Switching and Routing Technique

Switching and Routing Switching and Routing TechniqueTechniqueW.lilakiatsakunW.lilakiatsakun

AssessmentAssessment• Final 40 %Final 40 %• Midterm 30%Midterm 30%• LAB + Assignment 30%LAB + Assignment 30%

TopicsTopics• Review routing fundamental Review routing fundamental • Routing TechniquesRouting Techniques

– Distance Vector – RIP V1,2 /IGRP /EIGRPDistance Vector – RIP V1,2 /IGRP /EIGRP– Link state Protocol – OSPF ,IS-ISLink state Protocol – OSPF ,IS-IS– Hierarchical –BGPv4 Hierarchical –BGPv4

• Review Switching OperationReview Switching Operation• Switching TechniquesSwitching Techniques

– Spanning Tree ProtocolSpanning Tree Protocol– VLAN and TrunkVLAN and Trunk

• Network DesignNetwork Design– Case study – campus network designCase study – campus network design

Review Routing Review Routing FundamentalFundamental• VLSM VLSM • Static & Dynamic Routing Static & Dynamic Routing • Routing algorithm conceptRouting algorithm concept

VLSM VLSM • Variable Length Subnet MaskVariable Length Subnet Mask• VLSM allows an organization to use VLSM allows an organization to use

more than one subnet mask within the more than one subnet mask within the same network address spacesame network address space

• VLSM implementation maximizes VLSM implementation maximizes address efficiency, and is often referred address efficiency, and is often referred to as subnetting a subnetto as subnetting a subnet

• Main reason – addressing crisis Main reason – addressing crisis

Short-term solution Short-term solution of addressing crisisof addressing crisis• Subnetting (1985)Subnetting (1985)• VLSM VLSM (1987)(1987)• Classless interdomain routing (1993)Classless interdomain routing (1993)• Private IP Private IP • NAT (Network Address Translation) NAT (Network Address Translation)

/PAT (Port Address Translation)/PAT (Port Address Translation)

Classful routing protocolClassful routing protocol• RIP V1 (Routing Information Protocol) RIP V1 (Routing Information Protocol) • IGRP (Interior Gateway Routing IGRP (Interior Gateway Routing

Protocol)Protocol)• Routing table is considered by class of Routing table is considered by class of

IP addressIP address– 192.168.10.X 192.168.10.X 192.168.10.0 192.168.10.0 – 172.10.X.X 172.10.X.X 172.10.0.0 172.10.0.0– 10.X.X.X 10.X.X.X 10.0.0.0 10.0.0.0

Supporting protocolsSupporting protocols• OSPFOSPF• Integrated IS-ISIntegrated IS-IS• EIGRPEIGRP• RIP V2RIP V2• Static RoutingStatic Routing• Subnet informationSubnet information will be exchanged as well will be exchanged as well

as routing informationas routing information– 172.16.10.0 /172.16.10.0 /255.255.255.0255.255.255.0 – 10.5.2.0 /10.5.2.0 /255.255.255.0 255.255.255.0

VLSM - exampleVLSM - example

Calculating VLSMCalculating VLSM

Subnet MaskSubnet Mask• 255.255.255.252 - /30255.255.255.252 - /30• 255.255.255.248 - /29255.255.255.248 - /29• 255.255.255.240 - /28255.255.255.240 - /28• 255.255.255.224 - /27255.255.255.224 - /27• 255.255.255.192 - /26255.255.255.192 - /26

• 255.255.255.128 - /25255.255.255.128 - /25• 255.255.255.0 - /24255.255.255.0 - /24• 255.255.254.0 - /23255.255.254.0 - /23• 255.255.252.0 - /22255.255.252.0 - /22• 255.255.248.0 - /21255.255.248.0 - /21

Waste of Space (1/2)Waste of Space (1/2)

• All one subnet and all zero subnet can be All one subnet and all zero subnet can be used to reduce the waste of spaceused to reduce the waste of space

Waste of space (2/2)Waste of space (2/2)

Sub-subnetSub-subnet (1/2)(1/2)

Sub-subnetSub-subnet (2/2)(2/2)

Calculating VLSM (1/6)Calculating VLSM (1/6)






Problem 1- 192.168.10.0/24Problem 1- 192.168.10.0/24

Route Aggregation Route Aggregation • The use of classless interdomain The use of classless interdomain

routing (CIDR) and VLSM prevents routing (CIDR) and VLSM prevents address waste and promotes route address waste and promotes route aggregation, or summarizationaggregation, or summarization

• Aka. Route SummarizationAka. Route Summarization• Save routing table spaceSave routing table space

Route summarization (1/3)Route summarization (1/3)



Review Routing Review Routing fundamentalfundamental

• Routing is the process that a router uses to Routing is the process that a router uses to forward packets toward the destination forward packets toward the destination network. network.

