CCNA Exploration Semester 1-Chapter 4 pot

531 AOL Instant Messenger, IRC Source Port 16 bits | Destination Port 16 bits | ‘Well Known or Registered aa Port Number @ Well Known Ports Numbers 0 to 1023 | | ^ | Source Port 16 b

Cisco SYSTEMS

Networking manor

Chapter 4

Transport Layer

Cisco SYSTEMS

etworking

Academy —

Overview

® Explain the role of Transport Layer protocols and

services in Supporting communications across data

networks

® Analyze the application and operation of TCP

mechanisms that support reliability

@® Analyze the application and operation of TCP

mechanisms that support reassembly and manage data

loss

@® Analyze the operation of UDP to support communicate

between two processes on end devices

OSI Model TCP/IP Model

5 Session TCP U DP ¬ | 4.Transport | | Transport |

@® Transport Layer:

Responsible for creating and maintaining a logical connection

between the endpoints

@ What are the two protocols at the transport layer?

TCP — Transmission Control Protocol

UDP — User Datagram Protocol

Cisco SYSTEMS

etworking Academ _

Transport Layer Role and Services

@ Major functions of the transport layer and the role it plays

in data networks

— Tracking the individual communication between

applications on the source and destination hosts

— Segmenting data and managing each piece

— Reassembling the segments into streams of application

data

— Identifying the different applications

CISCO SYSTEMS

TCP Header UDP Header

Source Port (16 bits) Destination Port (16 bits) Source Port (16 bits) Destination Port (16 bits)

Sequence Number (32 bits) Length (16 bits) Checksum (16 bits)

Data

Reserved |© [4 [| |= |x

đun (6 bits) = 5 ta |2 = = Window (16 bits)

Checksum (16 bits) Urgent Pointer (16 bits) What is the application

PDU called?

Options and Padding

Application PDU: Data Header + data

Managing each segment

CISCO SYSTEMS /

Metworking

Academy

TCP vs UDP Streaming media, real-time multiplayer

games and voice over IP (VoIP) applications that do not require reliability mechanisms and may even

be hindered by them

Why would any application use UDP?

What is the “cost” of all this reliability

and flow control of TCP?

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New product opportunty | Oecrite new product we | Í 24sys 3 Presset engmeering

TCP

TCP TCP ISP’s

Cisco SYSTEMS

Networking manor

Port Numbers: TCP and UDP

UDP Header Port Numbers

4-bit Header 6-bit U AI PỊ RỊ SỊ F

Length (Reserved) 4 ` a n N N 16-bit Window Size HTT D is Po rt 80

16-bit TCP Checksum 16-bit Urgent Pointer

Options (if any)

Data (if any)

@ Both TCP and UDP use ports (or sockets) numbers to pass information to the

upper layers

12

Port numbers are used to

by the sender to tell the

receiver which network = Port Number Ỷ

application it should use

for the “Data”

Port numbers are used by

the receiver so it knows Port Number

which application it should

send the “Data” to

spr-itunes 0/tcb Shirt Pocket netTunes

spl-itunes 0/tcp Shirt Pocket launchTunes

tcpmux 1/tcp TCP Port Service Multiplexer

tcpmux 1/udp TCP Port Service Multiplexer

+ Mark Lottor <MKLénisc.sri.com>

compressnet 2/tcp Management Utility

compressnet 2/udp Management Utility

compressnet 3/tcp Compression Process

compressnet 3/udp Compression Process

+ Bernie Volz <volzécisco.com>

rje 5/tcp Remote Job Entry

rje 5/udp Remote Job Entry

+ David Nanian <dnanianéshirt-pocket.com> 28 September 2007

Port Number Range Port Group

0 to 1023 Well Known (Contact) Ports "

49152 to 65535 Private and/or Dynamic Ports

Well Known TCP Ports Well Known UDP Ports:

194 Internet Relay Chat (IRC) 461 SNMP

mm 531 AOL Instant Messenger, IRC

Source Port (16 bits) | Destination Port (16 bits) |

‘Well Known or Registered aa Port Number

@ Well Known Ports (Numbers 0 to 1023) | | ^ |

Source Port (16 bits) Destination Port (16 bits)

Reserved for common services and |

Client: TCP destination port

Port Number Range Port Group

0 to 1023 Well Known (Contact) Ports "

Registered UDP Ports:

1812 RADIUS Authentication Protocol Source Port (16 bits) Destination Port (16 bits)

2000 Cisco SCCP (VoIP)

5004 RTP (Voice and Video Transport Protocol) Well Known or Registered

Registered TCP/UDP Common Ports:

@ Registered Ports (Numbers 1024 to 49151)

Assigned to user processes or

Server: TCP source port ©

May also be used as dynamic or private

Port Number Range Port Group

somes Dost (26 Cate) Destination Port (16 bits) Source Port (16 bits) | Destination Port (16 bits) |

Well Known or Registered Well Known or Registered Private/Dynamic Port

@ Dynamic or Private Ports (Numbers 49152 to 65535)

