Re: [Agentx] Empty context in rfc2742

Mark Ellison <ellison@ieee.org> Sun, 30 August 2009 17:48 UTC

Return-Path: <mark@ellisonsoftware.com>
X-Original-To: agentx@core3.amsl.com
Delivered-To: agentx@core3.amsl.com
Received: from localhost (localhost [127.0.0.1]) by core3.amsl.com (Postfix) with ESMTP id 7AF263A6A8D for <agentx@core3.amsl.com>; Sun, 30 Aug 2009 10:48:30 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -101.902
X-Spam-Level:
X-Spam-Status: No, score=-101.902 tagged_above=-999 required=5 tests=[AWL=0.075, BAYES_00=-2.599, FM_FORGED_GMAIL=0.622, USER_IN_WHITELIST=-100]
Received: from mail.ietf.org ([64.170.98.32]) by localhost (core3.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id wpsOmlXs5hLH for <agentx@core3.amsl.com>; Sun, 30 Aug 2009 10:48:29 -0700 (PDT)
Received: from mail-yw0-f174.google.com (mail-yw0-f174.google.com [209.85.211.174]) by core3.amsl.com (Postfix) with ESMTP id 5B9893A682F for <agentx@ietf.org>; Sun, 30 Aug 2009 10:48:29 -0700 (PDT)
Received: by ywh4 with SMTP id 4so6895205ywh.17 for <agentx@ietf.org>; Sun, 30 Aug 2009 10:48:34 -0700 (PDT)
MIME-Version: 1.0
Sender: mark@ellisonsoftware.com
Received: by 10.150.61.18 with SMTP id j18mr5928956yba.173.1251654514670; Sun, 30 Aug 2009 10:48:34 -0700 (PDT)
In-Reply-To: <1251623843.6043.6.camel@sara.home>
References: <1251623843.6043.6.camel@sara.home>
Date: Sun, 30 Aug 2009 13:48:34 -0400
X-Google-Sender-Auth: 2f40d4508d66ee7a
Message-ID: <8a0268750908301048i2b4a477dod97e582238098bbe@mail.gmail.com>
From: Mark Ellison <ellison@ieee.org>
To: Magnus Fromreide <magfr@lysator.liu.se>
Content-Type: text/plain; charset=ISO-8859-1
Cc: agentx@ietf.org
Subject: Re: [Agentx] Empty context in rfc2742
X-BeenThere: agentx@ietf.org
X-Mailman-Version: 2.1.9
Precedence: list
List-Id: SNMP Agent Extensibility <agentx.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/listinfo/agentx>, <mailto:agentx-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/agentx>
List-Post: <mailto:agentx@ietf.org>
List-Help: <mailto:agentx-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/agentx>, <mailto:agentx-request@ietf.org?subject=subscribe>
X-List-Received-Date: Sun, 30 Aug 2009 17:48:30 -0000

On Sun, Aug 30, 2009 at 5:17 AM, Magnus Fromreide<magfr@lysator.liu.se> 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.   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.

- Mark
http://EllisonSoftware.com