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CCNA Semester 1

Chapter 10Chap

ter 10

LAYER 3LAYER 3

PROTOCOLSPROTOCOLS

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LAYER 3 DEVICESLAYER 3 DEVICES

ANDAND

NETWORK TO NETWORKNETWORK TO NETWORK

COMMUNICATIONCOMMUNICATION

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InternetworkingInternetworking

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Path determinationPath 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 ...

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RouterRouter

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.

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IP addressesIP addresses

IP addresses are implemented in software,and refer to the network on which a device

is located.

IP addressing scheme, according to theirgeographical location, department, or floor

within a building. Because they are implemented in software,

IP addresses are fairly easy to change.

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Router and BridgeRouter and Bridge

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Router connectionsRouter 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.

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Router InterfaceRouter Interface

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Router functionRouter function

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Router function (cont.1)Router function (cont.1)

Strips off the data link header,

carried by the frame.(The data link header contains the

MAC addresses of the source and

destination.)

Strips off the data link header,

carried by the frame.(The data link header contains the

MAC addresses of the source and

destination.)

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Examines the network layeraddress to determine the

destination network.

Examines the network layeraddress to determine the

destination network.

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Consults its routing tables to

determine which of its interfaces itwill use to send the data, in order

for it to reach its destination

network.

Consults its routing tables to

determine which of its interfaces itwill use to send the data, in order

for it to reach its destination

network.

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Send the data out interface B1, therouter would encapsulate the data

in the appropriate data link frame.

Send the data out interface B1, therouter would encapsulate the data

in the appropriate data link frame.

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Router Interface exampleRouter Interface example

Interface is a routers attachment to anetwork, it may also be referred to as aport. In IP routing.

Each interface must have a separate,

unique network address.

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IP address assignmentIP address assignment

static addressing and dynamic addressing

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Static addressingStatic addressing

You must go to each individual device andconfigure it with an IP address.

You should keep very meticulous records,because problems can occur on the

network if you use duplicate IP addresses.

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Dynamic addressingDynamic addressing

There are a few different methods that youcan use to assign IP addresses dynamically:

RARP: Reverse Address Resolution Protocol.

BOOTP: BOOTstrap Protocol.

DHCP: Dynamic Host Configuration Protocol.

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Dynamic addressing:Dynamic addressing: RARPRARP

MAC:MAC: KnownKnown

IP:IP: UnknownUnknown

MAC:MAC: KnownKnown


RARP RequestRARP Request

RARP ReplyRARP Reply

RARP serverRARP server

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Dynamic addressing:Dynamic addressing: BOOTPBOOTP

MAC:MAC: KnownKnown


MAC:MAC: KnownKnown


UDP BroadcastUDP Broadcast


BOOTP serverBOOTP server

MACMAC11 IP IP11

MACMAC22 IP IP22

MACMAC33 IP IP33

MACMAC11 IP IP11

MACMAC22 IP IP22

MACMAC33 IP IP33

IP AddressIP Address

IP of serverIP of server

Vendor-specificVendor-specific


IP of serverIP of serverVendor-specificVendor-specific

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Dynamic addressing:Dynamic addressing: DHCPDHCP

MAC:MAC: KnownKnownIP:IP: UnknownUnknownMAC:MAC: KnownKnownIP:IP: UnknownUnknown

DHCP DiscoverDHCP DiscoverUDP BroadcastUDP Broadcast

DHCP OfferDHCP Offer


DHCP serverDHCP server

IPIP11

IPIP22

IPIP33

IPIP11

IPIP22

IPIP33

DHCP RequestDHCP Request

DHCP AckDHCP Ack


GatewayGateway

IP of serversIP of servers

And more And more


GatewayGateway

IP of serversIP of servers

And more And more

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ARP CONCEPTARP CONCEPT

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EncapsulationEncapsulation

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Address resolution protocolAddress resolution protocol

In order for devices to communicate, thesending devices need both the IP addressesand the MAC addresses of the destination

devices. When they try to communicate with devices

whose IP addresses they know, they mustdetermine the MAC addresses.

ARP enables a computer to find the MACaddress of the computer that is associatedwith an IP address.

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Address resolution protocolAddress resolution protocol

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ARP table in hostARP table in host

RAM

RAM

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10.0.2.1

A.B.C.1.2.3

10.0.2.9

A.B.C.7.8.9

10.0.2.5

A.B.C.4.5.6

AA BB CC

ARP operationARP operation

ARP Table:

? MACA.B.C.1.2.3

MAC

?IP

10.0.2.1

IP

10.0.2.9Data

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10.0.2.1

A.B.C.1.2.3

10.0.2.9

A.B.C.7.8.9

10.0.2.5

A.B.C.4.5.6

AA BB CC

ARP operation:ARP operation: ARP requestARP request

MAC

A.B.C.1.2.3

MAC

ff.ff.ff.ff.ff.ff

IP

10.0.2.1

IP

10.0.2.9What is your MAC Addr?

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10.0.2.1

A.B.C.1.2.3

10.0.2.9

A.B.C.7.8.9

10.0.2.5

A.B.C.4.5.6

AA BB CC

ARP operation:ARP operation: CheckingChecking

MAC

A.B.C.1.2.3

MAC

ff.ff.ff.ff.ff.ff

IP

10.0.2.1

IP

10.0.2.9What is your MAC Addr?

