nwt routing

7/25/2019 NWT Routing

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Network Troubleshooting

CT046-3-3

Routing


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CT046-3-3 Network Troubleshooting Routing

Routing Components

Types of Routing

Routing Protocol Routing Loops

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Topics & structure of this lesson


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CT046-3-3 Network Troubleshooting Routing 3

Learning Outcomes

To understand the concepts of routing and

routing protocol

To understand the concepts distancevector and link state routing protocol


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Routing

Process of moving information (packet) across

an internetork from a source to a destination!

Process of selecting paths in a netork along

hich to send data or physical traffic! Routing directs forarding" the passing of

logically addressed packets from their source to

destination through intermediary nodes


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Routing

Performed #y a router!

Refers to routing ta#leshich maintain arecord of the routes to various netorkdestinations!

Routing is a key feature of the $nternet

% ena#les messages to pass from one

computer to another%naly'es a routing ta#leto determine the

#est path!


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Routing Components

Routing involves to#asic activities

% determining optimal routing paths% transporting information groups knon as

packets through an internetork!

Routers maintain a routing ta#le to routepackets!


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Routing Ta#le

ource % source of routing information% C % connected

% R * R$P

u#net+,ask % define the $P address of anetork or a su#net

Out $nt % outgoing interface" informs routerhich interface to send the packets

-e.t*/op % ne.t*hop router" address of therouter here the packets need to #e forarded


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Routing Ta#le



Connected Routes

u#nets to hich the routers interface are

connected is knon as connected routes

utomatically added to router0s routingta#le



Types of Routing

tatic routing

% Route is entered #y the netork administrator!

1ynamic Routing% Route is #uilt automatically #y the routing

protocol

% follo rules defined #y a routing protocol

% independently select the #est path!



tatic Routing

tatic routing descri#es a system that does notimplement adaptive routing! !

fi.ed paths

constructs the routing ta#le in every router% putting in the entries for every netork that could#e a destination!

tatic routesare unchangea#le!



tatic Routes

added to the routing ta#le using a command

tatic routes can #e used hen*

% mall internetork hich seldom change and has no

redundant link% Router need to dial #ackup to call other router hen a

leased line is don

% mall #ranch offices here each can #e reached ith

only one possi#le path

% 2orard packets to hosts in $nternet and not to the

enterprise netork!



tatic Routing

tatic route operations can #e divided into % -etork administrator configures the route

% Router installs the route in the routing ta#le

% The static route is used to route packets! use the i routecommand to manually

configure a static route!

The administrative distance is an optional

parameter that indicates the relia#ility of a route!



dministrative 1istance

loer value indicates a more relia#le route!

route ith a loer administrative distance ill #e

installed #efore a similar route ith a higher

administrative distance! 1efault administrative distance of a static route is

3!

$n routing ta#le" static route ith the outgoing

interface option as directly connected!



1efault Route

to forard packets that do not match any

other routes in the routing ta#le

no default route4 discard the packet other router must have either a route to

that destination or its on default route

One of the routers should have a route tothe destination!


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dvantages of tatic Routing

Lo Processor Overhead% 1on0t calculate #est path

% need less processor poer and less memory

-o 5andidth 6tili'ation% -o updating each other ith static routes

ecure Operation% Less vulnera#le to attack as don0t accept updates

% 1on0t send updates to untrusted source

Predicta#ility% dministrator precisely control path0s selection

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1isadvantages of tatic Routing

/igh ,aintenance Configuration% Configure routes manually

% Comple. netork re7uires high maintenance

-o adapta#ility -ot fault tolerant

% 8hen there is a change in the netork or a failure occurs #eteen to

statically defined nodes" traffic ill not #e rerouted!

% packets ill have to ait for the failure to #e repaired or the static routeto #e updated #y the administrator #efore #eing transmitted!

% ,ost re7uests ill time out (ultimately failing) #efore these repairs can

#e made!

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1ynamic Routing

constructs routing ta#les automatically

#ased on information #y routing protocols!

dominates the $nternet!



dvantages of 1ynamic Routing

/igh degree of adapta#ility

% Learn netork topology

%lert each other a#out other links

Lo maintenance configuration

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1isadvantages of 1ynamic

Routing

/igh #andidth utili'ation

% end and receive routing updates

% lo performance

$ncreased processor overhead and

memory utili'ation

% Re7uire large memory and more CP6 time

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Routing Protocol

specifies ho routers communicate

select routes #eteen any to nodes

router hasa

prioriknoledge only a#outits immediate neigh#ors!

shares this information for knoledge of

the netork topology operates at Layer 9 of the O$ model

defined in documents called R2C


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Routing Protocol 2unctions

learn routing information

advertise routing information

select the #est route #ased on the metric any changes in topology" converge 7uickly


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Routed Protocols

Referred as netork protocols! transported #y routing protocols across an internetork!

perform a variety of functions re7uired for communication#eteen user applications in source and destinationdevices

occur at the upper five layers of the O$ reference model

i! netork layer

ii! transport layer

iii! session layer

iv! presentation layer

v! application layer!


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Routed protocol vs Routing protocol

Routed Protocols Routing Protocols

protocols that are routed overan internetwork

protocols that implementrouting algorithms

Internet Protocol (IP) used by intermediate systems tobuild tables used in determiningpath selection of routedprotocols.

