Question

An IP address is a 32-bit number that uniquely identifies a host (computer or other device, such as a printer or router) on a TCP/IP network. IP addresses are normally expressed in dotted-decimal format, with four numbers separated by periods, such as 192.168.123.132. To understand how subnet masks are used to distinguish be- tween hosts, networks, and subnetworks, examine an IP address in binary notation. For example, the dotted-decimal IP address 192.168.123.132 is (in binary notation) the 32 bit num- ber 11000000101010000111101110000100. This number may be hard to make sense of, so divide it into four parts of eight binary digits. These eight bit sections are known as octets. The ex- ample IP address, then, becomes 11000000.10101000.01111011.10000100. This number only makes a little more sense, so for most uses, convert the binary address into dotted-decimal for- mat (192.168.123.132). The decimal numbers separated by periods are the octets converted from binary to decimal notation. Some TCP servers accept requests only coming from the machines which are in their networks. To decide which IP addresses is in their networks they use a network address and a netmask. For example, consider the case: Network Address 192.168.0.1 1000000.10101000.00000000.00000001 Machine address 192.168.0.7 | 1000000.10101000.00000000.00000111 Netmask: | 255.255.255.240 | 1111111.11111111.11111111.11110000 If Network Address & Netmask is equal to Request sending Machine address & Netmask, where & is bitwise AND operator, then server allows the request packet arrive, otherwise rejects the request. 1. (5 pt) Find the local network address, netmask value of your LAN and your computer's local network address (You should be able to be doing it in Windows, OSX, and linux pretty easily. Do not fiddle with your router) 2. (15 pt) Using the Network address and Netmask value given in the above table, if the TCP connection request is coming from a machine with IP 192.168.0.18, does the server accept that request? [22] : 00010010 # That is how you do binary representation in python Ob010010 & 0b010010 # bitwise AND operator in Python pass

Answer 1

1: Local network address (192.168.43.1), Netwok mask (255.255.255.0) and computer's local network address (192.168.43.95)

// {for linux we can find network mask and local network address using the "netstat -r" command and computer's local network address using "ip addr")

// for window it can be done with only "ifconfig" command or by checking the network manager.

2: No, because (192^255, 168^255, 0^255, 1^240)=((63, 87, 255, 241)) // (bitwise and of mask and network address for TCP server)

and (192^255,168^255,0^255,14^240) = (63, 87, 255, 254) //( bitwise and of mask and network address for machine address)

and we see result calculated using Network Address & Netmast is not equal to Network address of machine with ip (192,168,0,18) & Network mast. So it will not be allowed.