ccna1-mod9-TCPIP

7/27/2019 ccna1-mod9-TCPIP

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Module 9 TCP/IP Suite and IP Addressing

CCNA 1 version 3.1

Hc vin mng Cisco BchKhoa - Website: www.ciscobachkhoa.com

Contents

9.1 Introduction to TCP/IP

9.2 Internet Addresses

9.3 Obtaining an IP Address


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In this module, we learn...

TCP/IP introduction; The four-layer model; Comparing with OSI model; IPv4 and its addressing; Subnet concept; Private and public addresses; IPv6 introduction; Dynamic and static IP addresses; ARP.

Overview

IP

TCP UDP

Ethernet PPP HDLC ...

HTTP SMTP SNMP ...


The U.S. Department of Defense (DoD) created the TCP/IP reference model. Itwanted a network that could survive any conditions.

TCP/IP also adopts layer model similar to OSI. There are four layers: NetworkApplication, Transport, Internet, and Network Access.

1981: IPv4. It is mostly used today. 1992: IPv6 (orIPng). It is not popular yet, however it is supported by most of

networking vendors.

Students needs to master the comparision between TCP/IP and OSI.

History in brief

LAN and WAN technology.

Best path determination and

packet switching.

Transport services from the

end to end.

High-level protocols, issues of

representation, encoding, and

dialog control.


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IPv4 Addresses

IPv4 addresses are 32 bits long, written in dotted

decimal, and separated by periods.


IPv6 Addresses

IPv6 addresses are 128 bits long, written in hexadecimal, and separated by colons. Colons

separate 16-bit fields. Leading zeros can be omitted in each field.


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The application l ayerof the TCP/IP model handles high-level protocols, issues

ofrepresentation , encoding, and dialog control. The TCP/IP protocol suitecombines all application related issues into one layer.

Application Layer


File Transfer Protoco l (FTP) is a reliable, connection-oriented service that uses TCP totransfer files. It supports bi-directional binary file and ASCII file transfers.

Trivial File Transfer Protocol (TFTP) is a connectionless service that uses the UDP.Example: TFTP is used on the router to transfer configuration files and IOS images.

Network File System (NFS) is a distributed file system protocol suite developed by SunMicrosystems that allows file access to a remote storage device.

Application Layer

IP

TCP UDP


FTP ... TFTP NFS


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IP

TCP UDP


SMTP Telnet ... ...

Simple Mail Transfer Protocol (SMTP) administers the transmission of e-mail over networks. It does not provide support for transmission of dataother than plaintext.

Terminal emulation (Telnet) provides the capability to remotely accessanother computer. It enables a user to log in to an Internet host and execute

commands.

Application Layer


IP

TCP UDP


... ... DNS SNMP

Simple Network Management Protocol (SNMP) is a protocol that provides away to monitor and control network devices, and to manage configurations,

statistics collection, performance, and security.

Domain Name System (DNS) is a system used on the Internet for translatingnames of domains and their publicly advertised network nodes into IP addresses.

Application Layer


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Transport protocols segment and reassemble upper-layer applicationsinto the same data stream between endpoints. The transport layer data

stream provides end-to-end transport services. There are two protocols in this layer: TCP (Transmission Control Protocol), and

UDP (User Datagram Protocol).

Transport Layer


The transport layer constitutes:A logical connection between the endpoints;

The sending host, and

The receiving host.

The Internet is often represented by a cloud. The transport layer sends datapackets from the sending source to the receiving destination through the

cloud.

There are varieties of techniques: silding windows, sequencing numbers andacknowledgments, etc.

Transport Layersending

host

receiving

host

logical

connection

Internet

cloud

TCP and UDP provide end-to-

end communications between

host applications over the

cloud of IP packets.


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TCP and UDP: Segmenting upper-layer application data;

Sending segments from end to end.

TCP only:

Establishing end-to-end operations (connection oriented); Flow control (end-to-end control) provided by sliding windows;

Reliability provided by sequence numbers and acknowledgments.

Transport Layer

That cloud of IP packets deal with the

issues such as Which of several paths is

the best path for a given route?


