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The Third CEENet WorkshopZagreb, Croatia 1Iskra Djonova-Popova

Distance Vector ProtocolsDistance Vector Protocols(contents)(contents)

IGPs - what are they and why they

are needed

Routing algorithms - the designgoals

Distance vector versus Link state

RIP (Routing Information Protocol)

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IGP

IGP -- What Are TheyWhat Are They

Internal Gateway Protocols

Single network administration Unique routing policy

Make best use of network resources

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IGPIGP -- Why They are NeededWhy They are Needed

A B C

D E

2

3 4

5

1

Routing algorithms would scale

better

Static routes would be fine

6

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Routing AlgorithmsRouting Algorithms -- thethe

Design GoalsDesign Goals

O

ptimallySimplicity/Low overhead

Robustness/ Stability

Rapid Convergence

Flexibility

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Routing on the InternetRouting on the Internet -- thethe

Two ParadigmsTwo ParadigmsCentralized approach

good routes can be found but reliability is

questionable

too much traffic on lines connected to the

network center

Distributed approachthe failure of one part doesnt affect the

functioning of the rest of the network

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Distributed Approach WinsDistributed Approach Wins

GGP - Predecessor of RIP

No distinction between hosts androuters

Attempts to keep track of the load

in the network

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InternetGrowsInternetGrows

Autonomous systems are introduced

to support hierarchical routing

The distance vector protocols are notany more sutable

Link state protocols are developed

Routers routs

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HostReleased from BurdenHostReleased from Burden

ofRoutingofRouting The subnet masked bits of the

destination address mach those of thelocal address

true - the destination is on the local network

(next hops address is the destination

address)

false - the destination is remote (next hops

address is some of the routers)

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Distance Vector ProtocolsDistance Vector Protocols

Neighboring nodes send information in

regular time intervals

Install routes directly in tables, lowest

cost wins

The information sent (the distancevectors) are all routes from the table

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TheR

outing AlgorithmTheR

outing Algorithm

the shortest path tree is contained

in the routing table

Calculations are based on the

Bellman-Ford algorithm

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The Centralized Version of theThe Centralized Version of the

AlgorithmAlgorithm

Cycle Node B C D E

Initial (., g) (., g) (., g) (., g)

1 (1, 1) (2, 2) (3, 1) (4, 2)

A B C

D E

2

3 4

56

1 A B C

D E

2

3 4

1

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The Distributed VersionThe Distributed Version

A B C

D E

1 2

3 4

5

6

Example of simple network with 5 nodes (routers)

and 6 links (interfaces)

The cost of all links is assumed to be 1

From A to Link CostB 1 1

C 1 2

D 3 1

E 1 2

Routing table for A

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AdvantagesAdvantages

simple to implement

low requirement in processing andmemory at the nodes

suitable for small networks

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DisadvantagesDisadvantagesSlow convergence

Bouncing effectCounting to infinity problem

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S

low Convergence

A B C

D E

2

3 4

5

6

XXX

When a link breaks the routers are supposed to

reestablish the routing tables

link 1 breaks

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The Bouncing Effect

link 2 breaks and A sends its routing

table to B before B sends it to A

A B C

D E

3 4

5

6

XXX

1

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Counting to Infinity Problems

D E

3

A B C2

4

5

XXX

XXX

Links 1 and 6

break.

A sends its old routing table

before D sends the new routing table

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SplitHorizon for Preventing

Two-hop Loops

Simple

the information about destination routed on

the link is omitted

With poisonous reverse

the corresponding distance is set to infinity

if the destination is routed on the link

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Triggered UpdatesTriggered Updates

A timer is associated with each entry in

the routing table

much longer than the period of transmission

of information

Triggered updatesrequest nodes to send messages as soon

as they notice a change in the routing table

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Different Distance VectorDifferent Distance Vector

ProtocolsProtocols

Metric they use

Structure of the addresses

Range of links they support

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RIPRIP -- RoutingInformationRoutingInformation

ProtocolProtocol

first used in XNS (Xerox Network

Systems)

designed as a component of thenetworking code for the BSD release of

UNIX incorporated in program routed (rote management

daemon)

documented in rfc 1058

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RIPRIP -- CharacteristicsCharacteristics

the metric is a hop-countThe value of 1 to 15 is used (16 denotes infinity)

supports point-to-point links andbroadcast networks

doesn't support CIDR

used only in IP networksat first the intention was to be used in variety of

networks

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RIPRIP -- CharacteristicsCharacteristics

packets are sent every 30 seconds

or faster when necessary

route is considered down if notrefreshed within 180 sec. (distance

set to infinity)

two kinds of messages request

response

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RIPRIP -- Message FormatMessage Format

command (1) version (1) must be zero(2)

address family identifier (2) must be zero(2)

