Organizing the Organizing the Internet Internet Chapter 9
Dec 22, 2015
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Organizing the InternetOrganizing the Internet
Chapter 9
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Knowledge CheckpointsKnowledge Checkpoints
Internet protocols Routing and protocols Internet addressing Organization of the Internet How ISPs work
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Terms to RememberTerms to Remember
TCP/IP suite Packet sequence numbers Port numbers UDP, ICMP,IGMP ARP, RARP RIP, OSPF, IGP, EGP, BGP ARIN, RIPE,APNIC,ICANN CIDR NSP ASP
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TCP/IPTCP/IP Transmission Control Protocol / Internet
Protocol Oldest networking standard (DoD, 1974) Most popular network protocol (70%) Small packet size TCP/IP allows reasonable efficient and error-
free transmission Combination of two protocols
TCP - Transmission Control Protocol IP - Internet Protocol
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Internet ProtocolsInternet Protocols
TCP/IP (suite) Provides layer 4 functionality TCP divides data into packets with a sequence number Assigned to a port (range 1-65,535) Ports identify applications on servers Ports identified by incoming and outgoing IP handles packet forwarding and transport of datagrams
across a network Defines the basic unit of data Functions at Layer 3 Provides host addressing, error notification, fragmentation,
reassembly, routing, and packet time-out
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Internet ProtocolsInternet Protocols
UDP Layer 4 Operates over IP End-to-end connectionless, unreliable datagram service Used for query based applications, multicasting and VoIP
ICMP Provides error-handling Messages related to network management
IGMP Layer 3 Allows Internet hosts to participate in multi-casting
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TCP/IPTCP/IP TCP performs the packetizing function
Breaking data into smaller packets Numbering packets Ensuring reliable delivery of packets Ordering packets at the destination
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TCP/IPTCP/IP
IP performs network routing and addressing functions IPv4 - 32-bit address - 192-bit header IPv6 - 128-bit address - 320-bit header
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Requirements for TCP/IPRequirements for TCP/IP
This information should either come from an internal configuration file or a bootp or DHCP server IP address Subnet mask IP address of DNS server IP address of router, gateway or switch
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1 2 3 4 5 6 7 8 9 10 11 User Data
1 Source port number 16 bits2 Destination port number 16 bits3 Sequence number 32 bits4 ACK number 32 bits5 Header length 4 bits6 Unused 6 bits7 Flags 6 bits8 Flow control 16 bits9 CRC 16 16 bits10 Urgent pointer 16 bits11 Options 16 bits
TCP PacketTCP Packet
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Network and Transport Network and Transport LayersLayers
The transport & network layers sit between the application layer and the data link layer
They accept messages from the application layer, format, and address them for transmission by the data link layer
Both the sender and receiver have to agree on the rules or protocols that govern how their network layers will communicate with each other.
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Transport ProtocolTransport Protocol
A transport protocol is responsible for:
End-to-end delivery of the message Breaking large messages into packets for
transmission and reassembling them at the receiver’s end (packetizing)
Determining the correct network layer and data link layer addresses (addressing)
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Network ProtocolNetwork Protocol
A network protocol is responsible for:
Determining where the message should be send next on its way to its final destination (routing)
Selecting the best path from computer to computer through the network
Can share the addressing function with the transport layer
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ProtocolsProtocols There are many transport and network
protocols They all perform the same or similar functions They are incompatible with each other Vendors now provide software with
multiprotocol stacks
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ProtocolsProtocols
The four most commonly used protocols are:
TCP/IP IPX/SPX X.25 SNA
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IP Packet version 4 vs 6IP Packet version 4 vs 6
1 2 3 4 5 6 7 8 9 10 11
1 Version number 4 bits2 Header length 4 bits3 Type of Service 8 bits4 Total length 16 bits5 Identifiers 16 bits6 Flags 3 bits7 Packet offset 13 bits8 Hop limit 8 bits
IP4
9 Protocol 8 bits10 CRC 16 16 bits11 Source address 32 bits12 Destination Address 32 bits13 Options varies14 User data varies15 Priority 4 bits16 Flow name 8 bits17 Next header
1 15 16 4 17 14
IP6
12 13 14
11 (128 bits)8 12 (128 bits)
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IPX/SPXIPX/SPX Internetwork Packet Exchange / Sequenced
Packet Exchange Based on a routing protocol developed by
XeroX (mid 70’s) Primary network protocol used by Novell up
until they released version 5 of Netware
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IPX/SPXIPX/SPX
A combination of two protocols SPX - Sequenced Packet Exchange
