Chapter 5 - OSI Network Layer CCNA Exploration version 4.0CCNA Exploration version 4.0 Overview • 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 Học viện mạng Bách khoa - Website: www.bkacad.com 2 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 Network Layer Protocols and Internet Protocol (IP) Học viện mạng Bách khoa - Website: www.bkacad.com 3 • Define the basic role of the Network Layer in data networks • The protocols of the OSI model Network layer specify addressing and processes that enable Transport layer data to be packaged and transported. The Network layer encapsulation allows its contents to be passed to the destination within a network or on another network with minimum overhead. Network Layer – Communication from Host to Host • Layer 3 uses four basic processes: 1. Addressing 2. Encapsulation 3. Routing: Intermediary devices that connect the networks are called routers. The role of the router is to select paths for and direct packets toward their destination. This process is known as routing. 4. Decapsulation Học viện mạng Bách khoa - Website: www.bkacad.com 4 ( Refer to 5.1.1 ) Network Layer Protocols • Protocols implemented at the Network layer that carry user data include: – Internet Protocol version 4 (IPv4)* – Internet Protocol version 6 (IPv6)* Học viện mạng Bách khoa - Website: www.bkacad.com 5 – Novell Internetwork Packet Exchange (IPX). – AppleTalk. – Connectionless Network Service (CLNS/DECNet). The roles of IPv4 protocol • IPv4 is currently the most widely-used version of IP • The Internet Protocol was designed as a protocol with low overhead. It provides only the functions that are necessary to deliver a packet from a source to a destination over an interconnected system of networks. • The protocol was not designed to track and manage the flow of packets. These functions are performed by other protocols in Học viện mạng Bách khoa - Website: www.bkacad.com 6 packets. These functions are performed by other protocols in other layers. • IPv4 basic characteristic – Connectionless. – Best-effort. – Media Independent. The IPv4 protocol – Connectionless • Describe the implications for the use of the IP protocol as it is connectionless. Học viện mạng Bách khoa - Website: www.bkacad.com 7 The IPv4 protocol – Best Effort • Describe the implications for the use of the IP protocol as it is considered an unreliable protocol • Unreliable means simply that IP does not have the capability to manage, and Học viện mạng Bách khoa - Website: www.bkacad.com 8 capability to manage, and recover from, undelivered or corrupt packets. • Since protocols at other layers can manage reliability, IP is allowed to function very efficiently at the Network layer. The IPv4 protocol – Media independent • Describe the implications for the use of the IP as it is media independent • One major characteristic of the media that the Network layer considers: the maximum size of PDU that each medium can Học viện mạng Bách khoa - Website: www.bkacad.com 9 PDU that each medium can transport. This characteristic is referred to as the Maximum Transmission Unit (MTU). Part of the control communication between the Data Link layer and the Network layer is the establishment of a maximum size for the packet. IPv4 packet – Packaging the Transport layer PD • In some cases, 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. This process is called fragmenting the packet or fragmentation. Học viện mạng Bách khoa - Website: www.bkacad.com 10 [...]... khoa - Website: www.bkacad.com 25 Network Layer Fields • • Variable length up to 64 Kb Contains upper -layer information H c vi n m ng Bách khoa - Website: www.bkacad.com 26 Grouping Devices into Networks • Reasons for grouping devices into sub-networks and define several terms used to identify the sub-networks – Geographic H c vi n m ng Bách khoa - Website: www.bkacad.com 27 Grouping Devices into Networks... - Website: www.bkacad.com 11 Network Layer Fields • 4 bits • Indicates version of IP used • IPv4: 0100; IPv6: 0110 H c vi n m ng Bách khoa - Website: www.bkacad.com 12 Network Layer Fields • • 4 bits Indicates datagram header length in 32 bit words H c vi n m ng Bách khoa - Website: www.bkacad.com 13 Network Layer Fields • • 8 bits Specifies the level of importance that has been assigned by upper -layer. .. devices into sub-networks and define several terms used to identify the sub-networks – Purpose H c vi n m ng Bách khoa - Website: www.bkacad.com 28 Grouping Devices into Networks • List several different reasons for grouping devices into sub-networks and define several terms used to identify the sub-networks – Ownership H c vi n m ng Bách khoa - Website: www.bkacad.com 29 Grouping Devices into Networks •... upper -layer protocol H c vi n m ng Bách khoa - Website: www.bkacad.com 14 Network Layer Fields • • 16 bits Specifies the length of the entire packet in bytes, including data and header H c vi n m ng Bách khoa - Website: www.bkacad.com 15 Network Layer Fields • • 16 bits Identifies the current datagram H c vi n m ng Bách khoa - Website: www.bkacad.com 16 Network Layer Fields • 3 bits(R, DF MF) – R(reserved):... addressing solves the problem of devices communicating across networks of networks H c vi n m ng Bách khoa - Website: www.bkacad.com 34 Hierarchical Addressing • Router only need to know network portion (network address) to indicate the best path to reach the network H c vi n m ng Bách khoa - Website: www.bkacad.com 35 Routing Protocols • Routing is an OSI Layer 3 function It is a hierarchical scheme and allows... sending node IP address H c vi n m ng Bách khoa - Website: www.bkacad.com 22 Network Layer Fields • • 32 bits Specifies the receiving node IP address H c vi n m ng Bách khoa - Website: www.bkacad.com 23 Network Layer Fields • • Variable length Allows IP to support various options, such as security H c vi n m ng Bách khoa - Website: www.bkacad.com 24 Network Layer Fields • • Variable length Extra zeros... devices into sub-networks and define several terms used to identify the sub-networks – Ownership H c vi n m ng Bách khoa - Website: www.bkacad.com 30 Broadcast domain ? - Performance • • A broadcast is a message sent from one host to all other hosts on the network Managing the size of broadcast domains by dividing a network into subnets or replace switch by router H c vi n m ng Bách khoa - Website: www.bkacad.com... ng Bách khoa - Website: www.bkacad.com 17 Network Layer Fields • • 13 bits Used to help piece together datagram fragments H c vi n m ng Bách khoa - Website: www.bkacad.com 18 Network Layer Fields • 8 bits • Specifies the number of hops a packet may travel This number is decreased by one as the packet travels through a router H c vi n m ng Bách khoa - Website: www.bkacad.com 19 Network Layer Fields... www.bkacad.com 31 Why separate hosts into networks ? - Security • List several ways in which dividing a large network can increase network security H c vi n m ng Bách khoa - Website: www.bkacad.com 32 Grouping Devices into Networks • Explain the communication problems that emerge when very large numbers of devices are included in one large network H c vi n m ng Bách khoa - Website: www.bkacad.com 33 Hierarchical... Fields • 8 bits • Indicates which upper -layer protocol, such as TCP(6) or UDP(17), receives incoming packets after IP processing has been completed H c vi n m ng Bách khoa - Website: www.bkacad.com 20 Network Layer Fields • • • 16 bits Helps ensure IP header integrity Not caculated for the encapsulation data H c vi n m ng Bách khoa - Website: www.bkacad.com 21 Network Layer Fields • • 32 bits Specifies . Chapter 5 - OSI Network Layer CCNA Exploration version 4. 0CCNA Exploration version 4. 0 Overview • Identify the role of the Network Layer, as. Indicates version of IP used • IPv4: 01 00; IPv6: 01 10 Network Layer Fields Học viện mạng Bách khoa - Website: www.bkacad.com 13 • 4 bits • Indicates datagram header