IP address(4)

must be zero(4)

must be zero(4)

metric(4)

0 31

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RIPRIP -- ProcessingProcessing

When processing an incoming

response a set of validation checks are

performed if each address is valid A, B orC address

the network number is not 127 (loopback) or 0

(except in in the case of default address 0.0.0.0) the host part is not a broadcast address

the metric is not larger than 16 (infinity)

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RIPRIP -- ProcessingProcessing

the metric associated with thedestination

the address of the next router

a recently updated flagseveral timers

Each entry in the routing tables

contains:

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RIPRIP -- LimitationsLimitations

Maximum hop count of 15

restricts the use of RIP in larger networks,

but prevents the count to infinity problem(endless loops)

Difference in links speed is not reflected

in the hop-count metricscongested links can be still included in the

best path

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RIP2RIP2 -- Why Was Developed?Why Was Developed?

many superior IGP exists (RIP is often

referred as Rest In Peace)

there are still many implementations ofRIP

given that RIP will still be used, it

deserves improvementsRIP 2 is documented in RFC-1287, RFC-

1388 and RFC-1389

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RIP2RIP2 -- Message FormatMessage Format

command (1) version (1) Routing domain(2)

address family identifier (2) Route Tag(2)

IP address(4)

Next Hop(4)

Subnet Mask(4)

metric(4)

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RIP2RIP2 -- The Added FieldsThe Added Fields

routing domain

used together with the next hop fieldto allow multiple autonomous systems

to share a single wire

route tag

to flag external routes and is for use

by EGP and BGP

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RIP2RIP2 -- ImprovementsImprovements

authentication

routing per subnet

support of multiple metrics

routing domainsmulticasting

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AuthenticationAuthentication

specifies that first entry in a packet

can be replaced by an authenticationsegment

currently the only algorithm defined is

simple password procedure

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Routing perSubnetRouting perSubnet

support CIDR

subnet mask included in themessage

compatible with RIP1 because the

subnet filed is ignored whencooperating with RIP1

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Multiple MetricsMultiple Metrics

metric contains two components

hop count

throughput, measured as 10logC ten times the decimal logarithm of the maximum data

rate in Kbs

selected path with largest throughputif two paths with same throughput the one

with lower hop count is chosen

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Routing DomainRouting Domain

different autonomous systems share

the same wire (Ethernet or FDDI)

routers dont want to process messages

bound to his network

routing domain number is theautonomous system number

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To create a routing process for RIP,

use the configuration command:

router rip

no router rip

To shut down the routing process

use the command:

RIPRIP -- ConfigurationConfiguration

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Specifying the List ofSpecifying the List of

NetworksNetworksSpecify the list of networks with the network routerSpecify the list of networks with the network router

configuration subcommand.configuration subcommand.

network networknetwork network--numbernumber

no network networkno network network--numbernumber

The argument networkThe argument network--number is a network number in dotted IPnumber is a network number in dotted IP

notation (of directly connected networks). Note that this numbernotation (of directly connected networks). Note that this number

must not contain subnet information. You may specify multiplemust not contain subnet information. You may specify multiple

network subcommands. RIP routing updates will be sent andnetwork subcommands. RIP routing updates will be sent andreceived only through interfaces on this network. The networkreceived only through interfaces on this network. The network

router subcommand is a mandatory configuration command androuter subcommand is a mandatory configuration command and

must be included in the configuration of each IP routing process.must be included in the configuration of each IP routing process.

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Example:

The following example configuration defines RIP as

the routing protocol to be used on all interfaces

connected to networks 128.99.0.0 and 192.31.7.0.

router rip

network 128.99.0.0

network 192.31.7.0

To remove a network from the list, use the nonetwork router subcommand followed by the

network address.

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RIP is not aloneRIP is not alone

IGRPIGRP

Developed in the mid1980s by cisco

Systems, Inc.

Designed to overcome the limitations

of RIP

Initially worked in IP environment, butlatter ported to OSI CLNP networks

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IGRPIGRP -- Main CharacteristicsMain Characteristics

Distance vector protocol

Uses a combination of metricsinternetwork, delay, bandwidth, reliability

and load

the weighting factors are set either byadministrators or default values are

used

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IGRPIGRP -- Additional flexibilityAdditional flexibility

Wide metric ranges

allow satisfactory metric setting in

internetworks with widely varying

performance characteristics

Permits multipath routing

dual equal-bandwidth lines may run a

single stream of traffic in round-robin

fashion

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IGRPIGRP -- Stability FeaturesStability Features

hold-downs

split horizons

poison reverse updates

timers

update timer

hold time periodinvalid timer

flush timer

Documents

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