NETWORK LAYER

Chapter 6

Intro to Routing & Switching

OBJECTIVES Upon completion of this chapter, you

should be able to: Describe the purpose of the network layer Explain why IPv4 uses other layers for

reliability Explain how host devices use routing tables to

direct packets Compare host and router routing tables Describe components of a router Describe the boot-up process of a Cisco router Configure a Cisco router and interfaces Configure a default gateway

THE NETWORK LAYER

6.1.1

NETWORK LAYER

ALL ABOUT IP

6.1.2

IP Low overhead

Delivers packet to destination onlyDoes NOT track or manage flow

Other layers handle that

ConnectionlessDoesn’t need a connection established w/

dest. Best effort delivery

Unreliable, no guarantee (other layers) Media independent

Doesn’t matter which type of cable being used

MEDIA INDEPENDENT Doesn’t matter what cables/media it

travels overWhat layer handles the prep for media?

ACTIVITY 6.1.2.6

Read each IP characteristic & decide if it describes connectionless, best effort, or media independent.

REVIEW- 3Q IP is described as connectionless, or

connection-oriented?Connectionless

When using IP, what protocol would be used to acknowledge delivery of packets and retransmission of missing ones?TCP

What layer does TCP operate at?Transport

IPV4 PACKET

6.1.3

IPV4 PACKET Includes Header & Payload Header includes:

Source & destination IPDS (Differentiated Services)

Defines the priority of each packetProtocol

TCP/UDPTTL (Time-to-Live)

Hops until dropped

SAMPLE IPV4 HEADER

Version, IP’s

DS, Total Length, Flags, TTL

REVIEW Which field in the IPv4 header…

Tells the priority of a packet? DS

Helps with fragmented packets when split to not exceed the MTU on media? Flags

Name a connectionless layer 3 protocol that is popular & in use today? IP

What helps IP with guaranteed delivery?TCP

IPV6 PACKET

6.1.4

WHAT’S WRONG WITH IPV4? Running out of addresses Routing tables growing Lack of end to end connectivity

NAT is normally used NAT allows certain private IP addresses to be

used within a network and not shared with the outside world

The internal private IP gets translated to a public one to send data across Internet

IPV4 TO IPV6

IPv4 IPv6

32-bit addresses 4 billion available

Many header fields

Must use NAT To conserve

addresses

128-bit addresses 340 undecillion avail.

Less header fields Better packet

handling No need for NAT

A lot of IPv6 addresses

IPV6 HEADER & IPV4 HEADER

SAMPLE IPV6 HEADER

Version, Payload

Length, Hop Limit, IPv6 addresses

ACTIVITY Handout to compare IPv4 & 6 headers

6.1.4.6Read each IPv6 header description & click

which field it belongs to.

REVIEW Explain NAT.

Private internal IP addresses. Can’t be seen outside network. Translate to a public IP for the entire internal network.

Why is NAT not needed with IPv6?A ton of addresses!

What field in an IPv6 header…Has routers use the same path for real-time

packets? Flow label

Is like the DS field for priority? Traffic Class

REVIEW Review the picture. What kind of IP is being used?

IPv4 How many hops from PC1 to PC33?

3

HOW A HOST ROUTES

6.2.1

HOST READY TO SEND Itself (loopback)

127.0.0.1 Local

Shares same network address Remote

On a different network

HOST IPV4 ROUTING TABLE PC has a “mini” routing table

ACTIVITY 6.2.1.7

Identify the parts of a host routing table

REVIEW How does a PC know where to send

packets? It has its own routing table

What 2 commands on a PC will view the routing table?Netstat –r or route print

REVIEW

ROUTER ROUTING TABLE

6.2.2

HOW TO ROUTE THE PACKET After packet reaches DG (router), it

looks at the routing table to see where to send it

What’s in the table?Directly connected routesRemote routes

WHAT WOULD IT KNOW?

ROUTING TABLE Show ip route

Stored in RAM

How it was learned When it was updated Which interface to use to get to that

network

PARTS OF ROUTING TABLE

ROUTING TABLE- OTHER NETWORKS

R1#show ip routeCodes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 2 subnets, 2 masksD 10.1.1.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0D 10.1.2.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 192.168.10.0/24 is variably subnetted, 2 subnets, 3 masksC 192.168.10.0/24 is directly connected, GigabitEthernet0/0L 192.168.10.1/32 is directly connected, GigabitEthernet0/0 192.168.11.0/24 is variably subnetted, 2 subnets, 3 masksC 192.168.11.0/24 is directly connected, GigabitEthernet0/1L 192.168.11.1/32 is directly connected, GigabitEthernet0/1 209.165.200.0/24 is variably subnetted, 2 subnets, 3 masksC 209.165.200.224/30 is directly connected, Serial0/0/0L 209.165.200.225/32 is directly connected, Serial0/0/0R1#

192.168.10.0/24

R2

192.168.11.0/24

10.1.1.0/24

10.1.2.0/24

209.165.200.224 /30

.226

.10

.10

.10

.10

.1

.1.1G0/1

.225S0/0/0

G0/0.1

R1

PC1

PC2

ACTIVITY 6.2.2.7

Identify the elements of a routing table

Lab 6.2.2.8Discover your PC’s routing table

REVIEW A packet comes into the interface of a

router. Which address does it check?Destination IP

What does it then use that address to look at?Routing table

What happens if a match is found for the destination network? It sends it out that port towards that

destination

REVIEW What command displays the routing

table on a router?Show ip route

Where is the routing table stored?RAM

What would happen if a destination network was not in the routing table and there was no default route configured?Packet is dropped

ANATOMY OF A ROUTER

6.3.1

THE ROUTER IS A COMPUTER OS RAM CPU ROM

ROUTER MEMORY

ROUTER INTERFACES

Console Port RJ45

AUX Port RJ45

LANinterfaces

WAN Serial Ports in slot

LANInterfaces in slot

ACTIVITY 6.3.1.8

Match the router interface or function with its description

Lab 6.3.1.9Explore the router externally & using show

commands

Lab 6.3.1.10Determine connectivity options on a router

REVIEW- 5Q Where is the IOS stored?

