information and communication engineering (ice) mut itec4610 network switching and routing ดร....

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ITEC4610Network Switching and Routing

ดร . ประวิ�ทย์ ชุ�มชุ�หั�วิหัน้�าสาขาวิ�ชุาวิ�ศวิกรรมสารสน้เทศและการส��อสาร(ICE)MUTEmail: prawit@mut.ac.thหั�องท�างาน้: F402เบอรโทรศ�พทท#�ท�างาน้: (02)9883655 ต่%อ 220เบอรโทรศ�พทเคล��อน้ท#�: 065343850

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Class VRouting Algorithms,

RIPv1&RIPv2

ดร . ประวิ�ทย์ ชุ�มชุ�หั�วิหัน้�าสาขาวิ�ชุาวิ�ศวิกรรมสารสน้เทศและการส��อสาร(ICE)MUTEmail: prawit@mut.ac.thหั�องท�างาน้: F402เบอรโทรศ�พทท#�ท�างาน้: (02)9883655 ต่%อ 220เบอรโทรศ�พทเคล��อน้ท#�: 065343850

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หั�วิข�อท#�จะบรรย์าย์Routing Algorithm

– Distance-vector routing– Link state routing

• RIPv1• RIPv2

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IP components

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Routing protocol• Define how routers exchange

network– What type of information– The format of information– When to exchange– Which router to exchange information

with

• RIP, OSPF,BGP, IGRP,EIGRP etc.

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Routing algorithm• To choose or compute a route based on

the available network information• A routing algorithm is defined by

– The type of network information exchanges– Which router to exchange with – Method to compute the routes

• Distance vector routing, Link state routing,

Diffusing update algorithm (DUAL) etc.

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Routing Algorithm classification

Global or decentralized information?

Global:• all routers have complete

topology, link cost info• “link state” algorithmsDecentralized: • router knows physically-

connected neighbors, link costs to neighbors

• iterative process of computation, exchange of info with neighbors

• “distance vector” algorithms

Static or dynamic?Static: • routes change slowly

over timeDynamic: • routes change more

quickly– periodic update– in response to link

cost changes

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Upon completion you will be able to:

• Distinguish between intra and interdomain routing• Understand distance vector routing and RIP• Understand link state routing

Objectives

Unicast Routing Protocols:Unicast Routing Protocols:RIPRIP

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Routing inside an autonomous system is referred to as intradomain Routing inside an autonomous system is referred to as intradomain routing. Routing between autonomous systems is referred to as routing. Routing between autonomous systems is referred to as interdomain routing. interdomain routing.

INTRA- AND INTERDOMAIN ROUTING

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Autonomous systems

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Popular routing protocols

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Routing in the Internet

Path- or distance-vector protocols

Link-state protocols

Inter-domain(policy)

BGP

Intra-domain(performance)

RIP, IGRP, EIGRP(advance DV)

OSPF, IS-IS

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In distance vector routing, the least cost route between any two nodes is In distance vector routing, the least cost route between any two nodes is the route with minimum distance. In this protocol each node maintains a the route with minimum distance. In this protocol each node maintains a vector (table) of minimum distances to every nodevector (table) of minimum distances to every node

The topics discussed in this section include:The topics discussed in this section include:

Initialization Initialization Sharing Sharing Updating Updating When to Share When to Share Two-Node Loop Instability Two-Node Loop Instability Three-Node Instability Three-Node Instability

DISTANCE VECTOR ROUTING

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Distance vector routing tables

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ขบวิน้การสร�าง routing table

• Initialization• Sharing• Updating

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Initialization of tables in distance vector routing

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Initialization

• ได�มาจากท#�ไหัน้– ICMP

- Router Solicitation - Router Advertisement

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In distance vector routing, each node shares its routing table with its

immediate neighbors periodically and when there is a change.

Note:Note:

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Updating in distance vector routing of A

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Trigger Updates

• A cost update distributed immediately in response to a detected change in the cost estimate for a route to destination

• May delay trigger updates for a short time

• The trigger updates contain information about only changed routes– RIP

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Holddowns

• Prevent the reinstatement of old routes• When a router moves from its routing

table a route to a particular destination, it invokes a holddown that disables acceptance of new routes to this detination for a specified time interval

• Disadvantage– Increase the time for routers to learn the

correct new routes

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การแสดงใน้ร�ปแบบของเวิกเต่อรBellman-Ford algorithm on a

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ต่�วิอย์%างการค�าน้วิน้1

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ต่�วิอย์%างการค�าน้วิน้

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ต่�วิอย์%างการค�าน้วิน้

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Two-node instabilityBA

Unsolicited Response (change in routing table)

Normal

X failure

BUnsolicited Response

(every 30s or change in routing table)

