CCNA1 M10 Routing Fundamentals Subnets

8/14/2019 CCNA1 M10 Routing Fundamentals Subnets

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CCNA Semester1

Module 10

Rout ing Fundam ent a ls and Subnet s

Objectives

Routed protocol

IP routing protocols

The mechanics of subnetting


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Internet Protocol - Routed

Routed protocols

A routed protocol allows the router to forwarddata between different networks

In order for a protocol to be routable, it must

provide the ability to assign a network numberand a host number to each individual device.

The network address is obtained by ANDing theaddress with the network mask.


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Routed protocols

Connection oriented network services

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

All packets travel sequentially across the same circuit, or

more commonly, across the same virtual circuit.


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Connectionless network services

Each packet is treated separately When the packets pass from source to destination, they can:

Switch to different paths. Arrive out of order.

IP as a Routed Protocol

IP is a connectionless,unreliable, best-effortdelivery protocol.

IP does not verify that

the data reached itsdestination. Thisfunction is handled bythe upper layerprotocols.


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Packet Propagation

Process in Router


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IP header format

20bytes

IP header format: Version

4 bits.

Indicates the version ofIP currently used.

IPv4 : 0100

IPv6 : 0110

4 bits.

Indicates the version ofIP currently used.

IPv4 : 0100

IPv6 : 0110


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IP header format: Header length

4 bits.

IP header length : Indicates thedatagram header length in 32 bitwords (4 bits), and thus points to

the beginning of the data.

4 bits.

IP header length : Indicates thedatagram header length in 32 bitwords (4 bits), and thus points to

the beginning of the data.

IP header format: Service type

8 bits.

Specifies the level of importancethat has been requested for thisdatagram by an upper-layerprotocol.

Precedence.

Reliability. Speed.

8 bits.

Specifies the level of importancethat has been requested for thisdatagram by an upper-layerprotocol.

Precedence.

Reliability. Speed.


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IP header format: Total length

16 bits.

Specifies the length in bytes ofthe entire IP packet, includingdata and header.

16 bits.

Specifies the length in bytes ofthe entire IP packet, including

data and header.

IP header format: Identification

16 bits.

Contains an integer that identifiesthe current datagram.

Assigned by the sender to aid in

assembling the fragments of adatagram.

16 bits.

Contains an integer that identifiesthe current datagram.

Assigned by the sender to aid inassembling the fragments of adatagram.


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IP header format: Time to Live

8 bits, specifies the time and distance thisdatagram is allowed to travel.

Each router routing this datagram subtractsfrom this field its processing time for this

datagram, which gradually decreases it. It helps prevent packets from looping

endlessly.

8 bits, specifies the time and distance thisdatagram is allowed to travel.

Each router routing this datagram subtractsfrom this field its processing time for thisdatagram, which gradually decreases it.

It helps prevent packets from loopingendlessly.

IP header format: Protocol

Indicates which upper protocolreceives incoming packets after IPprocessing has been completed 06 : TCP

17 : UDP 01: ICMP

Indicates which upper protocolreceives incoming packets after IPprocessing has been completed 06 : TCP

17 : UDP

01: ICMP


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IP header format: Header checksum

16 bits.

A checksum on the header only,helps ensure IP header integrity.

16 bits.

A checksum on the header only,helps ensure IP header integrity.

IP header format: Addresses

32 bits each.

Source IP Address

Destination IP Address

32 bits each.

Source IP Address

Destination IP Address


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IP header format: Options

Variable length.

Allows IP to support variousoptions, such as security, route,error report ...

Variable length.

Allows IP to support variousoptions, such as security, route,error report ...

IP header format: Padding

The header padding is used to

ensure that the internet header endson a 32 bit boundary.

The header padding is used to

ensure that the internet header endson a 32 bit boundary.


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IP header format: Padding

Contains upper-protocol information,variable length up to 64 Kb.

Contains upper-protocol information,variable length up to 64 Kb.

www.ietf.org and RFC-760.

IP Routing Protocol


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Routing Overview

Routing is an OSI Layer 3function.

Routing is the process offinding the most efficient path

from one device to another. Two key functions of router:

maintain routing tables

use the routing table to forwardpackets

Layer 2 Switching and Layer 3 Routing


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Routing vs. Switching

Routing Protocol

Routing protocols allowrouters to choose the bestpath for data from source todestination. A routingprotocol functions includes

the following: Provides processes for

sharing route information

Allows routers to

communicate with otherrouters to update andmaintain the routing tables

Eg:RIP, IGRP, OSPF, EIGRP,BGP


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Routed vs. Routing protocol

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Path Determination

Path determination enables a router to compare thedestination address to the available routes in itsrouting table, and to select the best path.

The router uses path determination to decide which

port an incoming packet should be sent out of totravel on to its destination.


