Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

Enjoy The TCP/IP Guide? Get the complete PDF!
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Network Configuration and Management Protocols (BOOTP, DHCP, SNMP and RMON)
           9  TCP/IP Network Management Framework and Protocols (SNMP and RMON)
                9  TCP/IP Simple Network Management Protocol (SNMP) Protocol
                     9  SNMP Protocol Messaging and Message Formats

Previous Topic/Section
SNMP Protocol Message Generation, Addressing, Transport and Retransmission
Previous Page
Pages in Current Topic/Section
1
2
3
Next Page
SNMP Version 1 (SNMPv1) Message Format
Next Topic/Section

SNMP Message Field Definitions, General Message Format and Message Sections
(Page 2 of 3)

General Message Format

To understand SNMP messages, it is important that we first grasp the difference between SNMP messages and SNMP protocol data units (PDUs). We've seen in looking at SNMP protocol operations that the two terms are often used interchangeably. This is because each message carries one PDU, and the PDU is the most important part of the message.

However, strictly speaking, an SNMP PDU and an SNMP message are not exactly the same. The PDU is the actual piece of information that is being communicated between SNMP entities. It is carried within the SNMP message along with a number of header fields, which are used to carry identification and security information. Thus, conceptually, the SNMP message format can be considered to have two overall sections:

  • Message Header: Contains fields used to control how the message is processed, including fields for implementing SNMP security.

  • Message Body (PDU): Contains the main portion of the message. In this case, the message body is the protocol data unit (PDU) being transmitted.

The overall SNMP message is sometimes called a wrapper for the PDU, since it encapsulates the PDU and precedes it with additional fields. The distinction between the PDU and the message format as a whole began as a formality in SNMP version 1, but became quite important in later versions. The reason is that it allows the fields used for basic protocol operations (which are in the PDU) to be kept separate from fields used to implement security features. In SNMPv2, the implementation of security became a very big deal indeed, as we will see, so this flexibility was quite important.


Previous Topic/Section
SNMP Protocol Message Generation, Addressing, Transport and Retransmission
Previous Page
Pages in Current Topic/Section
1
2
3
Next Page
SNMP Version 1 (SNMPv1) Message Format
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.