chapter 16 Internetwork Operation

William Stallings

Data and Computer

Communications

Chapter 16

Routing Protocols

 _{Routing Information}

 _{About topology and delays in the}

internet

 _{Routing Algorithm}

 _{Used to make routing decisions based}

Autonomous Systems (AS)

 _{Group of routers}

 _{Exchange information}

 _{Common routing protocol}

 _{Set of routers and networks managed by}

signle organization

 _{A connected network}

 _{There is at least one route between any}

Interior Router Protocol (IRP)

 _{Passes routing information between routers}

within AS

 _{May be more than one AS in internet}

 _{Routing algorithms and tables may differ}

between different AS

 _{Routers need some info about networks outside}

their AS

 _{Used exterior router protocol (ERP)}  _{IRP needs detailed model}

 _{ERP supports summary information on}

Border Gateway Protocol (BGP)

 _{For use with TCP/IP internets}

 _{Preferred EGP of the Internet}

 _{Messages sent over TCP connections}

 _Open  _Update

 _{Keep alive}  _Notification

 _Procedures

BGP Procedure

 _{Open TCP connection}  _{Send Open message}

 _{Includes proposed hold time}

 _{Receiver selects minimum of its hold time}

and that sent

 _{Max time between Keep alive and/or}

Message Types

 Keep Alive

 _{To tell other routers that this router is still here}

 _Update

 _{Info about single routes through internet}  _{List of routes being withdrawn}

 _{Includes path info}

 _{Origin (IGP or EGP)}

 _{AS_Path (list of AS traversed)}

 _{Next_hop (IP address of boarder router)}

 _{Multi_Exit_Disc (Info about routers internal to AS)}  _{Local_pref (Inform other routers within AS)}

 _{Atomic_Aggregate, Aggregator (Uses address}

Uses of AS_Path and Next_Hop

 _{AS_Path}

 _{Enables routing policy}  _{Avoid a particular AS}  _Security

 _Performance  _Quality

 _{Number of AS crossed}

 _{Next_Hop}

 _{Only a few routers implement BGP}

 _{Responsible for informing outside routers of}

Notification Message

 _{Message header error}

 _{Authentication and syntax}

 _{Open message error}

 _{Syntax and option not recognized}  _{Unacceptable hold time}

 _{Update message error}

 _{Syntax and validity errors}

 _{Hold time expired}

 _{Connection is closed}

 Finite state machine error

 _Cease

BGP Routing Information Exchange

 _{Within AS, router builds topology picture}

using IGP

 _{Router issues Update message to other}

routers outside AS using BGP

 _{These routers exchange info with other}

routers in other AS

Open Shortest Path First (1)

 _OSPF

 _{IGP of Internet}

 _{Replaced Routing Information Protocol (RIP)}  _{Uses Link State Routing Algorithm}

 _{Each router keeps list of state of local}

links to network

 _{Transmits update state info}

 _{Little traffic as messages are small and}

not sent often

 _{RFC 2328}

 _{Route computed on least cost based on}

Open Shortest Path First (2)

 _{Topology stored as directed graph}  _{Vertices or nodes}

 _Router  _Network

 _Transit  _Stub  _Edges

 _{Graph edge}

 _{Connect two router}

Directed

Operation

 _{Dijkstra’s algorithm (Appendix 10A) used}

to find least cost path to all other networks

Integrates Services Architecture

 _{Changes in traffic demands require variety}

of quality of service

 _{Internet phone, multimedia, multicast}  _{New functionality required in routers}  _{New means of requesting QoS}

