chapter 5 ip routing routing.pdf · –routing updates are broadcast or multicast every 30 seconds,...

Chapter 5 IP RoutingRouting Protocol

Routed Protocol

Chapter 5 IP RoutingRouting Protocol

Routed Protocol

Topics• Review

– Internetworking– Path determination– Router– IP Address

• Routed and Routing Protocols– Network protocols

• Routed• Routing

– Interior Protocols vs. Exterior Protocols• Routing Protocol Activity

• Review– Internetworking– Path determination– Router– IP Address

• Routed and Routing Protocols– Network protocols

• Routed• Routing

– Interior Protocols vs. Exterior Protocols• Routing Protocol Activity

Review

Router and IP Address

Review

Router and IP Address

Internetworking

Path determination

• Path determination is the process that therouter uses to choose the next hop in thepath for the packet to travel to itsdestination based on the link bandwidth,hop, delay ...

Router• A router is a type of internetworking device

that passes data packets betweennetworks, based on Layer 3 addresses.

• A router has the ability to make intelligentdecisions regarding the best path fordelivery of data on the network.

• A router is a type of internetworking devicethat passes data packets betweennetworks, based on Layer 3 addresses.

• A router has the ability to make intelligentdecisions regarding the best path fordelivery of data on the network.

IP addresses• IP addresses are implemented in software,

and refer to the network on which a deviceis located.

• IP addressing scheme, according to theirgeographical location, department, or floorwithin a building.

• Because they are implemented in software,IP addresses are fairly easy to change.

• IP addresses are implemented in software,and refer to the network on which a deviceis located.

• IP addressing scheme, according to theirgeographical location, department, or floorwithin a building.

• Because they are implemented in software,IP addresses are fairly easy to change.

Router and Bridge

Router connections• Routers connect two or more networks,

each of which must have a unique networknumber in order for routing to besuccessful.

• The unique network number is incorporatedinto the IP address that is assigned to eachdevice attached to that network.

• Routers connect two or more networks,each of which must have a unique networknumber in order for routing to besuccessful.

• The unique network number is incorporatedinto the IP address that is assigned to eachdevice attached to that network.

Router Interface

Router function

Router function (cont.1)

Strips off the data link header,carried by the frame.(The data link header contains theMAC addresses of the source anddestination.) 12

Strips off the data link header,carried by the frame.(The data link header contains theMAC addresses of the source anddestination.)

Examines the network layeraddress to determine thedestination network.

Consults its routing tables todetermine which of its interfaces itwill use to send the data, in orderfor it to reach its destinationnetwork.

Send the data out interface B1, therouter would encapsulate the datain the appropriate data link frame.

Router Interface example

• Interface is a router’s attachment to anetwork, it may also be referred to as aport. In IP routing.

• Each interface must have a separate,unique network address.

ROUTED AND ROUTING

PROTOCOLS

ROUTED AND ROUTING

PROTOCOLS

Network protocols

• In order to allow two host communicatetogether through internetwork, they need asame network protocol.

• Protocols are like languages.• IP is a network layer protocol.

Network protocol operation

Routed protocol• Protocols that provide

support for thenetwork layer arecalled routed orroutable protocols.

• IP is a network layerprotocol, and becauseof that, it can berouted over aninternetwork.

• Protocols that providesupport for thenetwork layer arecalled routed orroutable protocols.

• IP is a network layerprotocol, and becauseof that, it can berouted over aninternetwork.

Protocol addressing variations

Three important routedprotocols• TCP/IP: 04 bytes

– Class A: 1 byte network + 3 bytes host– Class B: 2 bytes network + 2 bytes host– Class C: 3 bytes network + 1 byte host

• IPX/SPX: 10 bytes– 4 bytes network + 6 bytes host

• AppleTalk: 03 bytes– 2 bytes network + 1 byte host

• TCP/IP: 04 bytes– Class A: 1 byte network + 3 bytes host– Class B: 2 bytes network + 2 bytes host– Class C: 3 bytes network + 1 byte host

• IPX/SPX: 10 bytes– 4 bytes network + 6 bytes host

• AppleTalk: 03 bytes– 2 bytes network + 1 byte host

Non-routable protocol• Non-routable protocols are

protocols that do notsupport Layer 3.

