diff --git a/doc/erko_howto_tools.txt b/doc/erko_howto_tools.txt
index 613878db9dc9674ec44c52bbea3a51d3dac81e74..4d647eb069d5ea1e5aa21179e81639d54b0028c0 100755
--- a/doc/erko_howto_tools.txt
+++ b/doc/erko_howto_tools.txt
@@ -468,7 +468,10 @@ then:
 
 
 4) tcpdump
-   sudo tcpdump -vvXXSnelfi enp5s0
+   > ifconfig   # to find ethernet port
+   > sudo tcpdump -vvXXSnelfi enp5s0 port 5001 # for UDP only
+   > sudo tcpdump -vvXXSnelfi enp5s0 port 5001 > tcpdump.txt  (> is new file, >> is append)
+
 
 *******************************************************************************
 * Polarion: