Introduction to TCP/IP Chapter 2

TCP/IP Structure and Addressing - OSI Model Review Primary Functions of the OSI Model Layers The OSI Model Layers Table provides an overview of each OSI model layer’s primary functions. OSI Model Layer Unit of Information Layer Function Address type Application User Functionality Program Presentation Character representation Compression Security Character and words Session Establishing, conducting, and ending sessions Transmitting messages from sending computer process to receiving computer process Message Process to process between applications Transport

Primary Functions of the OSI Model Layers TCP/IP Structure and Addressing - OSI Model Review Primary Functions of the OSI Model Layers OSI Model Layer Unit of Information Layer Function Address type Network Transmitting individual packets across a network Packet Packet address identifying receiver’s network and host location Data Link Transmitting frames containing a packet across a link en route to final destination Frame NIC (next node in network) Physical Transmitting bits in the form of signals across physical media Bit

OSI Reference Model Review Allows users to transfer files, send mail, etc. Only layer that users can communicate with directly Key features are ease of use and functionality 7 Application Provides Services Standardized data encoding and decoding Data compression Data encryption and decryption 6 Presentation Manages user sessions Reports upper-layer errors Supports Remote Procedure Call activities 5 Session Connects processes Connection management (e.g., TCP) Error and flow control Connectionless, unreliable (e.g., UDP) 4 Transport Internetwork packet routing Minimizes subnet congestion Resolves differences between subnets 3 Network Moves Data Network access control - MAC address Packet framing Error and flow control The Open Systems Interconnection Reference Model was developed by the International Organization for Standardization and released in 1984. Layer 1: Realm of Electrical Engineering. Deals with impedance, signals, connectors. Layer 2: Understands a frame, what gets to talk on the network, generates or checks the CRC/checksum. Delivers frames based on the DLC address. Layer 3: Connects networks, unreliable delivery based on the network address, routing. Layer 4: Guaranteed delivery to an application address. TCP is an example. Can also be connectionless (unreliable). UDP is an example. Layer 5: Session-oriented conversations. RPC is an example. Layer 6: ASCII to EBCDIC conversion, video compression, security encryption. Layer 7: Protocol Application — not the user application. The OSI model is the key to interoperability between diverse types of environments connected by devices purchased from a variety of vendors. It is also the key enabling Sniffer Portable to make sense of the electrical pulses that fly by on a network cable or phone line. All layers support the layer above it. When troubleshooting, always start from the bottom up. A problem at a lower layer can create a problem at an upper layer. 2 Data Link Moves bits across a physical medium Interface between network medium and network devices Defines electrical and mechanical characteristics of LAN 1 Physical

The Physical Layer operates depending on the chosen network topology. TCP/IP Structure and Addressing - OSI Model Review The Physical Layer The Physical Layer only transmits bits to, and receives bits from, the physical medium, and does not “see” the bits as organized into meaningful patterns, such as an address. The Physical Layer operates depending on the chosen network topology.

A physical address is also referred to as a: TCP/IP Structure and Addressing - OSI Model Review Physical Addresses A physical address is also referred to as a: Hardware address Adapter address Network interface card (NIC) address Medium Access Control (MAC) address A physical address is required for network devices to ultimately deliver information to a given network node.

TCP/IP Structure and Addressing - OSI Model Review The Data Link Layer We can categorize physical addresses, for the purposes of networking, into two general types: A LAN address is commonly found in an Ethernet or Token Ring LAN environment. WAN addresses in High-Level Data Link Control (HDLC) or frame relay network protocol addressing Divided into two distinct parts MAC The MAC address of the node – interfaces with lower layers LLC Tags and identifies protocols - interfaces with upper layers

There are two primary types of logical addresses, as follows: TCP/IP Structure and Addressing - OSI Model Review Logical Addresses A logical address is generally implemented as a software entity rather than a hardware entity. There are two primary types of logical addresses, as follows: Network addresses, processed at the Network Layer Port or process addresses, processed at the Transport Layer

The Three-Layer Network Hierarchy Diagram illustrates this concept. TCP/IP Structure and Addressing - OSI Model Review The Network Layer Because layer protocols designate both a host and a network, they allow us to build hierarchical networks. The Three-Layer Network Hierarchy Diagram illustrates this concept.

