SNMP/SMTP/MIME
- 1. SNMP / SMTP / MIME Visvesvaraya National Institute of Technology
- 3. What is Network Management? • A network management system (NMS) is a set of hardware and/or software tools that allow an IT professional to supervise the individual components of a network within a larger network management framework. • Network management system components assist with: ➢ Network device discovery - identifying what devices are present on a network. ➢ Network device monitoring - monitoring at the device level to determine the health of network components and the extent to which their performance matches capacity plans and intra-enterprise service-level agreements (SLAs). ➢ Network performance analysis - tracking performance indicators such as bandwidth utilization, packet loss, latency, availability and uptime of routers, switches and other Simple Network Management Protocol (SNMP) -enabled devices. ➢ Intelligent notifications - configurable alerts that will respond to specific network scenarios by paging, emailing, calling or texting a network administrator.
- 4. Functional Areas of Network Management • Configuration Management - inventory, configuration, provisioning • Fault Management - reactive and proactive network fault management • Performance Management - # of packets dropped, timeouts, collisions, CRC errors • Security Management - SNMP doesn’t provide much here • Accounting Management - cost management and chargeback assessment • Asset Management - statistics of equipment, facility, and administration personnel • Planning Management - analysis of trends to help justify a network upgrade or bandwidth increase.
- 5. What is SNMP? • The Simple Network Management Protocol (SNMP) is a framework for managing devices in an internet using the TCP/IP protocol suite. It provides a set of fundamental operations for monitoring and maintaining an internet • Comprised of agents and managers ▫ Agent - process running on each managed node collecting information about the device it is running on. ▫ Manager - process running on a management workstation that requests information about devices on the network.
- 6. • SNMP is based on three basic ideas. ▫A manager checks an agent by requesting information that reflects the behavior of the agent. ▫A manager forces an agent to perform a task by resetting values in the agent database. ▫An agent contributes to the management process by warning the manager of an unusual situation.
- 8. Advantages of using SNMP • Standardized • Universally supported • Extendible • Portable • Allows distributed management access • Lightweight protocol
- 9. Client Pull & Server Push • SNMP is a “client pull” model ▫ The management system (client) “pulls” data from the agent (server). • SNMP is a “server push” model ▫ The agent (server) “pushes” out a trap message to a (client) management system
- 10. SNMP & The OSI Model Application Layer Management and Agent API’s SNMP Presentation Layer ASN.1 and BER(basic encoding rules) Session Layer RPC and NetBIOS Transport Layer TCP and UDP Network Layer IP and IPX Data Link Layer Ethernet | Token Ring | FDDI Physical Layer Ethernet | Token Ring | FDDI
- 11. Ports & UDP • SNMP uses User Datagram Protocol (UDP) as the transport mechanism for SNMP messages • Like FTP, SNMP uses two well-known ports to operate: • UDP Port 161 - SNMP Messages • UDP Port 162 - SNMP Trap Messages
- 12. The Three Parts of SNMP • SNMP network management is based on three parts: – SNMP Protocol • Defines format of messages exchanged by management systems and agents. • Specifies the Get, GetNext, Set, and Trap operations – Structure of Management Information (SMI) • Rules specifying the format used to define objects managed on the network that the SNMP protocol accesses – Management Information Base (MIB) • A map of the hierarchical order of all managed objects and how they are accessed
- 13. Role of SMI SMI defines the general rules for naming objects, defining object types (including range and length), and showing how to encode objects and values. SMI does not define the number of objects an entity should manage or name the objects to be managed or define the association between the objects and their values.
- 14. Role of MIB MIB creates a collection of named objects, their types, and their relationships to each other in an entity to be managed.
- 15. SMTP Simple Mail Transfer Protocol
- 16. What is SMTP ? • Simple Mail Transfer Protocol (SMTP) is an Internet Standard for electronic mail (email) transmission. • SMTP is a TCP/IP protocol used in sending and receiving e-mail. • Users typically use a program that uses SMTP for sending e-mail and either POP3 or IMAP for receiving e-mail. • SMTP communication between mail servers uses TCP port 25. Mail clients on the other hand, often submit the outgoing emails to a mail server on port 587. A few Web email services, such as Gmail, use the unofficial TCP port 465 for SMTP. • SMTP is an application layer protocol.
- 17. Protocol Overview • SMTP is a connection-oriented, text-based protocol in which a mail sender communicates with a mail receiver by issuing command strings and supplying necessary data over a reliable ordered data stream channel, typically a Transmission Control Protocol (TCP) connection. • An SMTP session consists of commands originated by an SMTP client (sender) and corresponding responses from the SMTP server (receiver) so that the session is opened, and session parameters are exchanged. • The sender’s, user agent prepare the message and send it to the MTA(Message Transfer Agent). The MTA functioning is to transfer the mail across the network to the receiver’s MTA.
- 18. Model of SMTP system
- 19. Sending Email • Mail is send by a series of request and response messages between the client and a server. • The message which is send across consists of a header and the body. • A null line is used to terminate the mail header. Everything which is after the null line is considered as body of the message which is a sequence of ASCII characters. • The message body contains the actual information read by the receipt.
