CCNA :) Be a Good Network Administrator

Introduction to WANs 1.1.1 A WAN is a data communications network that spans a large geographic area such as a state, province, or country. WANs often use transmission facilities provided by common carriers such as telephone companies. These are the major characteristics of WANs: They connect devices that are separated by wide geographical areas. They use the services of carriers such as the Regional Bell Operating Companies (RBOCs), Sprint, MCI, and VPM Internet Services, Inc. to establish the link or connection between sites. They use serial connections of various types to access bandwidth over large geographic areas. A WAN differs from a LAN in several ways. For example, unlike a LAN, which connects workstations, peripherals, terminals, and other devices in a single building, a WAN makes data connections across a broad geographic area. Companies use a WAN to connect various company sites so that information can be exchanged between distant offices. A WAN operates at the...

Overview A wide-area network (WAN) is a data communications network that connects user networks over a large geographical area. WANs have several important characteristics that distinguish them from LANs. The first lesson in this module will provide an overview of WAN technologies and protocols. It will also explain how WANs and LANs are different, and ways in which they are similar.   It is important to understand the physical layer components of a router. This knowledge builds a foundation for other information and skills that are needed to configure routers and manage routed networks. This module provides a close examination of the internal and external physical components of the router. The module also describes techniques for physically connecting the various router interfaces.   This module covers some of the objectives for the CCNA 640-801, INTRO 640-821, and ICND 640-811 exams. - Students who complete this module should be able to perform the following tasks: ...

Notice The first semester of CCNA has publised with 11 Chapter . Please send feed back on my email, if all reader of have any question, please must write back. I feel happy. The second semester will update after few days, this is under process. Hope all will enjoy. Aqeel Haider (Writer)

Summary This page summarizes the topics discussed in this module. The primary duties of the transport layer, Layer 4 of the OSI model, are to transport and regulate the flow of information from the source to the destination reliably and accurately. The transport layer multiplexes data from upper layer applications into a stream of data packets. It uses port (socket) numbers to identify different conversations and delivers the data to the correct application. The Transmission Control Protocol (TCP) is a connection-oriented transport protocol that provides flow control as well as reliability. TCP uses a three-way handshake to establish a synchronized circuit between end-user applications. Each datagram is numbered before transmission. At the receiving station, TCP reassembles the segments into a complete message. If a sequence number is missing in the series, that segment is retransmitted. Flow control ensures that a transmitting node does not overwhelm a receiving node with da...

SMTP 11.2.5 This page will discuss the features of SMTP. Email servers communicate with each other using the Simple Mail Transfer Protocol (SMTP) to send and receive mail. The SMTP protocol transports email messages in ASCII format using TCP. When a mail server receives a message destined for a local client, it stores that message and waits for the client to collect the mail. There are several ways for mail clients to collect their mail. They can use programs that access the mail server files directly or collect their mail using one of many network protocols. The most popular mail client protocols are POP3 and IMAP4, which both use TCP to transport data. Even though mail clients use these special protocols to collect mail, they almost always use SMTP to send mail. Since two different protocols, and possibly two different servers, are used to send and receive mail, it is possible that mail clients can perform one task and not the other. Therefore, it is usually a good idea to trou...

FTP and TFTP 11.2.3 This page will describe the features of FTP and TFPT. FTP is a reliable, connection-oriented service that uses TCP to transfer files between systems that support FTP. The main purpose of FTP is to transfer files from one computer to another by copying and moving files from servers to clients, and from clients to servers. When files are copied from a server, FTP first establishes a control connection between the client and the server. Then a second connection is established, which is a link between the computers through which the data is transferred. Data transfer can occur in ASCII mode or in binary mode. These modes determine the encoding used for data file, which in the OSI model is a presentation layer task. After the file transfer has ended, the data connection terminates automatically. When the entire session of copying and moving files is complete, the command link is closed when the user logs off and ends the session. TFTP is a connectionless service th...

Introduction to the TCP/IP application layer 11.2.1 This page will introduce some TCP/IP application layer protocols. The session, presentation, and application layers of the OSI model are bundled into the application layer of the TCP/IP model. This means that representation, encoding, and dialog control are all handled in the TCP/IP application layer. This design ensures that the TCP/IP model provides maximum flexibility at the application layer for software developers. The TCP/IP protocols that support file transfer, e-mail, and remote login are probably the most familiar to users of the Internet. These protocols include the following applications: • DNS • FTP • HTTP • SMTP • SNMP • Telnet The next page will discuss DNS. DNS 11.2.2 This page will describe DNS. The Internet is built on a hierarchical addressing scheme. This scheme allows for routing to be based on classes of addresses rather than based on individual addresses. The problem this creates for the use...