The purpose of the Internet layeris to select the best path through thenetwork for packets to travel. The main protocol that functions at this layer is

the Internet Protocol (IP). Best path determination and packet switching occurat this layer.

IP performs the following operations: Defines a packet and an addressing scheme;

Transfers data between the Internet layer and network access layers;

Routes packets to remote hosts.

Internet Layer Protocols


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Internet Protocol (IP) provides connectionless , best-effort delivery routing of packets. IPis not concerned with the content of the packets but looks for a path to the destination.

Internet Control Message Protocol (ICMP) provides control and messaging capabilities. Address Resolution Protocol (ARP) determines the data link layer address, MAC address,

for known IP addresses.

Reverse Address Resolution Protocol (RARP) determines IP addresses when the MACaddress is known.

Internet Layer Protocols

IP

TCP UDP

Ethernet, PPP, HDLC, ...

ARP/RARP

ICMP

InternetLayer


In a reliable

protocol, thereceiver

confirms (ACK)

the packet

its received.Example: TCP.

In a best

effort ornon-reliable

protocol,

the receiverkeeps silent

instead.Example: IP, UDP.

Reliable vs. Best-effort Protocols

Receiver:

I confirm that

Ive received

the packet #n.

Sender:

Ive sent the

packet #n.

Protocol:

I have the mechanism to know

if the packet is received.

Receiver:

I keep silence

upon receivingpackets.

Sender:

Ive sent thepacket #n.

Protocol:

I do not have the mechanism to

know if the packet is received.

This is a classification of networking protocols. Non-reliable does not mean inaccurately data delivery.


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Path Determination

The purpose of the Internet layer is to select the best path through the

network for packets to travel.

sender

receiver


The network access layer is also called the host-to-network layer. It includesthe LAN and WAN technologies. Examples:

Ethernet familly;

SLIP and PPP;

HDLC;

ARP and RARP.

In computers, we see them as system NIC drivers.

Network Access Protocols

ARP and RARP work at both Internet layer

and Network Access layer.


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Comparing TCP/IP and OSI

The Internet is developed by the standards of the TCP/IP protocols. The TCP/IP model gains

credibility because of its protocols. In contrast, networks typically are not built on the OSI

protocol. The OSI model is used as a guide for understanding the communication process.

TCP/IPTCP/IP OSIOSI


The OSI model & the TCP/IP model

Similarities of the OSI and TCP/IP models: Both have layers;

Both have application layers, though they include very different

services;

Both have comparable transport and network layers;

Packet-switched, not circuit-switched, technology is assumed;

Networking professionals need to know both models.

Differences of the OSI and TCP/IP models: TCP/IP combines the presentation and session layer; into its

application layer;

TCP/IP combines the OSI data link and physical layers into onelayer;

TCP/IP appears simpler because it has fewer layers;

TCP/IP transport layer using UDP does not always guarantee

reliable delivery of packets as the transport layer in the OSI model

does.


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The Internet Introduction

Interconnection between two LANs with a router

Interconnection between three LANs with two routers


The Internet Introduction

The Internet provide connections among a good number of users (300 million). Yet it appears

practically simple enough so that users view it as cloud where the reliable connection

sevice is provided between any two hosts, regardless to the hosts platforms. However, with

its bulky size (over 90 thousand routers), Internet is truelly complex, with a lot of standards,

protocols, ... getting involved.


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For any two systems to communicate, they must be able to identify and locateeach other. We call it addressing.

The hosts are grouped into networks. In the illustration, we use the A or B

to identify the network and the number sequence to identify the individual

host.

The combination of letter (network address) and the number (host address)create a unique address for each device on the network.

Addressing


An address generally represents the connection to the network. A device thathave two connection points may need two addresses beloging to two

networks.

Each connection points (espcially in LAN technologies) also has its ID(example: MAC address) which is called physical address. There is also the

need to map between physical adresses (layer 2) and logical addresses

(layer 3).

Addressing


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IP address is 32-bit long. It is often writen in dotted decimal format. CCNA is supposed to master the BIN-DEC conversion. Remember: practice

makes perfect.

IP Address (IPv4)


Every IP address has two parts. One part identifies the network where thesystem is connected, and a second part identifies that particular system on the

network.

