NETWORK LAYER

Ch 19. Logical Addressing

19.1 IPv4 Addresses For world-wide communications IPv4 Address Uniquely identify a device in the network Logical address = IP address (in TCP/IP protocol) IPv4 Address 32 bits long  232 address space Globally unique Notation (binary or dotted-decimal)

Classful Addressing Address space is divided into five classes: A, B, C, D, and E netid hostid

Classful Addressing Mask is used to find the netid and hostid Subnetting – divide a large block of addresses into several groups (increases the number of 1s in the mask) Supernetting – combine small blocks of addresses due to depletion of class A and B addresses. Address depletion A large part of addresses were wasted

Classless Addressing To overcome address depletion classless addressing is used. Allow a different size of address blocks with restrictions of Addresses in a block must be contiguous The number of addresses in a block is a power of 2 The first address must be divisible by the number of addresses

Classless Addressing A block of addresses can be defined as x.y.z.t /n where x.y.z.t is any address in the block /n defines the mask First n bits are the netid The block can have up to 2(32–n) hosts Practice with example 19.9

Exp: 205.16.37.39/28 will be represented in binary as 11001101 00010000 00100101 00100111 (205.16.37.32 is the first address in the block) The first address is often assigned to a special device, e.g., a gateway

Hierarchy of IPv4 Address Comparison Telephone number IPv4 Address

Subnetting (Multi-level Hierarchy) “Internally” divide a block of addresses into clusters of networks (called subnets) An outside device still sees them as a single block Needs to split in 3 groups. 17.12.14. Example: Organization is given 17.12.14.0/26 00110000 00111111 17.12.14. 17.12.14. 00000000 00100000 00011111 00101111

Example 19.10 A block of addresses 190.100.0.0/16 needs to be distributed to three groups as follows: 64 customers; each needs 256 addresses 128 customers; each needs 128 addresses 128 customers; each needs 64 addresses

Network Address Translation (NAT) Addresses for private network Home users have a small network, where each device needs an IP address Some addresses are reserved for “internal network” Anyone can use these addresses without permission

NAT The private network should has one single connection to the Internet Address translation

Translation Table

Translation Table Entry of a table may … NAT and ISP use one (global) IP address use a pool of (global) IP addresses – often used by ISP (see below) use both IP address and port number – often known as IP sharing NAT and ISP

19.2 IPv6 Addresses IPv6 Address 128 bits long  2128 address space Globally unique Notation (hexadecimal colon)

Abbreviated representation

Address Structure Unicast Multicast

Homework Exercise 18 19 22 26