Data and Computer Communications Chapter 19 Internetwork Operation

Data and Computer Communications Chapter 19 – Internetwork Operation Eighth Edition by William Stallings Lecture slides by Lawrie Brown

Multicasting-1 S S R 1 R 2 m 1 R 3 m 2 m 3 Multiple Unicast R 2 m 1 R 3 m 2 m 3 True Multicast (IP Multicast)

Multicasting-2 Element-1: Group ID (IP Multicast Address) Element-2: Group Membership Management (IGMP) Element-3: Multicast Routing Protocols S R 1 Multicast Routing Protocol R 1 IGMP m 1 R 4 R 3 IGMP m 2 m 3

Multicasting-3 Multicast Routing Tree Source-based Tree m 1 S 2 m 3 E. g. DVMRP, MOSPF Group Shared Tree m 1 S 2 m 3 E. g. CBT

RSVP Internet Qo. S Datagram + Qo. S Flow (Im/Ex-plicit) Integrated Per Service Flow Architecture Per Class IPv 4 IPv 6 Complicated Differentiated Service Manageable DS Codepoint IP Performance Metric Sevice Level Agreement

Internetwork Operation She occupied herself with studying a map on the opposite wall because she knew she would have to change trains at some point. Tottenham Court Road must be that point, an interchange from the black line to the red. This train would take her there, was bearing her there rapidly now, and at the station she would follow the signs, for signs there must be, to the Central Line going westward —King Solomon's Carpet, Barbara Vine (Ruth Rendell)

Internetwork Operation Ø consider mechanisms for handling growth in network traffic l l from low-volume text based terminal/email to high volume multi-media web/voice/video historically IP nets gave best-effort datagram delivery to all services Ø now want variety of Qo. S in IP networks Ø explore some new network services / functions Ø

Multicasting Ø sending packet to addresses referring to group of hosts on one or more networks l l l multimedia “broadcast” teleconferencing database distributed computing real time workgroups Ø have design issues in addressing / routing

LAN Multicast Ø LAN multicast is easy l l send to IEEE 802 multicast MAC address since broadcast all stations will see packet those in multicast group will accept it only single copy of packet is needed Ø but much harder in internetwork

Example Config

Broadcast / Multiple Unicast / Multicast Ø could broadcast packet to each network l l if server does not know members of group requires 13 packets Ø could send multiple unicast packets l l to each net with members in multicast group requires 11 packets Ø or use true multicast l l l which send single packets over any link duplicating as needed to reach dest nets requires 8 packets

True Multicast Ø determine least cost path to each network that has host in group l l results in a spanning tree of just those nets with members in group Ø transmit single packet along spanning tree Ø routers replicate packets at branch points of spanning tree

Multicast Example

Requirements for Multicasting Ø router may have to forward more than one copy of packet Ø need convention to identify multicast addresses (IPv 4 Class D or IPv 6 prefix) Ø nodes translate between IP multicast addresses and list of networks containing group members Ø router must translate between IP multicast address and network multicast address

Requirements for Multicasting Ø mechanism required for hosts to join and leave multicast group Ø routers must exchange info l l which networks include members of given group sufficient info to work out shortest path to each network Ø routing algorithm to work out shortest path Ø routers must determine routing paths based on source and destination addresses

Spanning Tree from Router C to Multicast Group

Internet Group Management Protocol (IGMP) Ø RFC 3376 to exchange multicast group info between hosts & routers on a LAN Ø hosts send messages to routers to subscribe to and unsubscribe from multicast group Ø routers check which multicast groups of interest to which hosts Ø IGMP currently version 3

Operation of IGMPv 1 & v 2 Ø IGMPv 1 l l hosts could join group routers used timer to unsubscribe members IGMPv 2 enabled hosts to unsubscribe Ø operational model: Ø l l l Ø receivers have to subscribe to groups sources do not have to subscribe to groups any host can send traffic to any multicast group problems: l l l spamming of multicast groups establishment of distribution trees is problematic finding globally unique multicast addresses difficult

IGMP v 3 Ø addresses weaknesses: l l l allows hosts to specify list from which they want to receive traffic from other hosts blocked at routers allows hosts to block packets from sources that send unwanted traffic

IGMP Message Formats Membership Query sent by multicast router Ø three types: general query, group-specific query, groupand-source specific query Ø

Membership Query Fields Type Ø Max Response Time Ø Checksum Ø Group Address Ø S Flag Ø QRV (querier's robustness variable) Ø QQIC (querier's querier interval code) Ø Number of Sources Ø Source addresses Ø