UDP 11.1.8 This page will discuss UDP. UDP is the connectionless transport protocol in the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams without guaranteed delivery. It relies on higher-layer protocols to handle errors and retransmit data. UDP does not use windows or ACKs. Reliability is provided by application layer protocols. UDP is designed for applications that do not need to put sequences of segments together. The following protocols use UDP: • TFTP • SNMP • DHCP • DNS The following are the definitions of the fields in the UDP segment: • Source port – Number of the port that sends data • Destination port – Number of the port that receives data • Length – Number of bytes in header and data • Checksum – Calculated checksum of the header and data fields • Data – Upper-layer protocol data The next page discusses port numbers used by both TCP and UDP. TCP and UDP port numbers 11.1.9 This page examines port numbers. Both TCP and U...

Acknowledgment 11.1.6 This page will discuss acknowledgments and the sequence of segments. Reliable delivery guarantees that a stream of data sent from one device is delivered through a data link to another device without duplication or data loss. Positive acknowledgment with retransmission is one technique that guarantees reliable delivery of data. Positive acknowledgment requires a recipient to communicate with the source and send back an ACK when the data is received. The sender keeps a record of each data packet, or TCP segment, that it sends and expects an ACK. The sender also starts a timer when it sends a segment and will retransmit a segment if the timer expires before an ACK arrives. Figure shows a sender that transmits data packets 1, 2, and 3. The receiver acknowledges receipt of the packets with a request for packet 4. When the sender receives the ACK, it sends packets 4, 5, and 6. If packet 5 does not arrive at the destination, the receiver acknowledges with a reques...

Windowing 11.1.5 This page will explain how windows are used to transmit data. Data packets must be delivered to the recipient in the same order in which they were transmitted to have a reliable, connection-oriented data transfer. The protocol fails if any data packets are lost, damaged, duplicated, or received in a different order. An easy solution is to have a recipient acknowledge the receipt of each packet before the next packet is sent. If a sender had to wait for an ACK after each packet was sent, throughput would be low. Therefore, most connection-oriented, reliable protocols allow multiple packets to be sent before an ACK is received. The time interval after the sender transmits a data packet and before the sender processes any ACKs is used to transmit more data. The number of data packets the sender can transmit before it receives an ACK is known as the window size, or window. TCP uses expectational ACKs. This means that the ACK number refers to the next packet that is...

Three-way handshake 11.1.4 This page will explain how TCP uses three-way handshakes for data transmission. TCP is a connection-oriented protocol. TCP requires a connection to be established before data transfer begins. The two hosts must synchronize their initial sequence numbers to establish a connection. Synchronization occurs through an exchange of segments that carry a synchronize (SYN) control bit and the initial sequence numbers. This solution requires a mechanism that picks the initial sequence numbers and a handshake to exchange them. The synchronization requires each side to send its own initial sequence number and to receive a confirmation of exchange in an acknowledgment (ACK) from the other side. Each side must receive the initial sequence number from the other side and respond with an ACK. The sequence is as follows: 1. The sending host (A) initiates a connection by sending a SYN packet to the receiving host (B) indicating its INS = X: A - > B SYN, seq of A =...

Flow control 11.1.2 This page will describe how the transport layer provides flow control. As the transport layer sends data segments, it tries to ensure that data is not lost. Data loss may occur if a host cannot process data as quickly as it arrives. The host is then forced to discard the data. Flow control ensures that a source host does not overflow the buffers in a destination host. To provide flow control, TCP allows the source and destination hosts to communicate. The two hosts then establish a data-transfer rate that is agreeable to both. The next page will discuss data transport connections Session establishment, maintenance, and termination 11.1.3 This page discusses transport functionality and how it is accomplished on a segment-by-segment basis. Applications can send data segments on a first-come, first-served basis. The segments that arrive first will be taken care of first. These segments can be routed to the same or different destinations. Multiple applicatio...

