ISO/OSI Model Layers Application: applications that use the network. This is were mail, browsers, ftp, etc reside Presentation: data formats, character encoding, compression, encryption, ssl Session: Manages communication sessions. Examples: AppleTalk, name binding, netbios, rpc Transport: Data reliability, error checking, recovery, virtual circuits Network: Logical Addressing and routing Data Link: Interface addressing, flow control, low-level error notification Physical: Actual medium used to carry the data

TCP/IP Implementation

TCP/IP Definitions TCP – Transport Control Protocol A reliable, byte-stream, connection-oriented data delivery service UDP – User Datagram Protocol An unreliable, connectionless, low overhead protocol that uses datagrams to deliver data IP – Internet Protocol Provides the necessary information to allow the information to be routed from one computer to the next IGMP – Internet Group Management Protocol Provides the intercommunications required to manage multicasting between computers and routers ICMP – Internet Control Message Protocol Communicates error message and other conditions that require attention on the network

TCP/IP Definitions ARP – Address Resolution Protocol Discovers MAC addresses for given IP addresses RARP – Reverse Resolution Protocol Discovers IP addresses for given MAC addresses

MAC Addresses MAC addresses are unique numbers that are “burned” into a nic card –They are 6 bytes long –Each nic manufacturer is given a range of numbers to “burn” onto the cards –They are generally expresses as 12 hex numbers 00:02:B3:1D:E3:E4The MAC address of one nic card in the EOS lab –MAC Addresses are used solely within ethernet networks –All ethernet switches and nic cards use the MAC address to route frames from one machine to another.

Ethernet Frame Preamble Destination MAC Address Source MAC Address typeDataCRC Preamble –62 alternating 1’s and 0’s followed by 2 1’s –Used to synchronize the nic cards Destination MAC address –The MAC address the frame is supposed to go to –If the address is FF:FF:FF:FF:FF (all 1’s) the the frame is broadcast to all nic cards

Ethernet Frame Preamble Destination MAC Address Source MAC Address typeDataCRC Source MAC address –MAC address of the nic card sending out the frame Type –Indicated the type of data in the data field 0800IP data 0806ARP 0835RARP

Ethernet Frame Preamble Destination MAC Address Source MAC Address typeDataCRC Data –A minimum of 46 bytes to a max of 1500 bytes CRC –Error checking –If the CRC is wrong the frame is discarded without moving to the Network layer

IP Packet Version Header Length (IHL) Type of Service (TOS) Total Packet Length ID numberFlagsFragment Offset Time of Live (TTL)ProtocolChecksum Source IP Address Destination IP Address Options (if any) Data

TCP Packet Source PortDestination Port Sequence Number Acknowledgement Number Header Length ReservedFlagsWindow Size TCP ChecksumUrgent Pointer Options (if any) Data URGACKPSHRSTSYNFIN