IGMP Message Formats Membership Report

IGMP Message Formats Group Record

IGMP Operation - Joining IGMP host wants to make itself known as group member to other hosts and routers on LAN Ø IGMPv 3 can signal group membership with filtering capabilities with respect to sources Ø l l Ø EXCLUDE mode – all members except those listed INCLUDE mode – only from group members listed to join send IGMP membership report message l l address field multicast address of group sent in IP datagram current group members receive & learn new member routers listen to all IP multicast addresses to hear all reports

IGMP Operation – Keeping Lists Valid Ø routers periodically issue IGMP general query message l l l Ø in datagram with all-hosts multicast address hosts must read such datagrams hosts respond with report message router don’t know every host in a group l l l needs to know at least one group member still active each host in group sets timer with random delay host hearing another report cancels own if timer expires, host sends report only one member of each group reports to router

IGMP Operation - Leaving Ø host leaves group by sending leave group message to all-routers static multicast address l sends a membership report message with EXCLUDE option and null list of source addresses Ø router determines if have any remaining group members using group-specific query message

Group Membership with IPv 6 Ø IGMP defined for IPv 4 l uses 32 -bit addresses Ø IPv 6 internets need functionality Ø IGMP functions included in Internet Control Message Protocol v 6 (ICMPv 6) l ICMPv 6 has functionality of ICMPv 4 & IGMP Ø ICMPv 6 includes group-membership query and group-membership report message

Routing Protocols Ø routers receive and forward packets Ø make decisions based on knowledge of topology and traffic/delay conditions Ø use dynamic routing algorithm Ø distinguish between: l l routing information - about topology & delays routing algorithm - that makes routing decisions based on information

Autonomous Systems (AS) Ø is a group of routers and networks managed by single organization Ø which exchange information via a common routing protocol Ø form a connected network l l at least one path between any pair of nodes except in times of failure

Interior Router Protocol & Exterior Routing Protocol Ø Ø interior router protocol (IRP) l passes routing information between routers within AS l can be tailored to specific applications l needs detailed model of network to function may have more than one AS in internet l routing algorithms & tables may differ between them Ø routers need info on networks outside own AS Ø use an exterior router protocol (ERP) for this l supports summary information on AS reachability

Application of IRP and ERP

Approaches to Routing – Distance-vector each node (router or host) exchange information with neighboring nodes Ø first generation routing algorithm for ARPANET Ø l eg. used by Routing Information Protocol (RIP) each node maintains vector of link costs for each directly attached network and distance and nexthop vectors for each destination Ø requires transmission of much info by routers Ø l Ø distance vector & estimated path costs changes take long time to propagate

Approaches to Routing – Link-state Ø Ø Ø designed to overcome drawbacks of distance-vector each router determines link cost on each interface advertises set of link costs to all other routers in topology if link costs change, router advertises new values each router constructs topology of entire configuration l l can calculate shortest path to each dest use to construct routing table with first hop to each dest do not use distributed routing algorithm, but any suitable alg to determine shortest paths, eg. Dijkstra's algorithm Ø Open Shortest Path First (OSPF) is a link-state protocol Ø

What Exterior Routing Protocols are not link-state and distance-vector not effective for exterior router protocol Ø distance-vector Ø l l l Ø assumes routers share common distance metric but different ASs may have different priorities & needs but have no info on AS’s visited along route link-state l l different ASs may use different metrics and have different restrictions flooding of link state information to all routers unmanageable

Exterior Router Protocols – Path-vector Ø alternative path-vector routing protocol l provides info about which networks can be reached by a given router and ASs crossed to get there does not include distance or cost estimate hence dispenses with concept of routing metrics have list of all ASs visited on a route Ø enables router to perform policy routing Ø l l l eg. avoid path to avoid transiting particular AS eg. link speed, capacity, tendency to become congested, and overall quality of operation, security eg. minimizing number of transit ASs

Border Gateway Protocol (BGP) Ø developed for use with TCP/IP internets Ø is preferred EGP of the Internet Ø uses messages sent over TCP connection Ø current version is BGP-4 (RFC 1771) Ø functional procedures l neighbor acquisition - when agree to exchange info l neighbor reachability - to maintain relationship l network reachability - to update database of routes

BGP Messages Open Ø Update Ø Keep alive Ø Notification Ø

Message Types Open & Keep. Alive Ø router makes TCP connection to neighbor Ø Open message l l sent by connection initiator includes proposed hold time receiver uses minimum of own/sent hold time max time between Keepalive and/or Update Ø Keep Alive message l To tell other routers that this router is still here

