diff --git a/.zk/notebook.db b/.zk/notebook.db
index 8c03819..ccf9261 100644
Binary files a/.zk/notebook.db and b/.zk/notebook.db differ
diff --git a/zk/IP_addresses.md b/zk/IP_addresses.md
index 777e055..e0f9557 100644
--- a/zk/IP_addresses.md
+++ b/zk/IP_addresses.md
@@ -31,3 +31,12 @@ The 32 bits comprise two major groupings
 
 - the **network prefix**
 - the **host**
+
+![Different sections of IP address](../img/ip-address-anatomy.png)
+
+Devices connected to the same network share the same network prefix. They are
+said to be on the same **subnet**. However each device will have a unique value
+for the host octet.
+
+(This account is somewhat idealised. The length of the prefix does not always
+align with the octet boundary. For instance )
diff --git a/zk/Internet_Layer_of_Internet_Protocol.md b/zk/Internet_Layer_of_Internet_Protocol.md
index 98bdeb9..e88867d 100644
--- a/zk/Internet_Layer_of_Internet_Protocol.md
+++ b/zk/Internet_Layer_of_Internet_Protocol.md
@@ -27,7 +27,7 @@ when sent and received within the
 [Link Layer](Link_Layer_of_Internet_Protocol.md) on the local network, are
 enclosed within a Link Layer frame (in its payload section):
 
-![Internet Layer packet](../img/internet-layer-packet.png)
+![Internet Layer packet](../img/internet-layer-packet-revised.png)
 
 Like a frame, an IP packet has a header and a payload. The payload comprises the
 data between sent between hosts. The header contains a source IP address and a
diff --git a/zk/Link_Layer_of_Internet_Protocol.md b/zk/Link_Layer_of_Internet_Protocol.md
index 3f00bc6..a6687b2 100644
--- a/zk/Link_Layer_of_Internet_Protocol.md
+++ b/zk/Link_Layer_of_Internet_Protocol.md
@@ -43,7 +43,7 @@ a specific MAC address. This is off-limits from the outside.
 Link Layer data is divided into small units called "frames". The anatomy of a
 frame is as follows:
 
-![Link Layer frame](../img/link-layer-frame.drawio.png)
+![Link Layer frame](../img/link-layer-frame-revised.png)
 
 The header contains the source and destination MAC address plus a descriptor of
 the type of data it contains. The data is the payload. The footer is used to