• The most common ofthese non-routableprotocols is NetBEUI.

• NetBEUI is a small, fast,and efficient protocol thatis limited to running on onesegment.

• Non-routable protocols areprotocols that do notsupport Layer 3.

• The most common ofthese non-routableprotocols is NetBEUI.

• NetBEUI is a small, fast,and efficient protocol thatis limited to running on onesegment.

Addressing of a routableprotocol

Routing table

131.108.1.0 E0131.108.2.0 E1131.108.3.0 E2

Multi-protocol routing

Classification #1: Static andDynamic• Static routes:

– The network administrator manually enter therouting information in the router.

• Dynamic routes:– Routers can learn the information from each

other on the fly.– Using routing protocol to update routing

information.– RIP, IGRP, EIGRP, OSPF …

• Static routes:– The network administrator manually enter the

routing information in the router.• Dynamic routes:

– Routers can learn the information from eachother on the fly.

– Using routing protocol to update routinginformation.

– RIP, IGRP, EIGRP, OSPF …

Static routes

Dynamic routes

Static vs. dynamic routes• Static routes:

– For hiding parts of an internetwork.– To test a particular link in a network.– For maintaining routing tables whenever there is only one path to a

destination network.

• Dynamic routes:– Maintenance of routing table.– Timely distribution of information in the form of routing updates.– Relies on routing protocol to share knowledge.– Routers can adjust to changing network conditions.

• Static routes:– For hiding parts of an internetwork.– To test a particular link in a network.– For maintaining routing tables whenever there is only one path to a

destination network.

• Dynamic routes:– Maintenance of routing table.– Timely distribution of information in the form of routing updates.– Relies on routing protocol to share knowledge.– Routers can adjust to changing network conditions.

Routing protocol• Routing protocols

determine the paths thatrouted protocols follow totheir destinations.

• Routing protocols enablerouters that are connectedto create a map, internally,of other routers in thenetwork or on the Internet.

• Routing protocolsdetermine the paths thatrouted protocols follow totheir destinations.

• Routing protocols enablerouters that are connectedto create a map, internally,of other routers in thenetwork or on the Internet.

Routed vs. Routing protocol

Classification #2: IGP andEGP• Dynamic routes.

• Interior Gateway Protocols (RIP, IGRP, EIGRP,OSPF):– Be used within an autonomous system, a network of

routers under one administration, like a corporatenetwork, a school district's network, or a governmentagency's network.

• Exterior Gateway Protocols (EGP, BGP):– Be used to route packets between autonomous systems.

• Dynamic routes.• Interior Gateway Protocols (RIP, IGRP, EIGRP,

OSPF):– Be used within an autonomous system, a network of

routers under one administration, like a corporatenetwork, a school district's network, or a governmentagency's network.

• Exterior Gateway Protocols (EGP, BGP):– Be used to route packets between autonomous systems.

IGPIGPIGPIGP

IGP vs. EGP

EGPEGP

IGPIGPIGPIGP EGPEGP

Classification #3: DVP andLSP• Distance-Vector Protocols (RIP, IGRP):

– View network topology from neighbor’s perspective.– Add distance vectors from router to router.– Frequent, periodic updates.– Pass copy of routing tables to neighbor routers.

• Link State Protocols (OSPF):– Gets common view of entire network topology.– Calculates the shortest path to other routers.– Event-triggered updates.– Passes link state routing updates to other routers.

• Distance-Vector Protocols (RIP, IGRP):– View network topology from neighbor’s perspective.– Add distance vectors from router to router.– Frequent, periodic updates.– Pass copy of routing tables to neighbor routers.

• Link State Protocols (OSPF):– Gets common view of entire network topology.– Calculates the shortest path to other routers.– Event-triggered updates.– Passes link state routing updates to other routers.

Distance vector routing

Link state routing

Part II

Distance VectorRouting

Distance Vector RoutingProtocols

• Dynamic routing protocols help the network administrator overcome the time-consuming and exacting process of configuring and maintaining static routes.

