Re: [Netconf] the name "checksum" in YANG library

[Juergen Schoenwaelder <[e-mail]>]

I think the point is that we do not require this to be a counter nor
do we require this to be a hash of the yang library. Implementations
can do what they think is best as long as the content-id changes when
the content of the yang library changes, i.e., the content-id value
can be used to check whether a cached version of yang library can
still be used.

/js

On Fri, Oct 12, 2018 at 12:26:50PM +0100, Robert Wilton wrote:
> Hi Rohit,
> 
> If the server restarts, or the YANG management daemon on the server
> restarts, and the YANG library content is the same then it is less work on
> the client to return the same content-id value.
> 
> It isn't the end of the world if it is different because it just forces the
> client to re-download and re-parse YANG library. However, it could be a
> problem for the client if the server returns the same value if the server
> reboots and uses a different set of YANG modules after it has rebooted (e.g.
> after a software upgrade).
> 
> Perhaps if you write the counter to persistent storage this can still be
> made to work in a reliable way, but using a robust hash function over the
> contents in YANG library is probably a simpler approach.   I would predict
> that if MurmurHash3, generating a 128 bit hash value, is used over the Yang
> Library contents then the risk of a collision (i.e. where the content
> differs, but hashes to the same value) would be extremely low in practice.
> 
> Thanks,
> Rob
> 
> 
> On 12/10/2018 06:59, Rohit R Ranade wrote:
> > Hi Martin,
> > 
> > " The value of this leaf MUST change whenever the
> >        information in the YANG library changes." ==> This statement in Section 3, indicates that the value must change when content changes.
> > 
> > The draft has also placed a constraint that it is a " unique implementation-specific identifier". When the contents changes, especially if the length of the data which is used for checksum changes, then the resulting checksum values may not be unique.
> > 
> > So I feel it is simpler, if a counter is used.
> > 
> > With Regards,
> > Rohit
> > 
> > -----Original Message-----
> > From: Martin Bjorklund [mailto:[e-mail]]
> > Sent: 11 October 2018 17:01
> > To: Rohit R Ranade <[e-mail]>
> > Cc: [e-mail]
> > Subject: Re: [Netconf] the name "checksum" in YANG library
> > 
> > Rohit R Ranade <[e-mail]> wrote:
> > > Since this leaf has to change every-time the content of YANG library
> > > changes, "content-modify-count" can also be used which is simple for a
> > > server to implement (just increment when content changes) and also for
> > > client or a human reader to understand.
> > But it doesn't have to change everytime, it could very well be implemented as a checksum of the contents.
> > 
> > 
> > /martin
> > 
> > 
> > > 
> > > -----Original Message-----
> > > From: Netconf [mailto:[e-mail]] On Behalf Of Martin
> > > Bjorklund
> > > Sent: 11 October 2018 16:16
> > > To: [e-mail]
> > > Subject: [Netconf] the name "checksum" in YANG library
> > > 
> > > Hi,
> > > 
> > > Several reviewers in the IESG have commented that the name "checksum"
> > > in YANG library is misleading.  It is not really a checksum ('There is
> > > no requirement that the same information always results in the same
> > > "checksum" value.')
> > > 
> > > So since many people have complained, maybe we should change it.
> > > 
> > > After a quick discussion among (some of the) authors, we suggest that
> > > we call it "YANG library content identifier" or "content-id" for
> > > short.
> > > 
> > > The changes would be:
> > > 
> > > OLD:
> > > 
> > >     o  YANG library checksum: A server-generated checksum of the contents
> > >        of the YANG library.
> > > 
> > > NEW:
> > > 
> > >     o  YANG library content identifier: A server-generated identifier of
> > >        the contents of the YANG library.
> > > 
> > > 
> > > OLD:
> > > 
> > >     o  The "/yang-library/checksum" leaf contains the YANG library
> > >        checksum, which is a unique implementation-specific identifier
> > >        representing the current information in the YANG library on a
> > >        specific server.
> > > 
> > > 
> > > NEW:
> > > 
> > >     o  The "/yang-library/content-id" leaf contains the YANG library
> > >        content identifier, which is a unique implementation-specific
> > >        identifier representing the current information in the YANG
> > >        library on a specific server.
> > > 
> > > 
> > > .... and various simpler search&replaces.
> > > 
> > > 
> > > We would also update the schema-mount and netconf-nmda documents to
> > > use the new term.
> > > 
> > > 
> > > Does anyone object to this change?
> > > 
> > > 
> > > 
> > > /martin
> > > 
> > > _______________________________________________
> > > Netconf mailing list
> > > [e-mail]
> > > https://www.ietf.org/mailman/listinfo/netconf
> > > 
> > _______________________________________________
> > Netconf mailing list
> > [e-mail]
> > https://www.ietf.org/mailman/listinfo/netconf
> > .
> > 
> 
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-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
Fax:   [phone]         <https://www.jacobs-university.de/>