Network+ Guide to Networks 5 th Edition Chapter 4 Introduction to TCP/IP Protocols

Objectives Identify and explain the functions of the core TCP/IP protocols Explain how the TCP/IP protocols correlate to layers of the OSI model Discuss addressing schemes for TCP/IP in IPv4 and IPv6 protocols Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Objectives (cont’d.) Describe the purpose and implementation of DNS (Domain Name System) and DHCP (Dynamic Host Configuration Protocol) Identify the well-known ports for key TCP/IP services Describe common Application layer TCP/IP protocols Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Characteristics of TCP/IP (Transmission Control Protocol/ Internet Protocol) Protocols : set of instructions designed and coded by programmers--  defines network communication standards TCP/IP –Network layer –Protocol Suite –Subprotocols TCP, IP, UDP, ARP –Developed by Department of Defense ARPANET (1960s) (Internet precursor) Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Characteristics of TCP/IP (cont’d.) Popularity –Low cost –Communicates between dissimilar platforms –Open nature (free use and modification by developers) –Routable Spans more than one LAN (LAN segment) NetBEUI is not routable –Flexible Runs on combinations of network operating systems or network media Disadvantage – requires more configuration Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan

The TCP/IP Core Protocols It is a certain subprotocols of the TCP/IP suite Operates in Transport or Network layers of OSI model Provide basic services to protocols in other layers Most significant core protocols in TCP/IP –TCP –IP Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

TCP (Transmission Control Protocol) Transport layer protocol Provides reliable data delivery services –Connection-oriented subprotocol Establish connection before transmitting, with the TCP Handshake –Sequencing and checksums –Flow control Transmitter waits for ACK before sending more TCP segment format –Encapsulated by IP datagram in Network layer Becomes IP datagram’s “data” Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

TCP Segment Figure 4-1 A TCP segment Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

TCP Segment Source port: Port number at the source node Destination port: Port number at the destination node –Port number : 16 bits Address on the host where the application makes itself available to incoming or outgoing data. 80 is the port number for Web requests via HTTP protocol Sequence number: 32 bits –Identifies the data segment’s position in the stream of data segment already sent. Acknowledgement number: 32 bits – Confirms receipt of the data Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

TCP Segment TCP header length: 4 bits –Indicates the length of the TCP header Reserved: 6 bits –Future use Flags : 6 bits –Collection of six 1-bit fields that signal special conditions. –URG –ACK –PSH –RST –SYN –FIN Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

TCP Segment Sliding-window size: 16 bits –Performs flow control –Maximum number of bytes the sender can issue to a receiver while acknowlegment is outstanding –Ex: 4000 bytes and 1000bytes issues, 250 ack, buffering 750, remaining:? Checksum: 16 bits –Allows receiving node to determine if the TCP segment is corrupted Urgent pointer: 16 bits –Indicates a location in the data field whether urgent data resides Options: 0-32 bits – maximum segment size a network can handle. Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

TCP Segment Padding: variable –Contains filler information to ensure that size of TCP segment is multiple of 32 bits –Often 0 Sequence number: 32 bits –Identifies the data segment’s position in the stream of data segment already sent. Data: variable – Contains original sent data –Size depends on Size of data sent Constrains on TCP segment size  network type Segment limitation  IP datagram Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Important TCP Header Fields Flags, especially SYN and ACK –Indicates purpose of segment Source Port and Destination Port –Guides data to the correct process on the destination computer SEQ number and ACK number –Used to arrange segments in the correct order Data Analyzer : is a program that translates the unlabeled hexadecimal TCP packet into user friendly form Example : text book p140 Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

TCP Handshake Computer A sends SYN to Computer B –SYN flag set SEQ field: Random initial sequence number (ISN) ACK field: Empty (zeroes) Computer B replies with SYN/ACK –SYN and ACK flags set SEQ field: Computer B's random initial sequence number (ISN) ACK field: Computer A's ISN plus 1 Computer A responds with ACK –ACK flag set SEQ field: Computer A's ISN plus 1 (Computer B ACK) ACK field: Computer B's ISN plus 1 FIN flag indicates transmission end Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Figure 4-3 Establishing a TCP connection SYN with SEQ= Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Wireshark Demonstration Relative SEQ and ACK numbers at top Absolute SEQ and ACK values at bottom, in hexadecimal Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

