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Routing
Introduction to Routing
Static Routing
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Objectives
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Review
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IP Addressing
Introduction to
Routing
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Static Routing
Dynamic Routing overview
Examples – static routing
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Data Forwarding
128.2.254.11/24
128.2.254.15/24
Host A Host B
LAN 1
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WA
N
hostF hostD
router WAN router
hostE
LAN 2
How to send information to a distant host?
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What path is it sent on?
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router
Host C
112.32.224.60/24
How to find the path?
When a computer wants to send data, how does the
sending computer know if the Destination computer
is on the same network?
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Review – IP Addressing
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What do all devices on a LAN
segment have in common?
Host Stevens:
 172.16.10.10
 255.255.255.0
 172.16.10.0
Host Cerf:
Host Perlman
172.16.10.25
172.16.20.12
255.255.255.0
255.255.255.0
172.16.10.0
172.16.20.0
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Data Flow Through a Network
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Routers –Interfaces
Ethernet
0
172.16.1.1/ 255.255.255.0
MAC: 0cddeeffaabb
Serial
0
192.168.10.1
255.255.255.252
Ethernet
1172.16.2.1/ 255.255.255.0
MAC: 0abbccddeeff
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Routers have
 LAN interfaces
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Ethernet interfaces:
 Have MAC Addresses
 IP addresses
 WAN interfaces
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Serial interfaces
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Have IP addresses
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What is Routing?
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Routing - Selecting the
correct path towards
destination
 Build Routing table for path
selection
 Two methods
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Static
Dynamic
routing algorithm
local forwarding table
header value output link
0100
0101
0111
1001
3
2
2
1
0111
1
value in arriving
packet’s header
3 2
Router
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Static Routes
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A network administrator manually enters route into
the router's configuration
 When network only consists of a few routers
 -Network is connected to internet only through one
ISP
route entry manually updated whenever network
topology changes
Static routing reduces overhead
Better security
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Dynamic Routes
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Route knowledge is updated
automatically by a routing
process whenever new
information is received from the
network.
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Routing Table Structure
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Routing Table is stored in
RAM and contains information
about:
 Directly connected networks
 when a device is
connected to another
router interface
 Remotely connected
networks
 network that is not
directly connected to a
particular router
Show ip route command is
used to view a routing table
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Static Routes
Specifying Outgoing Interface
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Static Routes
Specifying the Next-hop IP Address
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Routing Table Structure
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Static routes in the routing
table
 -Includes: network
address and subnet
mask
 IP address of next hop
router or exit interface
 Denoted with the code S
in the routing table
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Review: Default Gateway
LAN
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When a LAN is
connected to a Router,
Default Gateway is the
address of router
interface connected to
that LAN.
Default Gateway
The IP address and
subnet mask is on the
same network as the
hosts on that network
Router
Router
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Static Routes
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Verifying Static Route Configuration:
The command show running-config is used to
view the active configuration in RAM to verify that
the static route was entered correctly.
The show ip route command is used to make
sure that the static route is present in the routing
table.
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Static Routes
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Troubleshooting Static Route Configuration:
The show interfaces command
The ping command
The traceroute command
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Review: Cisco Router backplane
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Identify the different interfaces on router
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Interface 1
Interface 2
Interface 3
Interface 4
Interface 1
Interface 2
Ethernet interface
Interface 4
console
Interface 3 interface
Serial interface
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Review: Establishing a Hyper-terminal Session
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All Cisco routers include an
EIA/TIA-232 asynchronous serial
console port (RJ-45).
How do you connect to router to
configure?
Router configured from PC
connected to router console port
using a rollover cable
Rollover cable has
•Serial interface adapter on
one side and
•RJ45 adapter on the other
RJ45 adapter
PC
Serial adapter
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Connections to the Router- cables
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Connections of a Router for Ethernet
 2 types of cables can be used:
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Straight through and Cross-over
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Straight through used to connect
dissimilar devices
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Switch-to-Router,
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Switch-to-PC,
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Cross-over used to connect
similar devices:
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Switch-to-Switch,
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Router to PC (Host)
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PC-to-PC,
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Switch-to-Hub,
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Hub-to-Hub, Router-to-Router
Cross-over
Straight-thru
Straight-thru
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Configuring router Interfaces
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-By default all
interfaces are down
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Ethernet interface
Ethernet
Serial
Interface configured
with IP address and
subnet mask
No Shutdown
command used to
enable the interface
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Configuring Interfaces –Ethernet
Interface
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To configure an Ethernet interface
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-Enter interface configuration mode (config)
-Enter IP address and subnet mask
-Enter no shutdown command
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Example:
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-R2(config)#interface fastethernet 0/0
-R2(config-if)#ip address 172.16.1.1 255.255.255.0
-R2(config-if)#no shutdown
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