Transmission Control Protocol TCP

Transport layer function

3-Way Handshake TCP hosts establish a connection-oriented session with one another using a ______________________. A virtual connection _________________________________ _________________________________ ________________________________ The process occurs by…

3-Way Handshake cont… Host 1 sends a ____ packet to Host 2 (1st data packet) Host 2 _____ the packet from Host 1 (2nd data packet) ______________________________________ for Host 1 (2nd data packet) Host 1 __________ packet from Host 2 (3rd data packet) Communication can now begin

DoS using SYN flooding Denial of service (DoS) attacks are designed to ______________________ _______________________________ SYN flooding exploits the normal three- way handshake causes targeted devices (generally a server) to __________________________________ ____________________________________ Never completing the handshake and keeping the server in a state of wait During this time, memory is allocated until the connection times out The server get flooded with these types of requests

Solutions to this type of DoS system administrators may _______ _____________________________ _____________________________ Purchase additional software used to detect and defend against these types of attacks

Review of these fields to follow…

TCP Segment Fields Following are the definitions of some of the fields in the TCP segment:  Source port -- __________________________  Destination port -- _______________________  Sequence number -- number used to ________ _____________________________________  Acknowledgment number - ______________ __________________________  Window -- number of octets that the sender is ______________________________________ _____________________________________  More to come…..

TCP simple acknowledgment and windowing Window size determines the ______ __________________________________ __________________________________ ___________ (ACK) from the destination TCP “Sliding Windows” _______________ __________________ by negotiating the window size to account for more or less segments to be transmitted as conditions warrant TCP _______________________________ __________________________________

TCP Sequencing Each segment is numbered before transmission. _______________________________ ______________________________ If a sequence number is missing in the series, retransmission is needed NOTE: the ACK (and SYN) field aka code field

Review- UDP Segment Fields UDP very simple segment Header contains 4 fields Least amount of info as possible UDP header determines the application to which a UDP segment will be delivered. Calculated sum of header and data fields

TCP & UDP Port Number Review Both TCP and UDP use port (or socket) numbers to pass information to the upper layers. _________________________________________ _________________________________________ _________________________________________ 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. Port numbers in the range of _________________ ___________________________________ (IANA) Well known and agreed upon port numbers…

Review of Common Port Numbers Numbers below are for public applications- most common are… FTP, Telnet, SMTP, and HTTP- port #80 (for TCP) TFTP for UDP

Need for ports… A host might have a telnet connection (port 23) open, 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. Each conversation on the source side needs its own port number, and each service requested needs its own port number (ports 23 and 80). SOCKET = _________________________ __________________________________

Mod 10 LAB Finish previous MOD labs Lab 10-1: Multiple Active Host Sessions Lab 10-2: Well –Known port numbers and multiple sessions Start reviewing for hands-on-practical Know how to program an “out-of-the-box” router using line commands only- NOT setup mode