Re: difference between the usmUserName and the usmSecurityName

2008/4/24 Karthick Babu <[email protected]>:
> What`s the difference between the usmUserName and the usmSecurityName?

SNMPv3 was deliberately designed to accomodate several different
security models (SMs) - different mechanisms for deciding "who" is
making a given request.

As such, it works with the idea of a (SM-independent) "security name".
Each security model is responsible for defining the credentials it will
use, and how it will map these credentials into the security name
(and back again).


The User-based Security Model (USM) is one such example
of a Security Model (albeit the most commonly used by far!),
Part of the credentials it defines is the idea of a "User Name".
It's this user name (plus engineID), that is mapped into
the SM-independent security name.


>  "securityName is the same as the userName" - why is it not
>  enough to have only one of these columns within the usm table.

The description for usmSecurityName actually says

   The default transformation ,,,,, is the identity function
     so that the securityName is the same as the userName.

So the security name is *normally* the same as the user name.
But it's quite possible (in principle, at least) for a user name
to be mapped to a different security name.
  Or for two versions of the same user name (with different
security engine IDs) to be mapped to different security
names - one of which would therefore *have* to be different
to the original user name.


The whole point of the usmUserTable is to define this
    user name <-> security name
            mapping.
That inherently requires the table to include two separate fields.

Dave

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