Network layer
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Transcript of Network layer
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NETWORK LAYER
Chapter 6
Intro to Routing & Switching
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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
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THE NETWORK LAYER
6.1.1
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NETWORK LAYER
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ALL ABOUT IP
6.1.2
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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
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MEDIA INDEPENDENT Doesn’t matter what cables/media it
travels overWhat layer handles the prep for media?
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ACTIVITY 6.1.2.6
Read each IP characteristic & decide if it describes connectionless, best effort, or media independent.
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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
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IPV4 PACKET
6.1.3
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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
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SAMPLE IPV4 HEADER
Version, IP’s
DS, Total Length, Flags, TTL
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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
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IPV6 PACKET
6.1.4
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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
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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
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IPV6 HEADER & IPV4 HEADER
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SAMPLE IPV6 HEADER
Version, Payload
Length, Hop Limit, IPv6 addresses
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ACTIVITY Handout to compare IPv4 & 6 headers
6.1.4.6Read each IPv6 header description & click
which field it belongs to.
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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
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REVIEW Review the picture. What kind of IP is being used?
IPv4 How many hops from PC1 to PC33?
3
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HOW A HOST ROUTES
6.2.1
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HOST READY TO SEND Itself (loopback)
127.0.0.1 Local
Shares same network address Remote
On a different network
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HOST IPV4 ROUTING TABLE PC has a “mini” routing table
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ACTIVITY 6.2.1.7
Identify the parts of a host routing table
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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
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REVIEW
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ROUTER ROUTING TABLE
6.2.2
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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
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WHAT WOULD IT KNOW?
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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
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PARTS OF ROUTING TABLE
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ROUTING TABLE- OTHER NETWORKS
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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
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ACTIVITY 6.2.2.7
Identify the elements of a routing table
Lab 6.2.2.8Discover your PC’s routing table
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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
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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
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ANATOMY OF A ROUTER
6.3.1
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THE ROUTER IS A COMPUTER OS RAM CPU ROM
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ROUTER MEMORY
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ROUTER INTERFACES
Console Port RJ45
AUX Port RJ45
LANinterfaces
WAN Serial Ports in slot
LANInterfaces in slot
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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
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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
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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
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ROUTER BOOT-UP
6.3.2
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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!
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STEP 1 POST tests hardware (CPU, Memory) ROM: Bootstrap
Boot ImageBegins search for IOS
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STEP 2 Locate & load IOS into RAM
Usually in Flash (default) or TFTP Server
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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
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VERIFY & TROUBLESHOOT Show version
IOS version Version of bootstrap Location & name of IOS CPU & RAM Interfaces Amount of NVRAM & Flash Config-register
0x2102
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Model & IOS
versionBootstrap
version
Amount of RAMTotal/Used
IOS locale & name
Interfaces
Amt. of NVRAM
Amt. of Flash
Config-register
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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
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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
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CONFIGURE A ROUTER
INITIAL SETTINGS
6.4.1
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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
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ACTIVITY Lab 6.4.1.2
Configure initial settings
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CONFIGURING A ROUTERINTERFACE CONFIGURATION
6.4.2
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CONFIGURE THE INTERFACES
6.4.2.1- #2
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VERIFY INTERFACES Show interfaces Show ip int brief
Show ip route- routing table
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DEFAULT GATEWAY QUIZ
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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
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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
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ACTIVITY Build a network or routers and switches
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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
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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
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REVIEW & STUDY Complete the study guide handout
Take the quiz on netacad.com
Jeopardy review
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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.
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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.
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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.
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NETWORK LAYER
Chapter 6
Intro to Routing & Switching