• A router makes decisions based upon A router makes decisions based upon the the destination IP address of a packet.destination IP address of a packet.

• To make the correct decisions, routers must To make the correct decisions, routers must learn how to reach remote networks. learn how to reach remote networks.

• When routers use When routers use dynamic routingdynamic routing, this , this information is learned from other routers. information is learned from other routers.

• When When static routingstatic routing is used, a network is used, a network administrator configures information about administrator configures information about remote networks manuallyremote networks manually

Static RoutingStatic Routing (1/2)(1/2)

• Since static routes are configured manu Since static routes are configured manu ally, network administrators must add a ally, network administrators must add a

nd delete static routes to reflect any net nd delete static routes to reflect any net work topology changes. work topology changes.

• In a large network, the manual maintena In a large network, the manual maintena nce of routing tables could require a lot nce of routing tables could require a lot

of administrative time. of administrative time.

Static Routing (2/2)Static Routing (2/2)• Static routing is not as scalable as dyna Static routing is not as scalable as dyna

mic routing because of the extra admin mic routing because of the extra admin istrative requirements. istrative requirements.

• InIn large networks, static routes that are large networks, static routes that are intended to accomplish a specific purp intended to accomplish a specific purp

ose ose• They They are often configured in conjunctio are often configured in conjunctio

n with a dynamic routing protocol. n with a dynamic routing protocol.

Static route operationStatic route operation• Network administrator configures the route Network administrator configures the route• Router installs the route in the routing table Router installs the route in the routing table• The static route is used to route packets. The static route is used to route packets.

Static route - TopologyStatic route - Topology

Static route – R1 Static route – R1 configurationconfiguration

Static route – R1 Static route – R1 configurationconfiguration

Summary static routes (1/3)Summary static routes (1/3)• Route SummarizationRoute Summarization

– Multiple static routes can be summarized Multiple static routes can be summarized into a single static route if:into a single static route if:

– The destination networks can be The destination networks can be summarized into a single network address, summarized into a single network address, and and

– The multiple static routes all use the same The multiple static routes all use the same exit-interface or next-hop IP address exit-interface or next-hop IP address

Summary static routes (2/3)Summary static routes (2/3)

R3(config)#ip route 172.16.0.0 255.255.252.0 serial0/0/1

Summary static routes (3/3)Summary static routes (3/3)

Default route (1/4)Default route (1/4)• Default routes are used to route packets Default routes are used to route packets

with destinations that do not match any with destinations that do not match any of the other routes in the routing table. of the other routes in the routing table.

• Routers are typically configured with a d Routers are typically configured with a d - efault route for Internet bound traffic, si - efault route for Internet bound traffic, si

nce it is often impractical and unnecess nce it is often impractical and unnecess ary to maintain routes to all networks in ary to maintain routes to all networks in the Internet. the Internet.

• A default route is actually a special stati A default route is actually a special stati c route that uses this format: c route that uses this format:

Default route (2/4)Default route (2/4)• ip route ip route 0.0.0.0 0.0.0.00.0.0.0 0.0.0.0 [ [ - -next hop ad- -next hop ad

dress dress | | outgoing interface outgoing interface ] ]• The The 0.0.0.00.0.0.0 mask, when logically ANDe mask, when logically ANDe

d to the destination IP address of the pa d to the destination IP address of the pa cket to be routed, will always yield the cket to be routed, will always yield the

network network 0.0.0.00.0.0.0• If the packet does not match a more sp If the packet does not match a more sp

ecific route in the routing table, it will b ecific route in the routing table, it will b e routed to the e routed to the 0.0.0.00.0.0.0 network. network.

Default route (3/4)Default route (3/4)

Default route (4/4)Default route (4/4)Before using default route

After using default route

Dynamic Routing Protocol Dynamic Routing Protocol • A routing protocol is a set of processes, A routing protocol is a set of processes,

algorithms, and messages that are used to algorithms, and messages that are used to exchange routing information and populate exchange routing information and populate the routing table with the routing protocol's the routing table with the routing protocol's choice of best paths. choice of best paths.

