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.
|
|
|
|
SNMP Version 3 (SNMPv3) Message Format
In the late 1990s, SNMP version 3
was created to resolve the problems that occurred with the many
different variations of SNMPv2. The SNMPv3
Framework adopts many components that were created in SNMPv2, including
the SNMPv2 protocol operations, PDU types and PDU format. Amongst the
significant changes made in SNMPv3 include a more flexible way of defining
security methods and parameters, to allow the coexistence of multiple
security techniques.
The general message format for SNMPv3
still follows the same idea of an overall message wrapper
that contains a header and an encapsulated PDU. However, in version
3 this concept is further refined. The fields in the header have themselves
been divided into those dealing with security and those that do not
deal with security matters. The non-security fields are
common to all SNMPv3 implementations, while the use of the security
fields can be tailored by each SNMPv3 security model, and processed
by the module in an SNMP entity that deals with security. This solution
provides considerable flexibility while avoiding the problems that plagued
SNMPv2.
The overall SNMPv3 message format
is described in RFC 3412, which describes version 3 message processing
and dispatching. It is shown in Table 221
and Figure 285.
Figure 285: SNMP Version 3 (SNMPv3) General Message Format
|
Table 221: SNMP Version 3 (SNMPv3) General Message Format
Field
Name
|
Syntax
|
Size (bytes)
|
Description
|
Msg Version
|
Integer
|
4
|
Message Version Number:
Describes the SNMP version number of this message; used for ensuring
compatibility between versions. For SNMPv3, this value is 3.
|
Msg
ID
|
Integer
|
4
|
Message
Identifier: A number used to identify an SNMPv3 message and
to match response messages to request messages. The use of this field
is similar to that of the Request ID field in the PDU format
(see Table 218),
but they are not identical. This field was created to allow matching
at the message processing level regardless of the contents of the PDU,
to protect against certain security attacks. Thus, Msg ID and
Request ID are used independently.
|
Msg Max
Size
|
Integer
|
4
|
Maximum Message Size:
The maximum size of message that the sender of this message can receive.
Minimum value of this field is 484.
|
Msg
Flags
|
Octet
String
|
1
|
|
Msg Security
Model
|
Integer
|
4
|
Message Security Model:
An integer value indicating which security model was used for this message.
For the user-based security model (the default in SNMPv3) this value
is 3.
|
Msg
Security Parameters
|
|
Variable
|
Message
Security Parameters: A set of fields that contain parameters
required to implement the particular security model used for this message.
The contents of this field are specified in each document describing
an SNMPv3 security model. For example, the parameters for the user-based
model are in RFC 3414.
|
Scoped
PDU
|
|
Variable
|
|
And now, let's look at
the PDU format for SNMPv3. Ah ha! We are spared this, because SNMPv3
uses the protocol operations from SNMPv2; this is described in RFC 3416,
which is just an update of RFC 1904. Thus, the PDU formats are the same
as in the
previous topic. Phew!
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! |
|
|
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.
|