Cisco Networking Academy S2 C9 TCP/IP

ensure communication across any set of interconnected networks Stack components such as protocols to support file transfer, , remote login UDPunreliable transport TCPreliable transport ICMPprovides control & message functions at network layer

TCP/IP and OSI Comparison Protocols –TCP/IP Application/transport/Internet –OSIApplication/Presentation/Session Networks –TCP/IPNetwork Access –OSIPhysical, Datalink, Network, Transport Protocol Stack –Transport to Transport –Network to Internet –Data Link & Physical to Network Access

TCP/IP is Important TCP/IP is a universally available protocol that you likely will use at work. TCP/IP is a useful reference for understanding other protocols because it includes elements that are representative of other protocols. TCP/IP is important because the router uses it as a configuration tool. TCP/IP enables communication among any set of interconnected networks and is equally well suited for both LAN and WAN communication

Transport Layer UDP –Connectionless, unreliable, no acknowledgements, is fast TCP –Connection oriented, flow control through sliding windows, re-sends anything not received, supplies virtual circuit between end- user applications; guaranteed delivery of segments

Application Layer DNS Hosts File FTP Telnet Tracert Netscape Explorer Ping NEBstat NETstat

TCP Fields source port -- the number of the called port sequence number -- the number used to ensure correct sequencing of the arriving data acknowledgment number -- the next expected TCP octet HLEN -- the number of 32-bit words in the header reserved -- set to 0 code bits -- the control functions (e.g. setup and termination of a session) window -- the number of octets that the sender s willing to accept checksum -- the calculated checksumof the header and data fields urgent pointer -- indicates the end of the urgent data option -- one currently defined: maximum TCP segment size

UDP Segment Format Source Port Destination Port Length Checksum Data

Port Numbers 21FTP 23 Telnet 25TMTP 53DNS 69TFTP 161SNMP

Three-Way Handshake A three-way handshake is necessary because TCPs may use different mechanisms for picking the ISN. either side can break the communication because TCP is a peer-to-peer (balanced) communication method TCP uses expectational acknowledgments, meaning that the acknowledgment number refers to the octet expected next.

Network Layer IPInternet Protocol ICMPInternet Control Message Protocol ARPAddress Resolution Protocol RARPReverse Address Resolution Protocol

IP Datagram VERS HLEN Type of Service Total Length Identification Flags Frag offset TTL Protocol Header Checksum Source IP address Destination IP address IP options Data

ICMP Defined Messages Destination Unreachable Time to Live Exceeded Parameter Problem Source Quench Redirect Echo Echo Reply Timestamp Timestamp Reply Information Request Information Reply Address Request Address Reply Echo is a successful reply to a ping command