• Examples of Distance Vector routing protocols: Routing Information Protocol (RIP)

–RFC 1058.–Hop count is used as the metric for path selection.–If the hop count for a network is greater than 15, RIP cannot supply a route to thatnetwork.–Routing updates are broadcast or multicast every 30 seconds, by default.

Interior Gateway Routing Protocol (IGRP)–proprietary protocol developed by Cisco.–Bandwidth, delay, load and reliability are used to create a composite metric.–Routing updates are broadcast every 90 seconds, by default.–IGRP is the predecessor of EIGRP and is now obsolete.

Enhanced Interior Gateway Routing Protocol (EIGRP)–Cisco proprietary distance vector routing protocol.–It can perform unequal cost load balancing.–It uses Diffusing Update Algorithm (DUAL) to calculate the shortest path.–There are no periodic updates as with RIP and IGRP. Routing updates are sent onlywhen there is a change in the topology.

• Dynamic routing protocols help the network administrator overcome the time-consuming and exacting process of configuring and maintaining static routes.

• Examples of Distance Vector routing protocols: Routing Information Protocol (RIP)

–RFC 1058.–Hop count is used as the metric for path selection.–If the hop count for a network is greater than 15, RIP cannot supply a route to thatnetwork.–Routing updates are broadcast or multicast every 30 seconds, by default.

Interior Gateway Routing Protocol (IGRP)–proprietary protocol developed by Cisco.–Bandwidth, delay, load and reliability are used to create a composite metric.–Routing updates are broadcast every 90 seconds, by default.–IGRP is the predecessor of EIGRP and is now obsolete.

Enhanced Interior Gateway Routing Protocol (EIGRP)–Cisco proprietary distance vector routing protocol.–It can perform unequal cost load balancing.–It uses Diffusing Update Algorithm (DUAL) to calculate the shortest path.–There are no periodic updates as with RIP and IGRP. Routing updates are sent onlywhen there is a change in the topology.

• The Meaning of Distance Vector:

–A router using distance vector routing protocols knows2 things:

Distance to final destinationThe distance or how far it is to the destination network

Vector, or direction, traffic should be directed

The direction or interface in which packets should be forwarded

• The Meaning of Distance Vector:

–A router using distance vector routing protocols knows2 things:

Distance to final destinationThe distance or how far it is to the destination network

Vector, or direction, traffic should be directed

The direction or interface in which packets should be forwarded

For example, in the figure, R1 knowsthat the distance to reach network172.16.3.0/24 is 1 hop and that thedirection is out the interface S0/0/0toward R2.

Distance Vector RoutingProtocols• Characteristics of Distance Vector routing protocols:

Periodic updates• Periodic Updates sent at regular intervals (30 seconds

for RIP). Even if the topology has not changed in severaldays,

Neighbors The router is only aware of the network addresses of its

own interfaces and the remote network addresses it canreach through its neighbors.

It has no broader knowledge of the network topology Broadcast updates Broadcast Updates are sent to 255.255.255.255. Some distance vector routing protocols use multicast

addresses instead of broadcast addresses. Entire routing table is included with routing update Entire Routing Table Updates are sent, with some

exceptions to be discussed later, periodically to allneighbors.

Neighbors receiving these updates must process theentire update to find pertinent information and discardthe rest.

Some distance vector routing protocols like EIGRP donot send periodic routing table updates.

• Characteristics of Distance Vector routing protocols: Periodic updates

• Periodic Updates sent at regular intervals (30 secondsfor RIP). Even if the topology has not changed in severaldays,

Neighbors The router is only aware of the network addresses of its

own interfaces and the remote network addresses it canreach through its neighbors.

It has no broader knowledge of the network topology Broadcast updates Broadcast Updates are sent to 255.255.255.255. Some distance vector routing protocols use multicast

addresses instead of broadcast addresses. Entire routing table is included with routing update Entire Routing Table Updates are sent, with some

exceptions to be discussed later, periodically to allneighbors.

Neighbors receiving these updates must process theentire update to find pertinent information and discardthe rest.

Some distance vector routing protocols like EIGRP donot send periodic routing table updates.

