Experiment No: Group B_4

Transcription

1 Experiment No: Group B_4 R (2) N (5) Oral (3) Total (10) Dated Sign Problem Definition: Study and perform Linux networking commands emulation using Python or C Prerequisite: Basics of Networking. 1.2 Learning Objective: To understand how network command working in detail. 1.3 Theory: Introduction A network consists of several computers connected together. The network can be as simple as a few computers connected in your home or office, or as complicated as a large university network or even the entire Internet. When your computer is part of a network, you have access to those systems either directly or through services like mail and the web.there are a variety of networking programs that you can use. Some are handy for performing diagnostics to see if everything is working properly Basic Networking Commands: finding host/domain name and IP address - hostname test network connection ping getting network configuration ifconfig Network connections, routing tables, interface statistics netstat query DNS lookup name nslookup communicate with other hostname telnet outing steps that packets take to get to network host traceroute view user information finger checking status of destination host - telnet 1

2 hostname hostname with no options displays the machines host name hostname d displays the domain name the machine belongs to hostname f displays the fully qualified host and domain name hostname i displays the IP address for the current machine ping It sends packets of information to the user-defined source. If the packets are received, the destination device sends packets back. Ping can be used for two purposes 1. To ensure that a network connection can be established. 2. Timing information as to the speed of the connection. If you do ping it will display its IP address. Use ctrl+c to stop the test. ifconfig View network configuration, it displays the current network adapter configuration. It is handy to determine if you are getting transmit (TX) or receive (RX) errors. netstat Most useful and very versatile for finding connection to and from the host. You can find out all the multicast groups (network) subscribed by this host by issuing "netstat -g" netstat -nap grep port will display process id of application which is using that port netstat -a or netstat all will display all connections including TCP and UDP netstat --tcp or netstat t will display only TCP connection netstat --udp or netstat u will display only UDP connection netstat -g will display all multicast network subscribed by this host. nslookup If you know the IP address it will display hostname. To find all the IP addresses for a given domain name, the command nslookup is used. You must have a connection to the internet for this utility to be useful. E.g. nslookup blogger.com You can also use nslookup to convert hostname to IP Address and IP Address from hostname. 2

3 traceroute A handy utility to view the number of hops and response time to get to a remote system or web site is traceroute. Again you need an internet connection to make use of this tool. finger View user information, displays a user s login name, real name, terminal name and write status. this is pretty old unix command and rarely used now days. telnet Connects destination host via telnet protocol, if telnet connection establish on any port means connectivity between two hosts is working fine. telnet hostname port will telnet hostname with the port specified. Normally it is used to see whether host is alive and network connection is fine or not traceroute command working in detail Traceroute attempts to trace the route an IP packet follows to some internet host. It finds out intermediate hops by launching probe packets with a small time-to-live (TTL) value, and then listens for an ICMP reply of time exceeded from an intermediate router. Traceroute starts probing with a TTL of one, and increments by one until an ICMP port unreachable reply is received. This means the probe either got through to host, or hit the maximum TTL. Tool used to trace path from source to destination host. Most traceroute programs, send UDP packets (User Datagram Protocol). Generates messages from each router used along the path. Every router that handles a packet subtracts one from the packet's TTL. If the TTL reaches zero, the packet has expired and is discarded. At that point, most routers send an ICMP Time Exceeded message back to the sender - traceroute uses this message. A TTL value of one should produce a message from the first router; two from the second; etc. 3

4 Traceroute returns these IP addresses & hostnames (via reverse lookup) Sender Target TTL = 1 TTL = 2 TTL = 3 TTL = 4 Figure : traceroute operation Traceroute syntax traceroute [ -f first_ttl ] [ -g gateway ] [ -i iface ] [ -m max_ttl ] [ -p port ] [ -q nqueries ] [ -s src_addr ] [ -t tos ] [ -w waittime ] [ -z pausemsecs ] host [ packetlen] -f Set the initial time-to-live used in the first outgoing probe packet. -F Set the "don't fragment" bit. -d Enable socket level debugging. -g Specify a loose source route gateway (8 maximum). -i Specify a network interface to obtain the source IP address for outgoing probe packets. -I Use ICMP ECHO instead of UDP datagrams. -m Set the max time-to-live (max number of hops) used in outgoing probe packets. The default is 30 hops. -n Print hop addresses numerically rather than symbolically and numerically EXAMPLES traceroute nis.nsf.net. traceroute to nis.nsf.net ( ), 30 hops max, 56 byte packet 1 helios.ee.lbl.gov ( ) 19 ms 19 ms 0 ms 2 lilac-dmc.berkeley.edu ( ) 39 ms 39 ms 19 ms 3 lilac-dmc.berkeley.edu ( ) 39 ms 39 ms 19 ms 4 ccngw-ner-cc.berkeley.edu ( ) 39 ms 40 ms 39 ms 5 ccn-nerif22.berkeley.edu ( ) 39 ms 39 ms 39 ms ( ) 40 ms 59 ms 59 ms ( ) 59 ms 59 ms 59 ms ( ) 99 ms 99 ms 80 ms 4

5 ( ) 139 ms 239 ms 319 ms ( ) 220 ms 199 ms 199 ms 11 nic.merit.edu ( ) 239 ms 239 ms 239 ms Python program for traceroute command simulation import socket def main(dest_name): #Getting IP address from Host Name dest_addr = socket.gethostbyname(dest_name) port = max_hops = 30 #initializing receiver and sender packets icmp = socket.getprotobyname('icmp') udp = socket.getprotobyname('udp') ttl = 1 while True: #sending UDP and Receiving ICMP packets recv_socket = socket.socket(socket.af_inet, socket.sock_raw, icmp) send_socket = socket.socket(socket.af_inet, socket.sock_dgram, udp) #setting sender packet TTL field to value of the ttl variable. ### TODO : Write your Code here send_socket.setsockopt(socket.sol_ip,socket.ip_ttl,ttl) recv_socket.bind(("", port)) # TODO Write a code to send pkt using send Socket send_socket.sendto("",(dest_name,port)) curr_addr = None curr_name = None try: #retrieving the router address from packet _, curr_addr = recv_socket.recvfrom(512) curr_addr = curr_addr[0] try: #getting hostname of the retrieved address curr_name = socket.gethostbyaddr(curr_addr)[0] except socket.error: curr_name = curr_addr except socket.error: pass finally: send_socket.close() recv_socket.close() #Printing data in the terminal if curr_addr is not None: 5

6 curr_host = "%s (%s)" % (curr_name, curr_addr) else: curr_host = "*" print "%d\t%s" % (ttl, curr_host) ttl += 1 if curr_addr == dest_addr or ttl > max_hops: break if name == " main ": main(' 1.4 Assignment Question: 1. List out different basic networking commands with their use. 2. Explain how traceroute command works in detail. 3. What is significance of TTL field in case of traceroute. Conclusion: Hence we studied that how traceroute works in detail using python programming. 6