Cisco Networking AcademyS2 C9

TCP/IP

TCP/IP

• ensure communication across any set of interconnected networks

• Stack components such as protocols to support file transfer, e-mail, remote login

• UDP unreliable transport• TCP reliable transport• ICMP provides control & message

functions at network layer

TCP/IP and OSI Comparison

• Protocols– TCP/IP Application/transport/Internet – OSI Application/Presentation/Session

• Networks– TCP/IP Network Access– OSI Physical, 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• E-mail• 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

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

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

• IP Internet Protocol

• ICMP Internet Control Message Protocol

• ARP Address Resolution Protocol

• RARP Reverse 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