- 20. Receiving Email • The user agent at the server side checks the mailboxes at a particular time of intervals. If any information is received it informs the user about the mail. • When user tries to read the mail it displays a list of mails with a short description of each mail in the mailbox. • By selecting any of the mail user can view its contents on the terminal.
- 21. SMTP Transaction Commands • HELO / EHLO - It initiate a new transaction between client and server. • RSET - to reset the SMTP connection to the initial state in which the sender and recipient buffers are erased and the connection is ready to begin a new mail transaction. • NOOP - an empty ("no operation") message designed as a kind of ping to check for responsiveness of the other end of the session • QUIT - terminates the protocol session
- 22. SMTP Transaction Commands • MAIL command, to establish the return address, also called return-path. • RCPT command, to establish a recipient of the message.This command can be issued multiple times, one for each recipient. These addresses are also part of the envelope. • DATA to signal the beginning of the message text; the content of the message, as opposed to its envelope. It consists of a message header and a message body separated by an empty line. DATA is actually a group of commands, and the server replies twice: 1. once to the DATA command itself, to acknowledge that it is ready to receive the text 2. second time after the end-of-data sequence, to either accept or reject the entire message.
- 24. SMTP Transport Example S: 220 smtp.example.com ESMTP Postfix C: HELO relay.example.com S: 250 smtp.example.com, I am glad to meet you C: MAIL FROM:<[email protected]> S: 250 Ok C: RCPT TO:<[email protected]> S: 250 Ok C: RCPT TO:<[email protected]> S: 250 Ok C: DATA S: 354 End data with <CR><LF>.<CR><LF> C: From: "Bob Example" <[email protected]> C: To: Alice Example <[email protected]> C: Cc: [email protected] C: Date: Tue, 15 January 2008 16:02:43 - 0500 C: Subject: Test message C: C: Hello Alice. This is a Test Email C: . S: 250 Ok: queued as 12345 C: QUIT S: 221 Bye {The server closes the connection}
- 25. SMTP Limitations • SMTP lacks built-in security features. Protection against spam has improved over the years but are not foolproof. • SMTP does not prevent spammers from setting (via the MAIL command) fake "From:" email addresses. • Also, body must be encoded in 7 bit ASCII. No binaries are allowed. ▫ Standards such as Multipurpose Internet Mail Extensions (MIME) were developed to encode binary files for transfer through SMTP.
- 26. MIME Multipurpose Internet Mail Extensions
- 27. INTRODUCTION •Multipurpose Internet Mail Extensions (MIME) provides a standardized way of dealing with a wide variety of information representations in a multimedia environment. It is an internet standard that extends the format of email to support: 1. Text in character sets other than ASCII, like US-ASCII. 2. Multi-media attachments: audio, video, images, application programs etc. 3. Multiple objects in a single message. 4. Multiple font messages.
- 28. 5. Messages of unlimited length. 6. Binary files. 7. Header information in non-ASCII character sets. •Virtually all human-written internet email and a fairly large proportion of automated email is transmitted via SMTP in MIME format.
- 29. •MIME was designed mainly for SMTP, but the content types defined by MIME standards are also of importance in communication protocols outside of email, such as Hyper Text Transfer Protocol (HTTP) for the World Wide Web.
- 30. • MIME encapsulates binary data in ASCII mail envelope. • Multipart – Used to combine several body parts of possibly different types & subtypes. • Application - Can be used to transmit application data, such as executables or binary data. ➢ Servers insert the MIME header at the beginning of any web transmission. ➢ Clients use this content type or media type header to select an appropriate viewer application for the type of data the header indicates. ➢ Some of these viewers are built into the web client or browser (for example, almost all browsers come with GIF and JPEG image viewers as well as the ability to handle HTML files).
- 31. •MIME Version : This field defines the version of MIME. •Content-Type : This field defines the type of data used in the body of message. Type and subtypes are separated by slash. MIME allows seven different types of data which are: Text, multipart, message, Image, Video, Audio, Application (post-script, stream). •Content-transfer-encoding : This field defines methods used to convert the message into 0s and 1s for transport. The various types are : 7-bit NVT ASCII, 8-bit Non ASCII, Binary Non- ASCII, Base-64 6-bit blocks of data encoded into 8-bit ASCII and Quoted-Printable Non-ASCII •Content Description : This field whether the body is image, audio or video.
- 32. Content- Type •This header is used to describe the content type of the message. The Content-Type header includes the type and a sub-type parts. eg: Content-Type: text/plain •Through the use of the multi-part type, MIME allows mail messages to have parts arranged in a tree structure where the leaf nodes are any non-multipart content type and the non-leaf nodes are a variety of multi-part types. This mechanism supports: 1) Simple text messages using text/plain. 2) Text plus attachments. A MIME message including an attached file generally indicates the file’s original name with the “Content-disposition:” header, so the type of file is indicated both by the MIME content-type and the filename extension. 3) Reply with original attached. 4) Alternative content, such as a message sent in both plain text and another format such as HTML. 5) Image, audio, video, and application (for example, image/jpeg, audio/mp3, video/mp4, and application/msword and so on). 6) Many other message constructs.