DECnet Interior ateway !outingProtocol (I!P)

"pple#alk $pen %hortest Path &irst($%P&)

'ovell 'etare order ateway Protocol (P)


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Routing Protocol

The router uses to #asic functions

% path determination function

% sitching function


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Path 1etermination 2unction

occurs at the netork layer

evaluate the paths to a destination

esta#lish the preferred ay to handle apacket!

uses the routing ta#le to determine the

#est path and uses the sitching functionto forard the packet!


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itching 2unction

the internal process of a router

accept a packet on one interface and

forard it to a second interface on thesame router!

key responsi#ility

% to encapsulate packets in the appropriate

frame type for the ne.t data link!


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Routing Protocol

$nterior :ateay Protocols ($:Ps)

e.change routing*information ithin a

single autonomous system!

% 6sed #eteen routers of same autonomous systems ()!

;.terior :ateay Protocols (;:Ps) route

#eteen separate autonomous systems!% 6sed #eteen routers of different autonomous systems

()!

% - num#ering are controlled glo#ally #y $- ($nternet

ssigned -um#ers uthority)


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Types of Routing Protocol

Interior routing protocols Exterior routing protocols

!outer Information Protocol(!IP)

E*terior ateway Protocol(EP)

$pen %hortest Path &irst($%P&)

order ateway Protocol(P)

Intermediate %ystem toIntermediate %ystem (I%+I%)

Interior ateway !outingProtocol (I!P)

Enhanced I!P (EI!P)


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$:P vs ;:P


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Classes of Routing Protocol

1istance vector

Periodically sends route ta#le to other routers

8orks #est on L-s" not 8-s

Link*state

Routing ta#les are #roadcast at startup and

then only hen they change

OP2 uses link*state


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1istance


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1istance acent neigh#ors!

router does not kno the e.act topology of

an internetork! 8hy?

C!n onl" see its neighboring

routers


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1istance


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1istance


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1istance


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1istance


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Link tate

Link*state algorithms% 6ses hortest Path 2irst (P2) algorithms+1>ikstra

lgorithms% flood routing information to all routers in the internetork

that creates a map of the entire netork!

assem#le all the information to calculate the shortestpath routes and #uilds routing ta#les shoing the #estpath

Once converged" send update packets" hich containonly changes rather than hole routing ta#le!

6pdate packets are passed across the netork in event*triggered updates


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Link tate

#uilds a complete data#ase of all the link states

router gathers enough information to create the

netork map

;ach router individually runs the P2 algorithmon its link*state data#ase

% to identify the #est paths

These paths form a tree ith the local router asits root!

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Link tate

advertise the states of their links to all otherrouters in the area

8hen a netork link changes state" anotification called a link*state advertisement(L) is flooded throughout the netork!

ll the routers note the change and ad>ust theirroutes accordingly!

lso has periodic reflooding of L #ut longer

interval time more relia#le" easier to de#ug" and less

#andidth*intensive

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Link tate

Link*state advertisements (Ls) % routing informationthat is sent #eteen routers!

% Router L % identifies router $1" router interfaces $Paddresses" status (up or don) of each interface" cost

(metric) associated ith each interface% Link L % identifies each su#net and routers that are

attached to that su#net

Topological data#ase % collection of information (datastructure) gathered from Ls!

P2 algorithm % calculation performed on the data#aseresulting in the P2 tree!

Routing ta#les % list of the knon paths and interfaces!


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Link tate


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dvantages of Link tate

2aster Convergence

$mproved #andidth utili'ation

support Classless $nter*1omain Routing(C$1R)"


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1isadvantages of Link tate

Processor overhead

,emory re7uirements

5andidth Consumption Comple. administration


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Link tate

Open hortest Path 2irst (OP2)

$ntermediate ystem to $ntermediate

ystem ($*$)


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Convergence

colla#orative and independent process

;ven though the routers share information #ut must

calculate routing ta#le on their on!

To have accurate ta#le" routers should have commonvie of the netork=s topology!

8hen all routers agree on the topology" they have

converged!

Rapid convergence means rapid recovery from linkfailure or other netork changes!

Routing protocols are >udged #y ho 7uickly they

converge!

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Convergence

8hen converging process happens" the

netork is suscepti#le to routing pro#lems!

8hen a link is don #ut routers are

unaare" individual ta#les ill #e

contradictory and routing pro#lems

Routing pro#lems such as

% dropped packets

% routing loop

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Convergence

2actors affecting convergence time*% routing protocol used

% router=s distance from the point of change

% num#er of routers in the netork% 5andidth and traffic load on communications links

% router=s load

% Traffic patterns in relation to the topology change

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Routing Loops

occurs hen the routers forard packets

hich ends up #ack at the same router!


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Routing Loops % Counting to

$nfinity

l i 1 fi i i


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olution 1efining a ma.imum

count


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olution plit /ori'on


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olution Route Poisoning


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olution Triggered 6pdates


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olution /olddon Timers


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ummary

%plit ,ori-on Per+interface feature limits the route senton the interface. Does not send the routingupdates to the original route.

Poison

!everse

/pon learning of a failed route advertise a

poisoned route suspending the splithori-on

rules.

#riggered

/pdate

%ends an immediate update(without waiting

for the periodic update) when there0s afailed route.

,olddown#imers

%ets a timer to confirm the failed route.

Poison !oute " route advertised with infinite metric.


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-e.t ession

Trou#leshooting pproach

Connectivity Pro#lems

Performance Pro#lems

ystematic Trou#leshooting ,ethod

Trou#leshooting Process

electing a Trou#leshooting pproach

nwt routing

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