• The purpose of a routing protocol includes:The purpose of a routing protocol includes:– Discovery of remote networksDiscovery of remote networks– Maintaining up-to-date routing informationMaintaining up-to-date routing information– Choosing the best path to destination networksChoosing the best path to destination networks– Ability to find a new best path if the current path Ability to find a new best path if the current path

is no longer availableis no longer available

Routing Protocol Routing Protocol

Dynamic Routing Protocol Dynamic Routing Protocol OperationOperation• In general, the operations of a dynamic In general, the operations of a dynamic

routing protocol can be described as follows: routing protocol can be described as follows: – The router sends and receives routing messages The router sends and receives routing messages

on its interfaces.on its interfaces.– The router shares routing messages and routing The router shares routing messages and routing

information with other routers that are using the information with other routers that are using the same routing protocolsame routing protocol

– Routers exchange routing information to learn Routers exchange routing information to learn about remote networks. about remote networks.

– When a router detects a topology change the When a router detects a topology change the routing protocol can advertise this change to other routing protocol can advertise this change to other routers.routers.

Static Routing VS Dynamic Static Routing VS Dynamic RoutingRouting

AS / IGP and EGPAS / IGP and EGP

• An autonomous system (AS) - otherwise An autonomous system (AS) - otherwise known as a routing domain - is a collection known as a routing domain - is a collection of routers under a common administration. of routers under a common administration.

• Interior Gateway Protocols (IGP) are used Interior Gateway Protocols (IGP) are used for intra-autonomous system routing - for intra-autonomous system routing - routing inside an autonomous system.routing inside an autonomous system.

• Exterior Gateway Protocols (EGP) are used Exterior Gateway Protocols (EGP) are used for inter-autonomous system routing - for inter-autonomous system routing - routing between autonomous systems.routing between autonomous systems.

AS /IGP and EGPAS /IGP and EGP

Class of routing protocol Class of routing protocol • Most routing algorithms can be classified Most routing algorithms can be classified

into one of two categories: into one of two categories:– Distance vector Distance vector– - Link state- Link state

• The distance vector The distance vector routing approach de routing approach de termines the direction, or vector, and dis termines the direction, or vector, and dis

tance to any link in an internetwork. tance to any link in an internetwork.• -The link state -The link state approach recreates the ex approach recreates the ex

act topology of an entire internetwork. act topology of an entire internetwork.

Distance Vector Routing Distance Vector Routing • The distance vector routing algorithm The distance vector routing algorithm

passes periodic copies of a routing tabl passes periodic copies of a routing tablee from router to router. from router to router.

• These regular updates between router These regular updates between router s communicate topology changes. s communicate topology changes.

• The distance vector routing algorithm i The distance vector routing algorithm i s also known as the s also known as the - Bellman Ford algor- Bellman Ford algor

ithmithm . .

Distance Vector Operation Distance Vector Operation (1/2)(1/2)

Distance Vector Operation Distance Vector Operation (2/2)(2/2)

• Each router receives a routing table from it Each router receives a routing table from it s directly connected neighbor routers. s directly connected neighbor routers.

• Router B receives information from Router Router B receives information from Router A. Router B adds a distance vector number A. Router B adds a distance vector number

, such as a number of hops. , such as a number of hops.• This number increases the distance vector. This number increases the distance vector.• Then Router B passes this new routing tabl Then Router B passes this new routing tabl

e to its other neighbor, Router C. e to its other neighbor, Router C.• - - This same step by step process occurs in a - - This same step by step process occurs in a

ll directions between neighbor routers ll directions between neighbor routers

Distance Vector Network Distance Vector Network DiscoveryDiscovery

Routing Metric ComponentRouting Metric Component

Work best situation for Work best situation for Distance VectorDistance Vector• Distance vector protocols work best in Distance vector protocols work best in

situations where:situations where:– The network is simple and flat and does not The network is simple and flat and does not

require a special hierarchical design.require a special hierarchical design.– The administrators do not have enough The administrators do not have enough

knowledge to configure and troubleshoot knowledge to configure and troubleshoot link-state protocols.link-state protocols.

– Specific types of networks, such as hub-and-Specific types of networks, such as hub-and-spoke networks, are being implemented.spoke networks, are being implemented.

– Worst-case convergence times in a network Worst-case convergence times in a network are not a concern.are not a concern.

Link State ProtocolLink State Protocol• - The link state algorithm is also known a - The link state algorithm is also known a

s Dijkstra's algorithm or as the shortest s Dijkstra's algorithm or as the shortest path first (SPF) algorithm. path first (SPF) algorithm.

