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SNMP Protocol Security Issues and Methods
(Page 3 of 3)
SNMPv2/v3 Security Methods
During the evolution
of SNMPv2 variants, and eventually the creation of SNMPv3, several new
security models were created to improve upon SNMPv1's security:
- Party-Based Security Model: This was the
security model for the original SNMPv2 standard, now called SNMPv2p.
A logical entity called a party is defined for communication
that specifies a particular authentication protocol and a privacy (encryption)
protocol. The information is used to verify that a particular request
is authentic, and to ensure that the sender and receiver agree on how
to encrypt and decrypt data.
- User-Based Security Model (USM): This
was developed in the SNMPv2u variant and used in SNMPv2* (SNMPv2 asterisk);
it eventually was adopted in SNMPv3. The idea here is to move away from
tying security to the machines and instead use more traditional security
based on access rights of a user of a machine. A variety of authentication
and encryption protocols can be used to ensure access rights are respected
and to protect message privacy. The method relies on time stamps, clock
synchronization and other techniques to protect against certain types
- View-Based Access Control Model (VACM):
VACM is part of SNMPv3, and defines a method where more fine control
can be placed on access to objects on a device. A view specifies
a particular set of MIB objects that can be accessed by a particular
group in a particular context. By controlling these views an administrator
can manage what information is accessed by whom.
These descriptions are grossly
simplified, to say the least. Security is probably the most complicated
subtopic in networking, and describing these methods in detail would
require dozens and dozens of topics. You can refer to the relevant standards
if you want more information, though unless you are well-read on security
topics, you will likely not be able to make heads or tails out of what
is written in them.
Use of SNMP Security Methods
Party-based security pretty much
died with SNMPv2p; USM and VACM are part of SNMPv3 and provide enhanced
security for those who need it (though again, it's interesting to note
how many networks continue to use SNMPv1, security warts and all.) SNMPv3
took another important security-related step in redefining the SNMP
architecture to seamlessly support multiple security models. This enables
different implementations to choose the security model that is best
for them. USM is the default model in SNMPv3.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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