Re: octet string as index

[Rajiv Raghunarayan <raraghun@cisco.com>]

Hi Tom,

Not sure what you mean by 'graphically', but if your question is
about how we represent instances with an octet string index, foll.
is what RFC 2578 says:

<snip>
(2)  string-valued, fixed-length strings (or variable-length preceded by
     the IMPLIED keyword):  `n' sub-identifiers, where `n' is the length
     of the string (each octet of the string is encoded in a separate
     sub-identifier);

(3)  string-valued, variable-length strings (not preceded by the IMPLIED
     keyword):  `n+1' sub-identifiers, where `n' is the length of the
     string (the first sub-identifier is `n' itself, following this,
     each octet of the string is encoded in a separate sub-identifier);
<snip>

i.e. if the index is an OCTET STRING is non-implied, an instance 
within the table is represented as:

<OID>.<length>.<zero or more octets of value>

Therefore a zero-length octet string is represented as <OID>.0.

An implied octet-string OTOH cannot be used as an index if the length
of the octet-string can be zero:

<snip - section 7.7, RFC 2578>
   Finally, the IMPLIED keyword may not be used on a variable-length
   string object if that string might have a value of zero-length.
<snip>

Hope this helps..

-Rajiv.

Tom Petch wrote:
> 
> If a zero length octet string is used as an index, how is it
> represented graphically as part of on OID?
> 0
> ..
> <null>
> ???
> And how does it collate w.r.t. non-zero length strings?
> 
> Tom Petch, Network Consultant
> nwnetworks@dial.pipex.com