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  1. Introduction
  2. Network Model
  3. Topology
  4. Physical Media
  5. Wireless Media
  6. Network Card
  7. Modems
  8. Outside Connections
  9. Wide Area Network Connections
  10. Repeaters, Bridges, Routers
  11. Network Types
  12. Ethernet
  13. Token Ring
  14. ARCnet
  15. AppleTalk
  16. FDDI
  17. Architecture Comparisons
  18. Categories
  19. TCP/IP
  20. IPX/SPX
  21. NetBEUI
  22. AppleTalk
  23. SNA
  24. Others
  25. Suites and Network Layers
  26. Installing Drivers
  27. DNS
  28. Network Operating Systems
  29. Applications, mail, groupware, DBMS
  30. Backing up the network
  31. Troubleshooting
  32. Web, SNMP, admin, firewalls
  33. Networking Terms and Definitions
  34. Credits


TCP/IP protocols include:

  • FTP - File Transport Protocol at the application layer.
  • Telnet - Remote session at the application layer.
  • SMTP - Simple Mail Transport Protocol at the application layer.
  • DHCP - Dynamic host configuration protocol is used to assign IP addresses dynamically to network cards. It works at the application layer.
  • TCP - Transport Control protocol is a connection oriented reliable protocol working at the transport layer.
  • UDP - User Datagram Protocol is a connection less unreliable protocol working at the transport layer.
  • ICMP - Internet Control Message Protocol is used to perform network error reporting and status. It works at the transport layer.
  • IGMP - Internet Group Management Protocol is used to manage multicast groups and it works at the transport layer.
  • IP - Internet Protocol is used for software addressing of computers and works at the data link layer.
  • ARP - Address Resolution Protocol is used to resolve the hardware address of a card to package the ethernet data. It works at the data link layer.
  • RARP - Reverse Address Resolution Protocol used for disk less computers to determine their IP address using the network. It works at the data link layer.

These give a sample of some of the TCP/IP protocols and there are many more.

Class A-E networks

The addressing scheme for class A through E networks is shown below. Note: We use the 'x' character here to denote don't care situations which includes all possible numbers at the location. It is many times used to denote networks.

Network TypeAddress RangeNormal MaskComments
Class A001.x.x.x to 126.x.x.x255.0.0.0For very large networks
Class B128.1.x.x to 191.254.x.x255.255.0.0For medium size networks
Class C192.0.1.x to 223.255.254.x255.255.255.0For small networks
Class D224.x.x.x to
Class E240.x.x.x to

RFCs 1518 and 1519 define a system called Classless Inter-Domain Routing (CIDR) which is used to allocate IP addresses more efficiently. This may be used with subnet masks to establish networks rather than the class system shown above. A class C subnet may be 8 bits but using CIDR, it may be 12 bits.

There are some network addresses reserved for private use by the Internet Assigned Numbers Authority (IANA) which can be hidden behind a computer which uses IP masquerading to connect the private network to the internet. There are three sets of addresses reserved. These address are shown below:

  • 10.x.x.x
  • 172.16.x.x - 172.31.x.x
  • 192.168.x.x

Other reserved or commonly used addresses:

  • - The loopback interface address
  • - This is reserved for hosts that don't know their address and use BOOTP or DHCP protocols to determine their addresses.
  • 255 - The value of 255 is never used as an address for any part of the IP address. It is reserved for broadcast addressing.