UDP (User Datagram Protocol) Transport layer protocol Provides unreliable data delivery services –Connectionless transport service No assurance packets received in correct sequence No guarantee packets received at all No error checking, sequencing –Lacks sophistication More efficient than TCP Useful situations –Great volume of data transferred quickly(live audio/video over Internet) Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

UDP (cont’d.) Figure 4-4 A UDP segment Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IP (Internet Protocol) Network layer protocol –Routes packets using IP addresses –Provides information on how and where data should be delivered (source and destination addresses) Enables TCP/IP to internetwork –Traverses more than one LAN segment and more than one type of network through a router Unreliable, connectionless protocol –No guaranteed data delivery, no handshake Some higher level protocols provide reliability, like TCP/IP suite  use IP to ensure that data packets are delivered to the right address Checksum: integrity of the routing information in the IP header Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IP (cont’d.) Figure 4-5 An IP datagram Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Important IP Header Fields Version –Version number of the protocol (IPv4 or IPv6) –Most networks support IPv4 thus it is 4 bits long IHL (Internet Header Length) –Identifies the IP header length –Indicates to the receiver where data will begin –Minimum 5 blocks DiffServ (Differentiated Services) Informs the router what level of precedence they should apply when processing the incoming packet Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Important IP Header Fields Total Length –The total IP datagram (header + data) length –Maximum bytes Identification –Identifies the message to which a datagrams belongs and enables reassembly of fragmented packets Flags –Indicates whether a message is fragmented and whether it is the last in the fragment Fragment offset –Indicates where the datagram belongs in the incoming set of fragments Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Important IP Header Fields TTL (Time to Live) –Indicates the maximum time the datagram remains in the network before it is discarded –Measured in number of times a datagram has been forwarded by a router or the number of router hops –Decreases by one for each router the packet passes through (a "hop") –When TTL reaches zero, the packet is discarded Protocol –Identifies the type of Transport layer protocol that will receive the datagram (TCP or UDP) Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Important IP Header Fields Header Checksum –Allows the receiver to calculate whether the IP header has been corrupted during transmission Source Destination IP Addresses –Used to deliver packet and response Options –Used to specify special options Padding –Contains filler information to ensure that the size of the TCP header is a multiple of 32 bits Data –Contains data originally sent by the source, in addition to the information added in the transport layer. Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

ICMP (Internet Control Message Protocol) Network layer protocol –Reports on data delivery success/failure Announces transmission failures to sender –Network congestion –Data fails to reach destination –Data discarded: TTL expired ICMP cannot correct errors –Provides critical network problem troubleshooting information (TCP corrects) Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IGMP (Internet Group Management Protocol) Network layer protocol Manages multicasting –Multicasting: is a transmission method that allows one node to send data to defined group of nodes not like broadcast Uses –Internet teleconferencing or videoconferencing –Routers sending traffic reports to each other Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

ARP (Address Resolution Protocol) Network layer protocol Obtains a MAC address from an IP address and then creates a database that maps the MAC address to the host’s IP(logical) address Broadcast is used to know addresses ARP table (ARP cache) –Computers store recently-used MAC-to-IP address mappings on their storage devices –Increases efficiency –Two entry types: dynamic and static Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

ARP Demonstration –Dynamic ARP table entries: entries that are created when a client makes an ARP request that can not be satisfied by data already in the ARP table –Static ARP table entries: entries that are created manually using ARP utility ARP utility is controlled by ARP command :used for troubleshooting ARP -D * –Clears the ARP cache ARP -A –Shows the ARP cache Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

ARP Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

RARP (Reverse Address Resolution Protocol) Converts MAC address to IP Address –Obsolete—replaced by DHCP Used if a node does not know its IP address Broadcast message with its MAC address Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IPv4 Addressing