Also known as Ephemeral Ports Usually assigned dynamically to client applications when initiating a connection

Client: TCP source port

Server: TCP destination port ©}

May also include the range of Registered Ports (Numbers 1024 to

62-proto-server.india.adventnet.com~

-Viminfo

AdventNet

CLIZ.QaprilO6 imp backup zip checkin

CLIaprilO3 zip hai.java

4-bit Header 6-bit UA P| R S| F

Length (Reserved) | 8} G 5} 5} ¥ 1 16-bit Window Size

KHTNN

16-bit TCP Checksum 16-bit Urgent Pointer

Options (if any)

Data for Telnet pata cf any

® Client sends TCP segment with:

Destination Port: 23 (Well Known port number)

source Port: 1028 (Dynamic Port assigned by client)

16-bit TCP Checksum 16-bit Urgent Pointer

Options (if any)

® Server responds with TCP segment with:

Destination Port: 1028 (Dynamic Port assigned by client)

source Port: 23 (Well known port number)

Server

CISCO SYSTEMS

16-bit Source Port Number 16-bit Destination Port Number 16-bit Source Port Number 16-bit D estination Port Number

32-bit Sequence Number 32-bit Sequence Number

32 bit Acknowledgem ent Number 32 bit Acknowledgem ent Number

4 bit Header 6-bt |U[ AlP|R|S| F | 4 bit Heater é-bit [UA PR S| F

Length (Reserved) Si q n 5 " N 16-bit Window Size Length (Reserved) cla HN M 16-bit Window Size

16-bit TCP Checksum 16-bit Urgent Pointer 16-bit TCP Checksum 16-bit Ur gent Pointer

Options Gif any) @ Options Gif any)

Client (initiating Telnet service):

———@® Destination Port = 23 (telnet)

-® Source Port = 1028 (dynamically assigned)

Server (responding to Telnet service):

-® Destination Port = 1028 (source port of client) ©}

>® Source Port = 23 (telnet)

Mobility '

Welcome to

Security TelePresence

@ Same client to same server - Two different HTTP sessions

@® Client: Same destination port

@® Client: Different source ports to uniquely identify this web session

Network Systems

Security TelePresence

Unified Communications

4 IH

@ Internet | Protected Mode: Off

Products & Services

16-bit Source Port Number

49890 16-bit Destination Port Number

Destination Port

State

\ Destination IP

TIME WALT TIME WALT

Connection State

⁄

What makes each connection unique? How does the server know

which source port 49888 is who?

@® Connection defined by the pair of numbers:

Source IP address, Source port (From Client to Server) Clon IP address, Destination port (From Server to ient

@ Different connections can use the same destination port on server

host as long as the source ports or source IPs are different 2B

WWW.CISCO.com

122.12.158.112:1332 1272.12.158.112:1333 1272.17.159.112:1334 1°72 17.1586.112:1335 122.12.158.112:1336

www.google.com

@ Note: When downloading a web document and its objects it is common that

there will be several TCP sessions created

198.133.213.25:808

198 133.219.25:86 198.133.213.25:80 64.154.86.254:86

66 162.7.99:86

State ESTABLISHED ESTABLISHED ESTABLISHED ESTABLISHED ESTABLISHED TIME_WAIT ESTABLISHED ESTABLISHED ESTABLISHED ESTABLISHED

netstat —n

26

Cisco SYSTEMS

Metworking Acadamy

Using NetStat

Open a web browser

Open a command prompt window (Start->Run->cmd)

Enter a URL of your choice

Type netstat —n in the command window

Questions:

What is/are the source ports on your client?

What is/are the destination ports on your client?

What would be the source port(s) on the server?

What would be the destination port(s) on the server?

What application layer protocol is being used? How can you tell?

What transport layer protocol is being used?

Trying more at home:

Use netstat to look at other networking applications such as FTP

or Telnet

27

16-bit Source Port Number 4 16-bit Destination Port Number Ea Data

16-bit UDP Length a 16-bit UDP Checksum Vv

@® What do you notice looking at the UDP protocol?

@® No frills, barebones transport protocol

Destination and Source Ports Length and Checksum (used for error checking)

16-bit UDP Length

Source port the number of the calling port

Sestination port the number of the called port

UDP length the length of the UDP header

Checksum the calculated checksum of the header and data fields

Data upper-layer protocol data

Cisco SYSTEMS

Metworking

Acadamy

30

Metworking

Academy

Current Directory |E: \ethernut-á 1.1 xnutXbinSarrn7tdmi Browse |

16-bit Source Port Number 16-bit Destination Port Number

Server interfaces |1321 69 192 222 xị

Tft

16-bit UDP Length 16-bit UDP Checksum p Server | Syslog server |

X| P4 [12/01 12:42:41.B22]

| File size : 104420 BT eae bee)

Data (if any) ; 13824 Bytes sent 13824 Bytes/sec

Clear Copy Current Action lead request for file <xsvfexec.bin> Mod

Why would an application developer choose UDP rather than TCP?

