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OSI Network Layer
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Module 5
OSI Network Layer
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• IPv4• Networks – Dividing Hosts into Groups• Routing – How Our Data Packets are Handled• Routing Process: How Routes are Learned
Objectives
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IPv4
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Network Layer – Communication from Host to Host
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Network Layer ProtocolsLayer 3 uses four basic processes:
• Addressing• Encapsulation• Routing• Decapsulation
Addressing (routed protocol)
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The IPv4 Protocol – Example Network Layer Protocol
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The IPv4 Protocol –Connectionless
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The IPv4 Protocol – Best Effort
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The IPv4 Protocol – Media Independent
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IPv4 Packet – Packaging the Transport Layer PDU
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IPv4 Packet – Header
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Networks – Dividing Hosts into Groups
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Networks – Separating Hosts into Common Groups
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Grouping Hosts Geographically
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Grouping Hosts for Specific Purposes
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Grouping Hosts for Ownership
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Why Separate Hosts Into Networks ? –Performance
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Why Separate Hosts Into Networks ? –Performance
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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
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Why Separate Hosts Into Networks ? –Address Management
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How Do We Separate Hosts Into Networks ? –Hierarchical Addressing
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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.
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Routing – How Our Data Packets are Handled
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IP Address – Carrying Data End to End
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A Gateway – The Way Out of Our Network
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Confirming the Gateway Settings
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Local Router Routing Table
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A Route – The Path to a Network
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A Route – The Path to a Network
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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
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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.
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The Next Hop – Where the Packet Goes Next
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Packet Forwarding – Moving the Packet Towards its Destination
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Packet Forwarding – Moving the Packet Towards its Destination
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Packet Forwarding – Moving the Packet Towards its Destination
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Routing ProcessHow Routes are Learned
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Routing Protocols – Sharing the Routes
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Static Routing
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Dynamic Routing
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Good luck with this module!