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Hands-on Networking Fundamentals

Hands-on Networking Fundamentals. Chapter 3: Using Network Communication Protocols. An Overview of Network Protocols. Protocols enable effortless interchange among connected devices Computer communication requires common protocol Just as human communication requires a common dialect

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Hands-on Networking Fundamentals

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  1. Hands-on Networking Fundamentals Chapter 3: Using Network Communication Protocols

  2. An Overview of Network Protocols • Protocols enable effortless interchange among connected devices • Computer communication requires common protocol • Just as human communication requires a common dialect • LANs may transport multiple protocols • Network devices (such as routers) makes distinctions • Example: router that connects two LANs and a WAN must recognize each protocol in use on each LAN and WAN network BUSI-138

  3. Figure 3-1 Transporting multiple protocols on a network BUSI-138

  4. Properties of a LAN Protocol • Capabilities included in properties of LAN protocol • Enable reliable network links • Communicate at relatively high speeds • Handle source and destination node addressing • Follow standards, particularly the IEEE 802 standards • Protocols have different strengths and drawbacks • Example 1: some (not all) protocols are routable • Example 2: some protocols have poor error checking • Protocols typically used on LANs • IPX/SPX, NetBEUI, AppleTalk, and TCP/IP • TCP is most widely used due to relation to Internet BUSI-138

  5. LAN Protocols and Operating Systems • Protocols typically used for communication between networks include TCP/IP, IPX/SPX, NetBEUI, and AppleTalk • TCP/IP is nearly universally used today • It’s popularity has caused the others listed above to become replaced or used only on much older networks BUSI-138

  6. TCP/IP • Currently the most widely used protocol suite and the protocol of the Internet • Supported by most network server and workstation operating systems • Network device vendors write their operating system software for TCP/IP • Initially used on UNIX systems • Was rapidly adopted on many kinds of networks BUSI-138

  7. The History and Role of TCP/IP • Advanced Research Projects Agency (ARPA) • Networking goal: enable university, research, and Defense Department to communicate (ARPANET) • Difficult at first because computer manufacturers were very proprietary so not all computers could communicate with each other • An early protocol: Network Control Protocol (NCP) • Enabled DEC, IBM, and other hosts to communicate • Did not provide wholly reliable communication • TCP/IP combination: an improvement over NCP • TCP (Transmission Control Protocol) • IP (Internet Protocol) BUSI-138

  8. The History and Role of TCP/IP • Five advantages of TCP/IP • Used worldwide on most networks and the Internet • Influences design of wide range of network devices • Main protocol of most computer operating systems • Subject to many troubleshooting and network analysis tools • Understood by large body of network professionals • TCP/IP is associated with a suite of protocols and applications BUSI-138

  9. Protocols and Applications of the TCP/IP Suite • TCP/IP is a layered set of protocols, similar to, but not identical to the OSI layers • Nearly 100 standard protocols • Core components of TCP/IP protocol suite • Transmission Control Protocol (TCP) • User Datagram Protocol (UDP) • Internet Protocol (IP) BUSI-138

  10. How TCP Works • TCP is a transport protocol (Layer 4 in OSI model) • Establishes sessions between network nodes • Sequences and acknowledges frames • Provides for reliable end-to-end delivery • Sequence number placed in TCP frame header • Shows frame sequence in stream of frames • Indicates amount of data in frames • Sequence number checked for frame correctness • Sliding window: number of data bytes in frame • May be dynamically adjusted if two nodes agree BUSI-138

  11. How TCP Works • Main TCP functions (similar in OSI Transport layer) • Monitor for session requests • Establish sessions with other TCP nodes • Transmit and receive data • Close transmission sessions • TCP ports: used to form virtual circuit between nodes • Enable multiple processes to communicate in session • TCP segment: header and data payload in TCP frame • TCP header contains 11 fields (see page 96-97) • Minimum length is 20 bytes BUSI-138

  12. Figure 3-2 TCP frame BUSI-138

  13. Table 3-3 Sample TCP port BUSI-138

  14. How the User Datagram Protocol (UDP) Works • User Datagram Protocol (UDP) • Connectionless protocol • Operates at OSI Layer 4 (like TCP) • Alternative to TCP when high reliability not required • Frame has four-field header and data • Relies only on checksum to ensure reliability • Connectionless protocol • No flow control, sequencing, or acknowledgment • Advantages: adds little overhead onto IP • Used with transaction processing applications • Carries important network status messages BUSI-138