Message Types - Update Ø Update message conveys two info types: l Info about single routes through internet l List of routes being withdrawn Ø info on a route uses 3 fields: l Network Layer Reachability Information (NLRI) l Total Path Attributes Length l Path Attributes Ø withdraw route identified by dest IP address

Message Types - Update Ø Origin - IGP or EGP Ø AS_Path - list of AS traversed Ø Next_hop - IP address of border router Ø Multi_Exit_Disc - info on routers internal to AS Ø Local_pref - inform routers in AS of route pref Ø Atomic_Aggregate, Aggregator - implement route aggregation to reduce amount of info

AS_Path and Next_Hop Use Ø AS_Path l used to implement routing policies • eg. to avoid a particular AS, security, performance, quality, number of AS crossed Ø Next_Hop l l only a few routers implement BGP responsible for informing outside routers of routes to other networks in AS

Notification Message Ø sent when some error condition detected: Ø Message header error Ø Open message error Ø Update message error Ø Hold time expired Ø Finite state machine error Ø Cease

BGP Routing Information Exchange Ø within AS a router builds topology picture using IGP Ø router issues Update message to other routers outside AS using BGP Ø these routers exchange info with other routers in other AS l AS_Path field used to prevent loops Ø routers must then decide best routes

BGP Example Figure 19. 5 Ø Ø R 1 can issue an Update message to R 5 in AS 2: l AS_Path: The identity of AS 1 l Next_Hop: The IP address of R 1 l NLRI: A list of all of the networks in AS 1 R 5 also has a neighbor relationship with R 9 in AS 3, R 5 will forward a new Update msg to R 9: l AS_Path: The list of identifiers [AS 2, AS 1] l Next_Hop: The IP address of R 5 l NLRI: A list of all of the networks in AS 1

Open Shortest Path First (RFC 2328) IGP of Internet Ø replaced Routing Information Protocol (RIP) Ø uses Link State Routing Algorithm Ø l l l 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 uses least cost based on user cost metric Ø topology stored as directed graph Ø l l vertices or nodes (router, transit or stub network) edges (between routers or router to network)

Example OSPF AS

Directed Graph of AS

SPF Tree for Router 6

Integrated Services Architecture Ø changes in traffic demands require variety of quality of service l eg. internet phone, multimedia, multicast Ø new functionality required in routers Ø new means of requesting Qo. S Ø IETF developing a suite of Integrated Services Architecture (ISA) standards Ø RFC 1633 defines overall view of ISA

Internet Traffic Categories Ø elastic traffic l l can cope with wide changes in delay and/or throughput traditional TCP/IP traffic eg. FTP, email, telnet, SNMP, HTTP different sensitivity to throughput, delay, congestion Ø inelastic traffic l does not easily adapt to variations

Inelastic Traffic Requirements Ø throughput Ø delay Ø jitter Ø packet loss Ø need preferential treatment for some traffic types Ø require elastic traffic to be supported

ISA Approach Ø IP nets control congestion by l l routing algorithms packet discard ISA provides enhancements to traditional IP Ø in ISA associate each packet with a flow Ø ISA functions: Ø l l admission control routing algorithm queuing discipline discard policy

ISA in Router

ISA Services Ø Guaranteed l l l Ø Controlled load l l l Ø assured data rate upper bound on queuing delay no queuing loss approximates best effort behavior on unloaded net no specific upper bound on queuing delay very high delivery success Best Effort l traditional IP service

Token Bucket Scheme For Tspec

Queuing Discipline Ø traditionally FIFO l l l Ø no special treatment for high priority flow packets large packet can hold up smaller packets greedy connection can crowd out less greedy connection need some form of fair queuing l l multiple queues used on each output port packet is placed in queue for its flow round robin servicing of queues can have weighted fair queuing

FIFO and Fair Queue

Resource Reservation: RSVP RFC 2205 Ø unicast applications can reserve resources in routers to meet Qo. S Ø l Ø if router can not meet request, application informed multicast more demanding, but may be reduced l l l some members of group may not require delivery from particular source over given time some group members may only be able to handle a portion of the transmission reservation means routers can decide in advance if can meet requirements

Soft State Ø have different resource reservation needs to traditional connection-oriented networks l must dynamically change Ø use concept of Soft State l set of state info in router that expires unless refreshed Ø applications must periodically renew requests during transmission

RSVP Characteristics Ø unicast and multicast Ø simplex Ø receiver initiated reservation Ø maintain soft state in the internet Ø provide different reservation styles Ø transparent operation through non-RSVP routers Ø support for IPv 4 and IPv 6