Routing Protocol Algorithm:–The algorithm is used to calculate the best paths and then sendthat information to the neighbors.–Different routing protocols use different algorithms to install routesin the routing table, send updates to neighbors, and make pathdetermination decisions.

Distance Vector RoutingProtocolsRouting Protocol Characteristics

–Criteria used to compare routing protocols includes Time to convergence

Time to convergence defines how quickly the routers in the network topology sharerouting information and reach a state of consistent knowledge.The faster the convergence, the more preferable the protocol.

ScalabilityScalability defines how large a network can become based on the routing protocolthat is deployed.The larger the network is, the more scalable the routing protocol needs to be.

Resource usageResource usage includes the requirements of a routing protocol such as memoryspace, CPU utilization, and link bandwidth utilization.Higher resource requirements necessitate more powerful hardware to support therouting protocol operation

Classless (Use of VLSM) or ClassfulClassless routing protocols include the subnet mask in the updates.This feature supports the use of Variable Length Subnet Masking (VLSM) and betterroute summarization.

Implementation & maintenanceImplementation and maintenance describes the level of knowledge that is requiredfor a network administrator to implement and maintain the network based on therouting protocol deployed.

Routing Protocol Characteristics–Criteria used to compare routing protocols includes Time to convergence

Time to convergence defines how quickly the routers in the network topology sharerouting information and reach a state of consistent knowledge.The faster the convergence, the more preferable the protocol.

ScalabilityScalability defines how large a network can become based on the routing protocolthat is deployed.The larger the network is, the more scalable the routing protocol needs to be.

Resource usageResource usage includes the requirements of a routing protocol such as memoryspace, CPU utilization, and link bandwidth utilization.Higher resource requirements necessitate more powerful hardware to support therouting protocol operation

Classless (Use of VLSM) or ClassfulClassless routing protocols include the subnet mask in the updates.This feature supports the use of Variable Length Subnet Masking (VLSM) and betterroute summarization.

Implementation & maintenanceImplementation and maintenance describes the level of knowledge that is requiredfor a network administrator to implement and maintain the network based on therouting protocol deployed.

Distance Vector Routing Protocols

• Routers pass periodic copies of their routing table toneighboringrouters and accumulate distance vectors.

Sources of Information andDiscovering Routes

• Routers discover the best path to destinations from eachneighbor.

Selecting theBest Route with Metrics

Maintaining RoutingInformation

• Updates proceed step by step from router to router.

Inconsistent Routing Entries

• Each node maintains the distance from itself to eachpossible destination network.

Inconsistent Routing Entries(Cont.)

• Slow convergence produces inconsistent routing.

• Router C concludes that the best path to network 10.4.0.0 isthrough router B.

• Router A updates its table to reflect the new but erroneoushop count.

Count to Infinity

• The hop count for network 10.4.0.0 counts to infinity.

Routing Loops

• Packets for network 10.4.0.0 bounce (loop) betweenrouters B and C.

Routing Loops

• Routing loops can eliminate–Defining a maximum metric to prevent count to infinity–Holddown timers–Split horizon–Route poisoning or poison reverse–Triggered updates

• Note: The IP protocol has its own mechanism toprevent the possibility of a packet traversing thenetwork endlessly. IP has a Time-to-Live (TTL) fieldand its value is decremented by 1 at each router.

–If the TTL is zero, the router drops the packet.

• Routing loops can eliminate–Defining a maximum metric to prevent count to infinity–Holddown timers–Split horizon–Route poisoning or poison reverse–Triggered updates

• Note: The IP protocol has its own mechanism toprevent the possibility of a packet traversing thenetwork endlessly. IP has a Time-to-Live (TTL) fieldand its value is decremented by 1 at each router.

–If the TTL is zero, the router drops the packet.

Defining a Maximum

• A limit is set on the number of hops to prevent infiniteloops.

Triggered Updates

• The router sends updates when a change in itsrouting table occurs.

Route Poisoning

• Routers advertise the distance of routes that have gonedown to infinity.

Split Horizon

• It is never useful to send information about a route back inthe direction from which the original information came.

Poison Reverse

• Poison reverse overrides split horizon.

Holddown Timers

• The router keeps an entry for the “possibly down state” inthe network, allowing time for other routers to recompute forthis topology change.

