1. Planning the Addressing Structure
Working at a Small-to-Medium Business or ISP – Chapter 4

2. Implementation of IP Addressing in the LAN
IP addresses are made up of 32 total bits
divided into 4 octets with a decimal separating them
AKA: dotted decimal notation

3. IP Addressing IP addresses are HIERARCHIAL (like a family tree)
there are parents (networks)
there are children (hosts)

4. IP Address Classes Classes A – C Class D – reserved for multicasts
assigned to users
Class D – reserved for multicasts
Class E -- reserved for experimental use

5. Private IP Addressing
Private IP addresses assigned by IETF (Internet Engineering Task Force)
reduces the number of public IP addresses assigned to organizations

6. Implementation of IP Addressing in the LAN
SUBNETS

7. IP Addressing Practice
Class C address with a default subnet mask.
Question 1 – What is the default subnet mask
Question 2 – How many usable hosts are available?
254
IPv4
Question 1 – Class which provides the largest number of network bits?
Class C
Question 2 – Class which provides the largest number of hosts per network?
Class A

8. IP Addressing Practice
Class B address
Question 1 – What is the default subnet mask
Question 2 – The IP address is with a default subnet mask. What is the broadcast address for this network?
IPv4
Question 1 – The IP address is with a subnet mask of What is the maximum number of sub networks that could be created.
6 networks
Question 2 – The IP address is /27. What is the first usable host address in the first usable range?

9. IP Versions IPv4 IPv6 32 bits Separated by a period 133.15.6.4 RFC 791
Separated by colons
RFC 2460
More address space
Better address mgmt

10. Using Network Address Translation in a Network (NAT)
Allows a large group of private users to access the Internet by sharing a small group of public IPs
comparable to a company with a few phone lines, but many extensions
Developed to help save registered IP addresses
Provides security to PCs, servers, devices, etc

11. Advantages & Disadvantages of NAT
Reuse of IP addresses
Sharing of a global IP address
Security
Scalability
Router CPU load
Poor network performance
Remote access may be denied if trying to access a server with a private IP

12. NAT Terminology Inside local network Outside global network
any network connected to a router interface that is part of the privately addressed LAN
Outside global network
any network attached to a router that is external to the LAN

13. More NAT Terminology Inside local address Outside global address
Private IP address of a host on the local network
Must be translated to a public IP before it can travel outside
Outside global address
Actual public IP address of an external host

14. More NAT Terminology Inside global address Outside local address
IP address of inside host as it APPEARS to the outside network
Outside local address
Destination address of packet while on the local network
Usually the same as outside global address

15. Static NAT Provides access to a local host from the Internet
Allows hosts on public network to access selected hosts on a private network

16. Static NAT Example
The host with the IP address of will always translate to

17. Dynamic NAT
Maps an unregistered IP address to a registered IP address from a group of registered IP addresses.
The host with the IP address of will translate to the first available address in the range of to

18. PAT (NAT Overload)
A form of dynamic NAT that maps multiple private IP addresses to a single registered IP address by using different ports. This is known also as PAT (Port Address Translation), single address NAT or port-level multiplexed NAT.
Each computer on the private network is translated to the same IP address ( ), but with a different port number assignment.
Outside users are unable to initiate communication to a host if using PAT

19. PAT (Overloading)
Uses unique source port numbers in the inside global IP address
Uses first available port number
These port numbers must be above 1024

20. Summary
IP addressing can be tailored to the needs of the network design through the use of custom subnet masks.
Classless subnetting gives classful IP addressing schemes more flexibility through the use of variable length subnet masks.
Network Address Translation (NAT) is a way to shield private addresses from outside users.
Port Address Translation (PAT) translates multiple local addresses to a single global IP address, maximizing the use of both private and public IP addresses.