Subject: [OPSAWG] hierarchical SMI to XML translation

From: Andy Bierman <[email-masked]>
Date: Thu, 06 Dec 2007 13:48:05 -0800

Hi,

Phil asked about flat vs. nested SMI translations at
the meeting.  I thought I would explain what that is,
and why SMIv2 never worked for configuration because of it.

SMIv2 does not allow nested tables (i.e., one of the columns
in the row is actually another table). With XML, a 'column'
can be a leaf, or be another container.

CLI is hierarchical.  To create a deep hierarchy in SMIv2,
you have to unfold the table, which means replicate all the
INDEX components that got you to the current node in a new table,
then add more INDEX components to that new table.

So, if 'myIfTable' has an INDEX of [ifIndex] and you wanted a list
of MAC addresses in each row of the table, you create a new table
with an INDEX of [ifIndex, macAddressIndex].

Without going into the SNMP details, this unnatural act
of unfolding tables is really horrible for writable objects,
and takes at least 10X more work in the agent than supporting
the same thing with the CLI.

Creating a hierarchical SMIv2 to XML translation is a matter of
putting these 'extra' tables back where they belong in the
original table.  (Way over-simplifying here, because there
are many variants to the unfolding algorithm).

IMO, one should use the SNMP protocol if
they want to manage their agent with SMIv2 data models.
XML offers so many opportunities for improvement over SMIv2,
(as demonstrated in YANG ;-).

Andy

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