Two different networks must have different network address (net-id), and twodifferent hosts in the same network must have different host address (host-

id ). Of cause, hosts in the same network have the same network address.

Addressing Rule


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A router forwards packets from the originating network to the destination

network using the IP protocol. The packets must include an identifier for both

the source and destination networks. Using the IP address ofdestinationnetwork, a router can deliver a packet to the correct network. When the

packet arrives at a router connected to the destination network, the router

uses the IP address to locate the particular computer connected to that

network.

Routing Introduction

ROUTER:

I has routing table

inside and I know how to

forward packets so that

they will reach the

destination.

ROUTER:

I has routing table

inside and I know how to

forward packets so that

they will reach the

destination.


Classes of IP Addresses

As a hierachical addressingscheme, IP addresses are

divided into classes.

Class A addresses areassigned to larger networks.

Class B addresses areused for medium-sized

networks, and

Class C for small networks.


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When all host-bits are zeros, we have a number that represents network

address. This address is reserved, namely it cannot be assigned to any host.

Network Address


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When host-bits are all one, we have a number that represents broadcastaddress. This address is also reserved, namely it cannot be assigned to any

host.

Example where Broadcast addresses are used: a host need to locate a specificservice.

Broadcast Address


Unicast and Broadcast Transmission

Unicast transmission Broadcast transmission

The concept of unicast and broadcast transmission exist in both layer 2

and layer 3 protocols. There are refelections in the addressing scheme.


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Certain host addresses are reserved and cannot be assigned to devices on a

network. These reserved host addresses include the following:

Host-bits = all zeros (network address);

Host-bits = all ones (broadcast address);

Network-bits = all ones;

Network-bits = all zeros;

127.x.x.x (loopback address = 127.0.0.1).

Reserved IP Address


The stability of the Internet depends directly on the uniqueness of publiclyused network addresses. In the figure, there is an IP conflict issue.A procedure was needed to make sure that addresses were in fact unique.

Originally, an organization known as the Internet Network Information Center

(InterNIC) handled this procedure. InterNIC no longer exists and has been

succeeded by the Internet Assigned Numbers Authority (IANA).

Required Unique Address


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Public IP addresses are unique. No two machines that connect to a public network can have thesame IP address.

Public IP addresses must be obtained from an Internet service provider (ISP) or a registry at someexpense.

With the rapid growth of the Internet, public IP addresses were beginning to run out (IP addressdepletion).

New addressing schemes, such as classless interdomain routing (CIDR) and IPv6 were developed tohelp solve the problem. Private IP addresses are another solution.

Public IP Addresses


RFC 1918 sets aside three blocks of IP addresses forprivate, internal use.These three blocks consist of one Class A, a range of Class B addresses,

and a range of Class C addresses.

Addresses that fall within these ranges are not routed on the Internetbackbone. Internet routers immediately discard private addresses.

Private IP Addresses


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When addressing a nonpublic intranet, a test lab, or a home network, wenormally use private addresses instead of globally unique addresses.

Private addresses can be used to address point-to-point serial links withoutwasting real IP addresses.

Connecting a network using private addresses to the Internet requirestranslation of the private addresses to public addresses. This translationprocess is referred to as Network Address Translation (NAT).

Using Private Addresses


Subnetting is another method of managing IP addresses. This method ofdividing fullnetwork address classes into smaller pieces has prevented complete IP addressexhaustion.

The network is no longer limited to the default Class A, B, or C network masks andthere is more flexibility in the network design.

Analogy: telephone. Subnet addresses include the network portion, plus a subnet field and a host field. To create a subnet address, a network administratorborrows bits from the host field

and designates them as the subnet field.

Introduction to Subnetting


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When TCP/IP was adopted in the 1980s (IPv4), it relied on a two-leveladdressing scheme.

The ClassA and B addresses make up 75% of the address space, howeverfewer than 17,000 organizations can be assigned a Class A or B network

number. Class C network addresses are far more numerous than Class A and ClassB addresses, although they account for only 12.5% percent of the possiblefour billion IP addresses. Unfortunately, Class C addresses are limited to 254usable hosts.

