Switches & Routers

IIUSA – Internet Institute

Switches & Routers


Section Objectives

• Overview of Switches and Routers in a Network Environment

• Switch Configuration• Routing Basics and Configuration• Displaying Router Information• Troubleshooting Routers and Switches


Layer 3 (IP) Basics

• Provides ability to address devices with a logical address and route traffic not locally attached– Logical addresses are applied to source and

destination nodes or devices– Paths are determined to forward data from a

local device to a remote device on another network


Router FunctionalityNetwork A Network B

Routing TableNetwork A e0Network B e1

e0 e1

Routers Separate Broadcast Domains


Why a Logical Address

• Hierarchical addresses provide reachability across boundaries called subnets

• Similar to the phone system with area codes to differentiate geographical regions or zip codes to indicate different cities and towns

• A hierarchical logical computer address contains a network identifier and host or unit identifier


Network Segments• The size of a network dictates traffic load and

potential for overload• As growth overwhelms a network (similar to cars

crowding a highway), segments can be created to off load traffic

• Each new segment is autonomous of other network segments

• Without segmentation, all addressing would be done through a flat addressing scheme (MAC addressing) overwhelming segmentation discovery devices (routers)


Connectivity Between Segments

• Segments can communicate through devices that determine a path from one network to another over communications lines

• Devices (routers) can determine the best path in the case of multiple paths

• Paths or routes are stored in routing tables 172.16.0.0/24 is subnetted, 1 subnetsC 172.16.1.0 is directly connected, Ethernet0 10.0.0.0/24 is subnetted, 2 subnetsR 10.2.2.0 [120/1] via 10.1.1.2, 00:00:07, Serial2C 10.1.1.0 is directly connected, Serial2R 192.168.1.0/24 [120/2] via 10.1.1.2, 00:00:07, Serial2

Portion of aRouting Table


Network Layer Addressing

• Routers use a portion of the address to determination Network identification

• All hosts or devices within a given network segment are identified by a host portion of the address

• IP Addresses 172.16.10.100

Network ID Host ID


Path Determination• Network layer determines BEST path from

source to destination• A router examines reported paths over

links, determining best path from metrics associated with each path

Best Path


IP Header DetailData

Version 4

Header Length 4

Type of Service 8

Total Length 16

Identification 16

Flags 3

Fragment O

ffset 13

Time to Live 8

Protocol (Upper Level) 8

Header C

hecksum 16

SourceIP A

ddress 32

Destination

IP Address 32

IP Options V

ariable

Data

Padding (If Needed)


IP Address Numbering

• IP Addresses are 32 bits in length

172 16 122 204. . .Network Host

Each Octet is 8 bits in length, representing a byte

10101100 00010000 01111010 11001100


Converting IP Addresses from Binary to Decimal

1 1 1 1 1 1 1 1

128 64 32 16 8 4 2 1

8 Bits

255 Decimal Value

Note: All 0s indicates a decimal 0, totaling 256 Decimal Values


Conversion Example

1 0 1 1 0 1 0 1

128 64 32 16 8 4 2 1

8 Bits

255 Decimal Value

128+ 32+ 16+ 4+ 1 181


IP Classes

H HHN

H HNN

N HNN

Class A

Class B

Class C

- Network numbers are assigned by ARIN- Host numbers assigned by Network Administrators


Class A Notes

• Address range 1 to 126• Address 10 is reserved as a private address• Address 127 is reserved for loopback

purposes• First bit begins with a 0 (zero)

H HHN0


Class B Notes

• Address range 128 to 191• Address 172.16 to 172.31 is reserved as a

private address range• First two bits begin with a 10

H HNN10


Class C Notes

• Address range 192 to 223• Address 192.168 is reserved as a private

address range• First three bits begin with a 110

N HNN110


Reserved Address Space

• 0s (zeros) in the host portion of the address space is reserved for the network numbernetwork number– Example: 172.16.0.0

• 1s in the host portion of the address is reserved for the broadcast addressbroadcast address– Example: 172.16.255.255


A Case for Subnetting

• The original IP addressing scheme was sufficient for the early days of the internetworking environment

• As the Internet grew in the 1990s, addressing, using classful addressing became impractical

• Subnetting (classless) addressing became the answer for address space depletion