Breaking the data into smaller packets Numbering them Ensuring each packet is reliably delivered Putting them in proper order at the destination
IPX - internetwork packet exchange Routing Addressing
Similar to TCP/IP
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IPX PacketIPX Packet
1 2 3 4 5 6 7 8 9 10 User Data
1 Checksum 2 bytes2 Length 2 byte3 Control 1 byte4 Type 1 byte5 Destination address 6 bytes6 Destination network address 4 bytes7 Destination socket 2 bytes8 Source address 6 bytes9 Source network address 4 bytes10 Source socket 2 bytes
IPX packet
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SPX PacketSPX Packet
1 2 3 4 5 6 7 User Data
1 Control 1 byte2 Type 1 byte3 Source ID 2 bytes4 Destination ID 2 bytes5 Sequence number 2 bytes6 ACK number 2 bytes7 Allocation number 2 bytes
SPX packet
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SNA SNA Systems network architecture Developed by IBM in 1974, IBM proprietary non-
industry standard protocol Transmission control layer performs packetizing Path control layer performs routing and addressing Requires special equipment to translate between lans
and mainframes Advanced peer-to-peer networking (APPN) was
developed by IBM to support TCP/IP Uses SDLC as its data link layer protocol
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SNA - 7 Layer Model SNA - 7 Layer Model
Presentation Layer
Data Flow Layer
Transmission Control
Path Control
Data Link Control
Physical Layer
Application Layer
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Transport and Network Transport and Network Protocols - SummaryProtocols - Summary
TCP/IP
IPX/SPX
X.25
SNA
Packetizing Routing andAddressing
TCP IP
IPX
X.3
Transmission Control Layer
SPX
PLP
Path Control Layer
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Transport Layer Transport Layer FunctionsFunctions
Linking to the application layer Packetizing Connection-oriented routing Connectionless routing Quality of service (qos)
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Linking to the Linking to the Application LayerApplication Layer
Each type of application has a unique port address
Application software sends both source and destination port addresses to the transport layer
Standard port addresses Port 80 - web server Port 21 - FTP Port 23 - telnet Port 25 - SMTP
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PacketizingPacketizing Breaking large data messages into smaller packets for
transmission through the network Size is dependent of data link layer protocol
Default size without protocol is 536 bits Size can be negotiated between sender and receiver
Numbering packets (sequencing) when needed Ensuring reliable delivery of every packet
Delivered one at a time or held until all have arrived at the destination
Reassembling and ordering packets at the destination
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Connection-Oriented Connection-Oriented RoutingRouting
Sets up a virtual circuit between sender and receiver Transport layer sends a special packet called a SYN
Virtual circuit appears to the application software to use point-to-point circuit-switching Actually uses store-and-forward switching
Network layer decides which route the packets will be travelling and sends them sequentially
High overhead - open/close of circuit
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Connectionless RoutingConnectionless Routing Each packet of a large transmission is treated
separately and makes its own way through the network
Packets may travel different routes and at different speeds through the network
Sequence number must be added to each packet by the Network layer
Network layer at receivers side must reassemble packet in sequence
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Connectionless vs. Connectionless vs. Connection-Oriented Connection-Oriented RoutingRouting
TCP/IP can operate as connection-oriented or connectionless.
When connection-oriented routing is needed, both TCP and IP are used. TCP establishes the virtual circuit and IP routes the messages.
When connectionless routing is desired, only IP is needed, and the TCP packet is replaced with a User Datagram Protocol (UDP) packet.
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Connectionless vs. Connectionless vs. Connection-Oriented Connection-Oriented RoutingRouting
IPX/SPX can also operate as either as connection-oriented or connectionless.
When connection-oriented routing is needed, both IPX and SPX are used. SPX establishes the virtual circuit and IPX routes the messages.
When connectionless routing is desired, only IPX is needed.
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Quality of Service (QoS) RoutingQuality of Service (QoS) Routing
Special kind of connection-oriented dynamic routing Packets are assigned different priorities
Depending on the type of packet sent Different classes of service are defined to determine the priority
Transport layer specifies the class of service when requesting virtual circuit
Each path designed to support different service classes Qos protocols
Rsvp Rtsp Rtp
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AddressingAddressing
Application Layer
Network Layer
Data Link Layer
Example Software
ExampleAddress
Web Browser
IP
Ethernet
www.cob.niu.edu
131.156.120.128
00-0C-00-F5-03-5A
Address
Key ConceptEach computer has several addresses, each used by a different layer.
