From 60cfcc3638a536894ded17e55bf74b3db564d712 Mon Sep 17 00:00:00 2001
From: Jet Hughes <jethughes0@gmail.com>
Date: Tue, 18 Oct 2022 11:39:16 +1300
Subject: [PATCH] vault backup: 2022-10-18 11:39:16

---
 content/notes/19-network-layer-data-plane.md | 49 +++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/content/notes/19-network-layer-data-plane.md b/content/notes/19-network-layer-data-plane.md
index 9b326c5ce..5d964cbbc 100644
--- a/content/notes/19-network-layer-data-plane.md
+++ b/content/notes/19-network-layer-data-plane.md
@@ -71,6 +71,53 @@ input port queueing: if datagrams arrive faster than fowarding rate into switch
 overhead:
 - 20 bytes TCP
 - 20 bytes IP
-- = 40 bytes 
+- = 40 bytes + app layer overhead for TCP+IP
+
+
+interface: connection between host/router and physical link
+- router have multiple interfaces
+- host has one or two interfaces :e.g., ethernet and wireless
+
+IPv4 address: 32-bit id associated with each host or router interface
+![dotted decimal IP address notation](https://i.imgur.com/N0hB8u8.png)
+- two main components
+	- network ID
+		- addresses in the same network have the same network ID
+	- host ID
+- 5 classes
+	- ![](https://i.imgur.com/9dOLoyr.png)
+
+## subnetting
+- partitioning an IP network into multiple smaller network segments
+	- designate some high-order bits from host part as subnet ID
+	- ![](https://i.imgur.com/wGjPOJb.png)
+- netmask
+	- a 32-bit number with all 1s for network part and all 0s for host part
+
+![example](https://i.imgur.com/7COPiAh.png)
+- use bitwise and to find network part from address and mask
+
+
+## fragmentation
+- network links have an MTU (maximum transmission unit)
+	- different linktypes have different MTUs
+- large UP datagrams are fragmented at routers
+	- one datagram become several
+	- reassemble only at destination
+	- IP header bits are used to identify fragments
+
+
+header
+- identifier
+	- same for all fragments
+- flag: 3 bits
+	- 1st not used
+	- 2nd - do fragment
+	- 3rd - more fragment (0 for the last fragment)
+- offset
+	- offset of the fragment in the packets data field (units of 8 bytes)
+
+![example](https://i.imgur.com/eENmMTd.png)
+
 
 # IPv6
\ No newline at end of file