Link-State Routing

Link-State Routing• Link state routing protocols

–-Also known as shortest path first algorithms

-These protocols built around Dijkstra’s SPF

OSPF will be discussed in Chapter 11, and IS-IS will be discussed in CCNP.

Link-State Routing Protocols

64• After initial flood of LSAs, link-state routers pass small event-triggered

link-state updates to all other routers.

Link-State Routing

• Dikjstra’s algorithm also known as theshortest path first (SPF) algorithm

–This algorithm accumulates costs alongeach path, from source to destination.

• Dikjstra’s algorithm also known as theshortest path first (SPF) algorithm

–This algorithm accumulates costs alongeach path, from source to destination.

Link-State Routing:Step 1 – Learn about directly connected Networks

• LinkThis is an interface on arouter

• Link stateThis is the informationabout the state of thelinks

• LinkThis is an interface on arouter

• Link stateThis is the informationabout the state of thelinks

Link-State Routing:step 2 - Sending Hello Packets to Neighbors

• Link state routing protocols use a hello protocolPurpose of a hello protocol:

-To discover neighbors (that use the samelink state routing protocol) on its link

• Connected interfaces that areusing the same link state routingprotocols will exchange hellopackets.

• Once routers learn it hasneighbors they form an adjacency

–2 adjacent neighbors will exchangehello packets–These packets will serve as a keepalive function

Link-State Routing:step 2 - Sending Hello Packets to Neighbors

• Connected interfaces that areusing the same link state routingprotocols will exchange hellopackets.

• Once routers learn it hasneighbors they form an adjacency

–2 adjacent neighbors will exchangehello packets–These packets will serve as a keepalive function

• Contents of LSP:– State of each directly connectedlink– Includes information aboutneighbors such as neighbor ID, linktype, & bandwidth.

• A simplified version of the LSPsfrom R1 is:

–1. R1; Ethernet network10.1.0.0/16; Cost 2–2. R1 -> R2; Serial point-to-pointnetwork; 10.2.0.0/16; Cost 20–3. R1 -> R3; Serial point-to-pointnetwork; 10.3.0.0/16; Cost 5–4. R1 -> R4; Serial point-to-pointnetwork; 10.4.0.0/16; Cost 20

Link-State Routing:step 3 - Building the Link State Packet (LSP)

• Contents of LSP:– State of each directly connectedlink– Includes information aboutneighbors such as neighbor ID, linktype, & bandwidth.

• A simplified version of the LSPsfrom R1 is:

–1. R1; Ethernet network10.1.0.0/16; Cost 2–2. R1 -> R2; Serial point-to-pointnetwork; 10.2.0.0/16; Cost 20–3. R1 -> R3; Serial point-to-pointnetwork; 10.3.0.0/16; Cost 5–4. R1 -> R4; Serial point-to-pointnetwork; 10.4.0.0/16; Cost 20

• Once LSP are created they areforwarded out to neighbors.

–Each router floods its link-stateinformation to all other link-state routersin the routing area.–Whenever a router receives an LSPfrom a neighboring router, it immediatelysends that LSP out all other interfacesexcept the interface that received theLSP.–This process creates a flooding effect ofLSPs from all routers throughout therouting area.

Link-State Routing:step 4 - Flooding LSPs to Neighbors

• Once LSP are created they areforwarded out to neighbors.

–Each router floods its link-stateinformation to all other link-state routersin the routing area.–Whenever a router receives an LSPfrom a neighboring router, it immediatelysends that LSP out all other interfacesexcept the interface that received theLSP.–This process creates a flooding effect ofLSPs from all routers throughout therouting area.

• LSPs are sent out under the following conditions–Initial router start up or routing process–When there is a change in topology

• including a link going down or coming up, or a neighboradjacency being established or broken

Link-State Routing:step 4 - Flooding LSPs to Neighbors

• Routers use a database toconstruct a topology map of thenetwork

–After each router has propagatedits own LSPs using the link-stateflooding process, each router willthen have an LSP from every link-state router in the routing area.–These LSPs are stored in the link-state database.–Each router in the routing areacan now use the SPF algorithm toconstruct the SPF trees that yousaw earlier.

