Routing Fundamentals and Subnets

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CCNA 1 Chapter 8


Routing Fundamentals and
Subnets

By

Your Name

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Objectives

•
Routed protocol

•
IP routing protocols

•
The mechanics of subnetting

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Routed Protocols Versus

Routing Protocols

Routing protocols determine the path that routed
protocols follow to their destinations.

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Characteristics of a

Routable Protocol

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IP as a Routed Protocol

•
IP is a connectionless,
unreliable, best
-
effort
delivery protocol.

•
As information flows
down the layers of the
OSI model
;

the data is
processed at each layer.

•
IP accepts whatever data
is passed down to it from
the upper layers.


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Packet Propagation

Each router provides its services to
support upper
-
layer functions
.

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Connectionless Network Services

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A connection is established between the
sender and the recipient before any data is
transferred.

Connection
-
Oriented

Network Services

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Anatomy of an IP Packet

•
Version

•
IP header length (HLEN)

•
Type
-
of
-
service

•
Total length

•
Identification

•
Flags

•
Fragment offset

•
Time
-
to
-
live

•
Protocol

•
Header checksum

•
Source address

•
Destination address

•
Options

•
Padding

•
Data

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Routing Protocols

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Router Overview

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Layer 3 Addresses

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Routing Versus Switching

•
This distinction is routing and switching use
different information in the process of moving
data from source to destination.

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Routed Versus Routing

•
A routed protocol:

–
Includes any network protocol suite that provides
enough information in its network layer address to
allow a router to forward it to the next device and
ultimately to its destination.

–
Defines the format and use of the fields within a
packet.

•
A routing protocol:

–
Provides processes for sharing route information.

–
Allows routers to communicate with other routers to
update and maintain the routing tables.



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Path Determination

•
Path determination enables a router to compare
the destination address to the available routes in
its routing table, and to select the best path.


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Routing Tables

•
Routers keep track of

the following
:

–
Protocol type

–
Destination/next
-
hop associations

–
Routing metric

–
Outbound interfaces


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Routing Algorithms and Metrics

•
Routing protocols have one or more of the following design
goals:

–
Optimization

–
Simplicity and low overhead

–
Robustness and stability

–
Flexibility

–
Rapid convergence

•
Metrics most commonly used by routing protocols

include the
following
:

–
Bandwidth

–
Delay

–
Load

–
Reliability

–
Hop count

–
Ticks

–
Cost



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RIP and IGRP

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IGP and EGP

•
IGPs route data within an autonomous system.

•
EGPs route data between autonomous systems.


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Link

State and Distance Vector

•
Examples of distance
-
vector protocols:

–
Routing Information Protocol (RIP)

–
Interior Gateway Routing Protocol (IGRP)

–
Enhanced IGRP (EIGRP)

•
Examples of link
-
state protocols:

–
Open Shortest Path First (OSPF)

–
Intermediate System
-
to
-
Intermediate System (IS
-
IS)

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Routing Protocols

•
RIP

•
RIP v2

•
IGRP

•
EIGRP

•
OSPF

•
IS
-
IS

•
BGP

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Mechanics of Subnetting

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Classes of Network IP Addresses

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Subnetworks

To create a subnet address, a network
administrator borrows bits from the original host
portion and designates them as the subnet field.


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Subnetworks

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Subnet Mask

•
Determines which part of an IP address is the
network field and which part is the host field
.

•
Follow these steps to determine the subnet mask:

1. Express the subnetwork IP address in binary form.

2. Replace the network and subnet portion of the address
with all 1s.

3. Replace the host portion of the address with all 0s.

4. Convert the binary expression back to dotted
-
decimal
notation.

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Subnet mask in decimal = 255.255.240.0

Subnet Mask

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Subnet Addresses

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Class B address with 8 bits borrowed for the subnet

130.5.2.144 (8 bits borrowed for subnetting) routes to subnet
130.5.2.0 rather than just to network 130.5.0.0.

Determining Subnet Mask Size

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The address 197.15.22.131 would be on the
subnet 197.15.22.128.

11000101

00001111

00010110

100

00011

Network Field

SN

Host
Field

Class C address 197.15.22.131 with a subnet
mask of 255.255.255.224 (3 bits borrowed)

Determining Subnet Mask Size

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Subnetting Example

with AND Operation