Networks recognize two addresses –Logical (Network layer)  automatically or manually set using protocol standard rules –Physical (MAC, hardware) addresses ->by NIC’s manufacturer at factory IP protocol responsible to handle logical addressing  address on TCP/IP networks called IP addresses IP addresses are assigned and used according to very specific parameters Unique 32-bit number Divided into four octets/bytes (sets of eight bits) Separated by periods Example: Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IPv4 Addressing (cont’d.) IP address information –An IP Address contains two types of information network (network to which computer is attached) and host (a computer within that network) –Network Class determined by first octet (seeTable4-1) Class A, Class B, Class C Table 4-1 Commonly used TCP/IP classes Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IPv4 Addressing (cont’d.) Class D, Class E rarely used (never assigned to devices on our network) –Class D: value between 224 and 239 Multicasting –Class E: value between 240 and 254 Experimental use by IETF (Internet Engineering Task Force) Each of the other three octets consists of eight bits -  256 combinations –Networks use 1 through 254 –0: reserved as placeholder when referring to an entire group of computers on a network  all devices whose first octet is 10 –255: reserved for broadcast transmission  all devices on the network segment Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IPv4 Addressing (cont’d.) Class A devices –Net work ID share same first octet (bits 0-7) –Host: second through fourth octets (bits 8-31) –Large companies and government organizations  early Internet users such as IBM Class B devices –Share same first two octet (bits 0-15) –Host: second through fourth octets (bits 16-31) –Midsized organizations Class C devices –Share same first three octet (bits 0-23) –Host: second through fourth octets (bits 24-31) –Smaller organizations  colleges Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Figure 4-8 IP addresses and their classes Running out of addresses –IPv6 (next generation IP) incorporates new addressing scheme Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IPv4 Addressing (cont’d.) Loopback address –First octet equals 127 ( ) Loopback test –Attempting to connect to own machine (device communicating with itself) –Powerful troubleshooting tool A positive response from a loopback test means the TCP/IP core protocols are installed and in use on the workstation. Windows XP, Vista/ ipconfig command /IP/ /all Unix, Linux/ ifconfig command / innet /-s Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IPv4 Addressing (cont’d.) Figure 4-9 Results of the ipconfig /all command on a Windows XP or Windows Vista workstation Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IPv4 Addressing (cont’d.) Figure 4-10 Results of the ifconfig -a command on a UNIX workstation Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Binary and Dotted Decimal Notation Decimal number between 0 and 255 represents each binary octet Period (dot) separates each decimal Dotted decimal address has binary equivalent –Converting each octet –Remove decimal points Example : – – Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Subnet Mask A special 32-bit number (net mask) that identifies device’s subnet through combining it with device IP address. Informs network about segment, network where device attached Distinguishes Network ID from the Host ID Four octets (32 bits) –Expressed in binary or dotted decimal notation Assigned same way as IP addresses –Manually, or automatically (via DHCP) Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Subnetting –The process of subdividing network single class into multiple, smaller logical networks (segments) Control network traffic Make best use of limited number of IP addresses –Subnet mask varies depending on subnetting method Nonsubnetted networks use defaults Table 4-2 Default subnet masks Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Assigning IP Addresses

Government-sponsored organizations –Dole out IP address blocks to ISPs and other network providers –IANA, ICANN, RIRs Companies, individuals –Obtain IP addresses from ISPs Every network node must have unique IP address –Otherwise it cannot send or receive Internet packets –Error message generated on the new client and its TCP/IP services are disabled –Existing host may receive an error message but can continue to function Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Static and Automatic IP Address Assignment Static IP address –Manually typed into each device –Modify client workstation TCP/IP properties Only way to change –Human error cause duplicates Automatic IP addressing –BOOTP and DHCP –Reduce duplication error Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

BOOTP (Bootstrap Protocol) To facilitate IP address management  Administrating each configuration file (manual static addresses) that is stored on the hard disk of each networked computer Developed in Mid-1980s Application layer protocol Central list of IP addresses, associated devices’ MAC addresses –Assign client IP addresses dynamically Dynamic IP address –Assigned to device upon request –Changeable Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

BOOTP (cont’d.) BOOTP process –Client connects to network –Sends broadcast message asking for IP address Includes client’s NIC MAC address –BOOTP server looks up client’s MAC address in BOOTP table –Responds to client Client’s IP address Server IP address Server host name Default router IP address Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

BOOTP (cont’d.) Process resembles RARP –Difference RARP requests, responses not routable (RARP server for every LAN) RARP only capable of issuing IP address to client but BOOTP may issue additional information (client’s subnet mask) BOOTP surpassed by DHCP (Dynamic Host Configuration Protocol) –More sophisticated IP addressing utility –DHCP requires little intervention BOOTP difficult to maintain on large networks but useful for networked diskless workstations. Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

