Transcript Networking
Networking An Introduction History of the Internet ARPAnet • Advanced Research Project Agency • First four nodes – 1969 • Connect supercomputers DARPAnet • Defense Advanced Research Project Agency • Replaced ARPA and took over network History of Internet (2) NSFnet • Merged NSF network and DARPAnet when defense community moved to more secure network. (Internet) • Early 1990’s, administration of Internet moves to public utilities. †Based upon Null and Lobur, Computer Organization and Architecture, Jones and Barttlett, 2003. Characteristics of Internet Originally designed to survive thermonuclear war Adopted datagrams that could be individually routed Uniform protocol over dissimilar hardware Philosophy of free and open information interchange TCP/IP Protocol Three layered protocol • Process layer Application uses protocol from TCP/IP suite FTP HTTP STMP TELNET • TCP layer • IP layer TCP/IP Architecture IP Header Network Header †Based IP Header User data Application TCP Header User data TCP Segment TCP Header User data TCP Header User data IP Datagram Network Layer (e.g. Ethernet) upon Stallings, Data and Computer Communications, Prentice-Hall, 1997. IP Internet Protocol Two versions • IPv4 • IPv6 Divides packets into units called datagrams Adds Routing Information Purpose – route datagrams over network IP Routing Send Message ` Datagram 1 Datagram 1 Datagram 2 ` Receive Message IPv4 Datagram Header Header length - minimum of 5 - 32 bit words Word 1 • • • • Version – IP version Header Length – in 32 bit words (min is 5) Type of Service - priority Total Length of datagram – total length (65,535 max) Word 2 • Packet Id – number assigned as placed on network • Flags – can packet be broken to smaller fragments • Fragment offset – offset of fragment in original datagram IPv4 Datagram Header (2) Word 3 • Time to Live (TTL) – number of hops left in datagram lifetime • Protocol Number – higher level protocol sending packet • Header Checksum Word 4 – Source IP address Word 5 – Destination IP address Word 6 – IP options IPv4 Address Classes Three Classes of addresses • Class A network • Class B network • Class C network IP address 32 bits long Uses dotted decimal notation • 4 groups each representing 8 bits • E.g. 168.47.23.8 Class A Networks Format • • • • 0|Network|Host High bit: 0 Network: 7 bits Host: 24 bits Reserved networks • 127.x.x.x – loop back address • 0.0.0.0 – default route 126 Networks • 0.x.x.x to 127.x.x.x Each has 224 (16.7 million) nodes 10.x.x.x is internal network number Class B Networks Format • High two bits: 10 • Network: 14 bits • Host 16 bits 214 (16,382) networks • 128.0.x.x to 191.255.x.x 216-2 (65,534)hosts per network 168.x.x.x is internal IP Class C Network Format • High three bits: 110 • Network: 21 bits • Host 8 bits 221 (2,097,152)Networks • 192.0.0.x to 223.255.255.x 28 (256) Hosts per network 192.x.x.x is an internal network number IPv4 Problems 65,536 byte packet is too small • Can pass router in 1Gb network in less than 1 ms Too few Addresses • 126 Class A with 16.7 million nodes each – too large • Class C address has only 256 nodes – too small Typical Backbone routing table must contain ~70,000+ routes Transmission Control Protocol TCP uses services provided by IP More sophisticated than IP TCP opens a connection – conservation Service Access Port • SAP - numerical • Socket - SAP, host ID, and protocol designation • Ports 0 – 1023 Well known ports Use is reserved (e.g. 23 used by Telnet) • Ports 1024 – 65,535 User defined Transmission Control Protocol Is reliable TCP assures • Proper sequence • No duplicates • Overflow prevented (transmission speed) • Connection-oriented • Retransmission of lost data TCP: Three-way Handshake A B Open Connection • SYN – Synchronize T i m e ACK – Acknowledge Note the acknowledgement of each msg Negotiate connection w. sequence numbers next seq# t+2 for A, and j+2 for B Establishes connection Windows and Payload Size Window • Number of bytes to send between acknowledgements • i.e. send window size bytes before expecting an ACK to be returned Payload Size • Number of bytes sent in each packet Negotiated after connection is established TCP Data Transfer B Window = 500 bytes Payload = 100 bytes A A can now send packets 300 to 600 w/o acknowledgement TCP Segment Format Word 1 • Source Port – 16 bits • Destination Port – 16 bits Word 2 – Sequence Number Word 3 – Acknowledgement Number Word 4 • • • • Data Offset – Number of 32-bit words in header Reserved Flags – URG, ACK, PSH, RST, SYN, FIN Window – 16 bits Word 5 • Checksum – 16 bits • Urgent Pointer 16 bits Word 6 Options IPv6 Protocol Addresses the Class B Problem 32 addresses IPv4 – 2 IPv6 – 2128 addresses • 2128 - 1 oz NIC → 1.61 quadrillion x mass earth • That’s enough addresses! Requires management Implementation by 2010 IPv6 Address Organization Aggregatable Global Unicast Address Format Organization • High 3 bits – flag indicating AGUA addr. • Next 13 bits Top-Level Aggregation (TLA) ID Country, major global telecomm carrier • Next 8 bits –Reserved (growing room) • Next 24 bits Level Aggregation (NLA) ID Large company, government, ISP IPv6 Address Organization (2) • Next 16 bits Site-Level Aggregation Id Can break up addresses into 65,536 sub-netwroks • Next 64 bits Specify host Each sub-network can have 264 hosts Stateless Address Autoconfiguration • Use 48 bit MAC address • Completes address with net. info. from nearby router Prevents address spoofing Has a transitional phase Network Devices Hub • Physical layer • Input port copied to all output ports • Non-switched Ethernet Switches • Create point-to-point connection between input port and one output port • Switched Ethernet Bridges • Both networks must be same type Gateways • Point of entrance to a network • Connects networks using different protocols Routers Connected to at least two networks Determines the destination to which a packet should be sent Layer 3 Device • Switch at the OSI Network layer • Can bridge different network media Computer that implements a routing algorithm Routing NP-complete problem • Consider a complete graph • Number of simple paths between any two nodes – N! Add finding the best path Best • Shortest? • Fastest? Routing information must be kept dynamically Very hard but important task Types of Routing Algorithms • Distance-Vector Routing • Link State Routing Distance Vector Routing ` ` ` M L D ` ` B • Dest • Next Hop • Hop Count N 4 1 r 3 2 ` T ` C ` ` ` W A R Each router keeps table Table Routers exchange hop information with each neighbor Based upon Fig. 11.21 from Null, Computer Organization and Architecture, Jones & Bartlett, 2003 Distance Vector Routing Tables Router 2 Router 3 Router 1 Dest Next Hop Hop Count Dest Next Hop Hop Count Dest Next Hop Hop Count A -- 0 A R3 1 A R2 2 B R4 1 B R3 2 B R4 1 C R2 1 C -- 0 C R2 1 D R4 1 D R3 2 D R4 1 L R4 2 L R1 1 L -- 0 M R4 2 M R1 1 M -- 0 N R4 2 N R1 1 N -- 0 R R2 1 R -- 0 R R2 1 T -- 0 T R3 1 T R4 2 W -- 0 W R3 1 W R4 2 Based upon Fig. 11.21 from Null, Computer Organization and Architecture, Jones & Bartlett, 2003 Distance Vector Routing Problems Long time for routing tables to stabilize Considerable traffic to keep tables updated Obsolete routes • Count-to-infinity problem • Cycles in the routing can cause each to keep updating hop count until infinite value results