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Chapter 11
Internet Operation
Internet Addressing
IPv4 Addressing
IPv4 uses 32-bit address fieldAddresses are usually written in dotted decimal notation
A decimal number represents each of the octets of the 32-bit addressIP address 11000000 11100100 00010001 00111001 is written 192.228.17.57
Class-Based IP AddressesRightmost bits of the 32-bit IP address designate a hostThe leftmost bits of the 32-bit address designate a networkClass-based, or classful, IP addressing was adopted to allow for a variable allocation of bits to specify network and host
The first few leftmost bits specify how the rest of the address should be separated into network and host fieldsThis provides flexibility in assigning addresses to hosts and allows a mix of network sizes on an internet
Address Classes
Subnets and Subnet Masks
Allows for subdivision of internets within an organizationEach LAN can have a subnet number, allowing routing among networksHost portion is partitioned into subnet and host numbers
Table 11.1
IP Addresses and Subnet
Masks
Exampleof
Subnetworking
Classless Inter-Domain Routing (CIDR)
Makes more efficient use of the 32-bit IP address than the class-based method
Does away with the class designation and with the use of leading bits to identify a class
Each 32-bit address consists of a leftmost network part and a rightmost host part, with all 32 bits used for addressing
Associated with each IP address is a prefix value that indicates the length of the network portion of the addressA CIDR IP address is written as a.b.c.d/p
a is the value of the first byte of the addressb the value of the second bytec the value of the third byted the value of the fourth bytep is in the range of 1 through 32 and indicates the length of the network portion of the address
IPv6 Addresses
Internet Routing Protocols
Autonomous Systems
A set of routers and networks managed by a single organizationConsists of a group of routers exchanging information via a common routing protocolExcept in times of failure, there is a path between any pair of nodesInterior Router Protocol (IRP) passes information between routers within an ASThe protocol used within the AS does not need to be implemented outside of the system
This flexibility allows IRPs to be custom tailored to specific applications and requirements
Application of
Exterior and
Interior Routing
Protocols
Border Gateway Protocol (BGP)
Developed for use in conjunction with internets that employ the TCP/IP suiteHas become the preferred ERP for the InternetWas designed to allow routers in different ASs to cooperate in the exchange of routing informationOperates in terms of messages, which are sent over TCP connectionsBGP-4 is the current versionThree functional procedures:
Neighbor acquisitionNeighbor reachabilityNetwork reachability
BGP Functional Procedures
Open Shortest Path First (OSPF) Protocol
Widely used as an IRP in TCP/IP networksUses a link state routing algorithmComputes a route through the internet that incurs the least cost base on a user-configurable metric of costEach router maintains a database that reflects the known topology of the AS of which it is a part
The topology is expressed as a directed graph consisting of:Vertices, or nodes of two types:
RouterNetwork, which is in turn of two types:
TransitStub
Edges, of two types:A graph edge that connects two router vertices when the corresponding routers are connected to each other by a direct point-to-point linkA graph edge that connects a router vertex to a network vertex when the router is directly connected to the network
A Sample Autonomous
System
Multicasting
Sending a packet from a source to the members of a multicast groupMulticast addresses
Addresses that refer to a group of hosts on one or more networks
Practical applications include:MultimediaTeleconferencingDatabaseDistributed computationReal-time workgroup
Illustration of
Multicasting
Traffic Generated by Various Multicasting Strategies
Multicast Routing Protocols
At the local level, individual hosts need a method of joining or leaving a multicast groupInternet Group Management Protocol (IGMP)
Used between hosts and routers on a broadcast network such as Ethernet or a wireless LAN to exchange multicast group membership informationSupports two principal operations:
Hosts send messages to routers to subscribe to and unsubscribe from a multicast group defined by a given multicast addressRouters periodically check which multicast groups are of interest to which hosts
Interior Routing Protocols
Routers must cooperate across an organization’s internet or across the Internet to route and deliver multicast IP packets
Routers need to know which networks include members of a given multicast groupRouters need sufficient information to calculate the shortest path to each network containing group members
Multicast Extensions to OSPF (MOSPF)Enhancement to OSPF for the exchange of multicast routing information
Protocol Independent Multicast (PIM)Designed to extract needed routing information from any unicast routing protocol and may support routing protocols that operate across multiple ASs with a number of different unicast routing protocols
Emergence of High-Speed LANs
Corporate WAN Needs
Greater dispersal of employee baseGrowing use of telecommutingChanging application structures
Increased client/server and intranetMore reliance on personal computers, workstations, and serversGUIs enables the end user to exploit graphic applications, multimedia, and other data-intensive applicationsDependence on Internet access
More data must be transported off premises and onto WANs
Internet Traffic
Elastic TrafficCan adjust, over wide ranges, to changes in delay and throughput across an internet and still meet the needs of its applicationsType of traffic for which internets were designedApplications include file transfer, electronic mail, remote logon, network management, and Web access
Inelastic TrafficDoes not adapt well, if at all, to changes in delay and throughput across an internetExamples include real-time traffic, such as voice and video
Requirements of Inelastic Traffic
Differentiated Services (DS)
Provide QoS on the basis of the needs of different groups of users
Most widely accepted QoS mechanism in enterprise networks
Key characteristics:No change is required to IPExisting applications need not be modified to use DSProvides a built-in aggregation mechanism – all traffic with the same DS octet is treated the same by the network serviceRouters deal with each packet individually and do not have to save state information on packet flows
Services
DS Services Provided
DS Field
DS Domains
DS Configuration and Operation
Interior NodesImplement simple mechanisms for handling packets based on their DS codepoint values Includes:
A queuing discipline to give preferential treatment depending on codepoint valuePacket-dropping rules to dictate which packets should be dropped first in the event of buffer saturation
Forwarding treatment is per-hop behavior (PHB)
Must be available at all routersIs the only part of DS implemented in interior routers
Boundary NodesIncludes PHB mechanisms as well as more sophisticated traffic conditioning mechanisms required to provide the desired serviceCan also be provided by a host system attached to the domain on behalf of the applications at that host system
Traffic Conditioning Function Elements:
Traffic Conditioning Diagram
Service Level Agreements (SLA)
Contract between the network provider and a customer that defines specific aspects of the service to be providedTypically includes:
A description of the nature of service to be providedExpected performance level of the serviceProcess for monitoring and reporting the service level
Typical Framework for SLA
IP Performance Metrics Working Group (IPPM)
Chartered by IETF to develop standard metrics that relate to the quality, performance, and reliability of Internet data deliveryTrends dictating need:
The Internet has grown and continues to grow at a dramatic rateThe Internet serves a large and growing number of commercial and personal users across an expanding spectrum of applications
Table 11.3(a) Sampled Metrics
Src = IP address of a host Dst = IP address of a host
Table 11.3(b) Other Metrics
Model for Defining Packet Delay Variation
Summary Internet addressing
IPv4 addressing IPv6 addressing
Internet routing protocols Autonomous systems Border gateway protocol OSPF protocol
Multicasting Multicast transmission Multicast routing
protocolsChapter 11: Internet Operation
Quality of service Emergence of high-
speed LANs Corporate WAN
needs Internet traffic
Differentiated services DS field DS configuration
and operation SLAs IP performance
metrics
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