Flash Where is the running-config at?

RAM Where is the startup-config stored?

NVRAM Where is the limited IOS at?

ROM Where is the routing table stored?

RAM

REVIEW- 4Q Based on the last 5 questions, which ones will get

“lost” if you lose power to the router & why? Running-config & routing table because they are in

RAM Which ports on the router will allow out-of-band

management? Console & AUX

If you want to gain access to router configuration remotely through Telnet or SSH, which interfaces would you be “connecting” to? Ethernet/LAN or Serial/WAN

What 2 things get copied into RAM upon a normal boot? IOS & startup-config

ROUTER BOOT-UP

6.3.2

BOOT SUMMARY Similar to PC booting

POST IOS in flash memory & loads into RAM Startup-config loads into RAM

Becomes running-config

Changes made to config happen in RAM/running-configMUST SAVE THEM!

STEP 1 POST tests hardware (CPU, Memory) ROM: Bootstrap

Boot ImageBegins search for IOS

STEP 2 Locate & load IOS into RAM

Usually in Flash (default) or TFTP Server

STEP 3 Configuration File or Setup

NVRAM (1st), TFTP Server (2nd), Console (3rd) If found, copies into RAM

Becomes the running-config If not found, enters Setup Mode

VERIFY & TROUBLESHOOT Show version

IOS version Version of bootstrap Location & name of IOS CPU & RAM Interfaces Amount of NVRAM & Flash Config-register

0x2102

Model & IOS

versionBootstrap

version

Amount of RAMTotal/Used

IOS locale & name

Interfaces

Amt. of NVRAM

Amt. of Flash

Config-register

ACTIVITY In Packet Tracer…

Add an 1841 routerGo in & answer questions based on show

version output on handout

Add a 2960 switch and do the same

6.3.2.6The router boot processPut the steps in order

REVIEW- 4Q When would a limited version of the IOS

load? If the full IOS can’t be found

What does this mean?Flash0: c1841-universal.152-4.binThe IOS is in flash & that’s its file name

What happens first when booting a router?POST

When loading the IOS, where does it look?Flash, TFTP Server, ROM

REVIEW- 8Q

CONFIGURE A ROUTER

INITIAL SETTINGS

6.4.1

INITIAL SETTINGS Hostname Passwords

Enable, enable secret, console, vty Banner motd Service password-encryption Save= copy run start Show run/ show start

Complete 6.4.1.1- #5

ACTIVITY Lab 6.4.1.2

Configure initial settings

CONFIGURING A ROUTERINTERFACE CONFIGURATION

6.4.2

CONFIGURE THE INTERFACES

6.4.2.1- #2

VERIFY INTERFACES Show interfaces Show ip int brief

Show ip route- routing table

DEFAULT GATEWAY QUIZ

CONFIGURE DG ON SWITCH S1(config)#interface vlan1 S1(config-vlan)#ip address

192.168.10.50 255.255.255.0 S1(config-vlan)#no shutdown

6.4.3.2- #2

ACTIVITY 6.4.3.3 Configuring the Default Gateway

You will use various show commands to display the current state of the router. You will then use the Addressing Table to configure router Ethernet interfaces. Finally, you will use commands to verify and test your configurations.

6.4.3.4 Troubleshooting DG Issues

ACTIVITY Build a network or routers and switches

REVIEW- 4Q What command saves the config?

Copy run start What command displays all interface

statuses and IP addresses in summary? Show ip int brief

What command displays router memory, IOS name, and config-register? Show version

What does your PC need to have configured in order to get out of your network? Default gateway

REVIEW- 3Q When will a packet go through a router?

To go to another network if destined for it When configuring an interface, what

command turns it on?No shutdown

2 routers connect with a serial cable. You configured one of their S0/0 interfaces but the link still isn’t working. Why?Both connected must be configured before

it works

REVIEW & STUDY Complete the study guide handout

Take the quiz on netacad.com

Jeopardy review

SUMMARYIn this chapter, you learned: The network layer, or OSI Layer 3, provides services

to allow end devices to exchange data across the network.

The network layer uses four basic processes: IP addressing for end devices, encapsulation, routing, and de-encapsulation.

The Internet is largely based on IPv4, which is still the most widely-used network layer protocol.

An IPv4 packet contains the IP header and the payload.

The IPv6 simplified header offers several advantages over IPv4, including better routing efficiency, simplified extension headers, and capability for per-flow processing.

SUMMARY In addition to IP addressing, the network

layer is also responsible for routing. Hosts require a local routing table to ensure

that packets are directed to the correct destination network.

The local default route is the route to the default gateway.

The default gateway is the IP address of a router interface connected to the local network.

When a router receives a packet, it examines the destination IP address to determine the destination network.

SUMMARY The routing table of a router stores information

about directly-connected routes and remote routes to IP networks. If the router has an entry in its routing table for the

destination network, the router forwards the packet. If no routing entry exists, the router may forward the

packet to its own default route, if one is configured, or it will drop the packet.

Routing table entries can be configured manually on each router to provide static routing or the routers may communicate route information dynamically between each other using a routing protocol.

In order for routers to be reachable, the router interface must be configured.

NETWORK LAYER

Chapter 6

Intro to Routing & Switching