Chapter 6 Network Layer

Report
Chapter 6
Intro to Routing & Switching
 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
6.1.1
6.1.2
 Low


overhead
Delivers packet to destination only
Does NOT track or manage flow

Other layers handle that
 Connectionless

Doesn’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
 Doesn’t
matter what cables/media it travels
over

What layer handles the prep for media?
 6.1.2.6
 Read
each IP characteristic & decide if it
describes connectionless, best effort, or
media independent.
 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
6.1.3
 Includes
Header & Payload
 Header includes:


Source & destination IP
DS (Differentiated Services)


Protocol


Defines the priority of each packet
TCP/UDP
TTL (Time-to-Live)

Hops until dropped
Version,
IP’s
DS, Total Length, Flags,
TTL
 Which

Tells the priority of a packet?


field in the IPv4 header…
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

TCP
helps IP with guaranteed delivery?
6.1.4
 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

32-bit addresses



4 billion available
Many header fields
128-bit addresses


Less header fields


Must use NAT

To conserve addresses
IPv4

340 undecillion avail.
Better packet handling
No need for NAT

A lot of IPv6 addresses
IPv6
Version, Payload
Length, Hop Limit,
IPv6 addresses
 Handout
to compare IPv4 & 6 headers
 6.1.4.6

Read each IPv6 header description & click which
field it belongs to.
 Explain

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?


NAT.
Flow label
Is like the DS field for priority?

Traffic Class
 Review
the picture.
 What kind of IP is being used?

IPv4
 How

3
many hops from PC1 to PC33?
6.2.1
 Itself

(loopback)
127.0.0.1
 Local

Shares same network address
 Remote

On a different network
 PC
has a “mini” routing table
 6.2.1.7
 Identify
the parts of a host routing table
 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
6.2.2
 After
packet reaches DG (router), it looks at
the routing table to see where to send it
 What’s


in the table?
Directly connected routes
Remote routes
 Show

ip route
Stored in RAM
 How
it was learned
 When it was updated
 Which interface to use to get to that network
192.168.10.0/24
.10
PC1
10.1.1.0/24
G0/0
.1
.1
R1
.1
G0/1
.10
PC2
.10
209.165.200.224 /30
192.168.11.0/24
.225
S0/0/0
.226
R2
.10
.1
10.1.2.0/24
R1#show ip route
Codes: 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
D
D
C
L
C
L
C
L
R1#
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
10.1.1.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0
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 masks
192.168.10.0/24 is directly connected, GigabitEthernet0/0
192.168.10.1/32 is directly connected, GigabitEthernet0/0
192.168.11.0/24 is variably subnetted, 2 subnets, 3 masks
192.168.11.0/24 is directly connected, GigabitEthernet0/1
192.168.11.1/32 is directly connected, GigabitEthernet0/1
209.165.200.0/24 is variably subnetted, 2 subnets, 3 masks
209.165.200.224/30 is directly connected, Serial0/0/0
209.165.200.225/32 is directly connected, Serial0/0/0
 6.2.2.7

Identify the elements of a routing table
 Lab

6.2.2.8
Discover your PC’s routing table
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
 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
6.3.1
 OS
 RAM
 CPU
 ROM
WAN Serial
Ports in slot
LAN
interfaces
Console
Port RJ45
AUX
Port RJ45
LAN
Interfaces in slot
 6.3.1.8

Match the router interface or function with its
description
 Lab

Explore the router externally & using show
commands
 Lab

6.3.1.9
6.3.1.10
Determine connectivity options on a router
 Where

Flash
 Where

is the limited IOS at?
ROM
 Where

is the startup-config stored?
NVRAM
 Where

is the running-config at?
RAM
 Where

is the IOS stored?
RAM
is the routing table stored?

Based on the last 5 questions, which ones will
get “lost” if you lose power to the router & why?


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?


Running-config & routing table because they are in
RAM
Ethernet/LAN or Serial/WAN
What 2 things get copied into RAM upon a normal
boot?

IOS & startup-config
6.3.2
 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-config

MUST SAVE THEM!
 POST
tests hardware (CPU, Memory)
 ROM: Bootstrap


Boot Image
Begins search for IOS
 Locate

& load IOS into RAM
Usually in Flash (default) or TFTP Server
 Configuration


NVRAM (1st), TFTP Server (2nd), Console (3rd)
If found, copies into RAM


File or Setup
Becomes the running-config
If not found, enters Setup Mode
 Show
version
 IOS
version
 Version of bootstrap
 Location & name of IOS
 CPU & RAM
 Interfaces
 Amount of NVRAM & Flash
 Config-register

0x2102
Bootstrap
version
Model &
IOS
version
IOS locale
& name
Amount of
RAM
Total/Used
Amt. of NVRAM
Amt. of Flash
Config-register
Interfaces
 In
Packet Tracer…

Add an 1841 router
Go in & answer questions based on show version
output on handout

Add a 2960 switch and do the same

 6.3.2.6


The router boot process
Put the steps in order
 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.bin

The IOS is in flash & that’s its file name
 What

POST
 When

happens first when booting a router?
loading the IOS, where does it look?
Flash, TFTP Server, ROM
6.4.1
 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
 Lab

6.4.1.2
Configure initial settings
6.4.2
 6.4.2.1-
#2
 Show
interfaces
 Show ip int brief
 Show
ip route- routing table
 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
 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
 Build
a network or routers and switches
 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
 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
 Complete
 Take
the study guide handout
the quiz on netacad.com
 Jeopardy
review
In 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 perflow processing.
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.


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.

Chapter 6
Intro to Routing & Switching

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