 _ISA

Internet Traffic

 _Elastic

 _{Can cope with wide changes in delay}

and/or throughput

 FTP sensitive to throughput

 _{E-Mail insensitive to delay}

 _{Network Management sensitive to delay}

in times of heavy congestion

 _{Web sensitive to delay}

 _Inelastic

 _{Does not easily adapt to variations}

Requirements for Inelastic Traffic

 _Throughput

 _Delay

 _Jitter

 _{Delay variation}

 _{Packet loss}

 _{Require preferential treatment for certain}

types of traffic

ISA Approach

 _{Congestion controlled by}  _{Routing algorithms}

 _{Packet discard}

 _{Associate each packet with a flow}  _{Unidirectional}

Token Bucket Traffic Specification

 _{Token replenishment rate R}

 _{Continually sustainable data rate}  _{Bucket size B}

 _{Amount that data rate can exceed R for}

short period

 _{During time period T amount of data}

ISA Services

 _Guaranteed

 _{Assured data rate}

 _{Upper bound on queuing delay}

 _{No queuing loss}

 _{Real time playback}

 _{Controlled load}

 _{Approximates behavior to best efforts on}

unloaded network

 _{No specific upper bound on queuing delay}

 _{Very high delivery success}

Queuing Discipline

 _{Traditionally FIFO}

 _{No special treatment for high priority flow}

packets

 _{Large packet can hold up smaller packets}

 Greedy connection can crowd out less

greedy connection

 _{Fair queuing}

 _{Queue maintained at each output port}

 _{Packet placed in queue for its flow}

 _{Round robin servicing}

 _{Skip empty queues}

Resource Reservation: RSVP

 _{Unicast applications can reserve resources in}

routers to meet QoS

 _{If router can not meet request, application}

informed

 _{Multicast is more demanding}  _{May be reduced}

 _{Some members of group may not require}

delivery from particular source over given time

 _{e.g. selection of one from a number of}

“channels”

 _{Some group members may only be able to}

Soft State

 _{Set of state info in router that expires}

unless refreshed

 _{Applications must periodically renew}

requests during transmission

RSVP Goals

 _{Ability for receivers to make reservations}  _{Deal gracefully with changes in multicast}

group membership

 _{Specify resource requirements such that}

aggregate resources reflect requirements

 _{Enable receivers to select one source}  _{Deal gracefully with changes in routes}  _{Control protocol overhead}

RSVP Characteristics

 _{Unicast and Multicast}

 _Simplex

 _{Receiver initiated reservation}

 _{Maintain soft state in the internet}  _{Provide different reservation styles}

 _{Transparent operation through non-RSVP}

routers

Data Flow Concepts

 _Session

 _{Data flow identified by its destination}  _{Flow descriptor}

 _{Reservation request issued by}

destination

 _{Made up of flowspec and filterspec}  _{Flowspec gives required QoS}

 _{Filterspec defines set of packets for}

RSVP Message Types

 _Resv

 _{Originate at multicast receivers}  _{Propagate upstream through}

distribution tree

 _{Create soft states within routers}

 _{Reach sending host enabling it to set up}

traffic control for first hop

 _Path

Operation From Host Perspective

 _{Receiver joins multicast group (IGMP)}

 _{Potential sender issues Path message}

 _{Receiver gets message identifying sender}  _{Receiver has reverse path info and may}

start sending Resv messages

 _{Resv messages propagate through}

internet and is delivered to sender

Differentiated Services

 _{Provide simple, easy to implement, low overhead}

tool to support range of network services differentiated on basis of performance

 _{IP Packets labeled for differing QoS using existing}

IPv4 Type of Service or IPv6 Traffic calss

 _{Service level agreement established between}

provider and customer prior to use of DS

 _{Built in aggregation}

 _{Good scaling to larger networks and loads}

 _{Implemented by queuing and forwarding based}

on DS octet

DS Services

 _{Defined within DS domain}

 _{Contiguous portion of internet over}

which consistent set of DS policies are administered

 _{Typically under control of one}

organization

 _{Defined by service level agreements}

SLA Parameters

 _{Detailed service performance}  _{Expected throughput}

 _{Drop probability}  _Latency

 _{Constraints on ingress and egress points}  _{Traffic profiles}

 _{e.g. token bucket parameters}

Example Services

 _{Level A - low latency}  _{Level B - low loss}

 _{Level C - 90% of traffic < 50ms latency}  _{Level D - 95% in profile traffic delivered}

 _{Level E - allotted twice bandwidth of level}

F traffic

 _{Traffic with drop precedence X higher}

DS Octet - Code Pools

 _{Leftmost 6 bits used}

 _{3 pools of code points}  _xxxxx0

 _{assignment as standards}  _xxxx11

 _{experimental or local use}  _xxxx01

 _{experimental or local but may be}

DS Octet - Precedence Fiedl

 _{Routing selection}

DS Configuration and Operation

 _{Within domain, interpretation of DS code}

points is uniform

 _{Routers in domain are boundary nodes or}

interior nodes

 _{Traffic conditioning functions}  _Classifier

Required Reading

 _{Stallings chapter 16}  _{RFCs identified in text}

 _{Comer, Internetworking with TCP/IP}