Re: [Agentx] Empty context in rfc2742

[Magnus Fromreide <[e-mail]>]

On Sun, 2009-08-30 at 13:48 -0400, Mark Ellison wrote:
> On Sun, Aug 30, 2009 at 5:17 AM, Magnus Fromreide<[e-mail]> wrote:
> > Hello.
> >
> > According to rfc2742 agentxRegContext (octet string) is
> >     "The context in which the session supports the objects in this
> >      region.  A zero-length context indicates the default context.
> >     "
> >
> > Now I am would like to know how a zero-length context should be
> > represented?
> >
> The default context is an OCTET STRING of zero-length.

Not according to RFC 2741 6.1.1 §4.

In agentxRegContext we are looking a AgentX registrations and in this
domain it is explicitly stated that NON_DEFAULT_CONTEXT "" is distinct
from DEFAULT_CONTEXT but I can see no provision for the MIB to represent
that.

> How to represent this depends upon where it is being represented.
> 
> On the wire, the tag is "OCTET STRING" the length is zero(0) and the
> value occupies no octets.  There are numerous examples of OCTET
> STRINGs that may be zero-length in IETF standard MIB modules.
> 
> For example, in the UsmUserTable, the usmUserPublic may be a
> zero-length string.  In the USM MIB module, tthe usmUserPublic object
> definition shows he zero-length string as represented by the DEFVAL
> clause:  { ''H }  -- the empty string.
> 
> A zero-length string and the empty-string are synonymous.

This is about the specific case of AgentX - we are talking about a
zero-length string and a non-existing string. 

> - Mark
> http://EllisonSoftware.com