DHCP (Dynamic Host Configuration Protocol) Assigns network device unique IP address –Automatically Application layer protocol Developed by IETF (BOOTP replacement) Operation –Similar to BOOTP –Lower administrative burden Administrator does not maintain table but only requires DHCP service on DHCP server Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Reasons to Use DHCP Saves time spent assigning IP addresses Prevents accidental duplicate IP addresses Allows users to move devices (like laptops) without having to change their TCP/IP configuration as long as a workstation is configured to obtain its IP address from a central server. Makes IP addressing transparent for mobile users Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

DHCP Leasing Process Device borrows (leases) IP address –Devices use IP address temporarily for a specific time limit Lease time –Determine when client obtains IP address at log on –Lease time length depends on DHCP server and client configuration –User may force lease termination at client or network administrator at server DHCP service configuration –Specify leased address range –Configure lease duration Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

DHCP Leasing Process Several steps to negotiate client’s first lease that include four exchanged packets IP address remains in the client’s TCP/IP setting even after it shuts down or reboot IP address is changed only if the lease duration is terminated or it moves to another network Steps for lease Process: –Client connects to the network then sends broadcast DHCP discover packet via UDP protocol to DHCP/BOOTP server Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

DHCP Leasing Process –The broadcast message is received by every server on the same subnet and responds with available IP address, subnet mask, DHCP address and lease duration as broadcast message as well (client does not have IP address) –The client accepts the first received IP, responds with a broadcast confirmation message (the IP address is accepted) and each other server returns the IP address they have reserved for the client to their pool of available addresses. –Finally the selected server replies to the client with an acknowledgement message and provides more information such as DNS, subnet mask, gateway address. Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

DHCP Leasing Process (cont’d.) Figure 4-11 The DHCP leasing process Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Terminating a DHCP Lease Lease expiration –Automatic Established in server configuration (lease duration) –Manually terminated at any time Client’s TCP/IP configuration Server’s DHCP configuration Circumstances requiring lease termination –DHCP server fails and replaced Windows: release of TCP/IP settings by typing ipconfig /release in command prompt DHCP services run on several server types –Installation and configurations vary Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

APIPA (Automatic Private IP Addressing) Client cannot communicate without valid IP address What if DHCP server not running? –Microsoft Windows offers Automatic Private IP Addressing Provides IP address automatically IANA (Internet Assigned Numbers Authority) reserved predefined pool of addresses – through Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

APIPA (cont’d.) APIPA –Assigns a random IP address from the y.x range –Assigns default Class B subnet mask Disadvantage –Computer only communicates with other nodes using addresses in APIPA range –Cannot normally connect to the Internet or any other WAN with a y.z address Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

APIPA (cont’d.) APIPA suitable use –Small networks: no DHCP servers APIPA unsuitable use –Networks communicating with other subnets, WAN APIPA enabled by default: OK –First checks for DHCP server Allows DHCP server to assign addresses –Does not reassign new address if static –Works with DHCP clients –Disabled in registry Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IPv4 Addressing (cont’d.) Addressing Guidelines –First octet represents the Class –Host ID and Network ID depend on the Class used –Network ID can not be 127 (127 is reserved for loopback test) –Network ID and Host ID can not be 255 (broadcast) –Network ID and Host ID can not be 0 (this network only) –IP can not be , , (subnet mask) –Host ID must be unique within a network Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IPv4 Addressing (cont’d.) Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan IP Class Network ID Host ID Binary notation Subnet mask Same network

Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan IP Class Network ID Host ID Binary notation Subnet mask Same network IP Class Network ID Host ID Binary notation Subnet mask Same network

Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan IP Class Network ID Host ID Binary notation Subnet mask Same network