Thatis

Thati

s

myIP

myIP

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10.0.2.1

A.B.C.1.2.3

10.0.2.9

A.B.C.7.8.9

10.0.2.5

A.B.C.4.5.6

AA BB CC

ARP operation:ARP operation: ARP replyARP reply

MAC

A.B.C.7.8.9

MAC

A.B.C.1.2.3

IP

10.0.2.9

IP

10.0.2.1This is my MAC Addr

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10.0.2.1

A.B.C.1.2.3

10.0.2.9

A.B.C.7.8.9

10.0.2.5

A.B.C.4.5.6

AA BB CC

ARP operation:ARP operation: CachingCaching

ARP Table:

A.B.C.7.8.9 10.0.2.9

MAC

A.B.C.1.2.3

MAC

A.B.C.7.8.9

IP

10.0.2.1

IP

10.0.2.9Data

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ARP:ARP: Destination localDestination local

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Internetwork communicationInternetwork communication

How to communicate with devices that arenot on the same physical network segment.

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Default gatewayDefault gateway

In order for a device to communicate withanother device on another network, youmust supply it with a default gateway.

A default gateway is the IP address of theinterface on the router that connects to thenetwork segment on which the source host islocated.

In order for a device to send data to theaddress of a device that is on anothernetwork segment, the source device sendsthe data to a default gateway.

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Proxy ARPProxy ARP

Proxy ARP is a variation of the ARP.

In the case the source host does not have a

default gateway configured.

ARPReply

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ARP:ARP: Destination not localDestination not local

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ARP FlowchartARP Flowchart

Send Datato a device

Send Data

Send an

ARP request

Get an

ARP reply

Is theMAC address

in my ARP

cache

NN

YY

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ARP table in routerARP table in router

The router interface connected to thenetwork has an IP address for that network.

Routers, just like every other device on thenetwork, send and receive data on thenetwork.

If router connects to a LAN, it builds ARPtables that maps IP addresses to MACaddresses in that interface.

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ARP table in routers and in hostsARP table in routers and in hosts

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Preparation for LABPreparation for LAB

Lab:

Protocol inspector and ARP

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ROUTED AND ROUTING PROTOCOLSROUTED AND ROUTING PROTOCOLS

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Network protocolsNetwork protocols

In order to allow two host communicate

together through internetwork, they need asame network protocol.

Protocols are like languages.

IP is a network layer protocol.

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Network protocol operationNetwork protocol operation

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Routed protocolRouted protocol

Protocols that providesupport for thenetwork layer are

called routed orroutable protocols.

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

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Protocol addressing variationsProtocol addressing variations

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Three important routed protocolsThree important routed protocols

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

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Non-routable protocolNon-routable protocol

Non-routable protocols areprotocols that do notsupport Layer 3.

The most common of thesenon-routable protocols isNetBEUI.

NetBEUI is a small, fast,and efficient protocol thatis limited to running onone segment.

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Addressing of a routable protocolAddressing of a routable protocol

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Routing tableRouting table

131.108.1.0 E0

131.108.2.0 E1

131.108.3.0 E2

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Multi-protocol routingMulti-protocol routing

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Classification #1:Classification #1: Static and DynamicStatic and Dynamic

Static routes:

The network administrator manually enter therouting 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

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Static routesStatic routes

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Dynamic routesDynamic routes

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Static vs. dynamic routesStatic 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 onepath to a destination network.

Dynamic routes:

Maintenance of routing table.

Timely distribution of information in the form of routingupdates.

Relies on routing protocol to share knowledge.

Routers can adjust to changing network conditions.

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Routing protocolRouting protocol

Routing protocolsdetermine the paths thatrouted protocols follow to

their destinations.

Routing protocols enablerouters that are connected

to create a map, internally,of other routers in thenetwork or on the Internet.

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Routed vs. Routing protocolRouted vs. Routing protocol

Rou

tingp

rotoc

ols

Rou

tingp

rotoc

ols

determi

neho

wrou

ted

determine

howr

outed

proto

colsarer

outed

protoc

olsare

routed

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Classification #2:Classification #2: IGP and EGPIGP and EGP

Dynamic routes.

Interior Gateway Protocols (RIP, IGRP, EIGRP, OSPF):

Be used within an autonomous system, a network ofrouters under one administration, like a corporate network,a school district's network, or a government agency'snetwork.

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

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IGPIGP

IGPIGP

IGP vs. EGPIGP vs. EGP

EGPEGP

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Classification #3:Classification #3: DVP and LSPDVP and LSP

Distance-Vector Protocols (RIP, IGRP):

View network topology from neighbors 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.

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Distance vector routingDistance vector routing

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Link state routingLink state routing

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RIPRIP

Most popular.

Interior Gateway Protocol.

Distance Vector Protocol.

Only metric is number of hops.

Maximum number of hops is 15.

Updates every 30 seconds. Doesnt always select fastest path.

Generates lots of network traffic.

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IGRP and EIGRPIGRP and EIGRP

Cisco proprietary.

Interior Gateway Protocol.

Distance Vector Protocol.

Metric is compose of bandwidth, load, delayand reliability.

Maximum number of hops is 255.

Updates every 90 seconds. EIGRP is an advanced version of IGRP, that

is hybrid routing protocol.

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OSPFOSPF

Open Shortest Path First.

Interior Gateway Protocol. Link State Protocol.

Metric is compose of cost, speed, traffic,reliability, and security.

Event-triggered updates.

Q&A

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Q&AQ&A

Documents

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