1 CCNA 2 v3.1 Module 10

2 Intermediate TCP/IP CCNA 2 Module 10

333 TCP/IP Operations IP addresses Allow for the routing of packets between networks Makes no guarantees about delivery Transport layer is responsible for Reliable transport of data and regulation of data flow from source to destination This is accomplished using sliding windows sequencing numbers a synchronization process that ensures each host is ready and willing to communicate

444 TCP/IP Segment Format

555 Synchronisation – 3 way handshaking Prior to data transmission the two communicating hosts go through a synchronization process to establish a virtual connection This synchronization process Insures both sides are ready for data transmission Allows the devices determine the initial sequence numbers

666 Synchronisation – 3 way handshaking

777 Sequence Numbers Part of initiating communication between the two devices Act as reference starting numbers between the two devices Give each host a way to ACK the SYN so that the receiver knows the sender is responding to the proper connection request

888 Denial Of Service Attacks Denial of service attacks (DoS) Designed to deny services to legitimate hosts attempting to establish connections Common method that hackers utilize to halt system response One type of DoS is known as SYN flooding Exploits the normal three-way handshake and causes targeted devices to ACK to source addresses that will not complete the handshake

999 SYN Flooding In a DoS attack, the hacker initiates a synchronization but spoofs the source IP address To defend against these attacks, system administrators may decrease the connection timeout period and increase the connection queue size.

10 Windowing and Window Size Sliding window allows the destination device to indicate to the source a need to decrease or increase the amount of data being sent because it is incapable at that time of dealing with that much data

11 Sequencing numbers

12 Positive Acknowledgment and Retransmission (PAR) With PAR, source sends a packet, starts a timer, and waits for an ACK before sending the next packet If timer expires before source receives an ACK, the source retransmits the packet and restarts the timer TCP uses expectational acknowledgments - ACK number refers to the next octet that is expected

13 UDP operation Not all applications need to guarantee delivery of the data packet They use UDP a faster, connectionless delivery Described in RFC 768 protocol that exchanges segments without acknowledgments or guaranteed delivery Does not use windowing Does not use acknowledgments Application layer protocols must provide error detection

14 Overview of Transport Layer Ports

15 Multiple Conversations Between Hosts A port number must be associated with the conversation between hosts to ensure that the packet reaches the appropriate service on the server Without a way to distinguish between different conversations, the client would be unable to send both an and browse a web page, using one server at the same time

16 Ports for Services

17 Ports for Services continued…

18 Ports for Clients Destination ports - ports for services Normally defined using the well-known ports Source ports Set by the client are determined dynamically Client determines the source port by randomly assigning a number above 1023

19 Port numbering & well-known port no’s Port numbers are represented by 2 bytes in the header of a TCP or UDP segment 16-bit value - port numbers from 0 to Port numbers are divided into 3 categories 1 to 1023 ports are well-known ports 1024 to are registered ports to are defined as dynamic or private ports

20 Multiple Sessions Between Hosts A pair of sockets, one on each host, forms a unique connection. For instance, a host might have a telnet connection, port 23, while at the same time be surfing the net, port 80. The IP and the MAC addresses would be the same because the packets are coming from the same host.

21 Sockets Transport layer Port numbers are located here Serviced by the network layer The network layer assigns the logical address (IP address) is then serviced by the data link layer Data link layer assigns the physical address (MAC address)