Differentiated Services simple, easily implemented, low overhead tool to support a range of differentiated network services Ø IP Packets labeled for differing Qo. S using existing IPv 4 Type of Service or IPv 6 DS field Ø have service level agreement established between provider and customer prior to use of DS Ø have built in aggregation Ø implemented by queuing and forwarding based on DS octet Ø most widely used Qo. S mechanism today Ø

DS Domains Traffic Conditioner Per Hop Behavior (PHB)

DS Services Ø is defined within a DS domain l l Ø a 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) specify service received for classes of packets once established customer submits packets with DS marked indicating class l l service provider ensures agreed Qo. S within domain if transit other domains, provider chooses closest Qo. S

SLA Parameters Ø detailed service performance such as: l l l expected throughput drop probability latency Ø constraints on ingress and egress points Ø traffic profiles Ø disposition of traffic in excess of profile

Example Services Ø level A - low latency Ø level B - low loss Qualitative Quantitative Ø level C - 90% of traffic < 50 ms latency Ø level D - 95% in profile traffic delivered Ø level E - allotted twice bandwidth of level F Ø level F - with drop precedence X has higher probability of delivery than that of Y Mixture

DS Field

DS Field - DS Codepoint Ø 6 bit field in IPv 4 & IPv 6 header Ø 3 pools of code points l xxxxx 0 - assignment as standards • 000000 - default best effort • xxx 000 - IPv 4 precedence compatibility l l xxxx 11 - experimental or local use xxxx 01 - experimental or local but may be allocated for standards in future

IPv 4 Precedence Service Ø IPv 4 TOS field included subfields l l precedence (3 bit) - datagram urgency/priority TOS(4 bit) - guidance on selecting next hop Ø can respond with l l l route selection - smaller queue, has priority network service - supports precedence queuing discipline - support precedence ordered queueing & discard lower precedence

DS Configuration and Operation Ø within domain, interpretation of DS code points is uniform Ø interior nodes l l implement simple mechanisms per-hop behavior (PHB) on all routers Ø boundary nodes l l have PHB & more sophisticated mechanisms hence most of complexity

DS Traffic Conditioner

Per Hop Behavior – Expedited Forwarding specific PHBs defined Ø expedited forwarding (EF) PHB (RFC 3246) Ø l l Ø difficult in internet or packet-switching network l l Ø low-loss, low-delay, low-jitter, assured bandwidth, end -to-end service through DS domains simulates a point-to-point connection or leased line queues on node/router result in loss, delays, and jitter unless internet grossly oversized, care needed in handling premium service traffic EF PHB intent is to use empty/short queues to minimise delay, jitter & packet loss.

Expedited Forwarding Requirements EF PHB designed to configure nodes so traffic aggregate has minimum departure rate Ø border routers condition traffic aggregate (via policing / shaping) so arrival rate is less than minimum departure rate for nodes Ø interior nodes treat traffic so no queuing effects Ø no specific queuing policy set for interior nodes Ø note a simple priority scheme can achieve this Ø l l l EF traffic given absolute priority EF traffic must not overwhelm interior node but packet flows for other PHB traffic disrupted

Assured Forwarding PHB provide service superior to best-effort Ø without needing reservation of resources or detailed flow discrimination Ø based on explicit allocation Ø l l l Ø users offered choice of classes of service traffic monitored at boundary node, marked in/out inside network, no separation of traffic from different users or classes when congested, drop out packets before in packets different users will see different levels of service advantage is simplicity

AF PHB RFC 2597 four AF classes / traffic profiles are defined Ø within each class, packets marked with three drop precedence values Ø l in congestion determines relative importance simpler, more flexible than resource reservation Ø within interior DS node, traffic from different classes is treated separately Ø l Ø different resources (buffer space, data rate) hence forwarding assurance depends on resources, current load & drop precedence

Service Level Agreements Ø is a contract between network provider and customer for aspects of service Ø typically includes: l l l description of nature of service expected performance level of service process for monitoring & reporting service level Ø similar to frame relay / ATM SLA’s Ø but more difficult to realize (∵Datagram)

Service Level Agreements SLA

IP Performance Metrics Ø IP Performance Metrics working group is developing a standard set of metrics l l on quality, performance, reliability to provide common understanding Ø 3 stages of metrics l l l singleton metric - elementary / atomic quantity sample metric - taken over time period statistical metric - derived from sample Ø active or passive measurement

IP Performance Metrics

Summary Ø reviewed various internetwork services & functions to support varying services Ø multicasting Ø routing protocols Ø integrated services architecture Ø differentiated services Ø service level agreements Ø IP performance metrics