Link-State Routing:step 5 - Constructing a link state data base

• Routers use a database toconstruct a topology map of thenetwork

–After each router has propagatedits own LSPs using the link-stateflooding process, each router willthen have an LSP from every link-state router in the routing area.–These LSPs are stored in the link-state database.–Each router in the routing areacan now use the SPF algorithm toconstruct the SPF trees that yousaw earlier.

Link-State Routing:step 5 - Constructing a link state data base

router R1 has learned the link-stateinformation for each router in itsrouting area.

With a complete link-state database, R1can now use the database and theshortest path first (SPF) algorithm tocalculate the preferred path or shortestpath to each network.

Drawbacks to Link-State RoutingProtocols

• Initial discovery may cause flooding.• Link-state routing is memory- and processor-

intensive.

How Routing Information IsMaintained

Link-State Routing ProtocolAlgorithms

Link-State Routing ProtocolsAdvantages of a Link-State Routing Protocol

Routingprotocol

BuildsTopological

Router canindependentlydetermine theshortest path

to everynetwork.

ConvergenceEvent driven

routingupdates

Router canindependentlydetermine theshortest path

to everynetwork.

Distancevector

No No Slow Generally No No

Link State Yes Yes Fast Generally Yes Yes

Link-State Routing Protocols• There are several advantages of link-state routing protocols compared to distance vector

routing protocols.• Builds a Topological Map

• Link-state routing protocols create a topological map, or SPF tree of the network topology.• Using the SPF tree, each router can independently determine the shortest path to every network.

• Distance vector routing protocols do not have a topological map of the network.• Routers implementing a distance vector routing protocol only have a list of networks, which

includes the cost (distance) and next-hop routers (direction) to those networks.• Fast Convergence

• When receiving a Link-state Packet (LSP), link-state routing protocols immediately flood the LSP out allinterfaces except for the interface from which the LSP was received.

• A router using a distance vector routing protocol needs to process each routing update and update itsrouting table before flooding them out other interfaces, even with triggered updates.

• Event-driven Updates• After the initial flooding of LSPs, link-state routing protocols only send out an LSP when there is a

change in the topology. The LSP contains only the information regarding the affected link.• Unlike some distance vector routing protocols, link-state routing protocols do not send periodic updates.

• Hierarchical Design• Link-state routing protocols such as OSPF and IS-IS use the concept of areas. Multiple areas create a

hierarchical design to networks, allowing for better route aggregation (summarization) and the isolationof routing issues within an area.

• There are several advantages of link-state routing protocols compared to distance vectorrouting protocols.

• Builds a Topological Map• Link-state routing protocols create a topological map, or SPF tree of the network topology.

• Using the SPF tree, each router can independently determine the shortest path to every network.• Distance vector routing protocols do not have a topological map of the network.

• Routers implementing a distance vector routing protocol only have a list of networks, whichincludes the cost (distance) and next-hop routers (direction) to those networks.

• Fast Convergence• When receiving a Link-state Packet (LSP), link-state routing protocols immediately flood the LSP out all

interfaces except for the interface from which the LSP was received.• A router using a distance vector routing protocol needs to process each routing update and update its

routing table before flooding them out other interfaces, even with triggered updates.• Event-driven Updates

• After the initial flooding of LSPs, link-state routing protocols only send out an LSP when there is achange in the topology. The LSP contains only the information regarding the affected link.

• Unlike some distance vector routing protocols, link-state routing protocols do not send periodic updates.• Hierarchical Design

• Link-state routing protocols such as OSPF and IS-IS use the concept of areas. Multiple areas create ahierarchical design to networks, allowing for better route aggregation (summarization) and the isolationof routing issues within an area.

Link-State Routing ProtocolsRequirements for using a link state routing protocol• Memory requirements

–Typically link state routing protocols use more memory• Processing Requirements

– More CPU processing is required of link state routingprotocols

• Bandwidth Requirements–Initial startup of link state routing protocols can consume lotsof bandwidth–This should only occur during initial startup of routers, butcan also be an issue on unstable networks.