Unstability

X failure

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Defining Infinity

BUnsolicited Response

(every 30s or change in routing table) X failure

x 2 - x 6 A

x 10 Bx 14 A

x 20 B x ∞ B=

∞ =16

x ∞ -

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Split Horizon

BUnsolicited Response

(every 30s or change in routing table) X failure

x 2 - x 6 A

x ∞ -x ∞ -

x ∞ -

Each node sends only part of its table through each interface

x 6A

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Problem of Split Horizon

• Node A could not guess that this is due to the split horizon strategy or because B has not received any news about X recently

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Split Horizon and Poison Reverse

BUnsolicited Response

(every 30s or change in routing table) X failure

x 2 - x 6 A

x ∞ -x ∞ -

x ∞ -

Do not use this value; What I know about this route come from you x ∞

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Three-node instability

B

X failure

x 2 -x 6 A

x ∞ -

x ∞C x 5 A

x 5 A

x ∞

x 8 Cx 12 B

Unstability Unstability

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Defining Infinity

B

X failure

x 2 -x 6 A

x ∞ -

x ∞C x 5 A

x 5 A

x ∞

x 8 Cx 12 B

∞=16

x 16 B x 15 B

x ∞ B=

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Loop-Free Distance Vector Routing

• Distributing enough information in update messages --> quickly detect, no prevent routing loop

• Controlling the order in which nodes distribute update messages and compute routes in response to an increase in link cost Prevent loop but require – A significant number of message exchanges– Slow convergence

• Refs– J. J. Garcia-Luna-Aceves: A Minimum-Hop Routing Algorithm

Based on Distributed Information. Computer Networks 16: 367-382 (1989)

– DUALEIGRP

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ค�าถาม?

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แบบฝึ,กหั�ดลองท�าด�

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เฉลย์

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แบบฝึ,กหั�ดลองท�าด� เป.น้การบ�าน้

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จงแสด้งการ้คำ านว้นหา node 1’ routing table ใช้� Bellman-Ford’s algorithm

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In link state routing, if each node in the domain has the entire topology In link state routing, if each node in the domain has the entire topology of the domain, the node can use Dijkstra’s algorithm to build a routing of the domain, the node can use Dijkstra’s algorithm to build a routing table.table.

The topics discussed in this section include:The topics discussed in this section include:

Building Routing Tables Building Routing Tables

LINK STATE ROUTING

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Concept of link state routing

Each router knows network topology

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Link state knowledge

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Dijkstra algorithm

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Example of formation of shortest path tree

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Table 14.1 Table 14.1 Routing table for node ARouting table for node A

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การแสดงใน้ร�ปแบบของเวิกเต่อร

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ต่�วิอย์%างFind A’s routing table

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ต่�วิอย์%าง

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ต่�วิอย์%าง

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ต่�วิอย์%าง

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ต่�วิอย์%าง

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สร�ปเป.น้ต่ารางStep P B

(cost, NH)

C(cost, NH)

D(cost, NH)

E(cost, NH)

0 A 5,A 2,A 3,A ∞

1 AC 5,A 3,A 6,C

2 ACD 5,A 6,C

3 ACDB 6,C

4 ACDBE

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Comparison of LS and DV algorithms

Message complexity• LS: with n nodes, E links,

O(nE) msgs sent • DV: exchange between

neighbors only– convergence time varies

Speed of Convergence• LS: O(n2) algorithm requires

O(nE) msgs– may have oscillations

• DV: convergence time varies– may be routing loops– count-to-infinity problem

Robustness: what happens if router malfunctions?

LS: – node can advertise

incorrect link cost– each node computes only

its own table

DV:– DV node can advertise

incorrect path cost– each node’s table used by

others • error propagate thru

network

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ค�าถาม?

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แบบฝึ,กหั�ดลองท�าด�

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สร�ปเป.น้ต่ารางStep P Node

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0 1 1,1 ∞ ∞ 7,1

1 12 3,1 ∞ 7,1

2 123 5,3 7,1

3 1234 6,4

4 12345

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แบบฝึ,กหั�ดลองท�าด�

2

6

5

3

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11

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1 14

14

จงแสด้งการ้คำ านว้นหา node 1’ routing table ใช้� Dijkstra’s algorithm

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เฉลย์ สร�ปเป.น้ต่าราง

Step P Node 2(cost, NH)

Node 3(cost, NH)

Node 4(cost, NH)

Node 5(cost, NH)

Node 5(cost, NH)

0

1

2

3

4

5

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The Routing Information Protocol (RIP) is an intradomain routing The Routing Information Protocol (RIP) is an intradomain routing protocol used inside an autonomous system. It is a very simple protocol protocol used inside an autonomous system. It is a very simple protocol based on distance vector routing. based on distance vector routing.

