1

Routing

Introduction to Routing

Static Routing

2

Objectives

• Review• IP Addressing

• Introduction to • Routing

• Static Routing• Dynamic Routing overview• Examples – static routing

3

Data Forwarding

How to send information to a distant host? What path is it sent on?

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?

Host A Host B Host C

LAN 1

hostF hostD hostE

LAN 2router router routerWA

NWAN

128.2.254.15/24 112.32.224.60/24128.2.254.11/24

4

Review – IP Addressing

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:

172.16.10.25

255.255.255.0

172.16.10.0

Host Perlman

172.16.20.12

255.255.255.0

172.16.20.0

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Data Flow Through a Network

6

Routers –Interfaces

Routers have LAN interfaces

Ethernet interfaces: Have MAC Addresses IP addresses

WAN interfaces Serial interfaces Have IP addresses

Serial 0

192.168.10.1 255.255.255.252

Ethernet 1172.16.2.1/ 255.255.255.0 MAC: 0abbccddeeff

Ethernet 0

172.16.1.1/ 255.255.255.0 MAC: 0cddeeffaabb

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What is Routing?

Routing - Selecting the correct path towards destination Build Routing table for path

selection Two methods

Static Dynamic

Router

1

23

0111

value in arrivingpacket’s header

routing algorithm

local forwarding table

header value output link

0100010101111001

3221

8

Static Routes

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

Route knowledge is updated automatically by a routing process whenever new information is received from the network.

10

Routing Table Structure 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

11

Static Routes

Specifying Outgoing Interface

12

Static Routes

Specifying the Next-hop IP Address

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Routing Table Structure

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

When a LAN is connected to a Router, Default Gateway is the address of router interface connected to that LAN.

The IP address and subnet mask is on the same network as the hosts on that network

Router

LAN

Router

Default Gateway

15

Static Routes

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

• Troubleshooting Static Route Configuration:• The show interfaces command• The ping command• The traceroute command

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Review: Cisco Router backplane Identify the different interfaces on router

Interface 1 Interface 2 Interface 3 Interface 4

Serial interface

console interfaceEthernet interface

Interface 1 Interface 2

Interface 3

Interface 4

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Review: Establishing a Hyper-terminal Session

• 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

PC

Serial adapter

RJ45 adapter

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Connections to the Router- cables

Connections of a Router for Ethernet 2 types of cables can be used:

Straight through and Cross-over Straight through used to connect

dissimilar devices Switch-to-Router, Switch-to-PC,

Cross-over used to connect

similar devices: Switch-to-Switch, Router to PC (Host) PC-to-PC, Switch-to-Hub, Hub-to-Hub, Router-to-Router

Cross-over Straight-thru

Straight-thru

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Configuring router Interfaces

-By default all interfaces are down Ethernet Serial

Interface configured with IP address and subnet mask

No Shutdown command used to enable the interface

Ethernet interface

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To configure an Ethernet interface -Enter interface configuration mode (config) -Enter IP address and subnet mask -Enter no shutdown command Example:

-R2(config)#interface fastethernet 0/0 -R2(config-if)#ip address 172.16.1.1 255.255.255.0 -R2(config-if)#no shutdown

Configuring Interfaces –Ethernet Interface