CCNA Guide to Cisco Networking Fundamentals Fourth Edition

CCNA Guide to Cisco Networking Fundamentals Fourth Edition Chapter 3 TCP/IP

Objectives • Discuss the origins of TCP/IP • Identify and discuss the different layer functions of TCP/IP • Describe the functions performed by protocols in the TCP/IP protocol suite, including ICMP, UDP, TCP, ARP, and RARP CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 2

Objectives (continued) • Use Ping and Trace and describe their functions • Explain how packets are transmitted • Describe the Cisco three-layer hierarchical model CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 3

Origins of TCP/IP • Transmission Control Protocol/Internet Protocol (TCP/IP) – Resulted from a coordinated effort by the U. S. Department of Defense (DOD) • Advanced Research Projects Agency (ARPA) – Charged with creating a wide area network (WAN) – Results were TCP/IP and ARPANET • DOD funded two projects – The adaptation of TCP/IP to work with UNIX – The inclusion of the TCP/IP protocol with Berkeley UNIX (BSD UNIX) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 4

Overview of the TCP/IP Protocol Suite • The TCP/IP model explains how the protocol suite works to provide communications – Four layers: Application, Transport, Internetwork, and Network Interface • Requests for Comments (RFCs) – Define, describe, and standardize the implementation and configuration of the TCP/IP protocol suite CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 5

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Application Layer • Protocols at the TCP/IP Application layer include: – – – – – File Transfer Protocol (FTP) Trivial File Transfer Protocol (TFTP) Network File System (NFS) Simple Mail Transfer Protocol (SMTP) Terminal emulation protocol (telnet) Remote login application (rlogin) Simple Network Management Protocol (SNMP) Domain Name System (DNS) Hypertext Transfer Protocol (HTTP) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 7

Transport Layer • Performs end-to-end packet delivery, reliability, and flow control • Protocols: – TCP provides reliable, connection-oriented communications between two hosts • Requires more network overhead – UDP provides connectionless datagram services between two hosts • Faster but less reliable • Reliability is left to the Application layer CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 8

Transport Layer (continued) • Ports – TCP and UDP use port numbers for communications between hosts – Port numbers are divided into three ranges: • Well Known Ports are those from 1 through 1, 023 • Registered Ports are those from 1, 024 through 49, 151 • Dynamic/Private Ports are those from 49, 152 through 65, 535 CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 9

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Transport Layer (continued) • TCP three-way handshake – Establishes a reliable connection between two points – TCP transmits three packets before the actual data transfer occurs – Before two computers can communicate over TCP, they must synchronize their initial sequence numbers (ISN) – A reset packet (RST) indicates that a TCP connection is to be terminated without further interaction CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 11

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Transport Layer (continued) • TCP sliding windows – Control the flow and efficiency of communication – Also known as windowing • A method of controlling packet flow between hosts • Allows multiple packets to be sent and affirmed with a single acknowledgment packet – The size of the TCP window determines the number of acknowledgments sent for a given data transfer – Networks that perform large data transfers should use large window sizes CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 15

Transport Layer (continued) • TCP sliding windows (continued) – Other flow control methods include • Buffering • Congestion avoidance CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 16

Internetwork Layer • Four main protocols function at this layer – – Internet Protocol (IP) Internet Control Message Protocol (ICMP) Address Resolution Protocol (ARP) Reverse Address Resolution Protocol (RARP) • ARP – A routed protocol – Maps IP addresses to MAC addresses – ARP tables contain the MAC and IP addresses of other devices on the network CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 17

Internetwork Layer (continued) • ARP (continued) – When a computer transmits a frame to a destination on the local network • It checks the ARP cache for an IP to MAC address mapping for the destination node • ARP request – If a source computer cannot locate an IP to MAC address mapping in its ARP table • It must obtain the correct mapping CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 18

Internetwork Layer (continued) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 19

Internetwork Layer (continued) • ARP request (continued) – A source computer broadcasts an ARP request to all hosts on the local segment • Host with the matching IP address responds this request • ARP request frame – See Figure 3 -7 • ARP cache life – Source checks its local ARP cache prior to sending packets on the local network CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 20

Internetwork Layer (continued) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 21

Internetwork Layer (continued) • ARP cache life (continued) – Important that the mappings are correct – Network devices place a timer on ARP entries – ARP tables reduce network traffic • Reverse Address Resolution Protocol (RARP) – Similar to ARP – Used primarily by diskless workstations • Which have MAC addresses burned into their network cards but no IP addresses – Client’s IP configuration is stored on a RARP server CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 22

Internetwork Layer (continued) • RARP request frame – See Figure 3 -8 • RARP client – Once a RARP client receives a RARP reply, it configures its IP networking components • By copying its IP address configuration information into its local RAM • ARP and RARP compared – ARP is concerned with obtaining the MAC address of other clients – RARP obtains the IP address of the local host CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 23

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Internetwork Layer (continued) • ARP and RARP compared (continued) – The local host maintains the ARP table – A RARP server maintains the RARP table – The local host uses an ARP reply to update its ARP table and to send frames to the destination – The RARP reply is used to configure the IP protocol on the local host • Routers and ARP – ARP requests use broadcasts – Routers filter broadcast traffic – Source must forward the frame to the router CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 25