® Finer application-layer control

TCP will continue to resend segments that are not acknowledged

Applications that use UDP can tolerate some data loss:

streaming video

VoIP (Voice over IP)

Application decides whether or not to resend entire file: TF TP

16-bit Source Port Number 16-bit Destination Port Number

16-bit UDP Length 16-bit UDP Checksum Time

Data (if any)

CISCO SYSTEMS

Metworking Acadamy

16-bit Source Port Number 16-bit Destination Port Number

16-bit UDP Length 16-bit UDP Checksum Time

Data (if any)

@® Small packet header overhead

TCP header has 20 bytes of overhead

UDP header has only 8 bytes of overhead

Total: @ UDP checksum provides error detection, any changed|bits or missing segments 1111111111111111

® Simplified explanation (see RFC 1071 for more details):

@® Sender

UDP adds 16 bit ‘words’ keeping a cumulative sum

Performs one’s complement of the sum of all the 16-bit words in the segment

What if there is an error?

@ UDP does nothing to recover the error

® Itis up to the application layer protocol (example TFITP) to decide what to do,

such as prompt the user to download/upload the entire file again

395

5 2./390/76192.168.1.101 204.127.199.8 DNS Standard query A www.ucsc.edu

/ 2 2.78462:192.168.1.101 128.114.124.7 ICMP Echo (ping) request

8 2.875/66128.114.124./ 192.168.1.101 ICMP Echo (ping) reply

9 3./8/42.192.166.1.101 128.114.124./ ICMP Echo (ping) request

10 3.88614 128.114.124./ 192.168.1.101 ICMP Echo (ping) reply

@ Frame 5 Cf2 bytes on wire, “2 bytes captured)

@ Ethernet II, Src: 192.168.1.101 (€00:20:e0:6b:17:62), Dst: 192.168.1.1 (C00:0f:66:09:4e:0f)

Checksum: Ox68/2 [correct]

& Domain Name System Cquery)

Transaction ID: Ôx1c02

G Flags: Ox0100 (Standard query)

1 eee eee Response: Message iS a query

.000 0 Opcode: Standard query (0)

weee 2 Oe Lee, Truncated: Message is not truncated

¬ Recursion desired: Do query recursively

Gwww.ucsc.edu: type A, class IN

Name: www.ucsc edu

Type: A CHost address)

0000 00 OF 66 09 4e OF O00 20 eÖ 6b 17 62 06 00 45 00 †,M .k.b E

0010 00 3a 27 60 00 00 60 11 bd 9d cŨ a6 Ô1 65 cc /f wee wee e

0020 c7 08 04 21 00 35 00 26 68 72 Ic O2 O1 00 00 01 .1,3,& hr

0030 00 00 00 00 00 00 03 77 77 7/7 04 75 B3 73 63 013 W WW.UCSC

0040 65 64 75 00 00 01 00 01 edu

A-bit Header 6-bit UAP RS) F

Length (Reserved) | 8} G S| 5} ¥ 1 16-bit Window Size

4-bit Header 6-bit UA P/ RSF

Length (Reserved) | GS} s) ¥ 1 16-bit Window Size

source port the number of the calling port

destination port the number of the called port

sequence number the number used to ensure correct sequencing of the arriving

data

acknowledgment number the next expected TCP octet

HLEN the number of 32-bit words in the header

reserved set to 0

code bits the control functions (e.g setup and termination of a session)

window the number of octets that the sender is willing to accept

checksum the calculated checksum of the header and data fields

urgent pointer indicates the end of the urgent data

option one currently defined: maximum TCP segment size

data upper-layer protocol data sỹ

32 bit Acknowledgement Number 4-bit Head -bit Header 6-bit -bi UA P fs] : ~ _ Ỏ Send SYN,ACK (2) - - -

Length (Reserved) | R dSỊ sỈy 16-bit Window Size SYN received (SEQ=300 ACK=101 CTL=SYN,ACK)

— (SEQ=101 ACK=301 CTL=ACK | ——————— »

16-bit TCP Checksum 16-bit Urgent Pointer

@® For aconnection to be established, the two end stations must synchronize

on each other's TCP initial sequence numbers (ISNs)

® Exchanging beginning sequence numbers during the connection sequence

ensures that lost data can be recovered 40

= Cisco SYSTEMS Metworking

Academy

SYN, SEQ=8563

There are several reasons for có ;

this including segments that may Soe Por Nats 6 Desinatn Por Numb

still be in buffers and also STi Sequence None

security issues (Beyond the a ene te

scope of this presentation.) Sook woo AT ste

16-bit TCP Checksum 16-bit Urgent Pointer

eed

Web Server

® The three-way handshake happens before any data, HTTP Request (GET),

is sent by the client

@® A TCP client begins the three-way handshake by sending a segment with

the SYN (Synchronize Sequence Number) control flag set, indicating an

initial value in the sequence number field in the header

® The sequence number is the Initial Sequence Number (ISN), is

randomly chosen and is used to begin tracking the flow of data from the @ client to the server for this session

41