CCNA 1 Chapter 8 Routing Fundamentals and Subnets

www.ciscopress.comCopyright 2003

CCNA 1 Chapter 8

Routing Fundamentals and Subnets

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Objectives

• Routed protocol

• IP routing protocols

• The mechanics of subnetting


Routed Protocols Versus Routing Protocols

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


Characteristics of a Routable Protocol


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.


Packet Propagation

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


Connectionless Network Services


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

Connection-Oriented Network Services


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


Routing Protocols


Router Overview


Layer 3 Addresses


Routing Versus Switching

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


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.


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.


Routing Tables

• Routers keep track of the following: – Protocol type– Destination/next-hop associations – Routing metric– Outbound interfaces


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


RIP and IGRP


IGP and EGP

• IGPs route data within an autonomous system.

• EGPs route data between autonomous systems.


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)


Routing Protocols

• RIP• RIP v2• IGRP• EIGRP• OSPF• IS-IS• BGP


Mechanics of Subnetting


Classes of Network IP Addresses


Subnetworks

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


Subnetworks


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.


Subnet mask in decimal = 255.255.240.0

Subnet Mask


Subnet Addresses


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


The address 197.15.22.131 would be on the subnet 197.15.22.128.

11000101 00001111 00010110 100 00011

Network Field SNHost Field

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

Determining Subnet Mask Size


Subnetting Example with AND Operation

CCNA 1 Chapter 8 Routing Fundamentals and Subnets

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