TCP/IP Honolulu Community College Cisco Academy Training Center Semester 2 Version 2.1

Overview 1. TCP/IP implementation of the OSI model. 2. TCP/IP functions: - of the transport layer. - of the network layer. 3. ICMP - Internet Control Message Protocol - control and message functions (network layer).

TCP/IP Introduction n Internet protocols communicate across any interconnected networks: LANs, MANs, WANs,.... n Internet Protocol suite includes: u Layer 3 and 4 specifications (such as IP and TCP). u Specifications for applications such as , remote login, terminal emulation, and file transfer. u Reliable and “unreliable” transport. u Connectionless datagram delivery at the network layer.

TCP IP

TCP/IP Protocol Stack n Maps closely with OSI model. n Supports all standard physical and data-link protocols, i.e. Ethernet, 802.3, 802.5, FDDI. n TCP/IP info is transferred in a sequence of datagrams, which are reassembled at the receiving location. OSI TCP/IP

Application Layer Overview n Application protocols support: u File transfer, , Remote login, Network management.

Transport Layer Overview n Transport Layer provides: u Flow Control - using windowing. u Reliability – via acknowledgments and sequence numbers. n Two transport layer protocols: u TCP - Transmission Control Protocol F connection-oriented, reliable protocol. u UDP - User Datagram Protocol F connectionless, ‘unreliable’ protocol.

TCP and UDP n TCP: u Breaks messages into segments, then reassembles them at destination. u Resends anything not received correctly. u Provides a virtual circuit between end-users. u Virtual circuits (connection oriented) use sequenced segments with acknowledgments and retransmission: reliable. n UDP: u Transmits messages. u No checking for segment delivery - “unreliable”. u Unsequenced, unreliable, connectionless, low overhead.

TCP Segment Format n TCP assembles the information into segments that follow a defined format.

Port Numbers n Used by TCP and UDP. n Identifies the specific application. n Ports 255 and below are for frequently used applications. n Ports 255 to 1023 are reserved for private use (assigned to companies). n Ports above 1023 are unregulated. n End systems use port numbers to select the proper application.

TCP 3-way Handshake: Synchronization n Both ends of the connection are synchronized with a three-way handshake/open connection sequence. Exchanging beginning sequence numbers ensures that lost data can be recovered if problems occur later.

TCP Sliding Window n Window size - # of data packets that can be sent while awaiting acknowledgement. n Larger window size allows more data to be transmitted pending acknowledgment. n Expectational acknowledgement - ACK number of next expected data packet. n Sliding window - window size is negotiated dynamically during TCP session. n Sliding window - more efficient use of bandwidth.

UDP Segment Format n UDP uses simpler format. n No windowing or acknowledgments. n Protocols that use UDP include: u TFTP, SNMP, NFS (network file system), DNS (domain name system).

Network Layer Protocols n Network Layer Protocols include: n IP - connectionless, best-effort delivery routing. n ICMP - control and messaging capabilities. n ARP - to determine MAC (hardware) addresses for know IP addresses. n RARP - to determine IP (logical or network) addresses from know MAC addresses.

IP Datagram IP header includes: Source and destination ip addresses. Protocol field. Checksum.

ICMP - Internet Control Message Protocol n Implemented on all TCP/IP hosts. n Used for error and control messages, i.e. u Destination Unreachable u Time Exceeded u Parameter Problem u Source Quench u Redirect u Echo & Echo Reply u Timestamp & Timestamp Reply u Information Request & Information Reply u Address Request & Address Reply

ICMP Example (1) n If a router is unable to deliver a packet, it sends an ICMP host unreachable message to the source.

ICMP Example (2) n An echo reply is a successful reply to a ping command.

ARP - address resolution protocol n Maps known IP address to a MAC address. n For destination IP address, ARP table is checked. n If no ARP entry, ARP request is broadcast. n Host with the known IP address responds with its MAC address. n Prior to ARP broadcast, subnet mask is consulted, to determine that node is on the same subnet.

Reverse ARP - RARP n Used if host does not know its IP address. n Requires a RARP server.

Summary (1) n TCP & UDP operate at Transport Layer. n Transport Layer Protocol: u supports application layer functions like FTP, , and remote login. u Provides reliable (TCP) and unreliable (UDP) transport. n Port Numbers - used to identify the application. n TCP Segment Format include: u port numbers, Sequence number, Window size, Checksum.

Summary (2) n UDP Segment Format: u no windowing or acknowledgements. u Used by TFTP, SNMP, NFS, DNS. n IP operates at the Network Layer. u Connectionless, best-effort delivery. n Network Layer features include: u ICMP, ARP, RARP n IP Datagram Header u Version, header length, total length, TTL. u Protocol Field - identifies Layer 4 protocol used. u IP address - source and destination.