- 33. Content-Disposition •The original MIME specifications only described the structure of mail messages. They did not address the issue of presentation styles. It specifies the presentation style. There are two types of Content-Disposition: 1. Inline Content-Disposition The Inline Content-Disposition would be automatically displayed when the message is shown. 2. Attachment Content-Disposition •The Attachment Content-Disposition will not be displayed automatically. It needs the user action to get opened and displayed. •The content-disposition header also provides fields for specifying the name of the file, the creation date, and modification date, which can be used by the reader’s mail user agent to store the attachment. eg: Content-Disposition: attachment; filename=genome.jpeg; •Now a day, a good majority of mail user agents do not follow this prescription fully. The widely used Mozilla Thunderbird mail client makes its own decisions about which MIME parts should be automatically displayed, ignoring the content-disposition headers in the messages.
- 34. Content-Transfer-Encoding •In June 1992, MIME defined a set of methods for representing binary data in formats other than ASCII text format. The content-transfer-encoding: MIME header has 2-sided significance: •It indicates whether or not a binary-to-text encoding scheme has been used on top of the original encoding as specified within the Content-Type header: 1) If such a binary-to-text encoding method has been used, it states which one. 2) If not, it provides a descriptive label for the format of content, with respect to the presence of 8-bit or binary content. •Note that ‘7bit’, ‘8bit’, and ‘binary’ mean that no binary-to-text encoding on top of the original encoding was used. In these cases, the header is actually redundant for the email client to decode the message body, but it may still be useful as an indicator of what type of object is being sent. • Values ‘quoted-printable’ and ‘base64’ tell the email client that a binary-to-text encoding scheme was used and that appropriate initial decoding is necessary before the message can be read with its original encoding.
- 35. How MIME works? •When you compose a message in an email program capable of MIME, the program does roughly the following: •If the message is in plain ASCII text only, it leaves it alone and only tells the recipient's email client to expect nothing but plain text. •If the message contains one or more attachments and a body with HTML formatting, each part is looked at and treated separately. •First, the format of the data is determined. This is necessary to tell the recipient's email client what to do with the data, and to ensure proper encoding so nothing is lost during transfer.
- 36. How MIME works? • Then the data is encoded if it is in a format other than plain ASCII text. In the encoding process, the data is converted to the plain text suitable for RFC 822 messages. • Finally, the encoded data is inserted in the message, and the recipient's email client is informed what kinds of data to expect: Are there attachments? How are they encoded? What format was the original file in? • On the recipient's end, the process is reversed. First, the email client reads the information that was added by the sender's email client: Do I have to look for attachments? How do I decode them? how do I handle the resulting files? • Then, each part of the message is extracted and decoded if necessary. Finally, the email client displays the resulting parts to the user. The plain text body is shown in line in the email client together with the image attachment.
- 37. Encoding •The transport systems of email is designed for plain ASCII text only. •Binary files need to be “packaged” as text in order to be sent over the internet •As a result of this encoding, standard SMTP servers did not require any changes •Encoding transforms binary data into a string •Decoding changes the data back into its original form
- 38. Encoding Formats
- 39. Base64 Encoding •Takes 3 bytes and represents them as four printable characters in ASCII standard •Each character is of 6 bits, corresponding to 2^6 = 64 characters •Steps involved are STEP 1 : Convert three bytes to four numbers of six bits STEP 2 : Convert to ASCII characters using Base64 encoding table •To ensure the encoded data can be properly printed and does not exceed any mail server's line length limit, newline characters are inserted to keep line lengths below 76 characters
- 41. Example: 155 162 233 1 0 0 1 1 0 1 1 1 0 1 0 0 0 1 0 1 1 1 0 1 0 0 1 38 58 11 41 m6Lp
- 42. Base64 Encoding • If the size of the original data in bytes is not a multiple of three, we might end up with one or two 8-bit bytes •Append enough bytes with a value of '0' to create a 3-byte group. •these artificial trailing '0's cannot be encoded using the encoding table below. •The Base64 padding character is '='. Naturally, it can only ever appear at the end of encoded data.
- 43. Conclusion •SNMP manages various devices attached to a TCP / IP network. •SMTP deals with the methods, to send and receive email from one client to another over the internet. •one can control SMTP servers and MTAs through SNMP Managers. Further, SNMP Managers are capable of sending alerts through SMTP mail servers. •The SMTP protocol understands only 7-bit ASCII characters so cannot use it to send graphics or programs. MIME provides a standard by specifying a set of encoding rules and header extensions to the Internet standard message specification.
- 44. Thank You ! -By Shantanu Hinge (BT14ECE028) Isha Sagote (BT14ECE068) Shubham Kanhere (BT14ECE081) Sibhali Hastey (BT14ECE082) Soumita Mandal (BT14ECE085) Srushti Gajbhiye (BT14ECE086) Utkarsha Warghade (BT14ECE098)