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Selected TCP/IP Applications
•Remote Terminal Emulation (TELNET)
•File Transfer Protocol (FTP)
•Trivial File Transfer Protocol (TFTP)
•Simple Mail Transfer Protocol (SMTP)
•Post Office Protocol (POP)
•Domain Name Service (DNS)
•Simple Network Management Protocol (SNMP)
TELNET
TELNETTELNETclientclient
HostHost
TELNET TELNET serverserver
TELNET TELNET serverserver
TELNET Options• Each side of the connection requests or tells its partner
the options it wants or can do.• Options are formatted in:
– WILL or WON’T <option> – DO or DON’T <option>
• Negotiates options such that symmetry can be set up between two stations.
• Options include:– Ability to echo– Terminal type– Setting line mode so that groups of characters can be
sent
File Transfer Protocol (FTP)
ClientClient
HostHost
StorageStorage
FTP Commands• open–creates a connection between two hosts.
• close–closes a connection between two hosts.
• bye–ends the FTP session.
• binary–indicate that the file is binary data.
• get–get the remote file.
• mget–wildcard to get multiple files.
• put - puts a file to the remote resource.
• mput - wildcard to put multiple files.
• cd - change directory on the remote device.
• dir - get a directory listing on the remote device.
• ldir - get a local directory.
• hash - display hash marks during the transfer.
FTP Example
99,760 bits per second
Trivial File Transfer Program (TFTP)
• A simplex file transfer program.
• Uses UDP.
• Transfers 512 bytes at a time.
• Transfers one segment at a time.
• Acknowledged by the application.
• Any datagram less than 512 bytes indicates the last datagram in the transfer.
• Popular for network booting of devices.
Domain Name Service (DNS)
• Provides a naming service for TCP/IP.– Provides many functions related to IP addresses and names
• Three components– A name server, a name resolver, and a database
• Hierarchical in structure.• Each level provides further definition.• Each branch is called a level (63 characters in length).• Internet Registry provides uniqueness in names.• A single domain is assigned and may be further defined
The extra top-level domains (TLDs) that are shown as the bottom setThe extra top-level domains (TLDs) that are shown as the bottom setof boxes are proposed, they are shown here as examples,of boxes are proposed, they are shown here as examples,
and as of this writing have not been adopted.and as of this writing have not been adopted.
IP address of IP address of “labhost.bnr.ca.us”“labhost.bnr.ca.us”
Referral to bnr.ca.us serverReferral to bnr.ca.us server
Referral to ca.us serverReferral to ca.us server
Referral to us serverReferral to us server
Root serverRoot server
.us server.us server
.ca.us server.ca.us server
bnr.ca.us serverbnr.ca.us server
Query Functions Types
• Two types of queries: recursive and iterative.– Recursion means that the server must find the answer or return an error code– The resolver is an example of a recursive query– Iterative allows a server to return the best-known information– Servers are examples of both recursive and iterative
Query “Host”Query “Host”
Response “Can’t find it”Response “Can’t find it”
Query “Host.jj.com”Query “Host.jj.com” Root serverRoot server
jj.comjj.com
Name ServerName Server jj.comjj.com
host.jj.com
host.jj.com
Response “IP Address”Response “IP Address”
Example DNS Database• Records in the database include:
– A–host’s IP address– PTR–host’s domain name, host identified by its IP address– CNAME–host’s canonical name, host identified by an alias
domain name– MX–host’s or domain’s mail exchanger– NS–host’s or domain’s name server(s)– SOA–Indicates authority for the domain– TXT–generic text record– SRV–service location record– RP–text name of the person responsible for the domain
DNS
SOA Record
Naugle.comNaugle.com ININ SOASOA ns1.Naugle.com. Matt.NT1Server.Naugle.com. (ns1.Naugle.com. Matt.NT1Server.Naugle.com. (15671567 ;Serial;Serial1800018000 ;Refresh after five hours;Refresh after five hours36003600 ;Retry after 1 hour;Retry after 1 hour604800604800 ;Expire after one week;Expire after one week86400)86400) ;Minimum TTL of 1 day;Minimum TTL of 1 day
Authoritative for domainAuthoritative for domainName server for domainName server for domain
Person responsiblePerson responsibleInformation for the secondary serverInformation for the secondary server
Name Server Records
• Naugle.com. IN NS ns0.Naugle.com.
• Naugle.com. IN NS ns1.Naugle.com.
• Naugle.com. IN NS ns2.Naugle.com.
• Naugle.com. IN NS ns3.Naugle.com.
• Naugle.com. IN NS ns4.Naugle.com.
