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

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.

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

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

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

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

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

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

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

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

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

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

NAT and PAT Inside local network Outside global network

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

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

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

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

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

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

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.