Introduction to the TCP/IP transport layer 11.1.1 This page will describe the functions of the transport layer. The primary duties of the transport layer are to transport and regulate the flow of information from a source to a destination, reliably and accurately. End-to-end control and reliability are provided by sliding windows, sequencing numbers, and acknowledgments. To understand reliability and flow control, think of someone who studies a foreign language for one year and then visits the country where that language is used. In conversation, words must be repeated for reliability. People must also speak slowly so that the conversation is understood, which relates to flow control. The transport layer establishes a logical connection between two endpoints of a network. Protocols in the transport layer segment and reassemble data sent by upper-layer applications into the same transport layer data stream. This transport layer data stream provides end-to-end transport services...

Overview The TCP/IP transport layer transports data between applications on source and destination devices. Familiarity with the transport layer is essential to understand modern data networks. This module will describe the functions and services of this layer. Many of the network applications that are found at the TCP/IP application layer are familiar to most network users. HTTP, FTP, and SMTP are acronyms that are commonly seen by users of Web browsers and e-mail clients. This module also describes the function of these and other applications from the TCP/IP networking model. This module covers some of the objectives for the CCNA 640-801, INTRO 640-821, and ICND 640-811 exams. Students who complete this module should be able to perform the following tasks: • Describe the functions of the TCP/IP transport layer • Describe flow control • Explain how a connection is established between peer systems • Describe windowing • Describe acknowledgment • Identify and describe trans...

Summary This page summarizes the topics discussed in this module. IP is referred to as a connectionless protocol because no dedicated circuit connection is established between source and destination prior to transmission, IP is referred to as unreliable because does not verify that the data reached its destination. If verification of delivery is required then a combination of IP and a connection-oriented transport protocol such as TCP is required. If verification of error-free delivery is not required IP can be used in combination with a connectionless transport protocol such as UDP. Connectionless network processes are often referred to as packet switched processes. Connection-oriented network processes are often referred to as circuit switched processes. Protocols at each layer of the OSI model add control information to the data as it moves through the network. Because this information is added at the beginning and end of the data, this process is referred to as encapsulating ...

Calculating the resident subnetwork through ANDing 10.3.6 This page will explain the concept of ANDing. Routers use subnet masks to determine the home subnetwork for individual nodes. This process is referred to as logical ANDing. ANDing is a binary process by which the router calculates the subnetwork ID for an incoming packet. ANDing is similar to multiplication. This process is handled at the binary level. Therefore, it is necessary to view the IP address and mask in binary. The IP address and the subnetwork address are ANDed with the result being the subnetwork ID. The router then uses that information to forward the packet across the correct interface. Subnetting is a learned skill. It will take many hours performing practice exercises to gain a development of flexible and workable schemes. A variety of subnet calculators are available on the web. However, a network administrator must know how to manually calculate subnets in order to effectively design the network scheme...

Subnetting Class A and B networks 10.3.5 This page will describe the process used to subnet Class A, B, and C networks. The Class A and B subnetting procedure is identical to the process for Class C, except there may be significantly more bits involved. The available bits for assignment to the subnet field in a Class A address is 22 bits while a Class B address has 14 bits. Assigning 12 bits of a Class B address to the subnet field creates a subnet mask of 255.255.255.240 or /28. All eight bits were assigned in the third octet resulting in 255, the total value of all eight bits. Four bits were assigned in the fourth octet resulting in 240. Recall that the slash mask is the sum total of all bits assigned to the subnet field plus the fixed network bits. Assigning 20 bits of a Class A address to the subnet field creates a subnet mask of 255.255.255.240 or /28. All eight bits of the second and third octets were assigned to the subnet field and four bits from the fourth octet. In...

Applying the subnet mask 10.3.4 This page will teach students how to apply a subnet mask. Once the subnet mask has been established it then can be used to create the subnet scheme. The chart in Figure is an example of the subnets and addresses created by assigning three bits to the subnet field. This will create eight subnets with 32 hosts per subnet. Start with zero (0) when numbering subnets. The first subnet is always referenced as the zero subnet. When filling in the subnet chart three of the fields are automatic, others require some calculation. The subnetwork ID of subnet zero is the same as the major network number, in this case 192.168.10.0. The broadcast ID for the whole network is the largest number possible, in this case 192.168.10.255. The third number that is given is the subnetwork ID for subnet number seven. This number is the three network octets with the subnet mask number inserted in the fourth octet position. Three bits were assigned to the subnet field with a c...

