Re: Truncation of trap by snmptrapd with DisplayString ending in null

On 16/09/2007, Jason Baekey <[email protected]> wrote:
>     I'm not sure whether this is a problem with snmptrapd or with the
> agent/mib declaration of the vendor.


>     sessionUserName  OBJECT-TYPE
>         SYNTAX  DisplayString (SIZE (0..31))
>         MAX-ACCESS  read-only
>         STATUS  current
>         DESCRIPTION
>         "The user name of the user logged-in."
>
> [Removed for clarity]
>
> The sessionUserName is transmitted to the trap station as a HEX STRING with
> a null character as the final character.

SNMP uses a length-value approach to representing strings.
It does not use the C-style trailing-NULL approach.

If you are receiving a sessionUserName varbind with the value
"dave\0"  (including the trailing null), then this implies that the
user name of the user logged in is "dave\0" (including the trailing null)

Somehow, I doubt this is the case!

I would suggest that this is probably a bug in the agent implementation.
The sessionUserName varbind value should not include the trailing null
character.

Now it could be argued that snmptrapd should be able to handle
embedded null characters, and display them sensibly.  But in
practise, NUL is not a character that you would ever expect to
find in a DisplayString value.

Dave

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