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Assigning AddressAssigning Address At the application layer
Server names are specified in a software configuration file
Most servers have an application address, clients are beginning to depending on the operating system
A network standards group must approve all server names to insure that the addresses are unique
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Assigning AddressAssigning Address At the Network Layer
Network layer software has a configuration file that specifies the network layer address for the computer
Every network has a standards group that defines what addresses can be used by each organization
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Assigning AddressAssigning Address At the data link layer
Address is permanently coded in each network card
Every network card in the world has a unique address that differs from every other computer in the world
Addresses are coded by the vendor
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ICANNICANN Internet corporation for assigned names and
numbers (ICANN) Manages the assignment of application layer and network
layer addresses Sets the rules by which new domain names are created and
IP address numbers are assigned Manages a set of internet domains Authorizes private companies to become domain name
registrars Approves request for application layer addresses and assigns
IP numbers for those request Organizations can use any registered company for the specific
domain for a fee
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AddressingAddressingIPv4 address is four bytes longAddress
Class
Dotted DecimalNotation
A
B
C
0
0
0
0
0
0
1
1
1
1 1
7 8
15 16
23 24
31
31
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1.0.0.0 to126.0.0.0
128.1.0.0 to191.254.0.0
192.0.1.0 to223.255.254.0
16 million user addresses
65,000 user addresses
254 addresses
Networknumber
Networknumber
Networknumber
Hostnumber
Hostnumber
Hostnumber
Assigned by ICANN
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SubnetsSubnets Each organization assigns IP addresses to
specific computers on its networks IP addresses are assigned so that all
computers on the same LAN have similar addresses
Each of these lans is known as a TCP/IP subnet
Any portion of the IP address can be designated as a subnet using a subnet mask*
* Subnet masks tell computers what part of an IP address is to be used to determine whether a destination is on the same or a different subnet
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Subnet AddressingSubnet Addressing
Figure 5-6
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Subnet AddressingSubnet AddressingExample 1
Suppose that the first two bytes are the subnet indicator with addresses of the form 131.156.x.x
Then, 131.156.29.156 and 131.156.34.215 would be on the same subnet.
The subnet mask would be 255.255.0.0, which corresponds to 11111111.11111111.00000000.00000000, where 1 indicates that the position is part of the subnet address and a 0 indicates that it is not.
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Subnet AddressingSubnet AddressingExample 2
Partial bytes can also be used as subnets.
For example, consider the subnet mask 255.255.255.128, which is 11111111.11111111.11111111.10000000.
Here, all computers with the same first three bytes and last byte from 128 to 254 would be on the same subnet.
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Providing AddressesProviding Addresses Providing addresses to networked computers
Static addressing Dynamic addressing
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Static AddressingStatic Addressing Each computer is given an address through a
configuration file Stored on individual computers Problems
Moves, changes, adds and deletes Individuals could change their own IP address Network renumbered
Companies do not have a good way of tracking the addresses
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Dynamic AddressingDynamic Addressing Server supplies a network layer address
automatically Each time user logs in For a specific lease period
Two standards for dynamic addressing Bootstrap protocol (bootp) - developed in 1985 Dynamic host control* protocol (DHCP), developed
in 1993
* some say C = configuration
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Dynamic AddressingDynamic Addressing Bootp and DHCP
Software installed on the client instructs the client to contact the server using data link layer addresses
Message asks server to assign the client a unique network layer address
Server runs corresponding software that sends the client its network address and subnet mask
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Leasing Leasing Bootp or DHCP server can either:
Assign the same network layer address to the client each time the client requests it (bootp)
Lease the network address from the next available on a list of authorized addresses for as long as the client is connected or for a specified amount of time -- common with isps and dial-up users (DHCP)
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Address ResolutionAddress Resolution The process of:
Translating an application layer address to a network address (server name resolution)
Translating the server name address to a data link layer address (data link layer address resolution)
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Address ResolutionAddress Resolution Server name resolution
Accomplished by the use of domain name service (DNS)
Computers called name servers provide these DNS services
Address data base includes: server names and their corresponding IP address
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Client computer
DNS Servernetmgr.cso.niu.edu131.156.1.11
DNS Request
LAN
LAN
Internet
DNS Request
Root DNS Server for .EDU
domain
Weber State University
Northern Illinois University
DNS Request
DNS Response
DNS Response
DNS Response DNS Serversol.acs.unt.edu137.90.2.122
Figure 5-7
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Address ResolutionAddress Resolution Data link layer address resolution
Broadcast message is sent to all computers in its subnet
“if your IP address is xxx.Yyy.Zzz.Ttt, please send your data link layer address”
Uses address resolution protocol (ARP)
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Network RoutingNetwork Routing The process of determining the route a
message will take through the network Centralized Decentralized
Static routing Dynamic routing Broadcast or multicast routing
