1. CCNA 2 v3.1 Module 10 Intermediate TCP/IP

2. Objectives

3. TCP Operation
The transport layer is responsible for the reliable transport of and regulation of data flow from source to destination.

4. Synchronization or Three-Way Handshake
TCP is connection oriented
Communicating hosts go through a synchronization process to establish a virtual connection.
This synchronization process insures that both sides are ready for data transmission and allows the devices to determine the initial sequence numbers.

5. Denial-of-Service Attacks
Hacker initiates a SYN but spoofs the source IP address.
Target replies to the unreachable IP address and waits for final ACK.
Hackers floods target with false SYN requests tying up its connection resources, preventing it from responding to legitimate connection requests.

6. TCP Sequence and Acknowledgment Numbers

7. Positive ACK
Acknowledgement is a common step in the synchronization process which includes sliding windows and data sequencing.

8. Sequence and ACK numbers
Each TCP segment is numbered before transmission so that the receiver will be able to properly reassemble the bytes _____________________.
They also identify missing data pieces so the sender can ____________ them.
Only the _________________ need to be re-transmitted.
in their original order
retransmit
missing segments
Positive Acknowledgement and Retransmission
TCP utilizes PAR to control data flow and confirm data delivery.
Source sends packet, starts timer, and waits for _____.
If timer expires before source receives ACK,source __________________ and ______________.
ACK
retransmits packet
re-starts timer

9. Acknowledgements

10. Flow Control
Flow control is used to control the data flow between the connection.
If for any reason one of the two hosts are unable to keep up with the data transfer, it is able to send special signals to the other end, asking it to either stop or slow down so it can keep up.
Windowing is the number of data segments the transmitting machine is allowed to send without receiving an acknowledgment for them

11. TCP Sliding Window

12. Windowing and Window Size
_______________ determines the amount of data that you can transmit before receiving an acknowledgment.
Window size
I didn’t get all of that, slow down.
Fast enough for you?
Sliding window refers to the fact that the window size is negotiated ___________ during the TCP session.
dynamically
Expectational acknowledgment means that the acknowledgment number refers to the octet that is ______________.
next expected
If the source receives no acknowledgment, it knows to retransmit at a ________ rate.
slower

13. TCP Segment Format Number of the calling port
Number of the called port
Used to ensure correct sequencing of the arriving data
Next expected Segment
Number of 32-bit words in the header
Number of octets sender is willing to accept
Control setup and termination of session
set to zero
Indicates the end of the urgent data
Upper layer protocol data

14. Protocol Graph: TCP/IP

15. UDP
Applications that do not need guaranteed delivery use the faster UDP.
UDP has no windowing or acknowledgments, or error detection.
TCP and UDP:
TCP enables connection-oriented, ________ transmission.
TCP is used by ________________________
UDP provides, ______________ non-guaranteed transmission.
UDP is used by __________________________.
reliable
FTP, HTTP, SMTP, and DNS.
connectionless
DNS, TFTP, SNMP, and DHCP

16. Specifies the application/protocol to which UDP needs to pass the data
UDP Segment Format
 – 
 
 
 – 
64 
Source Port
Destination Port
Length
Checksum
Data…
Optional - used only if
reply is expected
Specifies the application/protocol to which UDP needs to pass the data
Number of octets in
the UDP segment
Ensure that the data
has not been damaged
during transmission

17. Port Numbers and Socket

18. Port Numbers

19. Telnet Port Numbers

20. Ports for Clients
Whenever a client connects to a service on a server, a source and destination port must be specified.
TCP and UDP segments contain fields for source and destination ports.

21. Ports for Clients
The port number combines with the network address to form a socket.
Destination ports (services) are normally defined using the well-known ports.
Source ports set by the client are determined dynamically.
Usually source ports are randomly assigned a number above 1023.
Destination Port
Source Port
1. Client requests a web page from server
2. Server responds to client
1032 80 80
1032
Port numbers are 16-bit values ranging from 0 to
This range is divided into three different categories:
Below 1023 are well-known ports.
1024 to are registered ports (used by ordinary user processes).
Between and are defined as dynamic or private ports.

22. Port Numbering and Well-Known Port Numbers
Port numbers are divided into three different categories:
Well-known ports
Registered ports
Dynamic or private ports

23. Overview of Transport Layer Ports
Both _____ and _____ use port or socket numbers.
TCP
UDP
__________ work as source and destination addresses for TCP segments.
Port Nos.
Ports ensure packets reach the ______________________ on the server.
appropriate service
The _________________ field determines which service the source is requesting.
destination port
TCP/IP associate ______ at the transport layer with certain applications.
ports
Software developers have agreed on ____________ ports, for example:
a packet bound for an FTP server would use port ___.
well-known 21
Conversations that do not involve applications with well-known ports are assigned ports __________ selected from a specific range.
randomly
Port numbers have the following assigned ranges:
Below 255 are reserved for ___________________.
From ___ - ____ assigned to companies for marketable applications.
Above 1023 are ____________.
public applications
255
1023
unregulated
Source port numbers are dynamically assigned by the originating host, and are usually a number larger than _____.
1023
Port numbers in the range of _____ - _____ are controlled by ICANN.
1023

24. Reserved TCP and UDP Ports for Services
Key Word
Description
Reserved
1-4
Unassigned 5
RJE
Remote Job Entry 7
ECHO
Echo 9
DISCARD
Discard 11
USER
Active Users 13
DAYTIME
Daytime 15
NETSTAT
Who is UP on NETSTAT 17
QUOTE
Quote of the Day 19
CHARGEN
Character generator 20
FTP-DATA
FTP – Data channel 21 23 25 37
TIME
Time of day 39
RLP
Resource Location 42
NAMESERVER
Host Name Server 43
NICNAME
Who is… 53
Port
Key Word
Description 67
BOOTPS
BOOTP Server 68
BOOTPC
BOOTP Client 69 75
Any private Dial-out 77
Any private RJE service 79
FINGER
Finger 80 95
SUPDUP
SUPDUP Protocol
101
HOSTNAME
NIC Host name server
102
ISO-TSAP
110
113
AUTH
Authentication Service
117
UUCP-PATH
UUCP Path Service
123
NTP
Network Time Protocol
Unassigned
Reserved
161
HTTP
Hyper-Text Transfer
TELNET
Terminal connection
SMTP
Simple Mail Transfer

25. Reserved TCP and UDP Port Numbers

26. Summary