IIUSA – Internet Institute
Switches & Routers
IIUSA – Internet Institute
Section Objectives
• Overview of Switches and Routers in a
Network Environment
• Switch Configuration
• Routing Basics and Configuration
• Displaying Router Information
• Troubleshooting Routers and Switches
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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
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Router Functionality
Network A
Network B
e1
e0
Routing Table
Network A e0
Network B e1
Routers Separate Broadcast Domains
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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
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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)
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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
Portion of a
Routing Table
C
R
C
R
172.16.0.0/24 is subnetted, 1 subnets
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/24 is subnetted, 2 subnets
10.2.2.0 [120/1] via 10.1.1.2, 00:00:07, Serial2
10.1.1.0 is directly connected, Serial2
192.168.1.0/24 [120/2] via 10.1.1.2, 00:00:07, Serial2
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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
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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
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IP Header Detail
Data
Padding (If Needed)
Data
Type of Service
Total Length
Identification
Flags
Fragment Offset
Time to Live
Protocol (Upper Level)
Header Checksum
Source
IP Address
Destination
IP Address
4
8
16
16
3
13
8
8
16
32
32
Variable
Header Length
4
IP Options
Version
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IP Address Numbering
• IP Addresses are 32 bits in length
Network
172
10101100
.
Host
16
00010000
.
122
01111010
.
204
11001100
Each Octet is 8 bits in length, representing a byte
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Converting IP Addresses from Binary to
Decimal
8 Bits
1
1
1
1
1
1
1
1
128 64
32
16
8
4
2
1
255 Decimal Value
Note: All 0s indicates a decimal 0, totaling 256 Decimal Values
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Conversion Example
8 Bits
1
0
128 64
1
32
1
16
0
8
255 Decimal Value
1
4
0
2
1
1
128
+ 32
+ 16
+ 4
+ 1
181
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IP Classes
Class A
N
H
H
H
Class B
N
N
H
H
Class C
N
N
N
H
- Network numbers are assigned by ARIN
- Host numbers assigned by Network Administrators
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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)
0
N
H
H
H
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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
10
N
N
H
H
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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
110
N
N
N
H
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Reserved Address Space
• 0s (zeros) in the host portion of the address
space is reserved for the network number
– Example: 172.16.0.0
• 1s in the host portion of the address is
reserved for the broadcast address
– Example: 172.16.255.255
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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
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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
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A Subnetted Network
172.16.3.0
172.16.4.0
172.16.5.0
172.16.1.0
172.16.2.0
Original Network 172.16.0.0
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Subnet Mask without Subnets
Network
Host
172.16.2.160
10101100
00010000
00000010
10100000
255.255.0.0
11111111
11111111
00000000
00000000
Subnet Mask
10101100
00010000
00000000
00000000
172
16
0
0
Network
Number
• Subnets not in use—the default
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Subnet Mask with Subnets
Network
172.16.2.160
Host
10101100
00010000
00000010
10100000
11111111
11111111
11111111
00000000
10101100
00010000
00000010
00000000
172
16
128
192
224
240
248
252
254
255
255.255.255.0
Subnet
Network
Number
2
0
• Network number extended by eight bits
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Defining a Subnet Mask
1 Convert the Number of Segments to Binary
2 Count the Number of Required Bits
3 Convert the Required Number of Bits to Decimal
(High Order)
Example of Class B Address
Number of Subnets
6
Binary Value
0 0 0 0 0 1 1 0
(3 Bits)
4+2 = 6
Convert to Decimal
Subnet Mask
11111111
255
11111111
.
255
11100000 00000000
.
224
.
0
Ignore the first bit borrowed, add the additional bits borrowed to
determine the number of new subnets
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Defining Subnet IDs
1
255
255
224
0
11111111 11111111 11100000 00000000
Evaluate the bit patterns established
within the subnetted region
00000000 = 0
00100000 = 32
01000000 = 64
01100000 = 96
10000000 = 128
10100000 = 160
11000000 = 192
11100000 = 224
2
3
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Shortcut to Defining Subnet IDs
1
List the Number of Bits (High Order) Used for
Subnet Mask
2
Convert the Bit with the Lowest Value to Decimal
3
Increment the Value for Each Bit Combination
0
+ 64
= 64
+ 64
= 128
+ 64
192
w.x.64.1
w.x.127.254
w.x.128.1
w.x.191.254
11000000
64
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Defining Host IDs for a Subnet
Subnet IDs
00000000 = 0
00100000 = 32
01000000 = 64
01100000 = 96
10000000 = 128
10100000 = 160
11000000 = 192
11100000 = 224
Host ID Range
Invalid
x.y.32.1 –
x.y.64.1 –
x.y.96.1 –
x.y.128.1 –
x.y.160.1 –
x.y.192.1 –
Invalid
x.y.63.254
x.y.95.254
x.y.127.254
x.y.159.254
x.y.191.254
x.y.223.254
• 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
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Network to Network Connectivity
172.16.3.0
172.16.4.0
172.16.1.0
172.16.2.0
1

Router strips off the data link header
2

Examines the network layer address
3

Consults the routing table to find the interface for the network
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Network-Layer Protocol Operations
X
C
Y
A
Application
Application
Presentation
Session
B
A
Presentation
B
C
Transport
Session
Transport
Network
Network
Network
Network
Data Link
Data Link
Data Link
Data Link
Physical
Physical
Physical
Physical
Network
Data Link
Physical
Each router provides its services to support upper-layer functions
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Routed Versus Routing Protocols
Routed Protocols – Any network protocol
run on a workstation as a part of the
network operating system that provides
networking capabilities (Ex: TCP/IP)
Routing Protocols – Protocols run on a
router to provide the ability for the router to
share path information (Ex: RIP, IGRP)
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Routing Protocols
• Interior Routing Protocols – support the
sharing of routes or paths within the internal
internetwork
(Ex: RIP, IGRP, EIGRP, OSPF)
• Exterior Routing Protocols – support the
sharing of routes or paths across large
internetworks, such as the Internet
(Ex: BGP and EGP)
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Routing Metrics
• All routing protocols utilize metrics to
characterize best path information
–
–
–
–
–
–
–
Hop Count
Bandwidth
Delay
Load
Reliability
Ticks (Novell)
Cost – generic definition of metric information
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Static versus Dynamic Routes
• Static routes are established by a network
administrator and manually input directly
into the routing table
• Dynamic 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
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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
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Typical Router System Board Layout
Flash Card
Slot
System Code
Flash or PROM
Primary Memory
DRAM SIMM
Polarization
Notch
Memory Types:
RAM/DRAM
NVRAM
Flash Memory
ROM
Boot
ROMS
Serial
AUX
Console
Ethernet
Shared Memory
Fixed DRAM
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Typical Cisco Motherboard for a 2500 Series
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Sources For Configuring
VTY 0 - 4
Console Port
Auxiliary Port
Interfaces
TFTP Server
Modem Bank
Modem Bank
Dial-in Access with modems
Network
Management
Station
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Router and Switch Configuration