Establishing the subnet mask address 10.3.3 This page provides detailed information about subnet masks and how they are established on a network. Selecting the number of bits to use in the subnet process will depend on the maximum number of hosts required per subnet. An understanding of basic binary math and the position value of the bits in each octet is necessary when calculating the number of subnetworks and hosts created when bits were borrowed. The last two bits in the last octet, regardless of the IP address class, may never be assigned to the subnetwork. These bits are referred to as the last two significant bits. Use of all the available bits to create subnets, except these last two, will result in subnets with only two usable hosts. This is a practical address conservation method for addressing serial router links. However, for a working LAN this would result in prohibitive equipment costs. The subnet mask gives the router the information required to determine in whic...

Classes of network IP addresses 10.3.1 This page will review the classes of IP addresses. The combined classes of IP addresses offer a range from 256 to 16.8 million hosts. To efficiently manage a limited supply of IP addresses, all classes can be subdivided into smaller subnetworks. Figure provides an overview of the division between networks and hosts. The next page will explain why subnetting is important Introduction to and reason for subnetting 10.3.2 This page will describe how subnetting works and why it is important. To create the subnetwork structure, host bits must be reassigned as network bits. This is often referred to as ‘borrowing’ bits. However, a more accurate term would be ‘lending’ bits. The starting point for this process is always the leftmost host bit, the one closest to the last network octet. Subnet addresses include the Class A, Class B, and Class C network portion, plus a subnet field and a host field. The subnet field and the host field are cre...

Routing Protocols 10.2.9 This page will describe different types of router protocols. RIP is a distance vector routing protocol that uses hop count as its metric to determine the direction and distance to any link in the internetwork. If there are multiple paths to a destination, RIP selects the path with the least number of hops. However, because hop count is the only routing metric used by RIP, it does not always select the fastest path to a destination. Also, RIP cannot route a packet beyond 15 hops. RIP Version 1 (RIPv1) requires that all devices in the network use the same subnet mask, because it does not include subnet mask information in routing updates. This is also known as classful routing. RIP Version 2 (RIPv2) provides prefix routing, and does send subnet mask information in routing updates. This is also known as classless routing. With classless routing protocols, different subnets within the same network can have different subnet masks. The use of different subnet mask...

IGP and EGP 10.2.7 This page will introduce two types of routing protocols. An autonomous system is a network or set of networks under common administrative control, such as the cisco.com domain. An autonomous system consists of routers that present a consistent view of routing to the external world. Two families of routing protocols are Interior Gateway Protocols (IGPs) and Exterior Gateway Protocols (EGPs). IGPs route data within an autonomous system: • RIP and RIPv2 • IGRP • EIGRP • OSPF • Intermediate System-to-Intermediate System (IS-IS) protocol EGPs route data between autonomous systems. An example of an EGP is BGP. The next page will define link-state and distance vector protocols. Link state and distance vector 10.2.8 Routing protocols can be classified as either IGPs or EGPs. Which type is used depends on whether a group of routers is under a single administration or not. IGPs can be further categorized as either distance-vector or link-state protocols. ...

Routing tables 10.2.5 This page will describe the functions of a routing table. Routers use routing protocols to build and maintain routing tables that contain route information. This aids in the process of path determination. Routing protocols fill routing tables with a variety of route information. This information varies based on the routing protocol used. Routing tables contain the information necessary to forward data packets across connected networks. Layer 3 devices interconnect broadcast domains or LANs. A hierarchical address scheme is required for data transfers. Routers keep track of the following information in their routing tables: • Protocol type – Identifies the type of routing protocol that created each entry. • Next-hop associations – Tell a router that a destination is either directly connected to the router or that it can be reached through another router called the next-hop on the way to the destination. When a router receives a packet, it checks the dest...

Routed versus routing 10.2.3 This page explains the differences between routing protocols and routed protocols. Routed or routable protocols are used at the network layer to transfer data from one host to another across a router. Routed protocols transport data across a network. Routing protocols allow routers to choose the best path for data from a source to a destination. Some functions of a routed protocol are as follows: • Includes any network protocol suite that provides enough information in its network layer address to allow a router to forward it to the next device and ultimately to its destination • Defines the format and use of the fields within a packet The Internet Protocol (IP) and Novell Internetwork Packet Exchange (IPX) are examples of routed protocols. Other examples include DECnet, AppleTalk, Banyan VINES, and Xerox Network Systems (XNS). Routers use routing protocols to exchange routing tables and share routing information. In other words, routing prot...

