Network Addressing

IP Addresses

IP Address Space

• The Structure of an IP Address

– Binary Representation• The only thing a network device understands, 32 binary

bits:– 11011000 01111110 00011111 10101010

– Hexadecimal Representation• For nerdy humans, eight groups of four bits (nibbles) are

converted to their equivalent hexadecimal value:– D8:7E:1F:AA

– Dotted Decimal Notation• For the rest of us, four groups of eight bits (octets) are

converted to their equivalent decimal value.– 216.126.31.170

IP Address Space

• The 32 Bit IP Address

– 232 (4,294,967,296) possible addresses are grouped into contiguous blocks

– Historically, addresses were assigned by the Internet authorities in class-full licence units

• Ownership was transferred to the end user

– Currently, addresses are assigned by an ISP from appropriately sized CIDR blocks (which we discuss later)

– The ISP retains ownership

IP Address Space

• The 32 Bit IP Address:

– Assigned to all hosts (interfaces) in a local network from a contiguous block of IP addresses

– Provides each host with a Unique Logical Address

• Contains a network ID and unique host ID

– The network ID must be unique within all interconnected networks

– The Subnet Mask (which is the same for all interfaces in a network) determines where the division between the network ID and the host ID

IP Address Space

• Broadcast and Network addresses

• For any network the host portion cannot contain all zeros or all 1’s

• A host ID of all zeros is referred to as the Network address

• A host ID of all 1’s is referred to as the broadcast address

• Eg 11.0.0.0 or 11.255.255.255

• 200.43.15.0 or 200.43.15.255

IP Address Space

• Traditional Licence Classes

– Class A

– Class B

– Class C

– Class D

– Class E

7

IP Classes

• Traditional Licence Class A• NNN.HHH.HHH.HHH

• NNN = 000 to 127 decimal.

• nnnnnnnn = 00000000 to 01111111 binary.

• First Octet always begins with 0xxxxxxx

• 27 ( 128 ) available licences.

• 000 is not allowed / 127 is reserved / 010 is reserved

• 125 available licences (networks)

• 224-2 ( 16,777,216-2 ) hosts per network

8

IP Classes

• Traditional Licence Class B• NNN.NNN.HHH.HHH

• NNN.NNN = 128.000 to 191.255 decimal

• nnnnnnnn.nnnnnnnn =

• 10000000.00000000 to 10111111.11111111 binary.

• First Octet always begins with 10xxxxxx

• 26*28 or (214) or ( 64*256 ) = 16,384 available licences

• 172.016.000.000 to 172.31.000.000 are reserved.

• 216-2 ( 65,536 - 2 ) hosts per network.

9

IP Classes

• Traditional Licence Class C• NNN.NNN.NNN.HHH

• NNN.NNN.NNN = 192.000.000 to 223.255.255 decimal.

• nnnnnnnn.nnnnnnnn.nnnnnnnn =

• 11000000.00000000.00000000 to 11011111.11111111.11111111 binary.

• First Octet always begins with 110xxxxx

• 25*28*28 or (221) or ( 32*256*256 ) = 2,097,152 available licences (networks).

• 192. 168.000.000 to 192.168.255.000 are reserved.

• 28-2 ( 256 - 2 ) hosts per network.

10

IP Classes

• Traditional Licence Class D• Multicast Addresses

• MMM.HHH.HHH.HHH

• MMM = 224 to 239 decimal.

• mmmmmmmm = 11100000 to 11101111 binary.

• First Octet always begins with 1110xxxx.

11

IP Classes

• Traditional Licence Class E• Experimental Addresses

• 240.0.0.0 0 thru 255.255.255.255

12

IP Classes

13

IP Addressing

• IP Reserved and Private Addresses

– Some octet numbers are reserved for special functions (eg. 10.x.x.x, 127.x.x.x, 172.16.x.x-172.31.x.x, and 192.168.x.x)

• Loopback address

– IP address reserved for communicating from a node to itself for testing purposes

– Value of the loopback address is always 127.0.0.1

14

IP Address Exercise

• Are the following legal addresses for normal networks?

• Why or why not ?

1. 10.333.4.1

2. 222.12.15.0

3. 0.23.23.23

4. 127.5.32.22

5. 244.15.55.4

Assigning IP Addresses

• Two ways to assign IP addresses

– Dynamic

• Assigned by a Dynamic Host Configuration Protocol (DHCP) server

• Eliminates human error

• Allows for IP address reuse

– Static

• Assigned by a network administrator

• Never change

• Must ensure that the settings are correct

Summary

• IP address is composed of 32 bits

– Binary representation or dotted decimal

• Subnet mask is used to determine network ID and host ID

• Divided into classes

– A, B, and C are routable

• Some addresses are reserved or are private

• Can be assigned dynamically or statically

• ARP maps IP addresses to MAC addresses