OSI Model

OSI Model applied on TCP/IP

5 App
4 Transport  (segment TCP,UDP: port)
3Network    (packets IP)
2 Link       (frames)
1 Physical   (bits)

http://upload.wikimedia.org/wikipedia/commons/c/c4/IP_stack_connections.svg

http://upload.wikimedia.org/wikipedia/commons/3/3b/UDP_encapsulation.svg

Network Troubleshoot

Info from: http://www.petri.co.il/csc_how_to_use_the_osi_model_to_troubleshoot_networks.htm

Bottom up approach:

• Is your network cable plugged in? (physical)
• Is there a link light on the Ethernet switch and Ethernet NIC? (data-link)
• Do you have an IP address? (network)
• Can you ping your default gateway? (network, testing LAN IP connectivity)
• Do you have DNS server information?
• Can you ping your DNS server? (network, testing IP connectivity)
• Do you have a firewall configured? (network on up to application)
• Can you ping the host you are trying to get to by name? (application, DNS and network WAN IP connectivity)
• What format is the graphic in? Do you have a viewer for that format? (presentation)
• Can your web browser open up another website? (basic application troubleshooting)

More info

• http://www.infocellar.com/networks/osi-model.htm
• http://www.vlsm-calc.net/models.php

• http://en.wikipedia.org/wiki/TCP/IP_model
• http://en.wikipedia.org/wiki/Encapsulation_%28networking%29

OSI #	OSI Layer Name	TCP/IP #	TCP/IP Layer Name	Encapsulation Units	TCP/IP Protocols
7	Application	4	Application	data	FTP, HTTP, POP3, IMAP, telnet, SMTP, DNS, TFTP
6	Presentation			data
5	Session			data
4	Transport	3	Transport	segments	TCP, UDP
3	Network	2	Internet	packets	IP
2	Data Link	1	Network Access	frames
1	Physical			bits