Routing versus switching 10.2.2 This page will compare and contrast routing and switching. Routers and switches may seem to perform the same function. The primary difference is that switches operate at Layer 2 of the OSI model and routers operate at Layer 3. This distinction indicates that routers and switches use different information to send data from a source to a destination. The relationship between switching and routing can be compared to local and long-distance telephone calls. When a telephone call is made to a number within the same area code, a local switch handles the call. The local switch can only keep track of its local numbers. The local switch cannot handle all the telephone numbers in the world. When the switch receives a request for a call outside of its area code, it switches the call to a higher-level switch that recognizes area codes. The higher-level switch then switches the call so that it eventually gets to the local switch for the area code dialed. The r...

Routing overview 10.2.1 This page will discuss routing and the two main functions of a router. Routing is an OSI Layer 3 function. Routing is a hierarchical organizational scheme that allows individual addresses to be grouped together. These individual addresses are treated as a single unit until the destination address is needed for final delivery of the data. Routing finds the most efficient path from one device to another. The primary device that performs the routing process is the router. The following are the two key functions of a router: • Routers must maintain routing tables and make sure other routers know of changes in the network topology. They use routing protocols to communicate network information with other routers. • When packets arrive at an interface, the router must use the routing table to determine where to send them. The router switches the packets to the appropriate interface, adds the frame information for the interface, and then transmits the frame. ...

Anatomy of an IP packet 10.1.5 IP packets consist of the data from upper layers plus an IP header. This page will discuss the information contained in the IP header: • Version – Specifies the format of the IP packet header. The 4-bit version field contains the number 4 if it is an IPv4 packet and 6 if it is an IPv6 packet. However, this field is not used to distinguish between IPv4 and IPv6 packets. The protocol type field present in the Layer 2 envelope is used for that. • IP header length (HLEN) – Indicates the datagram header length in 32-bit words. This is the total length of all header information and includes the two variable-length header fields. • Type of service (ToS) – 8 bits that specify the level of importance that has been assigned by a particular upper-layer protocol. • Total length – 16 bits that specify the length of the entire packet in bytes. This includes the data and header. To get the length of the data payload subtract the HLEN from the total length. • Id...

Connectionless and connection-oriented delivery 10.1.4 This page will introduce two types of delivery systems, which are connectionless and connection-oriented. These two services provide the actual end-to-end delivery of data in an internetwork. Most network services use a connectionless delivery system. Different packets may take different paths to get through the network. The packets are reassembled after they arrive at the destination. In a connectionless system, the destination is not contacted before a packet is sent. A good comparison for a connectionless system is a postal system. The recipient is not contacted to see if they will accept the letter before it is sent. Also, the sender does not know if the letter arrived at the destination. In connection-oriented systems, a connection is established between the sender and the recipient before any data is transferred. An example of a connection-oriented network is the telephone system. The caller places the call, a connect...

Packet propagation and switching within a router 10.1.3 This page will explain the process that occurs as a packet moves through a network. As a packet travels through an internetwork to its final destination, the Layer 2 frame headers and trailers are removed and replaced at every Layer 3 device. This is because Layer 2 data units, or frames, are for local addressing. Layer 3 data units, or packets, are for end-to-end addressing. Layer 2 Ethernet frames are designed to operate within a broadcast domain with the MAC address that is burned into the physical device. Other Layer 2 frame types include PPP serial links and Frame Relay connections, which use different Layer 2 addressing schemes. Regardless of the type of Layer 2 addressing used, frames are designed to operate within a Layer 2 broadcast domain. When the data is sent to a Layer 3 device the Layer 2 information changes. As a frame is received at a router interface, the destination MAC address is extracted. The address i...

Routed Protocol Routable and routed protocols 10.1.1 This page will define routed and routable protocols. A protocol is a set of rules that determines how computers communicate with each other across networks. Computers exchange data messages to communicate with each other. To accept and act on these messages, computers must have sets of rules that determine how a message is interpreted. Examples include messages used to establish a connection to a remote machine, e-mail messages, and files transferred over a network. A protocol describes the following: • The required format of a message • The way that computers must exchange messages for specific activities A routed protocol allows the router to forward data between nodes on different networks. A routable protocol must provide the ability to assign a network number and a host number to each device. Some protocols, such as IPX, require only a network number. These protocols use the MAC address of the host for the host num...