Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
Network FundamentalsNetwork Fundamentals
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
Introduction
• Transport Layer allows end-to-end transfer of application data.• Network Layer allows end-to-end device communication.
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
Network Layer – Communication from host to host
• Layer 3 provides services to exchange the individual pieces of data over the network between identified end devices.
• To accomplish this end-to-end transport, Layer 3 uses four basic processes:
1. Addressing2. Encapsulation3. Routing4. Decapsulation
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
Network Layer Protocols
• Routed Protocols: carry user data1. Internet Protocol version 4(IP v4), IP v6.2. Novell Internetwork Packet Exchange (IPX).3. AppleTalk.4. Connectionless Network Service (CLNS/DECNet).• Routing Protocols: direct packet to destination1. RIP, BGP “application layer Protocols”2. IGRP, EIGRP3. OSPF4. IS-IS• Other supporting protocols1. ICMP2. ARP
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
IP v4 Characteristics
• IP v4 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.
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
Connectionless
• IP packets are sent without notifying the end host that they are coming.
• Connection-oriented protocols require that control data be exchanged to establish the connection.
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
Best effort «Unreliable»
• Means that IP does not have the capability to manage, and recover from, undelivered or corrupt packets.
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
Media Independent
• IPv4 and IPv6 operate independently of the media that carry the data at lower layers of the protocol stack.
• It is the responsibility of the OSI Data Link layer to take an IP packet and prepare it for transmission over the medium.
• MTU: the maximum sizeof a packet.
• The Data Link layer passesthe MTU upward to the Network layer.
• Intermediary device like a router usually fragments the packet
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
IP v4 Packet Header
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
IP v4 Packet Header
• Version: Contains the IP version number (4)• Header Length (IHL): Specifies the size of the packet header to know where
the header ends and hence data begins. • Packet Length: The entire packet size, including header and data. • Type-of-Service (TOS): reflect priority.• TTL: indicates the remaining "life" of the packet. TTL is decreased by at least
one each time the packet is processed by a router.• Identification: uniquely identifies fragments of an original IP packet.• Fragment offset: identifies the order in which to place the packet fragment in
the reconstruction. • MF & DF Flags• Header Checksum: used for error checking the packet header.• Protocol: Indicates the data payload type that the packet is carrying. Ex: 01
ICMP, 06 TCP, 17 UDP
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
IP Fragmentation
• A router may have to fragment a packet when forwarding it from one medium to another medium that has a smaller MTU.
• Packet does not get reconstructed until it reaches the host.If DF = 1, it will not fragment packet, but discards it.
• Fragment Offset field and MF flag are used to reconstruct the packet at the destination host.
Data = 1480 bytesIP
Data = 500IP
Data = 480IP
IP Packet Fragments
Original IP Packet
IP Header = 20 bytes
Data = 500IP
Data = 500L2 L2
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
Dividing Networks
• large network should be separated into smaller networks that are interconnected.
• These smaller networks are often called subnetworks or subnets.
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Grouping Hosts Geographically
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Grouping Hosts for Purpose
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Grouping Hosts for Ownership
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
Layer 3 Devices
Router:- Best path determination- Creating routing table- Connecting different LANs
• All interfaces of the router are members in a multiple broadcast domains, and multiple collision domains.
• Supports more than one technology
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
Device Parameters
• IP address• Subnet Mask• Default gateway• DNS Server
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
ARP
SIEMENSNIXDORF
SIEMENSNIXDORF
Host A
Host BIP Address: 128.0.10.4HW Address: 080020021545
ARP Reply
ARP Request - Broadcast to all hosts„What is the hardware address for IP address 128.0.10.4?“
SIEMENSNIXDORF
Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy
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