diff --git a/School/Analyse/Layers/3. Network Layer.md b/School/Analyse/Layers/3. Network Layer.md
index 1800dfd..655e582 100644
--- a/School/Analyse/Layers/3. Network Layer.md	
+++ b/School/Analyse/Layers/3. Network Layer.md	
@@ -84,7 +84,18 @@ We now do have a addressing issue because:
 
 So we need a new type of ID to uniquely identify a host in the internet.
 
-This address will we at a higher level of protocols 
-
+This address will we at a higher level of protocols (Network layer) and is therefore protocol dependent.
+
+### IPV4
+IPV4 are 4 byte integers. We use them in the following format:
+0-255.0-255.0-255.0-255 ex. 192.168.100.1
+
+This is called a dotted decimal, each address contains 4 decimals of 8 bits (octets)
+Example: 00000000.00000000.00000000.00000000
+
+## Classful addresses
+Classfull addresses define 3 networks types
+
+Class A: First decimal shows the network ID, remaining 3 decimals show the host ID. (Large networks)