  15. Figure 3-6 UDP frame BUSI-138

  16. How the Internet Protocol (IP) Works • A LAN may be composed of series of subnetworks • A WAN may consist of a series of autonomous networks • Examples: DSL, SONET, frame relay, and MPLS • Communications enabled by Internet Protocol (IP) • Between different subnetworks on a LAN • Between different networks on a WAN • Network transport options should be compatible with TCP/IP, such as: Ethernet, FDDI, ISDN, DSL, frame relay, ATM, MPLS, and SONET BUSI-138

  17. How the Internet Protocol (IP) Works • Basic IP Functions: data transfer, packet addressing, packet routing, fragmentation, detection of errors • Addressing essential for data transfer and routing • 32-bit network node address is used in IPv4 • 128-bit node address is used in IPv6 • Connectionless protocol • Provides network-to-network addressing and routing information • Changes packet size when size varies with network • Datagram: TCP segment formatted with IP header • IP packet header consists of thirteen fields BUSI-138

  18. Figure 3-7 TCP/IP packet encapsulation BUSI-138

  19. Using IPv4 and IPv4 Addressing • IP addresses are used to identify: • A specific node • The network on which that node resides • Unique IP address enables accurate packet delivery • Two nodes with the same IP address will create an error • Understanding IP addressing concepts is fundamental in networking BUSI-138

  20. Basic IPv4 Addressing • Dotted decimal notation: IP address format • Four fields totaling 32 bits • Fields are decimal values representing 8-bit binary octets • Part of the address is the network ID, other part is the host ID • Example in decimal format: 129.5.10.100 • Five IP address classes, Class A through Class E • Address reflects network size and transmission type • Three types of transmission • Unicast: packet sent to each requesting client • Multicast: packet sent to group of requesting clients • Broadcast: communication sent to all network nodes BUSI-138

  21. Basic IPv4 Addressing • Class A addresses: are identified by a value between 1 and 126 in the first position of the dotted decimal address (octet) • First octet identifies the network id and the last three octets identify the host id • Class B addresses: are identified by a value between 128-191 in the first octet • First two octets identify the network id and the last two octets identify the host id • Class C addresses: are identified by a value of 192-223 in the first octet • First three octets identify the network id and last octet identifies the host id BUSI-138

  22. Basic IPv4 Addressing • Class D addresses are used for multicasting • First octet contains the value 224 – 239 • Class E addresses are used for experimentation • First octet contains the value 240-254 • Special purpose IP addresses: • 255.255.255.255 – a broadcast packet sent to all network locations • Packets with 127 in the first octet are used for network testing BUSI-138

  23. Table 3-5 IP address classes BUSI-138

  24. The Role of the Subnet Mask • TCP/IP requires a configured subnet mask • Subnet mask is used for two purposes • Show the class of addressing used • Divide networks into subnetworks to control traffic • Example of a subnet mask: • 11111111.00000000.00000000.00000000 (255.0.0.0) • Indicates Class A network • Ones represent network/subnet identification bits • Zeroes represent host identification bits BUSI-138

  25. Creating Subnetworks • Subnet mask contains subnet ID • Subnet ID contained within network and host IDs • Subnet ID is determined by the network administrator • Ex: 11111111.11111111.11111111.00000000 (255.255.255.0) • Third octet in Class B address indicates subnet ID • Subnet mask overrides four-octet length limitation • Classless Interdomain Routing (CIDR) addressing • Puts a slash ( / ) after the dotted decimal notation • Number after slash represents bits in network ID • Example (decimal): 165.100.18.44/18 • 18 bits needed for network ID, 14 for host ID (32 -18) BUSI-138

  26. IPv4 Address Rules • Network number 127.0.0.0 cannot be assigned • Address used for diagnostic purposes • Certain IP network numbers reserved as private • No one can use private addresses on Internet • Designed for use behind a NAT device, such as a firewall or proxy server • May be used on a private network with NAT device • Network number cannot be assigned to any device • Highest number on a network cannot be assigned • Address interpreted as broadcast message for subnet • Example: cannot assign 198.92.4.255 BUSI-138

  27. Using IPv6 • IPv6 developed through IETF initiative • IPv6 overcomes limitations of IPv4 • Running out of IPv4 addresses • IPv4 has no provision for network security or advanced routing options • IPv4 offers no options for handling streaming video or video conferencing • Networks are beginning to transition to IPv6 BUSI-138

