diff --git a/content/notes/01-network and hardware protocols.md b/content/notes/01-network and hardware protocols.md
index 82caceea6..9a8c195fc 100644
--- a/content/notes/01-network and hardware protocols.md	
+++ b/content/notes/01-network and hardware protocols.md	
@@ -24,4 +24,9 @@ you can configure the swtich to send the packets to only the correct address
 
 Network Layer ≡ IP layer
 
-Port number distinguishes addresses at the IP layer
+Port number distinguishes addresses at the transport/application layer. 
+
+ARP - to find destination MAC address given IP address
+- send broadcast message to everyone - who had this IP address? What is your MAC address
+- the store the results of the MAC:IP pairing
+- 
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