ISO/OSI Model Layers Application: applications that use the network. This is were mail, browsers, ftp, etc reside Presentation: data formats, character.

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 ProtocolAn unreliable, connectionless, low overhead protocol that uses datagrams to deliver data

• IP – Internet ProtocolProvides the necessary information to allow the information to be routed from one computer to the next

• IGMP – Internet Group Management ProtocolProvides the intercommunications required to manage multicasting between computers and routers

• ICMP – Internet Control Message ProtocolCommunicates error message and other conditions that require attention on the network

TCP/IP Definitions

• ARP – Address Resolution ProtocolDiscovers MAC addresses for given IP addresses

• RARP – Reverse Resolution ProtocolDiscovers 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:E4 The 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

PreambleDestination

MAC AddressSource

MAC Addresstype Data CRC

8 6 6 2 46-1500 4

• 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

PreambleDestination

MAC AddressSource

MAC Addresstype Data CRC

8 6 6 2 46-1500 4

• Source MAC address– MAC address of the nic card sending out the frame

• Type– Indicated the type of data in the data field

0800 IP data

0806 ARP

0835 RARP

Ethernet Frame

PreambleDestination

MAC AddressSource

MAC Addresstype Data CRC

8 6 6 2 46-1500 4

• 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

VersionHeader Length (IHL)

Type of Service (TOS)

Total Packet Length

ID number Flags Fragment Offset

Time of Live (TTL) Protocol Checksum

Source IP Address

Destination IP Address

Options (if any)

Data

0 4 8 16 32

TCP Packet

Source Port Destination Port

Sequence Number

Acknowledgement Number

Header Length

Reserved Flags Window Size

TCP Checksum Urgent Pointer

Options (if any)

Data

0 4 8 16 32

URG ACK PSH RST SYN FIN