The topics discussed in this section include:The topics discussed in this section include:

RIP Message Format RIP Message Format Requests and Responses Requests and Responses Timers in RIP Timers in RIP RIP Version 2 RIP Version 2 Encapsulation Encapsulation

RIP

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Example of a domain using RIP

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RIP message format

Command : 1, request, 2 response

Version : version 1 or version 2

Family : Define family of the protocol used ex. 2 for TCP/IP

Network address : The address of destination address

Distance :Hop count to the destination networ

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Request messages

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Response Message

-Command field = 1-Solicited response is sent only answer to request-Unsolicited response is sent periodically, every 30 second

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Figure 14.11 shows the update message sent from router R1 to router R2 in Figure 14.8. The message is sent out of interface 130.10.0.2.

See Next Slide

The message is prepared with the combination of split horizon and poison reverse strategy in mind. Router R1 has obtained information about networks 195.2.4.0, 195.2.5.0, and 195.2.6.0 from router R2. When R1 sends an update message to R2, it replaces the actual value of the hop counts for these three networks with 16 (infinity) to prevent any confusion for R2. The figure also shows the table extracted from the message. Router R2 uses the source address of the IP datagram carrying the RIP message from R1 (130.10.02) as the next hop address.

Example 1

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Solution to Example 1it replaces the actual value of the hop counts for these three networks with 16 (infinity) to prevent any confusion for R2-- Split Horizon and Poison Reverse

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RIP timers

- Periodic timer = Controls the advertising of regular update message

- Expiration = Governs the validity of a route

- Garbage Collection= When to purge a route from the routing table

-This timer allows neighbors to become aware of the invalidity of the route prior to purging

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A routing table has 20 entries. It does not receive information about five routes for 200 s. How many timers are running at this time?

SolutionThe 21 timers are listed below: Periodic timer: 1 Expiration timer: 20 − 5 = 15 Garbage collection timer: 5

RIP timers

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RIP version 2 format

• Route tag– Carries information such as autonomous system

number• Subnet mask

– Carries subnet mask or prefix• Next-hop address

– Carries the address of next hop

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Authentication

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Multicasting

• RIP Version 1 uses broadcasting• RIP Version 2 uses the all router

multicast address

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RIP uses the services of UDP on well-known port 520.

Note:Note:

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RIPv1• Distance vector protocol• Uses UDP port 520• Classlfull protocol• Metric is router hop count• Maximum hop count is 15;infinite (unreachable) routes

have a metric of 16• Periodic updates sent every 30 seconds to multicast

address 224.0.0.9• 25 routes per RIP messages (24 if uses authentication)• Implement split horizon with poison reverse• Implements triggered updates• No support Authentication• Subnet mask included in route entry• Administrative of distance for RIPv2 is 120

– A rating of the trustworthiness of a routing information source. In Cisco routers, administrative distance is expressed as a numerica

l value between 0 and 2 5 5 . The higher the value, the lower th et r ust wor t hi ness r at i ng.

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RIPv2• Distance vector protocol• Uses UDP port 520• Classless protocol• Support VLSM• Metric is router hop count• Maximum hop count is 15;infinite (unreachable)

routes have a metric of 16• Periodic updates sent every 30 seconds to multicast

address 224.0.0.9• 25 routes per RIP messages (24 if uses authentication)• Implement split horizon with poison reverse• Implements triggered updates• Subnet mask included in route entry• Administrative of distance for RIPv2 is 120

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IP components

สร้�างได้�อย่างไร้?

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RIP Table processing

• RIP routing tables managed by application-level process called route-d (daemon)

• advertisements sent in UDP packets, periodically repeated

physical

link

network forwarding (IP) table

Transprt (UDP)

routed

physical

link

network (IP)

Transprt (UDP)

routed

forwardingtable

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ค�าถาม?

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Summary

• Distance Vector routing• Link State Routing• RIPv1 & RIPv2

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Homeworks

• เต่ร#ย์มบรรย์าย์เร��อง 2-3 คน้ต่%อ 1 กล�%ม– เปร#ย์บเท#ย์บ IPv4 และ IPv6 หัร�อ– เปร#ย์บเท#ย์บ ICMP4 และ ICMP6 หัร�อ – Mobile IPv4 หัร�อ– Mobile IPv6

• ใชุ� Microsoft PowerPoint ใน้การบรรย์าย์• บรรย์าย์กล�%มละ 10-15 น้าท# ถามต่อบ 5 น้าท#�• เก/บ 5 %• บรรย์าย์ 1 กรกฎาคม 2549 เวิลา 16.00 (ต่�องต่รง

เวิลา)