1

Module 5

OSI Network Layer

2

• IPv4• Networks – Dividing Hosts into Groups• Routing – How Our Data Packets are Handled• Routing Process: How Routes are Learned

Objectives

3

IPv4

4

Network Layer – Communication from Host to Host

5

Network Layer ProtocolsLayer 3 uses four basic processes:

• Addressing• Encapsulation• Routing• Decapsulation

Addressing (routed protocol)

6

The IPv4 Protocol – Example Network Layer Protocol

7

The IPv4 Protocol –Connectionless

8

The IPv4 Protocol – Best Effort

9

The IPv4 Protocol – Media Independent

10

IPv4 Packet – Packaging the Transport Layer PDU

11

IPv4 Packet – Header

12

Networks – Dividing Hosts into Groups

13

Networks – Separating Hosts into Common Groups

14

Grouping Hosts Geographically

15

Grouping Hosts for Specific Purposes

16

Grouping Hosts for Ownership

17

Why Separate Hosts Into Networks ? –Performance

18

Why Separate Hosts Into Networks ? –Performance

19

Why Separate Hosts Into Networks ? –Security

• All users have access to the Internet• Each user can reach servers in its own department• Each user is blocking form reaching servers in other department

20

Why Separate Hosts Into Networks ? –Address Management

21

How Do We Separate Hosts Into Networks ? –Hierarchical Addressing

22

Dividing the Network – Networks fromNetworks

• This is hierarchical addressing because the network portion indicates the network on which each unique host address is located.

• Routers only need to know how to reach each network, rather than needing to know the location of each individual host.

23

Routing – How Our Data Packets are Handled

24

IP Address – Carrying Data End to End

25

A Gateway – The Way Out of Our Network

26

Confirming the Gateway Settings

27

Local Router Routing Table

28

A Route – The Path to a Network

29

A Route – The Path to a Network

30

The Destination Network

• Packets with destination host addresses in one of the network ranges shown will be matched with the next hop that leads to that network

• The precedence of route selection for the packet going to 10.1.1.55 would be:1. 10.1.1.02. 10.1.0.03. 10.0.0.04. 0.0.0.0 (Default route if configured)5. Dropped

31

The Destination Network

• The routing table shows the default route 0.0.0.0• The router may also use a default route (gateway of last resort) to forward the

packet. • The default route is used when the destination network is not represented by

any other route in the routing table.

32

The Next Hop – Where the Packet Goes Next

33

Packet Forwarding – Moving the Packet Towards its Destination

34

Packet Forwarding – Moving the Packet Towards its Destination

35

Packet Forwarding – Moving the Packet Towards its Destination

36

Routing ProcessHow Routes are Learned

37

Routing Protocols – Sharing the Routes

38

Static Routing

39

Dynamic Routing

40

Good luck with this module!