IPv6 Addressing

IPv6, IP next generation or IPng –Replacing IPv4 (gradually) IPv6 support –Most new applications, servers, network devices Delay in implementation –Cost of upgrading infrastructure IPv6 advantages –More efficient header, better security, better prioritization provisions, automatic IP address configuration and additional IP addresses Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IPv6 Addressing (cont’d.) Difference between IPv4 and IPv6 addresses –Size IPv4: 32 bits IPv6: 128 bits (eight 16-bit fields) IPv6: 2 96 (4 billion times 4 billion times 4 billion) available IP addresses –Representation IPv4: binary numbers separated by period IPv6: hexadecimal numbers separated by colon IPv6 shorthand: “::” any number of multiple, zero-value fields, but zeroes substituted only once IPv6 loopback address is 0:0:0:0:0:0:0:1 not Abbreviated loopback address ::1 Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IPv6 Addressing (cont’d.) –Scope IPv6 addresses can reflect scope of transmission’s recipients (single node, group, special kind of group) Unicast address represents single device interface –ex: workstation’s NIC, loopback Multicast address represents multiple interfaces (often on multiple devices) –ex: point-to-multipoint, same data to several devices –Global (broadcast) or link-local (computers share same link as the sender) Anycast address represents any one interface from a group of interfaces –Any one can accept transmission –Identifying all routers that belong to one ISP  faster –Not assigned to hosts (servers, workstations) Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

IPv6 Addressing (cont’d.) –Format Prefix (IPv6) Beginning of address Variable-length field Indicates address type: unicast, multicast, anycast FE80 or FEC0  unicast or anycast FF0x  muticast, where x is a character that corresponds to a group scope ID. (ex FF02 link-local and FF0E global) Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Sockets and Ports

Processes assigned unique port numbers Process’s socket –Port number plus host machine’s IP address Port numbers –Simplify TCP/IP communications –Ensures data transmitted correctly (correct application) Example –Telnet port number: 23 –IPv4 host address: –Socket address: :23 Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Sockets and Ports (cont’d.) Figure 4-12 A virtual connection for the Telnet service Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Sockets and Ports (cont’d.) Port number range: 0 to Three types based on IANA –Well Known Ports Range: 0 to 1023 Operating system or administrator use –Registered Ports Range: 1024 to Network users, processes with no special administrative privileges Defaults assignment of these ports must be registered with IANA –Dynamic and/or Private Ports Range: through No restrictions and open use Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Sockets and Ports (cont’d.) Assigned by the operating system or software programs An editable text-based file of port numbers and associative services is maintained by server Using non standard ports : –A server could be configured to use an unusual port, such as a Web server on port 8080 Not good idea: standards violation and processes programmed to use the standard port will not be able to communicate Sometimes done for security or testing Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Sockets and Ports (cont’d.) Table 4-3 Commonly used TCP/IP port numbers Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Host Names and DNS (Domain Name System)

TCP/IP addressing consists of long, complicated numbers –Good for computers but people remember words better (ex: civil id or name)  Internet authorities established Internet node naming system Host –Internet device Host name –Name describing device Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Domain Names Domain –Group of computers belonging to same organization and share common part of their IP addresses4 Domain name –Identifies domain (loc.gov) –Associated with company, university, government organization –Represented by a series of character strings called labels separated by dots Fully qualified host name (jasmine.loc.gov) –Local host name + domain name Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Domain Names (cont’d.) Label (character string) –Separated by dots –Represents level in domain naming hierarchy Example: –Top-level domain (TLD): com –Second-level domain: google, may contain multiple third-level domains –Third-level domain: www ICANN established domain naming conventions  certain TLD apply to every type of organization that uses the Internet Domain names must be registered with Internet naming authority that works on behalf of ICANN Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Table 4-4 Top-level domains Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Domain Names (cont’d.) ICANN approved over 240 country codes Host and domain names restrictions –Any alphanumeric combination up to 63 characters –Include hyphens, underscores, periods in name –No other special characters Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Hosts Files ARPAnet used HOSTS.TXT file –Associated host names with IP addresses (< 1000 hosts) –ASCII host file –Host matched by one line Identifies host’s name, IP address Alias provides nickname for the host (third field) –Disadvantages: central Internet failure, difficult to maintain large files (bandwidth capacity strained by searching single file from different nations) UNIX-/Linux-based computer –Host file called hosts, located in the /etc directory Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Windows Hosts File Windows 9x, NT, 2000, XP, Vista computer –Host file called hosts –Located in %systemroot%\system32\drivers\etc folder Rarely used, but still present Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