Internetwork Layer (continued) • ARP tables – Routers maintain ARP tables to assist in transmitting frames from one network to another – A router uses ARP just as other hosts use ARP – Routers have multiple network interfaces and therefore also include the port numbers of their NICs in the ARP table • The Ping utility – Packet Internet Groper (Ping) utility verifies connectivity between two points – Uses ICMP echo request/reply messages CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 26

Internetwork Layer (continued) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 27

Internetwork Layer (continued) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 28

Internetwork Layer (continued) • The Trace utility – Uses ICMP echo request/reply messages – Can verify Internetwork layer (OSI-Network layer) connectivity – Shows the exact path a packet takes from the source to the destination • Accomplished through the use of the time-to-live (TTL) counter – Several different malicious network attacks have also been created using ICMP messages • Example: ICMP flood CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 29

Internetwork Layer (continued) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 30

Network Interface Layer • Plays the same role as the Data Link and Physical layers of the OSI model • The MAC address, network card drivers, and specific interfaces for the network card function at this level • No specific IP functions exist at this layer – Because the layer’s focus is on communication with the network card and other networking hardware CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 31

Understanding Frame Transmission • Each host on a segment evaluates the frame – To determine whether the listed destination MAC address matches its own or is a broadcast to all hosts • The host makes a copy of the frame and sends the original along the network path • On the destination host, frames are sent up the TCP/IP stack – Removing each layer header information • For a packet to be routed on a TCP/IP internetwork – An IP address and MAC address are required for both the source and destination hosts CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 32

Routers on the Network • A router requires: – An IP address for every network segment to which it is connected – A separate network interface or port for each network segment • Computers send frames to destinations that are not on their segment to the router (default gateway) • The router must determine which subnet should receive the frame – The router references its routing table CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 33

Routers on the Network (continued) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 34

Network to Network • Routers maintain routing tables that they use to route packets from one network to another • When a network uses TCP/IP, each port on a router requires an IP address – Allows the router to correctly forward the packet to the appropriate network segment • On a TCP/IP network, the logical addresses on a certain segment must be matched – If you move a computer from one segment to another, the IP address will have to be changed CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 35

Network to Network (continued) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 36

Dynamic or Static Tables • Routing tables match network addresses with the addresses of the routers that handle those networks – The tables can be built statically or dynamically • Dynamic updates are provided through routing protocols – A router capable of dynamic routing can choose from among the various routes on a network – The router communicates with other dynamic routers • To determine the most efficient route from one point to another on the network CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 37

Dynamic or Static Tables (continued) • Methods to determine the best path across a network – The distance-vector algorithm – The link-state algorithm CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 38

Transmitting Packets to Remote Segments • When TCP/IP hosts transmit packets to remote segments – They contact their default gateway (usually a router) • The router checks its routing tables against the destination IP address – To locate the appropriate network interface through which to forward the packet • Router re-addresses the frame or sends the packet to the next router in the path (indirect routing) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 39

Routing Packets CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 40

Routing Packets (continued) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 41

Routing Packets (continued) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 42

Routing Packets (continued) CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 43

The Cisco Three-Layer Hierarchical Model • Cisco Three-Layer Hierarchical model – Does not describe how communications take place – Focuses on how best to design a network • Especially a relatively large network or one that is expected to grow • Each layer of the model is involved in specific functions – Is typically defined by a particular type of device • The three layers of the model from bottom up are Access, Distribution, and Core CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 44

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Access Layer • The layer closest to the users, where they attach to the network • Could be a router if the network is very small – But typically a hub or layer 2 switch • Sometimes called the desktop layer because it deals with connecting workstations to the network • Frames are delivered to the users at this layer CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 46

Distribution Layer • Separates the Access layer from the Core layer • Implements network policies, and provides many networking services – Such as Network Address Translation (NAT), firewall protection, and quality of service (Qo. S) • IP addressing hierarchy is managed at this layer – IP addressing is the process of assigning unique IP addresses to devices on the network • Typically involves routers and includes all of the router functions – Provides almost all of the connectivity tasks CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 47

Core Layer • Responsible for switching large amounts of data quickly and efficiently • To prevent slowing down the switching process: – This layer should not be burdened with security or traffic control measures or any unnecessary additional equipment • The primary device at this layer is a high-end layer 3 switch – Essentially the backbone of the network CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 48

Summary • TCP/IP is not limited to transmission control and Internet protocols • TCP/IP was started by the Defense Advanced Research Projects Agency (DARPA) • TCP/IP maps to a four-layer network model: Application, Transport, Internetwork, and Network Interface • The Application layer in the TCP/IP model covers the Application, Presentation, and Session layers of the OSI reference model CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 49

Summary (continued) • The TCP and UDP protocols reside at the Transport layer of the TCP/IP networking model • Both TCP and UDP use port numbers from 1 to 65, 535 to establish their communications between two points • The Internet Protocol (IP) resides at the Internetwork layer and provides the logical address that can be passed through a router • You can use the Ping utility with IP and ICMP to diagnose and troubleshoot network connections CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 50

Summary (continued) • Address Resolution Protocol (ARP) and Reverse ARP (RARP) reside in the Internetwork layer • The MAC address is the final leg of communication between hosts • Routing tables can be created manually and dynamically • Cisco developed the Three-Layer Hierarchical model to help network administrators design more efficient networks CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 51