Address RecordsLocalHost.Naugle.com. IN A 127.0.0.1
DatabaseServer.Naugle.com. IN A 128.1.1.1
HRServer.Naugle.com. IN A 128.1.15.1
EngServer.Naugle.com. IN A 128.1.59.150
NS0.Naugle.com. IN A 128.1.1.2
NS1.Naugle.com. IN A 128.1.15.2
NS2.Naugle.com. IN A 128.1.16.190
NS3.Naugle.com. IN A 128.1.59.100
NS4.Naugle.com. IN A 128.1.59.101
;Aliases
NT1.Naugle.com. IN CNAME DBServer.Naugle.com
NT2.Naugle.com. IN CNAME HRServer.Naugle.com.
Mail Exchange Records (MX)
engineering.naugle.com. INMX 5 mail.naugle.com.
engineering.naugle.com. INMX 5 mail1.naugle.com.
engineering.naugle.com. INMX 10 mail2.naugle.com.
Playing with the Database
• nslookup <domain name> <IP Address>
• Go to Web site:://ds/internic.net/cool/dns.html
• Use this to see if a domain name is already assigned!!
WHOIS Command • Enables you to get more information on domain names, networks, etc.,
on the Web.
• ://ds.internic.net/cgi-bin/whois.
• “whois ascend.com” (without the quotes).
• Details Ascend.com domain such as:– Administrative contact (who to call)– Domain servers
• Can determine IP address blocks.– WHOIS net 192.1– BBN Corporation NETBLK-BBN-CNETBLK BBN-NCETBLK 192.1.0.0-
192.1.255.255
More DNS Information• 2136 PS: P. Vixie, S. Thomson, Y. Rekhter, J. Bound, “Dynamic Updates
in the Domain Name System (DNS UPDATE)”, 04/21/97 (26 pages).
• 2137 PS: D. Eastlake, “Secure Domain Name System Dynamic Update,” 04/21/97 (11 pages) (.txt format).
• 1996 PS: P. Vixie, “A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY),” 08/28/96 (7 pages) (.txt format).
• 1995 PS: M. Ohta, “Incremental Zone Transfer in DNS”, 08/28/96 (8 pages) (.txt format).
• www.isc.org
• DNS and BIND – Book by Paul Albitz and Cricket Liu– ISBN 1-56592-236-0
Simple Mail Transfer Protocol (SMTP)
•Today known as Electronic Mail, or email.•RFCs 821, 822, 974.•Email still cannot transport packages and other items.•Email is very fast and guarantees delivery.•Three protocols are used for today’s email.–SMTP–operates over TCP–POP–operates over TCP–DNS–operates over UDP
•SMTP allows for the sending/receiving of email.•POP allows us to intermittently retrieve email.•DNS makes it simple.
SMTP Functions• A message is created, properly addressed, and transmitted using
SMTP sender, which transmits it to an SMTP receiver, which stores the file.
• Address has the format of:– local-part@domain-name– Example: [email protected]– Mail service record in DNS:
• naugle.com IN MX 10 NT1mail_server.eng.naugle.com• SMTP was set up to handle only text.
– Based on the history of the protocol• Email applications convert using a variety of protocols like MIME
(Multipurpose Internet Mail Extensions).
SMTP Flow
SEND MAIL command SEND MAIL command
Send OKSend OK
Identify recipients to receiverIdentify recipients to receiverSend OKs forSend OKs forrecipients;recipients;otherwise, rejectotherwise, reject
SMTPSMTPsendersender
SMTP receiverSMTP receiver
TCP Call on port 25TCP Call on port 25Accept connectionAccept connectionsend READYsend READY
Send mailSend mailSend OK at endSend OK at end
QuitQuitResponse to QuitResponse to Quit
DNS Interaction for Mail
Sender SMTPSender SMTP
Receiver SMTPReceiver SMTP
InternetInternet
mail.ibm.commail.ibm.com
DNS lookup for MX record for ibm.comDNS lookup for MX record for ibm.com
Post Office Protocol (POP)• SMTP is set up to send and receive mail by hosts
that are up full time.– No rules for those hosts that are intermittent on
the LAN• POP emulates you as a host on the network.
– It receives SMTP mail for you to retrieve later• POP accounts are set up for you by an ISP or your
company.• POP retrieves your mail and downloads it to your
personal computer when you sign on to your POP account.
POP Operation
TCP port 110 connectionTCP port 110 connectionattemptattempt ““POP3 server ready” replyPOP3 server ready” reply
Wait for authentication Wait for authentication
Send authenticationSend authentication Process authentication and ifProcess authentication and ifokay, enter transaction stateokay, enter transaction stateLock mailbox for user.Lock mailbox for user.Assign messages numbersAssign messages numbersSend messagesSend messagesDelete (possibly) messagesDelete (possibly) messages
Retrieve all messagesRetrieve all messagesSend QUIT commandSend QUIT commandSession closedSession closed
Quit receivedQuit receivedPerform update on mailboxPerform update on mailbox