IP-adresses and IP-adresses and subnet maskssubnet masks

Figure 19.9 Dotted-decimal notation

IP addresses

• 32-bit address i today’s IP version 4 (IPv4).

• 128-bit in IPv6.

• Exampel of IP addres:

1100 0001 0000 1100 0101 1011 0001 11112 binary form.

• At punctured decimal form this is 193.12.91.31.

• Using hexadecimal form this is C10C5B1F.

FC 1 0 C 5 D 1

31193 12 91

1100 0001 0000 1100 0101 1011 0001 1111

. . .

Example 1Example 1

Change the following IP addresses from binary notation to dotted-decimal notation.

a. 10000001 00001011 00001011 11101111

b. 11111001 10011011 11111011 00001111

Example 1Example 1

Change the following IP addresses from binary notation to dotted-decimal notation.

a. 10000001 00001011 00001011 11101111

b. 11111001 10011011 11111011 00001111

SolutionSolution

We replace each group of 8 bits with its equivalent decimal number and add dots for separation:a. 129.11.11.239b. 249.155.251.15

Example 2Example 2

Change the following IP addresses from dotted-decimal notation to binary notation.

a. 111.56.45.78

b. 75.45.34.78

Example 2Example 2

Change the following IP addresses from dotted-decimal notation to binary notation.

a. 111.56.45.78

b. 75.45.34.78

SolutionSolution

We replace each decimal number with its binary equivalent:

a. 01101111 00111000 00101101 01001110b. 01001011 00101101 00100010 01001110

Hierarchical Addressing • Physical network address – A part used by the router• Host address – Specific device, node or network interface

on the physical network

A

3.1

2.1 1.1 1.2 1.3

network node

1 123

2 1

3 1

An example of hierarchical addressing

In classful addressing, the address space is divided into five classes: A, B,

C, D, and E.

NoteNote::

Figure 9.5 IP address formats and classes

Figure 19.10 Finding the class in binary notation

Figure 19.11 Finding the address class

Example 3Example 3

Find the class of each address:

a. 000000001 00001011 00001011 11101111

b. 111111110011 10011011 11111011 00001111

Example 3Example 3

Find the class of each address:

a. 000000001 00001011 00001011 11101111

b. 111111110011 10011011 11111011 00001111

SolutionSolution

a. The first bit is 0; this is a class A address.b. The first 4 bits are 1s; this is a class E address.

Figure 19.12 Finding the class in decimal notation

Example 4Example 4

Find the class of each address:

a. 227.12.14.87

b. 252.5.15.111

c. 134.11.78.56

Example 4Example 4

Find the class of each address:

a. 227.12.14.87

b. 252.5.15.111

c. 134.11.78.56

SolutionSolutiona. The first byte is 227 (between 224 and 239); the class is D.b. The first byte is 252 (between 240 and 255); the class is E.c. The first byte is 134 (between 128 and 191); the class is B.

Figure 19.13 Netid and hostid

Figure 19.14 Blocks in class A

Figure 19.15 Blocks in class B

Figure 19.16 Blocks in class C

Figure 19.17 Network address

Figure 19.13 Number of hosts and networks

N bit host ID allows 2N addresses, or 2N-2 hosts in the network.

The first address (the network address) and the last address (the broadcast address) are future addresses can not be used as host addresses.

M free bit net ID allows 2M networks.

Example 5Example 5

Given the address 23.56.7.91, find the network address.

Example 5Example 5

Given the address 23.56.7.91, find the network address.

SolutionSolution

The class is A. Only the first byte defines the netid. We can find the network address by replacing the hostid bytes (56.7.91) with 0s. Therefore, the network address is 23.0.0.0.

Example 6Example 6

Given the address 132.6.17.85, find the network address.

Example 6Example 6

Given the address 132.6.17.85, find the broadcast address.

SolutionSolution

The class is B. The first 2 bytes defines the netid. We can find the network address by replacing the hostid bytes (17.85) with 1s. Therefore, the broadcast address is 132.6.255.255.

Example 7Example 7

Given the network address 17.0.0.0, find the class.

Example 7Example 7

Given the network address 17.0.0.0, find the class.

SolutionSolution

The class is A because the netid is only 1 byte.

Class-less addresses

• Today subnetting and classless addresses are used instead of class-ful addressing.

• Then a network can be devided into several subnets, each corresponding to a physical network. Arbitrary number of host-bits can be used.

• A 0 in the subnet mask means that the corresponding bit in the address belongs to the host-ID, and a 1 that it belongs to the Net ID or subnet ID.

• Example: Subnet mask 255.255.0.0 = FFFF0000 (sixteen ones and sixteen zeros) means that the first 16 bits in the i IP-adressen are Net-ID or subnet ID, the rest are Host-ID.

