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