IP-adresses and subnet 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: binary form. At punctured decimal form this is Using hexadecimal form this is C10C5B1F.

Example 1 Change the following IP addresses from binary notation to dotted- decimal notation. a b

Example 1 Change the following IP addresses from binary notation to dotted- decimal notation. a b Solution We replace each group of 8 bits with its equivalent decimal number and add dots for separation: a b

Example 2 Change the following IP addresses from dotted-decimal notation to binary notation. a b

Example 2 Change the following IP addresses from dotted-decimal notation to binary notation. a b Solution We replace each decimal number with its binary equivalent: a b

Hierarchical Addressing Physical network address – A part used by the router Host address – Specific device, node or network interface on the physical network A networknode An example of hierarchical addressing

In classful addressing, the address space is divided into five classes: A, B, C, D, and E. Note:

Figure 9.5 IP address formats and classes

Figure Finding the class in binary notation

Figure Finding the address class

Example 3 Find the class of each address: 0 a b

Example 3 Find the class of each address: 0 a b Solution 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 Finding the class in decimal notation

Example 4 Find the class of each address: a b c

Example 4 Find the class of each address: a b c Solution a.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 Netid and hostid

Figure Blocks in class A

Figure Blocks in class B

Figure Blocks in class C

Figure Network address

Figure Number of hosts and networks N bit host ID allows 2 N addresses, or 2 N -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 2 M networks.

Example 5 Given the address , find the network address.

Example 5 Given the address , find the network address. Solution The class is A. Only the first byte defines the netid. We can find the network address by replacing the hostid bytes ( ) with 0s. Therefore, the network address is

Example 6 Given the address , find the network address.

Example 6 Given the address , find the broadcast address. Solution 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

Example 7 Given the network address , find the class.

Example 7 Given the network address , find the class. Solution 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 = 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: Network addresses Broadcast addresses Host addresses The mask is for all hosts

Figure Subnet mask

Figure Addresses in a network with and without subnetting

Table 19.1 Default masks Class In BinaryIn Dotted-Decimal Using Slash notation A /8 B /16 C /24

The network address can be found by 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. Note:

Example 8 A router outside the organization receives a packet with destination address Show how it finds the network address to route the packet.

Example 8 A router outside the organization receives a packet with destination address Show how it finds the network address to route the packet. Solution 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 The router ANDs this mask with the address to get 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 9 A router inside the organization receives the same packet with destination address Show how it finds the subnetwork address to route the packet. Solution The router follows three steps: 1.The router must know the mask. We assume it is /19, as shown in Figure The router applies the mask to the address, The subnet address is 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 ○ mask and all host addresses on this network are reserved for testing purposes = localhost. ○ – default route

Figure NAT

Figure Address translation

Figure Translation

Table 19.3 Five-column translation table Private Address Private Port External Address External Port Transport Protocol TCP TCP...

Table 19.2 Address ranges reserved for private NAT addresses Range Total to to to

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

Ipconfig /all - Example

Figure 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 ○…