9/15/2015© 2008 Raymond P. Jefferis IIILect Application Layer

9/15/2015© 2008 Raymond P. Jefferis IIILect Application Tasks To supply services to the user –file transfer –World Wide Web browsing –mail –network management –network name services

9/15/2015© 2008 Raymond P. Jefferis IIILect Application Layer Protocols FTP/TFTPPort 21/69 TelnetPort 23 HTTPPort 80 SMTPPort 25 SNMPPort 161 DNSPort 53

9/15/2015© 2008 Raymond P. Jefferis IIILect FTP/TFTP FTP (File Transfer Protocol) –uses TCP for transfer of files and data –additional parameters must be supplied –user shielded from file system properties –can be used by terminal or program TFTP (Trivial File Transfer Protocol) –similar to FTP but uses UDP

9/15/2015© 2008 Raymond P. Jefferis IIILect FTP Commands

9/15/2015© 2008 Raymond P. Jefferis IIILect FTP – Login (Two types) Supply server name Supply account (if not “anonymous”) Supply Password (user name if anonymous)

9/15/2015© 2008 Raymond P. Jefferis IIILect FTP - Directory Operations Change Directory (cd) List directory (ls)

9/15/2015© 2008 Raymond P. Jefferis IIILect FTP - File Transfer Set binary mode Put local file to server ftp directory

9/15/2015© 2008 Raymond P. Jefferis IIILect Telnet Telnet is a remote terminal protocol Remote logon permitted User gets virtual terminal (emulation) Uses a TCP connection protocol Requires two arguments –name of server –protocol port number of server (commercial software will use default)

9/15/2015© 2008 Raymond P. Jefferis IIILect Telnet - Terminal Setup Define terminal

9/15/2015© 2008 Raymond P. Jefferis IIILect Telnet - Connect from Prompt Type Telnet serverName

9/15/2015© 2008 Raymond P. Jefferis IIILect Telnet - Connect via Program Type Telnet Specify server and terminal type

9/15/2015© 2008 Raymond P. Jefferis IIILect HTTP Hypertext Transfer Protocol –used for World Wide Web (WWW) to retrieve hypertext documents –client/server mode –transaction-oriented (connection broken after document transmission is complete) –uses TCP to connect client and server (virtual “connection”)

9/15/2015© 2008 Raymond P. Jefferis IIILect HTTP Message Format Request –message type –requested source Response –response information General –additional information

9/15/2015© 2008 Raymond P. Jefferis IIILect HTTP Header Information Connection (header field names) Date (date and time stamp) Keep-alive (sender connection timeout)

9/15/2015© 2008 Raymond P. Jefferis IIILect HTTP Request Methods Get (from specified URL) Put (post to URL) Patch (post differences to URL) Copy, Move, Delete (URL info) Link/Unlink (add or delete link in URL)

9/15/2015© 2008 Raymond P. Jefferis IIILect HTTP Response Messages Status line –HTTP Version –Status Code –Reason Phrase General response Entity body (optional) –text, binary data, audio, images, video

9/15/2015© 2008 Raymond P. Jefferis IIILect SNMP/SNMPv2 Simple Network Management Protocol –network monitoring –network management Basic actions –Get (request named objects - various datatypes) –Set (request alteration of named objects) –Notify (inform request) –Uses UDP for communications

9/15/2015© 2008 Raymond P. Jefferis IIILect SNMP Network Components Management stations –restricted access –inspect, display, and alter network data Managed nodes –routers, gateways, bridges, switches, hubs, etc. –computers, printers, etc.

9/15/2015© 2008 Raymond P. Jefferis IIILect SNMP Management Objectives Fault detection Equipment configuration Gathering statistics –for accounting purposes –for diagnostic purposes Network security

9/15/2015© 2008 Raymond P. Jefferis IIILect SNMP Model Objects –written in ASN.1 syntax –defined in Management Information Base (MIB) - many types of objects pre-defined Agents –programs in managed nodes –supply requested information –alter information when requested

9/15/2015© 2008 Raymond P. Jefferis IIILect ASN.1 Data types in SNMP INTEGER Type code = 2 BIT STRING Type code = 3 OCTET STRING Type code = 4 NULL Type code = 5 OBJECT IDENTIFIERType code = 6 Syntax in use: identifier type ::= value or (range) or {id n (val n ),...}

9/15/2015© 2008 Raymond P. Jefferis IIILect SNMP Data Transfer Format Header byte –tag (2 bits) –tag extension (1 bit) –type code (5 bits) Length [bytes] Data bytes

9/15/2015© 2008 Raymond P. Jefferis IIILect Basic SNMP Objects System - equipment description Interfaces - with logged traffic AT - address translation IP - packet statistics ICMP - message statistics

Basic SNMP Objects (Cont’d) TCP - methods, parameters, statistics UDP - statistics EGP - gateway protocol statistics Transmission - media-specific SNMP - management traffic statistics 9/15/2015© 2008 Raymond P. Jefferis IIILect

9/15/2015© 2008 Raymond P. Jefferis IIILect SNMP Message Types (0)GetRequest - get variables (1)GetNextRequest - get next variable (2)GetResponse- get data (3)SetRequest - modify variable (4)Trap - agent trap message

9/15/2015© 2008 Raymond P. Jefferis IIILect SMTP Simple Mail Transfer Protocol Sent and received via Port 25 using TCP Envelope –list of recipients Body –message to be sent (7-bit ASCII) Outgoing messages are queued

9/15/2015© 2008 Raymond P. Jefferis IIILect SMTP Header TO:address FROM: (REPLY TO:)address CC:address SUBJECT:text DATE:date ENCRYPTED:pointer

9/15/2015© 2008 Raymond P. Jefferis IIILect Some SMTP Commands HELO (send ID - sent by client) MAIL FROM (identify originator) RCPT TO (identify recipient) DATA (transfer message text) QUIT (close TCP connection) (See text, p660 for example)

9/15/2015© 2008 Raymond P. Jefferis IIILect Some SMTP Replies 220“ready” - returned by server 221“destination closing” 250“okay” - transfer complete 345“ready for mail” - start 421“mail service unavailable” 550“mailbox not found” 554“mail transaction failed”

9/15/2015© 2008 Raymond P. Jefferis IIILect DNS To locate addresses in network domains Each host has resource records of format: –DomainName –TimeToLive [seconds] –Class (IN for internet) –Type (see table) –Value (data type depends on Type field)

9/15/2015© 2008 Raymond P. Jefferis IIILect DNS (continued) Database is distributed and hierarchical Names that cannot be resolved in the host are referred up the hierarchy of name servers

Name Servers (Continued) There is usually a specified name server for a network configuration A backup (second) name server is usually specified UDP protocol is used for name server queries and responses 9/15/2015© 2008 Raymond P. Jefferis IIILect

9/15/2015© 2008 Raymond P. Jefferis IIILect DNS Record Types

9/15/2015© 2008 Raymond P. Jefferis IIILect Example dcs.engr.widener.edu, ,A,IN

End 9/15/2015© 2008 Raymond P. Jefferis IIILect