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  1. Agustin's Linux Manual
  2. Networks & Servers
  3. About the Author
  4. Table of Contents
  5. IP Addresses Networks and Subnets
  6. Network Classes
  7. IP Address in Decimal Notation
  8. Sub-netting
  9. Designing Subnets
  10. Allocating Subnets
  11. Defining Host Addresses
  12. Variable Length Subnet Mask
  13. Routing Protocols
  14. Classless Internet Domain Routing
  15. Servers - Chapter 9
  16. Apache Web Server
  17. Configuring Apache
  18. Uploading Web Pages
  19. Apache Overview
  20. MIMEMagic
  21. DNS Servers
  22. Welcome to Webmin
  23. Creating the Master Domain
  24. Adding the Reverse Zone
  25. Querying the DNS server
  26. Adding Virtual Domain to DNS Server
  27. Reverse Zone for Virtual Zone
  28. Binding IP Address for Virtual Domain
  29. Virtual Web Hosting
  30. DNS Security Options
  31. FTP Server
  32. Securing the FTP Server
  33. Email Server
  34. Postfix Configuration
  35. Dealing with Identical Users
  36. Configuring Email Clients
  37. Configuring Outlook
  38. Samba Server
  39. Configuring SAMBA Server
  40. The smb.conf File
  41. smb.conf Analysis
  42. Adding Users to Samba

Sub-netting

Some of you may not have the need, but I will show the rest of you how to subnet a network in this section.

RFC 950 (Request for Comments) defined a standard to divide network classes A, B, C, into smaller pieces, known as subnetting. Believe it or not, subnetting was used to overcome the problem that the Internet faced with the growth problem.

Subnetting allowed a three level hierarchy by introducing the subnet number. It was accomplished by dividing the host number into two parts.

Class and Subnet Hierarchy
Fig 8.4

As far as the Internet is concerned, the data goes through the router; and the router looks up in its entry to find out if there is a subnet number defined. If yes, the data is sent directly to the host number and doesn't really care where the host is, since it is in the same network prefix. (And by the way the subnet number is not visible outside the internal LAN.)

Network Prefix
Fig 8.5

But how exactly is the data handled? When data is requested from an internal LAN to the Internet, it passes through the router encapsulated with an ID number that identifies itself from where the data was requested. The remote server then returns the requested information to the router. The router then acknowledges that host X requested the information. The router verifies in its entry to find out in which subnet host X is located. If the subnet is verified positive, the information then is routed to the destination host X.

The internal network can have a very high complexity, but only the router knows it.

Private Network
Fig 8.6

Observe Fig. 8.6, with a single router = gateway and a single IP address. A system administrator can route several networks to the Internet, without affecting the growth of the Internet. All internal networks can access the Internet as long as the router is active.