Connectionless Connection-oriented routing
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Route and Route TableRoute and Route Table
Computer B Destination Route
A AC CD AE EF EG C
A
B C
G
E
D F
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Internet RoutesInternet Routes
UEN
WSU CanadaOther destinations
West Coast
Europe Asia
WSUDestination RouteUEN UtahOxford EuropeU of Toronto CanadaU of Singapore AsiaUC Stanford West CoastOther Other
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Types of RoutingTypes of Routing Centralized routing Static routing (decentralized) Dynamic routing (adaptive and decentralized)
Distance vector Link state
Other types Broadcast routing Multicast routing
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Centralized RoutingCentralized Routing All routing decisions are made by one
computer Main routing for star and mesh topologies Routing tables located on each computer
Central computer sends updated tables as needed Routing table tells the device where to send
messages
Simplicity - no wasted resources Hardware failures or changing conditions
cause table to be out of sync
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Decentralized RoutingDecentralized Routing Each of the following types of routing fall under the
heading of decentralized routing Each device makes its own routing decisions with the
use of a formal routing protocol Routing protocols are self-adjusting
Can automatically adapt to changes in the network configuration
Drawbacks Slows down the network with status messages Requires more processing by each computer
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Static RoutingStatic Routing Routing table developed by the network
manager or some type of committee Initial table sent to each computer which then
updates the routing table as needed Reroutes as needed with down or removed circuits Updated when new devices announce their
presence Used in relatively static networks that have few
routing options
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Dynamic Routing Dynamic Routing (Adaptive)(Adaptive) Routing messages over the fastest route
Used when there are multiple routes in the network Improves network performance by selecting the
fastest route to avoid bottlenecks or busy circuits Initial table developed by network manager Dynamically updated with changing conditions by
the devices themselves Monitors message transmission time or each
device reports how busy it is to avoid bottlenecks Disadvantages
Requires more processing by each computer “Wastes” network capacity
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Dynamic Routing Dynamic Routing (Adaptive)(Adaptive)
Distance vector dynamic routing The number of hops along a route Exchange information with the neighboring computers every
few minutes
Link state dynamic routing The number of hops along a route The speed of the circuits on the route How busy the route is Exchanges information with other routing devices every 15-
30 minutes Tries to determine the fastest route Converges reliable routing information more quickly
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Routing ProtocolsRouting Protocols
RIP, IGP, OSPF, EGP, BGP Distance vector routing protocols (RIP,
Appletalk,IPX, IGRP) Routers inform neighboring routers of table Closest router is used to route packets
Link State routing protocols (OSPF) Routers have at least a partial map of the network Changes are flooded throughout network Routes are recomputed
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Interior and Exterior Interior and Exterior RoutingRouting
Interior routing is within an autonomous system (collection of routers under a single administrative control)—RIP, OSPF
Exterior routing occurs between autonomous systems
Network access protocols operate at Layer 2. Transport of IP datagrams IP over point-to-point connections is used by ISP
when you dial in
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Routing ProtocolsRouting Protocols Border Gateway Protocol Internet Control Message Protocol Routing Information Protocol Open Shortest Path First Enhanced Interior Gateway Routing Protocol
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Routing ProtocolsRouting Protocols Internet protocols
BGP (border gateway protocol) Exchanges information between autonomous systems
about the condition of the internet Complex, hard to administer, exterior routing protocol
ICMP (internet control message protocol) Simple, interior routing protocol used with the internet Reports routing errors but is limited in the ability to update
RIP (routing information protocol) Dynamic distance vector interior routing protocol Counts the number of devices on each route Selects the route with the least number of devices
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Routing ProtocolsRouting Protocols OSPF (open shortest path first)
Link state interior routing protocol used on the internet Counts number of computers, network traffic, network error
rates to select the best route Doesn’t broadcast to all devices just to routing devices Preferred TCP/IP, but also used by IPX/SPX
EIGRP (enhanced interior gateway routing protocol) Link state interior routing protocol developed by CISCO Uses route transmission capacity, delay, reliability and load to
select best route Stores multiple routing tables
SAP (service advertisement protocol) Netware servers send SAP advertisements Novell’s broadcast protocol
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Broadcast RoutingBroadcast Routing
Sends the message to all computers on the network
Only computer with correct address processes the message
Used only in bus networks Wastes network bandwidth
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MulticastingMulticasting Similar to broadcasting Only works within one LAN or subnet Messages sent from one computer to another on the
network is called a unicast message Messages sent to a group of computers is called a multicast message
Targeting a specific work group IGMP (internet group management protocol)
Sends an IGMP multicast request to the routing computer Assigned a special class D IP address to identify the group The routing computer sets the data link layer address All participating machines will process messages sent to this
address Sends a IGMP message notifying of end of session
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Figures and TablesFigures and Tables
P. 245 figures 9.2 & 9.3 P. 261 figure 9.7