  28. Using IPv6 • Features of IPv6 • 128-bit address capability • Single address associated with multiple interfaces • Address autoconfiguration and CIDR addressing • 40-byte header instead of IPv4’s 20-byte header • New IP extension headers for special needs • Includes more routing and security options • Use of IP security (IPsec) • Simpler automatic address configuration • More compact and efficient routing tables • Replacement of ARP by Neighbor Discovery BUSI-138

  29. Using IPv6 • In IPv6 addressing one IP identifier can be associated with several different interfaces • IPv6 is CIDR-compliant • Addresses can be configured using a range of options • Enables better communications for routing and subnetting • Offers options to create distinctions within a single address for network size, network location, organization, organization type, and workgroups within an organization BUSI-138

  30. Using IPv6 • IPv6 uses eight 16-bit hexadecimal fields • IPv6 address example: • 1042:0071:0000:0000:07ac:0522:210c:425b • Leading zeros can be removed & contiguous fields containing only zeros can be represented by :: • Example - the address above can be shown as: • 1042:71:0:0:7ac:522:210c:425b or • 1042:71::7ac:522:210c:425b BUSI-138

  31. In IPv6, the main header must appear in the packet before any extension header • Extension headers are optional • Only one of each type of extension header can be used in a single packet • Fields in the IPv6 main header may include version, traffic class, flow label, payload, length, next header, hop limit, source address, and destination address BUSI-138

  32. Figure 3-13 IPv6 packet BUSI-138

  33. IP Security • IP security (IPsec) – enables IP communications to be secured through authentication certificates and by encrypting data • IPsec – set of IP-based secure communications and encryption standards created through the IETF • When IPsec communications begins: • Computers first exchange certificates to authenticate the receiver and sender • Data is encrypted at the NIC of the sending computer as it is formatted BUSI-138

  34. IPv6 and Routing Tables • Routing table databases contain the addresses of other routers and networks • IPv6 enables routers to use global addresses on the Internet • Enhances the use of route aggregation (a technique for organizing network routes hierarchically • Enables routes to be summarized resulting in smaller routing tables and reduced route advertising (mean less network traffic) BUSI-138

  35. Types of IPv6 Packets • Three types of IPv6 packets: • Unicast – identified by its single address for a single NIC (transmitted point-to-point) • Anycast – contains a destination address that is associated with multiple interfaces (goes only to the closest interface) • Multicast – has a destination address that is associated with multiple interfaces (directed to each of the interfaces with that address BUSI-138

  36. Encryption and IPv6 Packet • IPv6 supports encryption techniques that are compatible with Data Encryption Standard (DES) security • DES – network symmetric-key encryption standard developed by the National Institute of Standards and Technology (NIST) and ANSI • Disadvantage of IPv6 encryption: • Latency – the time it takes for networked information to travel from the transmitting device to the receiving device BUSI-138

  37. TCP/IP Application Protocols • Useful protocols and applications in TCP/IP suite • Telnet • Secure Shell (SSH) • File Transfer Protocol (FTP), Trivial File Transfer Protocol (TFTP), and Network File System (NFS) • Simple Mail Transfer Protocol (SMTP) • Domain Name System (DNS) • Dynamic Host Configuration Protocol (DHCP) • Address Resolution Protocol (ARP) • Neighbor Discovery Protocol (ND) • Simple Network Management Protocol (SNMP) • Hypertext Transfer Protocol (HTTP), Secure Hypertext Transfer Protocol (S-HTTP), HTTP Secure (HTTPS) • Internet Control Message Protocol (ICMP) BUSI-138

  38. FTP, TFTP, and NFS • FTP: allows transfer of data between remote devices • Transmissions may be binary or ASCII formatted files • Transmissions ensured by connection-oriented service • Limitation of FTP: cannot transfer portion of file • TFTP: intended for transfer of small files • Example of use: transfer data to enable a diskless workstation to boot • Connectionless protocol running UDP instead of TCP • NFS: Sun Microsystem's alternative to FTP • Uses connection-oriented protocol running in TCP • Used mostly on UNIX/Linux based systems BUSI-138

  39. Simple Mail Transfer Protocol (SMTP) • Designed for exchange of electronic mail • Two implementations • For e-mail exchange between networked systems • In local e-mail systems for Internet transport • Provides alternative to FTP for file transfer • Requires e-mail address on receiving end • Does not require logon ID and password • Two part message: address header and message text • Supported in TCP by connection-oriented service BUSI-138