Requirements for using a link state routing protocol• Memory requirements

–Typically link state routing protocols use more memory• Processing Requirements

– More CPU processing is required of link state routingprotocols

• Bandwidth Requirements–Initial startup of link state routing protocols can consume lotsof bandwidth–This should only occur during initial startup of routers, butcan also be an issue on unstable networks.

Link-State Routing Protocols• Modern link-state routing protocols are designed to

minimize the effects on memory, CPU, andbandwidth.

• The use and configuration of multiple areas canreduce the size of the link-state databases. Multipleareas can also limit the amount of link-stateinformation flooding in a routing domain and sendLSPs only to those routers that need them.

• For example, when there is a change in the topology,only those routers in the affected area receive theLSP and run the SPF algorithm.

• This can help isolate an unstable link to a specificarea in the routing domain.

• In the figure, If a network in Area 51 goes down,the LSP with the information about this downedlink is only flooded to other routers in that area.

• Routers in other areas will learn that this route isdown, but this will be done with a type of link-statepacket that does not cause them to rerun their SPFalgorithm.

• Modern link-state routing protocols are designed tominimize the effects on memory, CPU, andbandwidth.

• The use and configuration of multiple areas canreduce the size of the link-state databases. Multipleareas can also limit the amount of link-stateinformation flooding in a routing domain and sendLSPs only to those routers that need them.

• For example, when there is a change in the topology,only those routers in the affected area receive theLSP and run the SPF algorithm.

• This can help isolate an unstable link to a specificarea in the routing domain.

• In the figure, If a network in Area 51 goes down,the LSP with the information about this downedlink is only flooded to other routers in that area.

• Routers in other areas will learn that this route isdown, but this will be done with a type of link-statepacket that does not cause them to rerun their SPFalgorithm.

Note: Multiple areaswith OSPF and IS-ISare discussed inCCNP

Link-State Routing Protocols• 2 link state routing protocols used for routing IP

-Open Shortest Path First (OSPF)-Intermediate System-Intermediate System (IS-IS)

Routing ProtocolRouting Protocol

RIP• Most popular.• Interior Gateway Protocol.• Distance Vector Protocol.• Only metric is number of hops.• Maximum number of hops is 15.• Updates every 30 seconds.• Doesn’t always select fastest path.• Generates lots of network traffic.

• Most popular.• Interior Gateway Protocol.• Distance Vector Protocol.• Only metric is number of hops.• Maximum number of hops is 15.• Updates every 30 seconds.• Doesn’t always select fastest path.• Generates lots of network traffic.

IGRP and EIGRP• Cisco proprietary.• Interior Gateway Protocol.• Distance Vector Protocol.• Metric is compose of bandwidth, load,

delay and reliability.• Maximum number of hops is 255.• Updates every 90 seconds.• EIGRP is an advanced version of IGRP,

that is hybrid routing protocol.

• Cisco proprietary.• Interior Gateway Protocol.• Distance Vector Protocol.• Metric is compose of bandwidth, load,

delay and reliability.• Maximum number of hops is 255.• Updates every 90 seconds.• EIGRP is an advanced version of IGRP,

that is hybrid routing protocol.

OSPF• Open Shortest Path First.• Interior Gateway Protocol.• Link State Protocol.• Metric is compose of cost, speed, traffic,

reliability, and security.• Event-triggered updates.

• Open Shortest Path First.• Interior Gateway Protocol.• Link State Protocol.• Metric is compose of cost, speed, traffic,

reliability, and security.• Event-triggered updates.

End Chapter V

chapter 5 ip routing routing.pdf · –routing updates are broadcast or multicast every 30 seconds,...

Documents

11 routing protocol

chapter 5 ip routing routing protocol vs. routed protocol

routing -...

routing protocol (ospf)

detailed routing -...

ipv6 routing...

network layer protocol routing protocol

ipv6 routing protocol

routing -...

chapter 7: routing protocols for ad hoc wireless...

bgp routing protocol

routing...

routing -...

secure routing protocol

multicast routing protocol

adhoc routing protocol

routing protocol basics -...

routing information protocol

multicast routing with aodv routing protocol

cisco - ospf routing protocol -...