Lab#2 Telnet & ssh, SMTP/POP3, DNS & FTP Reading: •

Kurose, sections 2.3, 2.4, 2.5

Additional info: •

Telnet: http://www.rfc-editor.org/rfc/rfc854.txt

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FTP: http://www.rfc-editor.org/rfc/rfc959.txt

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SMTP: http://www.rfc-editor.org/rfc/rfc821.txt

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DNS: http://www.rfc-editor.org/rfc/rfc1035.txt

telnet •

basic usage: ▪ telnet zoltar redes.upv.es

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extended usage: (try with zoltar.redes.upv.es by adding a port number after the server name): ▪ echo (7) ▪ daytime (13) ▪ quoteoftheday (17) •

Analiza el caso en que no esté activo

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Secure telnet: ssh

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Exercise#1: connect to zoltar.redes.upv.es using ssh

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SMTP/POP3 •

Quick reminder of SMTP (25) and POP3 (110)

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Exercise#2: Use SMTP and nc command to send an emal to your own account in zoltar.redes.upv.es. (Valid mailboxes are from redes01 to redes22 )

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Exercise#3: Using POP3 and nc command connecto to zoltar.redes.upv.es for reading the message you just sent. Delete it from the mailbox once you have read it.

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DNS Quick intro to DNS Usage of nslookup Samples: ◦ nslookup www.mit.edu ◦ nslookup –type=NS mit.edu • Exercise#4: What is the IP address of zoltar.redes.upv.es? • Exercise#5: This query: nslookup www.mit.edu returns a “Non-authoritative answer”. What do you need to obtain an “Authoritative” one? • Exercise#6: What is the server in charge of this email domain eurecom.fr ? 1. Exercise#7: Repeat the previous exercise with -debug y -d2. What happens? • Exercise#8: In nslookup, this sequence of commands: > set norecurse > www.stanford.edu returns: *** Can't find www.stanford.edu: No answer What needs to be done to obtain a response? > set type=NS > stanford.edu …. answer... > server argus.stanford.edu > www.stanford.edu Compare results if you use “set recurse”. • • •

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Exercise#9: Open Wireshark and set “port 53” as the capture filter. Start a capture and run in a terminal de command “ping www.ietf.org”. Stop the ongoing capture in Wireshark. ◦ Answer the following questions: ▪ Look for DNS requests and responses. What transport protocol did they use? ▪ What is the destination port number of a DNS request? What is the source port number of a DNS response? ▪ What is the destination IP address of DNS requests? Do you remember the IP address of your local DNS server from Exercise#4? Is it the same? ▪ Examine the type of the DNS request. What type is it? ▪ Examine the type of DNS response. How many answers does contain? What do you find on each one?

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Advanced exercises FTP •

Exercise#10: Using ftp command with DEBUG ON connect to zoltar.redes.upv.es. And observe the different commands and responses exchanged by the application protocol. You can get help from the program by typing help (or help ). ◦ Make a new folder in your account in zoltar and change to that folder. ◦ Upload file to your home folder in zoltar. ◦ Obtain a listing of the home folder in zoltar. ◦ Close the connection.

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Exercise#11: Using nc command instead of ftp command, connect to zoltar.redes.upv.es ftp server and obtain a listing of the home folder of your account. Try using both PORT and PASV commands (alternatively).

You can get some insight about ftp program here: http://www.webmonkey.com/2010/02/ftp_for_beginners/

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