Subnetting

• Subnetting borrows host bits to increase the number of networks

• The number of hosts is reduced in proportion to the number of bits borrowed


A Subnetted Network

Original Network 172.16.0.0

172.16.1.0 172.16.2.0

172.16.3.0

172.16.4.0172.16.5.0


16

Network Host

172 0 0

10101100

11111111

10101100

00010000

11111111

00010000

00000000

00000000

10100000

00000000

00000000

• Subnets not in use—the default

00000010

Subnet Mask without Subnets

172.16.2.160

255.255.0.0

NetworkNumber

Subnet Mask


• Network number extended by eight bits

Subnet Mask with Subnets

16

Network Host

172.16.2.160

255.255.255.0

172 2 0

10101100

11111111

10101100

00010000

11111111

00010000

11111111

00000010

10100000

00000000

00000000

00000010

Subnet

NetworkNumber

128

192

224

240

248

252

254

255

IIUSA – Internet Institute Defining a Subnet Mask

Convert the Number of Segments to Binary

Count the Number of Required Bits

Convert the Required Number of Bits to Decimal (High Order)

1

2

3

Example of Class B AddressNumber of Subnets

Binary Value

Convert to Decimal

6

0 0 0 0 0 1 1 0

= 6

(3 Bits)

4+2

255 . 255 . 224 . 011111111 11111111 11100000 00000000

Subnet Mask

Ignore the first bit borrowed, add the additional bits borrowed to determine the number of new subnets


Defining Subnet IDs

255 255 224 0

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0

00000000 = 000100000 = 3201000000 = 6401100000 = 9610000000 = 12810100000 = 16011000000 = 19211100000 = 224

1

2 3

Evaluate the bit patterns establishedwithin the subnetted region


Shortcut to Defining Subnet IDs

List the Number of Bits (High Order) Used for Subnet Mask

Convert the Bit with the Lowest Value to Decimal

Increment the Value for Each Bit Combination

11000000

64

0+ 64= 64+ 64= 128+ 64

192

w.x.64.1 w.x.127.254

w.x.128.1 w.x.191.254

1

2

3


Defining Host IDs for a SubnetSubnet IDs Host ID Range

Invalidx.y.32.1 – x.y.63.254x.y.64.1 – x.y.95.254x.y.96.1 – x.y.127.254x.y.128.1 – x.y.159.254x.y.160.1 – x.y.191.254x.y.192.1 – x.y.223.254Invalid

00000000 = 000100000 = 3201000000 = 6401100000 = 9610000000 = 12810100000 = 16011000000 = 19211100000 = 224

• Each Subnet ID Indicates the Beginning Value in a Host Range• The Ending Value Is One Less Than the Beginning Value of the

Next Subnet ID


Network to Network Connectivity

172.16.1.0 172.16.2.0

172.16.3.0

172.16.4.0

Router strips off the data link header Examines the network layer address Consults the routing table to find the interface for the network

1

2

3


Network-Layer Protocol Operations

Each router provides its services to support upper-layer functions

XY

AA

BB

CC

A B C

Physical

Data Link

Network

Physical

Data Link

Network

Physical

Data Link

Network

Physical

Data Link

Network

Transport

Session

Presentation

Application

Physical

Data Link

Network

Transport

Session

Presentation

Application


Routed Versus Routing Protocols

Routed ProtocolsRouted Protocols – Any network protocol run on a workstation as a part of the network operating system that provides networking capabilities (Ex: TCP/IP)

Routing ProtocolsRouting Protocols – Protocols run on a router to provide the ability for the router to share path information (Ex: RIP, IGRP)


Routing Protocols

• Interior Routing ProtocolsInterior Routing Protocols – support the sharing of routes or paths within the internal internetwork

(Ex: RIP, IGRP, EIGRP, OSPF)• Exterior Routing ProtocolsExterior Routing Protocols – support the

sharing of routes or paths across large internetworks, such as the Internet

(Ex: BGP and EGP)


Routing Metrics

• All routing protocols utilize metricsmetrics to characterize best path information – Hop Count– Bandwidth– Delay– Load– Reliability– Ticks (Novell)– Cost – generic definition of metric information


Static versus Dynamic Routes

• StaticStatic routes are established by a network administrator and manually input directly into the routing table

• DynamicDynamic routes are learned through the use of a Routing Protocol. Dynamic routes are adaptive. Changes to path availability or establishment of new paths are automatically shared with other routers


Routers

• A Router is a computer, with similar functionality• Forwards packets, from incoming interface to

outgoing interfaced, based on best path as determined by routes available in the routers Routing Table

• Segments a LAN into separate Broadcast Domains• Must be used when connecting LANs across wide

area network environment


Typical Router System Board Layout

Primary MemoryDRAM SIMM

Ethernet Serial

Console

AU

XShared Memory

Fixed DRAM

System CodeFlash or PROM

Flash CardSlot

BootROMS

PolarizationNotch

Memory Types: RAM/DRAM NVRAM Flash Memory ROM


Typical Cisco Motherboard for a 2500 Series


Sources For Configuring

Console Port

Auxiliary Port

Interfaces

VTY 0 - 4

TFTP Server

Modem Bank

Modem Bank

Dial-in Access with modems

NetworkManagement

Station


Router and Switch Configuration

Documents

Switches & Routers