1. 1 Version 3.1 Module 10 Intermediate TCP/IP (Layer 4)

2. 2 Version 3.1 TCP Protocol (Layer 4) Three Functions: Flow Control Reliability by sequence numbers and acknowledging Synchronization Two Protocols: TCP connection oriented UDP (tftp, DNS, SNMP) Connectionless

3. 3 Version 3.1 Three-Way Handshake This handshake establishes a round trip connection between sender and receiver before data is transferred

4. 4 Version 3.1 Denial of Service Attacks Designed to deny services to legitimate hosts attempting to establish connections. Commonly used by hackers - hacker initiates a synchronization but spoofs the source IP address (non- existent IP address) Administrators should guard against by –Decreasing the connection timeout period –Increase the connection queue size

5. 5 Version 3.1 With a window size of 1, each segment has to be acknowledged before another segment is sent. Inefficient use of bandwidth. Windowing

6. 6 Version 3.1 With windowing, data can be sent without an acknowledgment when sending a TCP segment. Communicating devices negotiate the amount of unacknowledged data that can be sent. TCP Sliding Windows

7. 7 Version 3.1 Sequencing Numbers TCP applies sequence numbers to the data segments it is transmitting so that the receiver will be able to properly reassemble the bytes in their original order. If TCP segments arrive out of order, the segments may be reassembled incorrectly. Sequencing numbers indicate to the destination device the correct order in which to put the bytes when they are received

8. 8 Version 3.1 Sequencing Numbers: Act as reference numbers so that the receiver will know if it has received all of the data Identifies missing data pieces to the sender so it can retransmit the missing data The sender only needs to re-transmit back to the missing segments instead of the entire set of data Each TCP segment is numbered before transmission At the receiving station, TCP uses the sequence numbers to reassemble the segments into a complete message If a sequence number is missing in the series, that segment is re- transmitted Positive Acknowledgment & Retransmission (PAR) ensures that the number of data segments sent by one host are received by another host before other segments are sent

9. 9 Version 3.1 UDP Connectionless Layer 4 protocol Non-guaranteed delivery UDP segments do not contain sequence or acknowledgement fields, so checksum is used to determine if the data or header has been transferred without corruption

10. 10 Version 3.1 Multiple Conversations and Port Numbers

11. 11 Version 3.1 Port Numbers The three categories of port numbers are: well-known ports, registered ports, and dynamic or private ports. 0 - 1023 are well-known ports. 1024 to 49151 are Registered ports 49152 – 65,535 are defined as dynamic or private ports. End systems use port numbers to select proper applications Port numbers in the range of 0-1023 are controlled by the Internet Assigned Numbers Authority (IANA) Well known ports (21, 23, 80) - dynamic port numbers are represented in the header of TCP & UDP segments

12. 12 Version 3.1 Port Numbers FTP DATA - Port 20 FTP - Port 21 Telnet -Port 23 SMTP - Port 25 DNS - Port 53 TFTP - Port 69 SNMP - Port 161 TCP Examples: UDP Examples:

13. 13 Version 3.1 Port numbers, MAC, & IP Addresses are included during encapsulation Port numbers IP addresses MAC addresses Network Layer Data Link Layer Transport Layer

14. 14 Version 3.1 Module 10 Intermediate TCP/IP (Layer 4) End