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OSI Network Layer

OSI Network Layer. Network Fundamentals – Chapter 5. Objectives. Identify the role of the Network Layer, as it describes communication from one end device to another end device

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OSI Network Layer

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  1. OSI Network Layer Network Fundamentals – Chapter 5

  2. Objectives • Identify the role of the Network Layer, as it describes communication from one end device to another end device • Examine the most common Network Layer protocol, Internet Protocol (IP), and its features for providing connectionless and best-effort service • Understand the principles used to guide the division or grouping of devices into networks • Understand the hierarchical addressing of devices and how this allows communication between networks • Understand the fundamentals of routes, next hop addresses and packet forwarding to a destination network

  3. Course Index • 5.1 IPv4 • 5.2 Networks – Dividing Hosts into Groups • 5.3 Routing – How Our Data Packets are Handled • 5.4 Routing Processes: How Routes are Learned • 5.5 Lab Activities

  4. 5.1 IPv4

  5. 5.1.1 Network Layer – Communication from Host to Host • Network Layer • Provides services to exchange the individual pieces of data over the network between identified end devices • Basic process: • Addressing • Encapsulation • Routing • Decapsulation • Protocols • Internet Protocol version 4 (IPv4) • Internet Protocol version 6 (IPv6) • Novell Internetwork Packet Exchange (IPX) • AppleTalk • Connectionless Network Service (CLNS/DECNet)

  6. 5.1.2 The IPv4 Protocol • Role of IPv4 It is used to carry user data over the Internet

  7. 5.1.3 The IPv4 Protocol – Connectionless • Connectionless Service

  8. 5.1.4 The IPv4 Protocol – Best Effort • Best Effort Service (unreliable)

  9. 5.1.5 The IPv4 Protocol – Media Independent • Media independent • Maximum Transmission Unit (MTU)：the maximum size of PDU that each medium can transport. • fragmenting the packet or fragmentation： the process of an intermediary device - usually a router - will need to split up a packet when forwarding it from one media to a media with a smaller MTU

  10. 5.1.6 IPv4 Packets – Packaging the Transport Layer PDU • IPv4 encapsulates, or packages, the Transport layer segment or datagram so that the network can deliver it to the destination host. • The encapsulated Transport layer PDU - remains unchanged during the Network layer processes.

  11. 5.1.7 IPv4 packet header

  12. 5.1.7 IPv4 packet header • Typical IP Packet

  13. 5.2 Networks – Dividing Hosts into Groups

  14. 5.2.1 Networks –Separating Hosts into Common Groups • Subnet • Separating hosts into common groups • The factors of group • Geographic location • Purpose • Ownership

  15. 5.2.2 Why Separate Hosts Into Networks? • Performance • Dividing large networks so that hosts who need to communicate are grouped together reduces the traffic across the internetworks. • Broadcasts are contained within a network, so a network is also known as a broadcast domain.

  16. 5.2.3 Why Separate Hosts Into Networks? • Security • Dividing networks based on ownership means that access to and from resources outside each network can be prohibited, allowed, or monitored.

  17. 5.2.4 Why Separate Hosts Into Networks? • Address Management • Dividing large networks so that hosts who need to communicate are grouped together reduces the unnecessary overhead of all hosts needing to know all addresses

  18. 5.2.5 How to divide networks? • Hierarchical addressing

  19. 5.2.6 Dividing the Networks – Networks from Networks • IPv4 is a Hierarchical addressing

  20. 5.3 Routing – How Our Data Packets are Handled

  21. 5.3.1 Device Parameters - Supporting Communication Outside Our Network

  22. 5.3.2 IP packet—carrying data end to end

  23. 5.3.3 A Gateway – The Way Out of Our Network • A router interface connected to the local network. • When a packet’s destination is a different network, the packet is sent to the gateway.

  24. 5.3.4 A Route – The Path to Network • Three main features of route: • Destination network • Next-hop • Metric • Routing table • Routing protocols.

  25. 5.3.5 Destination network

  26. 5.3.6 The Next Hop – Where the Packet Goes Next

  27. 5.3.7 Packet Forwarding • Forward it to the next-hop router • Have a exactly entry • No exactly entry but a default route exits • Forward it to the destination host • Direct connected network • Drop it • No entry and no default route

  28. 5.4 Routing Processes: How Routes are Learned

  29. 5.4.1 Routing Protocols • Used for Sharing the Routes

  30. 5.4.2 Static Routing • Manually configured on the router

  31. 5.4.3 Dynamic Routing • Dynamic Routing protocols are the set of rules by which routers dynamically share their routing information. • Common dynamic routing protocols: • Routing Information Protocol (RIP) • Enhanced Interior Gateway Protocol (EIGRP) • Open Shortest Path First (OSPF)

  32. Summary

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