IP Address Depletion

Class A & B: virtually exhausted

Class C: nearly exhausted, too


IPv4 and IPv6 Addresses

IPv4

32-bit

IPv6

128-bit


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After years of planning and development, IPv6 is slowly being implemented in

select networks. Eventually, IPv6 may replace IPv4 as the dominant Internetprotocol.

IPv4 and IPv6

4.3 e 9 IP addresses

3.4 e 38 IP addresses


Obtaining IP Addresses

Devices come with MAC addresses (layer-2). However, IP addresses (layer-3) require proper

configuration. There are basically two ways to obtain IP addresses: static and dynamic .


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Static assignment works best on

small, infrequently changing

networks. The system administrator

manually assigns and tracks IP

addresses for each computer,

printer, or server on the intranet.

Good recordkeeping is critical to

prevent problems which occur with

dupli cate IP addresses.

Static assignment works best on

small, infrequently changing

networks. The system administrator

manually assigns and tracks IP

addresses for each computer,

printer, or server on the intranet.

Good recordkeeping is critical toprevent problems which occur with

dupli cate IP addresses.


RARP

Reverse Address Resolution Protocol (RARP) associates a known MAC addresseswith an IP addresses. This association allows network devices to encapsulate data

before sending the data out on the network. A network device, such as a diskless

workstation, might know its MAC address but not its IP address. RARP allows the

device to make a request to learn its IP address.


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RARP

Operation:

1: ARP request

2: ARP response3: RARP request

4: RARP response

5: Dynamic RARP request

6: Dynamic RARP response

7: Dynamic RARP error8: InARP request

9: InARP response

ARP and RARP share the

same packet format,

which is encapsulated on

layer-2 frames. Theydifferentiate themselves by

the operation field.


RARP

Hardware Type specifies a hardware interface type for which thesender requires a response (ie. ~layer 2).

Protocol Type specifies the type of high level protocol address thesender has supplied (ie. ~layer 3).


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RARP

HLen: Hardware address length.

PLen: Protocol address length.


RARP

Sender Hardware Address: Hardware address of the sender. Sender Protoco l Address : Protocol address of the sender. Target Hardware Address: Hardware address of the targer. Target Protocol Address: Protocol address of the target.


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RARP

The workstation boots, and then generates an RARP request. It broadcasts the request to all hosts (using layer-2 broadcast address). All other host discard the request, except the RARP server, who accepts it.

I needs

an IP

address!


RARP

The RARP servergenerates the RARP response which contain its answer. It broadcasts the response to all the hosts. The workstation receives the answer and set its IP address.

Thanks. From

now on, I am

192.168.10.36

Here it is:192.168.10.36!


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BOOTP

The bootstrap protocol (BOOTP) operates in a client-server environment and only requires a

single packet exchange to obtain IP information. However, unlike RARP, BOOTP packets can

include the IP address, as well as the address of a router, the address of a server, and vendor-

specific information, etc. BOOTP is encapsulated on UDP datagram.


BOOTP

Op: Message operation code; can be BOOTREQUEST or BOOTREPLY. Htype: Hardware address type. HLen: Hardware address length. Hops: Clients place zero, this field is used by BOOTP server to send request to another network.


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BOOTP

Xid: Transaction ID Seconds: Seconds elapsed since the client began the address acquisition or renewal process.


BOOTP

Ciadder: Client IP address. Yiadder: Your (client) IP address. Siadder: IP address of the next server

to use in bootstrap.

Giadder: Relay agent IP address used inbooting via a relay agent.

Chadder: Client hardware address.


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BOOTP

Server Host Name: Specifiesparticular server to get BOOTP

information from.

Boot File Name:Alow multiple boot files(example: for different OSes).

Vendor Specific Area: Optional vendorinformation that can be passed to the host.


BOOTP

The workstation boots, and then generates an BOOTP request. It broadcasts the request to all hosts (IP source address = unknown). All other host discard the request, except the BOOTP server, who accepts it.

I needs

an IP

address!


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BOOTP

The BOOTP servergenerates the BOOTP reply which contain its answer. It broadcasts the response to all the hosts. The workstation receives the answer and set its IP address.