DNS (Domain Name System) Hierarchical Distributed Database –Associates domain names with IP addresses in hierarchal way. DNS refers to: –Application layer service accomplishing association –Organized system of computers; databases making association possible DNS redundancy –Many computers across globe related in hierarchical manner –Root servers 13 computers (ultimate authorities) Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Figure 4-14 Domain name resolution Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Name servers (DNS servers) Components for DNS service –Resolvers –Name servers –Name space Resolvers: Any host on the Internet that look up domain name information Name or DNS servers: Servers that contain databases of associated names, IP addresses Provide information on request –To convert names like into IP addresses like This process is called name resolution Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

DNS (cont’d.) Resource record –Describes one piece of DNS database information –Many different types Dependent on function –Contents Name field: domain name of host Type field: type of resource record involved Class field : IN or Internet Time to Live field : how long the record saved in temporary memory Data length field: data size Actual data Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

DNS (cont’d.) Resource records can be manually maintained by network administrators or dynamically maintained by clients. –Clients can be configured to trigger DNS update when Receive new IP address through DHCP Change host name Connect to network –User can force DNS record update by command Ipconfig /registerdns Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Demo: CCSF’s Name Servers Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Configuring DNS Large organizations –Often maintain two name servers Primary and secondary –Ensures Internet connectivity Each device must know how to find server –Automatically by DHCP –Manually configure workstation TCP/IP properties Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Configuring DNS (cont’d.) Figure 4-15 Windows XP Internet Protocol (TCP/IP) Properties dialog box Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

DDNS (Dynamic DNS) Additional service to DNS that allows a user to host a Web site on a computer with a dynamic IP address DNS is suitable for static IP Process –Service provider runs program on user’s computer Notifies service provider when IP address changes –Service provider’s server launches routine to automatically update DNS record Effective throughout Internet in minutes Not as good as a real static IP address Larger organizations pay for statically assigned IP address Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Application Layer Protocols

Work over TCP or UDP plus IP –Translate user requests Into format readable by network HTTP –Application layer protocol central to using Web BOOTP and DHCP –Automatic address assignment Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Telnet Terminal emulation protocol –Log on to remote hosts Using TCP/IP protocol suite –TCP connection established Keystrokes on user’s machine act like keystrokes on remotely connected machine Often connects two dissimilar systems Can control remote host Drawback –Notoriously insecure Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

FTP (File Transfer Protocol) Send and receive files via TCP/IP Host running FTP server portion –Accepts commands from host running FTP client FTP commands –Operating system’s command prompt No special client software required FTP hosts allow anonymous logons After connected to host –Additional commands available –Type help Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

FTP (cont’d.) Graphical FTP clients –MacFTP, WS_FTP, CuteFTP, SmartFTP Rendered command-line method less common FTP file transfers directly from modern Web browser –Point browser to FTP host –Move through directories, exchange files SFTP –More secure Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

TFTP (Trivial File Transfer Protocol) Enables file transfers between computers –Simpler (more trivial) than FTP TFTP relies on Transport layer UDP –Connectionless –Does not guarantee reliable data delivery No ID and password required –Security risk No directory browsing allowed Useful to load data, programs on diskless workstation Used to put software on IP phones and routers Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

NTP (Network Time Protocol) Synchronizes network computer clocks Depends on UDP Transport layer services –Benefits from UDP’s quick, connectionless nature Time sensitive Cannot wait for error checking Time synchronization importance –Routing –Time-stamped security methods –Maintaining accuracy, consistency between multiple storage systems Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

NNTP (Network News Transfer Protocol) Facilitates newsgroup messages exchange –Between multiple servers, users Similar to –Provides means of conveying messages Differs from –Distributes messages to wide group of users at once User subscribes to newsgroup server host News servers –Central collection, distribution point for newsgroup messages Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

PING (Packet Internet Groper) Provides verification –TCP/IP installed, bound to NIC, configured correctly, communicating with network –Host responding Uses ICMP services –Send echo request and echo reply messages Determine IP address validity Ping IP address or host name Ping loopback address: –Determine if workstation’s TCP/IP services running Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan

Operating system determines Ping command options, switches, syntax Figure 4-17 Output from successful and unsuccessful PING tests PING (cont’d.) Network+ Guide to Networks, 5th Edition modified by Dr. Feda ALShahwan