Planning the Addressing Structure

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.