Three-Layer Network Hierarchy TCP/IP Structure and Addressing - OSI Model Review The Network Layer Three-Layer Network Hierarchy

TCP/IP Structure and Addressing - OSI Model Review The Transport Layer The Well-Known Port Numbers Table lists some of the more commonly used TCP and User Datagram Protocol (UDP) addresses. Decimal Protocol-Description 20 21 23 25 53 67 69 161 TCP-FTP Data TCP-FTP TCP-TELNET TCP-SMTP TCP/UDP-DNS UDP-BOOTP/DHCP UDP-TFTP UDP-SNMP

The Transport Layer provides: TCP/IP Structure and Addressing - OSI Model Review The Transport Layer The Transport Layer is responsible not only for application addressing, but also for providing reliable communications over the best effort Layer 3 protocols. The Transport Layer provides: Flow control Windowing Data sequencing Recovery

TCP/IP Structure and Addressing - OSI Model Review Layers 5 through 7 The remaining OSI model layers work with the data itself. These layers leave the end-to-end data transport issues to the lower four layers: The Session Layer The Presentation Layer The Application Layer

TCP/IP Structure and Addressing - OSI Model Review The Session Layer The Session Layer: establishes, manages, and terminates sessions between applications. provides its services to the Presentation Layer. synchronizes dialog between Presentation Layer entities and manages their data exchange.

The Presentation Layer: TCP/IP Structure and Addressing - OSI Model Review The Presentation Layer The Presentation Layer: ensures that information sent by the Application Layer of one system is formatted in a manner in which the destination system’s Application Layer can read it. can translate between multiple data representation formats, if necessary.

The Application Layer: TCP/IP Structure and Addressing - OSI Model Review The Application Layer The Application Layer: is the layer closest to the user. provides user application services to application processes outside the OSI model’s scope and does not support the other layers. identifies and establishes the intended communication partners availability, synchronizes cooperating applications, and establishes agreed procedures for application error recovery and data integrity control. determines whether sufficient resources exist for the intended communications.

Lesson 2.3 – The TCP/IP protocol suite TCP/IP Structure and Addressing - Internet Protocol Suite This lesson covers important aspects and protocols of a TCP/IP system. Lesson 2.3 – The TCP/IP protocol suite TCP/IP suite pre-dates the OSI model The TCP/IP model is the defacto model in use on the internet KEY POINT Each TCP/IP architecture layer has a specific purpose.

TCP/IP Structure and Addressing - Internet Protocol Suite Overview of the TCP/IP Protocol Suite The TCP/IP Protocols Diagram shows a detailed picture of the TCP/IP layers. TCP/IP Protocols

The TCP/IP model layers function as follows: TCP/IP Structure and Addressing - Internet Protocol Suite Overview of the TCP/IP Protocol Suite The TCP/IP model layers function as follows: Network Interface Layer Internetwork Layer Transport Layer Application Layer

These low-level protocols define how a host connects to the network. TCP/IP Structure and Addressing - Internet Protocol Suite Network Interface Layer Protocols The Network Interface Layer protocols define rules that determine how a host accesses a LAN. These low-level protocols define how a host connects to the network.

IP, in its current version 4, provides the following functions: TCP/IP Structure and Addressing - Internet Protocol Suite Internetwork Layer Protocols The Internetwork Layer protocols define the basic unit of transfer across a network and provide support for a global addressing scheme and routing. IP, in its current version 4, provides the following functions: A global addressing structure Service type requests Packet fragmentation Packet reassembly

Other protocols at the Internetwork Layer include: TCP/IP Structure and Addressing - Internet Protocol Suite Internetwork Layer Protocols Other protocols at the Internetwork Layer include: Address Resolution Protocol (ARP)/ Reverse ARP (RARP) Internet Control Message Protocol (ICMP) Internet Group Management Protocol (IGMP)

TCP/IP provides applications two different levels of service: TCP/IP Structure and Addressing - Internet Protocol Suite Transport Layer Protocols The Transport Layer’s primary function is to provide communication from one application program to another. TCP/IP provides applications two different levels of service: TCP UDP

TCP/IP Structure and Addressing - Internet Protocol Suite Application Layer Protocols An application passes data to the Transport Layer protocols, which sequence the data into messages, or byte streams, for transport across the network. The TCP/IP protocol suite includes the following Application Layer protocols: Telnet File Transfer Protocol (FTP) Simple Mail Transfer Protocol (SMTP) Simple Network Management Protocol (SNMP)

Post Office Protocol 3 (POP3) Hypertext Transfer Protocol (HTTP) TCP/IP Structure and Addressing - Internet Protocol Suite Application Layer Protocols DNS Post Office Protocol 3 (POP3) Hypertext Transfer Protocol (HTTP) Network News Transfer Protocol (NNTP) UNIX-to-UNIX Copy Program (UUCP) protocol

TCP/IP address types Physical 00-00-23-55-46-78 Logical 10.10.1.2 Port 80, 443, 23, etc

Multiplexing Using TCP Port Numbers Multiplexing relies on the use of a concept called a socket. A socket consists of three things: An IP address A transport protocol A port number

Overview of TCP/IP Applications - Port Numbers Jessie receives 3 packets: A UDP-based ad application A TCP-based wire-transfer application A TCP web server application …Jessie needs to know which application to give the data to, but all three packets are from the same Ethernet and IP address. You might think that Jessie could look at whether the packet contains a UDP or a TCP header, but, as you see in the figure, two applications (wire transfer and web) both are using TCP.

OSI Reference Model Review