  40. Domain Name System (DNS) • Domain: logical grouping of network resources • Domains given unique names; e.g., Microsoft.com • DNS resolves domain names • Resolution: converts domain name to IP address • Internet host domain names have two parts • Top-level domain name (TLD): organization or country • Optional subdomain name: university/business name • Host name: name of computer • Example: myname@myorganization.com • ICANN coordinates and registers root domain names BUSI-138

  41. Table 3-8 TLDs for organizations BUSI-138

  42. Domain Name System (DNS) • Namespace: logical area with list of named objects • Zones: partitions in DNS server with resource records • Forward lookup zonelinks computer name to IP address • Reverse lookup zone links IP address to computer name • Three servers related to DNS • Primary DNS server: authoritative server for zone • Secondary DNS server: backup servers • Root servers: find TLDs on the Internet • Two DNS standards • Service resource record (SRV RR) • DNS dynamic update protocol BUSI-138

  43. Dynamic Host Configuration Protocol (DHCP) • Enables automatic assignment of IP address • Process of assigning address by DHCP server • Newly configured computer contacts DHCP server • DHCP server leases an IP address to new computer • Lease length set on DHCP server by network admin • Server or host may be given lease that does not expire • IP address will never change with permanent lease BUSI-138

  44. Address Resolution Protocol (ARP) • Enables sender to retrieve MAC address • Process of obtaining MAC address • Sending node sends ARP broadcast frame • Frame has (own) MAC address, IP address of recipient • Receiving node sends back its MAC address • Reverse Address Resolution Protocol (RARP) • Used by network node to determine its IP address • Used by applications to determine IP address of workstation or server BUSI-138

  45. Neighbor Discovery (ND) Protocol • ND uses messages and other means to discover the physical addresses and more information about computers and routers on a network • Similar to ARP but can also discover: • Physical addresses, configuration information, and the address prefixes of other hosts • The location of nearby routers and whether a computer or router can be reached • Provides info about whether an address has been changed (NIC was replaced) • IPv6 replaces the use of ARP with the use of ND BUSI-138

  46. Simple Network Management Protocol (SNMP) • Enables steady monitoring of network activity • Advantages • Operates independently on the network • Management functions carried out on special node • Has low memory overhead • Node types: network management station (NMS) and network agents • Each agent keeps a database of information called a Management Information Base (MIB) • MIB keeps track of # of packets sent, # of packets received, packet errors, # of connections, etc… BUSI-138

  47. Simple Network Management Protocol (SNMP) • SNMPv2 offers better security, error handling, multiprotocol support, transmissions • SNMPv3 has features to make sure: • No one has intercepted and changed a packet • The contents of the packet are fully encrypted • The source of each packet can be validated • Remote Network Monitoring (RMON) – SNMP tool used to monitor LANs connected through WANs • RMON MIB-II – database that enables remote nodes to gather network analysis data BUSI-138

  48. HTTP, S-HTTP, and HTTPS • Hypertext Transfer Protocol (HTTP) • Enables establishment of a Web connection • Provides for exchange of resources • Example: displaying Web page in browser • Secure Hypertext Transfer Protocol (S-HTTP) • Used primarily in native HTTP communications • Does not encrypt data in IP-level communications • Hypertext Transfer Protocol Secure (HTTPS) • Uses Secure Sockets Layer to implement security • More common than S-HTTP BUSI-138

  49. Internet Control Message Protocol (ICMP) • ICMP – helps IP track error conditions • Most common error condition: when a node, router, or switch is unavailable • Ping utility: used to test a network connection or the presence of a node (uses ICMP) • ICMP can report when a: • TCP or UDP port is unavailable • Destination network cannot be reached • Network service cannot be accessed • ICMP can also be used by attackers to immobilize a computer BUSI-138

  50. TCP/IP and the OSI Reference Model Compared • Portions of TCP/IP moving closer to OSI model • Physical layer: TCP/IP supports coaxial, twisted-pair, fiber-optic, wireless communication • Data Link layer: TCP/IP compatible with IEEE 802.2 LLC and MAC addressing • Network layer: IP operates here • Transport layer: both TCP and UDP operate here • Upper layers of OSI correspond to TCP/IP applications BUSI-138

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