9dec75d516fb1e3
--- a/tools/testing/selftests/net/forwarding/lib.sh
+++ b/tools/testing/selftests/net/forwarding/lib.sh
@@ -28,6 +28,7 @@ LOW_AGEING_TIME=${LOW_AGEING_TIME:=1000}
 REQUIRE_JQ=${REQUIRE_JQ:=yes}
 REQUIRE_MZ=${REQUIRE_MZ:=yes}
 STABLE_MAC_ADDRS=${STABLE_MAC_ADDRS:=no}
+TCPDUMP_EXTRA_FLAGS=${TCPDUMP_EXTRA_FLAGS:=}
 
 relative_path="${BASH_SOURCE%/*}"
 if [[ "$relative_path" == "${BASH_SOURCE}" ]]; then
@@ -1405,7 +1406,7 @@ tcpdump_start()
 		capuser="-Z $SUDO_USER"
 	fi
 
-	$ns_cmd tcpdump -e -n -Q in -i $if_name \
+	$ns_cmd tcpdump $TCPDUMP_EXTRA_FLAGS -e -n -Q in -i $if_name \
 		-s 65535 -B 32768 $capuser -w $capfile > "$capout" 2>&1 &
 	cappid=$!