Thanks. From

now on, I am

192.168.10.36

Here it is:

192.168.10.36!

I keep a profile

for each clients:

IP=..., MAC=...IP=..., MAC=...

IP=..., MAC=...


DHCP

Dynamic host configuration protocol (DHCP) is the successor to BOOTP. Unlike BOOTP, DHCP

allows a host to obtain an IP address dynamically without individual profile that the network

administrator having to set up for each device. All that is required when using DHCP is a defined

range of IP addresses on a DHCP server. The major advantage that DHCP has over BOOTP is

that it allows users to be mobile. DHCP offers a one to many ratio of IP addresses and that an

address is available to anyone who connects to the network.

client server

request

respon

se

client server

request

reply

client server

request

offer

request

ack

RARP BOOTP DHCP


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DHCP

DHCP uses the same message structure of BOOTP, withsome extentions (subnet masks, etc.) The idea is that the

entire network configuration of a computer can be

obtained in one message.


DHCP

The laptop boots, and then generates an DHCP request . It broadcasts the request to all hosts (to discover who is the server). All other host discard the request, except the DHCP servers, who accept it.

I needs

an IP

address!

Both of us aresupposed to

receive DHCP

messages.


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DHCP

The DHCP servers generates the DHCP offers which contain its answer. It broadcasts the response to all the hosts. The laptop receives the answers, select one of them (the first one).

OK, I accept

one offer of

yours.

My offer is:

192.168.10.35!

My offer is:

blah blah!


DHCP

The laptop sends DCHPREQUEST addressed to the specific DHCP serverthat has sent the accepted offer.

Heres my

DHCPREQUEST,

specifically for

you.

Good,

got it!


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DHCP

The DHCP server sends the DHCPACK And the laptop sets the IP address accordingly.

Thanks! From

now on I am

192.168.10.35!

Here is

the ACK


ARP

The issue of address mapping between level-2 and level-3 addresses are quite

relevent. In TCP/IP communication, a host needs to know both IP address and MAC

address of the destination host in order to send packet to it. So there comes Address

Resolution Protocol (ARP) which helps hosts in the same LAN segments to find each

other MAC addresses.


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Proxy ARP

Communications among LAN segments have an additional task. TCP/IP has a variation

on ARP called Proxy ARP that will provide the MAC address of an intermediate device

(example router) for transmission outside the LAN to another network segment.


Some devices keep the IP-MACmapping in a so-calledARP tablewhich is stored in RAM.

Example: arp -a, arp -d *. When a devices needs to send data

to a host --whose IP is known butMAC is unknown-- it send anARPrequest as a broadcast frame. Thenthe destination reply withARP reply.

Another way to build ARP table is tomonitorthe traffic.

Router generally do not forward suchthe broadcast. If this feature is turnedon, a router performs a Proxy ARP.

However, in reality, we apply thedefault gateway feature. When the

destination host is of the differentnetwork, then the IP packet is sent tothe default gateway (MAC) while IPaddress is set to the final destination.

If there is neither default gatewaynor Proxy ARP, no traffic can leavethe local network.

ARP

Please remember that both ARP and

RARP use the same message structure.


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Summary

Why the Internet was developed and how TCP/IP fits the design of the Internet The 4-layers of the TCP/IP model; the functions of each layerof the TCP/IP model The comparision between the OSI model and the TCP/IP model IP addressing gives each device on the Internet a unique identifier IP address classes are logical divisions of the address space used to meet the needs of

various sizes of networks

Subnetting is used to divide a network into smaller networks Reserved addresses fulfill a special role in IPaddressing and cannot be used for any

other purpose

Private addresses cannot be routed on the public Internet. The function of a subnet mask is to map the parts of an IP address that are the network

and the host

Someday IPV4 will be completely obsolete and IPV6 will be the commonly used version A computer must have an IP address to communicate on the Internet An IP address may be configured statically or dynamically, Dynamically IP addressing can be achived by using RARP,BOOTP orDHCP DHCP supplies more information to a client than BOOTP, DHCP allows computers to be

mobile

ARP and Proxy ARP can be used to solve address resolution problems

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