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

2. Objectives Describe how IP Addressing is implemented in the LAN.
Subnet a given network to allow for efficient use of IP address space.
Explain how Network Address Translation (NAT) and Port Address Translation (PAT) are used in a network.

3. IP Addressing in the LAN
IP addressing identifies hosts and network devices
IP address format: dotted-decimal notation
Hierarchical structure: network and host octets

4. IP Addressing in the LAN
Address classes A, B and C: used to identify hosts or networks
Address classes D and E: multicast and experimental uses

5. IP Addressing in the LAN
First octet bit patterns and classes:
Class A: first bit is always 0
Class B: first two bits are always 1 and 0
Class C: first three bits are always 1, 1 and 0

6. IP Addressing in the LAN
Reserved address space for private networks
Private IPs are not routable on the Internet
Consumer networking devices give out private IPs through DHCP

7. IP Addressing in the LAN
RFC 917, Internet Subnets
Subnet mask separates network bits from host bits
Routers read subnet masks left to right, bit for bit
Bits set to 1 are part of the network ID
Bits set to 0 are part of the host ID

8. IP Addressing in the LAN
Classful subnetting:
Use bits from the host space to designate a subnet ID
All resulting subnets use the same subnet ID

9. IP Addressing in the LAN
Classless subnetting features:
CIDR: identify networks based on the number of bits in the network prefix
VLSM: divide address space into networks of various sizes

10. IP Addressing in the LAN
Communicating between subnets:
Each subnet is a separate network
Router is needed to communicate between them
Each router interface is the default gateway for its subnet

11. NAT and PAT
Network address translation (NAT) allows private users to access the Internet by sharing one or more public IP addresses

12. NAT and PAT NAT operation is transparent to users
Benefits include improved security and scalability

13. NAT and PAT
Inside local network
Outside global network

14. NAT and PAT
Dynamic NAT assigns outside global addresses from a pre-defined pool
Static NAT assigns a permanent registered global IP to an individual private host IP

15. NAT and PAT
PAT translates multiple local addresses to a single global IP address

16. NAT and PAT
PAT conversations use a unique temporary IP address and port number combination
Port numbers above 1024
Maximizes use of addresses and security

17. NAT and PAT IP Nat issues:
Additional workload to support IP addresses and port translations
Careful network design and equipment selection
Accurate configuration

18. NAT and PAT
Temporary solutions to address depletion: subnetting, private IP addressing, and NAT
Improvements proposed by using IPv6:
More address space and better space management
Easier administration
Support for advanced network capabilities

19. NAT and PAT IPv6 address notation: 128 bits 32 hexadecimal digits
Three-part hierarchy: global prefix, subnet and interface ID

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.