• - The link state routing algorithm maintai - The link state routing algorithm maintai ns a complex database of topology infor ns a complex database of topology infor

mation mation• It also maintain It also maintain full knowledge of dista full knowledge of dista

nt routers and how they interconnect nt routers and how they interconnect

Link State ConceptLink State Concept

Link State ConceptLink State Concept• - Link state advertisement (LSA)- Link state advertisement (LSA) - a s - a s

mall packet of routing information that i mall packet of routing information that i s sent between routers s sent between routers

• Topological database Topological database - a collection of - a collection of information gathered from LSAs information gathered from LSAs

• SPF algorithm SPF algorithm - a calculation performe - a calculation performe d on the database that results in the SPF d on the database that results in the SPF

tree tree• Routing table Routing table - a list of the known path - a list of the known path

s and interfaces s and interfaces

Link state Network Link state Network discoverydiscovery

Link State ConcernLink State Concern

Work best situation for Link Work best situation for Link statestate• Link-state protocols work best in Link-state protocols work best in

situations where:situations where:– The network design is hierarchical, usually The network design is hierarchical, usually

occurring in large networks.occurring in large networks.– The administrators have a good The administrators have a good

knowledge of the implemented link-state knowledge of the implemented link-state routing protocol.routing protocol.

– Fast convergence of the network is crucial.Fast convergence of the network is crucial.

Classful routing protocols Classful routing protocols (1/3)(1/3)• Classful routing protocols Classful routing protocols do not send subnet do not send subnet

mask informationmask information in routing updates. in routing updates. • This was at a time when network addresses This was at a time when network addresses

were allocated based on classes, class A, B, or were allocated based on classes, class A, B, or C. C.

• A routing protocol did not need to include the A routing protocol did not need to include the subnet mask in the routing update because subnet mask in the routing update because the network mask could be determined based the network mask could be determined based on the on the first octet of the network addressfirst octet of the network address. .

Classful routing Classful routing protocols(2/3)protocols(2/3)• Classful routing protocols cannot be used when Classful routing protocols cannot be used when

a network is subnetted using more than one a network is subnetted using more than one subnet mask,subnet mask,– do not support variable length subnet masks (VLSM). do not support variable length subnet masks (VLSM).

• There are other limitations to classful routing There are other limitations to classful routing protocols including their inability to support protocols including their inability to support discontiguous networks.discontiguous networks.

• Classful routing protocols include RIPv1 and Classful routing protocols include RIPv1 and IGRP.IGRP.

Classful routing Classful routing protocols(3/3)protocols(3/3)

Classless Routing Protocols Classless Routing Protocols (1/3)(1/3)• Classless routing protocols include the subnet Classless routing protocols include the subnet

mask with the network address in routing mask with the network address in routing updates. updates.

• Today's networks are no longer allocated Today's networks are no longer allocated based on classes and the subnet mask cannot based on classes and the subnet mask cannot be determined by the value of the first octet. be determined by the value of the first octet.

• Classless routing protocols are required in Classless routing protocols are required in most networks today because of their support most networks today because of their support for VLSMfor VLSM

Classless Routing Protocols Classless Routing Protocols (2/3)(2/3)• In the figure, notice that the classless In the figure, notice that the classless

version of the network is using both /30 version of the network is using both /30 and /27 subnet masks in the same and /27 subnet masks in the same topology. topology. – Also notice that this topology is using a Also notice that this topology is using a

discontiguous design.discontiguous design.

• Classless routing protocols are RIPv2, Classless routing protocols are RIPv2, EIGRP, OSPF, IS-IS, BGP. EIGRP, OSPF, IS-IS, BGP.

Classless Routing Protocols Classless Routing Protocols (3/3)(3/3)

Convergence (1/3)Convergence (1/3)• Convergence is when all routers' routing Convergence is when all routers' routing

tables are at a state of consistency. tables are at a state of consistency. • The network has converged when all The network has converged when all

routers have complete and accurate routers have complete and accurate information about the network. information about the network.

• Convergence time is the time it takes Convergence time is the time it takes routers to share information, calculate best routers to share information, calculate best paths, and update their routing tables. paths, and update their routing tables.

• A network is not completely operable until A network is not completely operable until the network has converged; therefore, the network has converged; therefore, most networks require short convergence most networks require short convergence times.times.

Convergence (2/3)Convergence (2/3)• Convergence is both collaborative and Convergence is both collaborative and

independent. independent. – The routers share information with each other but The routers share information with each other but

must independently calculate the impacts of the must independently calculate the impacts of the topology change on their own routes. topology change on their own routes.

– Because they develop an agreement with the new Because they develop an agreement with the new topology independently, they are said to converge topology independently, they are said to converge on this consensus.on this consensus.

• Convergence properties include the speed of Convergence properties include the speed of propagation of routing information and the propagation of routing information and the calculation of optimal paths. calculation of optimal paths.