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Routing Tables

Routing tables contain the information of a route toforward data packets across connected networks :

Protocol type

Destination/next-hop associations

Route metric and routing protocol reliability

Outbound interfaces

Routing Algorithms

Routing protocols often have one or more of thefollowing design goals: Optimization

Simplicity and low overhead

Robustness and stability

Flexibility

Rapid convergence


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Routing Metrics

Metrics can be based on a single characteristic of a path, orcan be calculated based on several characteristics. Thefollowing are the metrics that are most commonly used byrouting protocols: Bandwidth: The data capacity of a link

Delay: The length of time required to move a packet along each link Load: The amount of activity on a network resource

Reliability: Usually a reference to the error rate

Hop count: The number of routers that a packet must travel throughbefore reaching its destination

Ticks: delay on a data link using IBM PC clock ticks. One tick isapproximately 1/18 second.

Cost: An arbitrary value, usually based on bandwidth, monetaryexpense, or other measurement, that is assigned by a networkadministrator.

IGP and EGP

An autonomous system is a network or set of networksunder common administrative control.

Two families of routing protocols are:

Interior Gateway Protocols(IGPs): exchange routes within an autonomous

system. Eg: RIP, IGRP, OSPF, IS-IS Exterior Gateway Protocols(EGPs): exchange routes between

autonomous systems. Eg: BGP


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Link state and distance vector

Distance-Vector Protocols (RIP, IGRP, EIGRP): View network topology from neighbors perspective.

Add distance vectors from router to router.

Frequent, periodic updates.

Pass copy of routing tables to neighbor routers. Link State Protocols (OSPF, IS - IS):

Gets common view of entire network topology.

Calculates the shortest path to other routers.

Event-triggered updates, respond quickly to network changes .

Passes link state advertisement, known as link-state refreshes,to other routers.

Distance vector routing


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Link state routing

The Mechanics of Subnetting


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Why we need to divide network?

Network administrators sometimes need to dividenetworks, especially large ones, into smaller networks: Reduce the size of a broadcast domain.

Support basic network security.

Implement the hierarchical managements. So we need more network addresses for your network.

But I want the outside networks see our network as asingle network.

Subnetting

Subnetworks are smaller divisions of network.

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

How ?

By using subnetmask


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Subnet mask

Extended Network Prefix.

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

32 bits long. Divided into four octets.

Network and Subnet portions all 1s.

Host portions all 0s.

Default subnet mask: Example

192.168.2.100 / 255.255.255.0.

11000000.10101000.00000010.01100100.

11111111.11111111.11111111.00000000.

11000000.10101000.00000010.01100100. Class C network: 24 bits for network portion.

0 bits for subnet portion.

8 bits for host portion.

Subnet address: 192.168.2.0


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Subnet mask: Example

172.16.65.100 / 255.255.240.0.

10101100.00010000.01000001.01100100.

11111111.11111111.11110000.00000000.

10101100.00010000.01000001.01100100. Class B network:

16 bits for network portion.

4 bits for subnet portion.

12 bits for host portion.

Subnet address: 172.16.64.0.

How many bits can I borrow?

All of subnet bits are:

0 : reserved for network address.

1 : reserved for broadcast address.

The minimum bits you can borrow is:

2 bits. The maximum bits you can borrow is:

Number of host bits -2 bits

Slash mask is the sum total of all bits assigned tothe subnet field plus the fixed network bits. So172.16.1.100 with subnet mask 255.255.240.0 maybe written as 172.16.1.100/20


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Subnetting example

Given network 172.16.0.0.

We need 8 usable subnets and up to1000 hosts on each subnet.

Calculating a subnet

1. Determine the class of network anddefault subnet mask.

2. Determine how many bits to borrow.

Determine the subnet mask and theactual number of subnets and hosts.

3. Determine the ranges of host address foreach subnet. Choose the subnets thatyou want to use.


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Calculating a subnet: STEP 1

Determine the Class of network

Class B

Determine the default subnet mask

255.255.0.0

Calculating a subnet: STEP 2

Number of subnets


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Calculating a subnet: STEP 2 (Cont.)

The subnet mask: 255.255.240.0.


Determine the subnets from 4 borrowedbits from the host portion (last 2 bytes):

1st subnet: .00000000.00000000

2nd

subnet: .00010000.00000000 3rd subnet: .00100000.00000000

15th subnet: .11110000.00000000


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No

Sub-networkaddress

Possible host addressBroadcastaddress

Use?

0 172.16.0.0 172.16.0.1 172.16.15.254 172.16.15.255 N

1 172.16.16.0 172.16.16.1 172.16.31.254 172.16.31.255 Y

2 172.16.32.0 172.16.32.1 172.16.47.254 172.16.47.255 Y

.. .. .. .. ..

.. .. .. .. ..

13 172.16.208.0 172.16.208.1 172.16.223.254 172.16.223.255 Y

14 172.16.224.0 172.16.224.1 172.16.239.254 172.16.239.255 Y

15 172.16.240.0 172.16.240.1 172.16.255.254 172.16.255.255 N


Using subnets No.1 to No.8.

Assign IP addresses to hosts and

interfaces on each network. IP addressconfiguration.


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Lab Companion

10.3.5b Subnetting a Class A Network

10.3.5c Subnetting a Class B Network

10.3.5d Subnetting a Class C Network

Summary

Router protocol

Connection-oriented vs. connectionless

Process in router

IP packet structure

Routing protocol and routing table

Routing algorithm and metrics

Routing categories

Subnetting and calculate subnetworks


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Documents

CCNA1 M10 Routing Fundamentals Subnets