Example:

192.16.5.0 192.16.5.3

192.16.5.2192.16.5.1

192.16.4.3

192.16.4.2192.16.4.1

192.16.4.0

192.16.3.0

192.16.3.3192.16.3.2192.16.3.1 192.16.3.4 192.16.3.5

Network addresses

172.16.3.255

172.16.5.255

172.16.4.255

Broadcast addressesHost addresses

192.16.5.255

192.16.4.255

192.16.3.255

The mask is 255.255.255.0 for all hosts

Figure 19.23 Subnet mask

Figure 19.21 Addresses in a network with and without subnetting

Table 19.1 Default masksTable 19.1 Default masks

Class In Binary In Dotted-DecimalUsing Slash

notation

A 11111111 00000000 00000000 00000000 255.0.0.0 /8

B 11111111 11111111 00000000 00000000 255.255.0.0 /16

C 11111111 111111111 11111111 00000000 255.255.255.0 /24

The network address can be foundby applying the default mask to any

address in the block (including itself).It retains the netid of the block and

sets the hostid to 0s.

NoteNote::

Example 8Example 8

A router outside the organization receives a packet with destination address 190.240.7.91. Show how it finds the network address to route the packet.

Example 8Example 8

A router outside the organization receives a packet with destination address 190.240.7.91. Show how it finds the network address to route the packet.

SolutionSolution

The router follows three steps:1. The router looks at the first byte of the address to find the

class. It is class B. 2. The default mask for class B is 255.255.0.0. The router ANDs

this mask with the address to get 190.240.0.0. 3. The router looks in its routing table to find out how to route the

packet to this destination. Later, we will see what happens if this destination does not exist.

Example 9Example 9

A router inside the organization receives the same packet with destination address 190.240.33.91. Show how it finds the subnetwork address to route the packet.

SolutionSolution

The router follows three steps:1. The router must know the mask. We assume it is /19, as shown in

Figure 19.23. 2. The router applies the mask to the address, 190.240.33.91. The subnet

address is 190.240.32.0. 3. The router looks in its routing table to find how to route the packet to

this destination. Later, we will see what happens if this destination does not exist.

Broadcast IP address

• Broadcast IP address is used when information needs to be sent to all the hosts on the same network○ Convenient in broadcast networks (such as Ethernet)

• Broadcast IP address is obtained when host bits are replaced by 1s.

Unicast, Multicast and Reserved Addresses

• Unicast address is used for one-to-one communication

• Multicast address is used for one-to-many communication (group communication) – D class

• Reserved addresses – Besides the addresses in class E reserved addresses are:○ Network addresses – all host bits are 0

○ Broadcast addresses – all host bits are 1

○ All network part 0 – host on this network

○ 127.0.0.0 mask 255.0.0.0 and all host addresses on this network are reserved for testing purposes. 127.0.0.1 = localhost.

○ 0.0.0.0 – default route

Figure 19.25 NAT

Figure 19.26 Address translation

Figure 19.27 Translation

Table 19.3 Five-column translation tableTable 19.3 Five-column translation table

Private Address

Private Port

ExternalAddress

External Port

TransportProtocol

172.18.3.1 1400 25.8.3.2 80 TCP

172.18.3.2 1401 25.8.3.2 80 TCP

... ... ... ... ...

Table 19.2 Address ranges reserved for private NAT addressesTable 19.2 Address ranges reserved for private NAT addresses

Range Total

10.0.0.0 to 10.255.255.255 224

172.16.0.0 to 172.31.255.255 220

192.168.0.0 to 192.168.255.255 216

Useful Programs

• These programs use ICMP to probe the Internet○ ping

• Sends packets that is echoed by remote computer

• Remote computer replies with echo packet

• Local computer reports receipt of reply○ traceroute

• Reports path to remote computer

• Sends packets to the destination starting with TTL=1

• Each successive packet identifies next router along path

• Reports list of packets ○ ipconfig – shows network configuration info

• Displays all configuration information

Ping - Example

Four packets are sent. Each has different round-trip time (RTT). Why?

Minimum, Maximum and average are also given.

Round-trip Time (RTT)

• Time for the packet to be sent and acknowledgement to come back to the sender

• Why the packets have different RTT?○ They might travel different paths

○ The load in some of the routers might be high. Therefore packet’s waiting time at the routers can be different.

○ Ping also shows the percentage of lost packets.

Traceroute - Example

The source is sending three packets with TTL=1, then another three with TTL=2 and so on until TTL is by one bigger then the number of hops. A response is thus obtained from each hop where the packets are dropped. RTT for each packet is presented.

VisualRoute

• A program that displays visually (on a map) traceroute

• Trial version can be obtained free from

www.visualroute.com

Ipconfig /all - Example

Figure 20.15 IPv6 address

Ipconfig

• Displays all the information about the IP configuration.○ IP address○ Subnet mask○ Default gateway (router)○ DNS servers○ DHCP servers○ MAC (physical) address○ Host name○ Domain suffix○ …