Convergence (3/3)Convergence (3/3)• Routing protocols can be rated based Routing protocols can be rated based

on the speed to convergenceon the speed to convergence; ; the the faster the convergence, the better faster the convergence, the better the routing protocol. the routing protocol.

• Generally, RIP and IGRP are slow to Generally, RIP and IGRP are slow to converge, whereas EIGRP and OSPF converge, whereas EIGRP and OSPF are faster to converge. are faster to converge.

Metrics (1/4)Metrics (1/4)• There are cases when a routing protocol learns There are cases when a routing protocol learns

of more than one route to the same of more than one route to the same destination. destination.

• To select the best path, the routing protocol To select the best path, the routing protocol must be able to evaluate and differentiate must be able to evaluate and differentiate between the available paths. between the available paths.

• A metric is a value used by routing protocols to A metric is a value used by routing protocols to assign costs to reach remote networks. assign costs to reach remote networks.

• The metric is used to determine which path is The metric is used to determine which path is most preferable when there are multiple paths most preferable when there are multiple paths to the same remote networkto the same remote network. .

Metrics (2/4)Metrics (2/4)

Metrics (3/4)Metrics (3/4)• Metrics used in IP routing protocols include:Metrics used in IP routing protocols include:

– Hop countHop count - A simple metric that counts the - A simple metric that counts the number of routers a packet must traversenumber of routers a packet must traverse

– BandwidthBandwidth - Influences path selection by - Influences path selection by preferring the path with the highest bandwidthpreferring the path with the highest bandwidth

– LoadLoad - Considers the traffic utilization of a certain - Considers the traffic utilization of a certain linklink

– DelayDelay - Considers the time a packet takes to - Considers the time a packet takes to traverse a pathtraverse a path

– ReliabilityReliability - Assesses the probability of a link - Assesses the probability of a link failure, calculated from the interface error count failure, calculated from the interface error count or previous link failuresor previous link failures

– Cost Cost - A value determined either by the IOS or by - A value determined either by the IOS or by the network administrator to indicate preference the network administrator to indicate preference for a route. for a route.

Metrics (4/4)Metrics (4/4)• The metric for each routing protocol is:The metric for each routing protocol is:

– RIPRIP: Hop count - Best path is chosen by the : Hop count - Best path is chosen by the route with the lowest hop count.route with the lowest hop count.

– IGRP and EIGRPIGRP and EIGRP: Bandwidth, Delay, : Bandwidth, Delay, Reliability, and Load - Best path is chosen Reliability, and Load - Best path is chosen by the route with the smallest composite by the route with the smallest composite metric value calculated from these multiple metric value calculated from these multiple parameters. By default, only bandwidth and parameters. By default, only bandwidth and delay are used. delay are used.

– IS-IS and OSPFIS-IS and OSPF: Cost - Best path is chosen : Cost - Best path is chosen by the route with the lowest cost. . by the route with the lowest cost. .

Metric in routing tableMetric in routing table

Load BalancingLoad Balancing• When two or more routes to the same When two or more routes to the same

destination have identical metric valuesdestination have identical metric values• The router does not choose only one route. The router does not choose only one route. • Instead, the router "load balances" between Instead, the router "load balances" between

these equal cost paths. The packets are these equal cost paths. The packets are forwarded using all equal-cost paths. forwarded using all equal-cost paths.

• Note: Load balancing can be done either per Note: Load balancing can be done either per packet or per destination. packet or per destination.

Administrative Distance (AD)Administrative Distance (AD)(1/3)(1/3)• Administrative distance (AD) defines the preference Administrative distance (AD) defines the preference

of a routing source. of a routing source. • Each routing source - including specific routing Each routing source - including specific routing

protocols, static routes, and even directly connected protocols, static routes, and even directly connected networks - is prioritized in order of most- to least-networks - is prioritized in order of most- to least-preferable using an administrative distance value. preferable using an administrative distance value.

• Administrative distance is an integer value from 0 to Administrative distance is an integer value from 0 to 255. 255. The lower the value the more preferred the The lower the value the more preferred the route source. route source.

• An administrative distance of 0 is the most preferred. An administrative distance of 0 is the most preferred. – Only a directly connected network has an administrative Only a directly connected network has an administrative

distance of 0, which cannot be changed. distance of 0, which cannot be changed.

Administrative Distance (AD) Administrative Distance (AD) (2/3)(2/3)

Administrative Distance (AD) Administrative Distance (AD) (3/3)(3/3)

Switching and Routing Technique

Documents

routing techniquew

routing information172

dynamic routing protocol

route router

static routes

route aggregation

destination network

address waste