Subject: Re: [ipfix-protocol] PROTO-5, 6, 7, 8, 9, 10, 11: SCTP and SCTP-PR

From: David Moore <[email-masked]>
Date: Thu, 05 Aug 2004 01:22:59 -0700

Stewart Bryant <[email-masked]> writes:

> The last para should be changed to:
>
> If the Collecting Process receives an IPFIX Message that it cannot
> decode, it MUST reset the SCTP association, discard the message
> and log the error.
>
> and then we should add the following paragraph:
>
> When an SCTP association is closed, the Collecting Process MUST
> discard all templates
> received over that association and stop decoding IPFIX Messages that
> use those templates.

Hi Stewart,

I think this needs better definition of what an 'SCTP association' is.
Is it a single SCTP connection, or is it all SCTP connections between
that particular exporter and this collector?  I might be mistaken, since
I haven't read this part of the proto drafts more than once, but I
thought it was permissible for an exporter to make multiple SCTP (or
even mixed SCTP/TCP/UDP/whatever) connections to a single collector, in
order to do things including `ship templates across one stream and data
records across another'.  Imagine 4 streams, one each for data
templates, option templates, flow records and option records.  If there
is an error with a data template, does it close just that one SCTP
connection or all 4?  If it closes the data template stream, SHOULD the
collector buffer flow records until it sees the template?  To me "stop
decoding IPFIX messages that use those templates" means 'discard' not
'buffer and wait for the template to be retransmitted'.

Also, this may raise an important issue for collector writers (which maybe
should be spelled out explicitly), that not only do you have to know
what Exporter IP address and Source ID a template came from, but you may
have to know which particularly SCTP/etc stream it came from.

What happens if an exporter sends the same template (ie a refresh) on
two different streams?  Should only the most recent stream be used for
purposes of discarding templates?  ie, the collector forgets that it
also got it on a different stream previously?  Or should the collector
remember all of the streams on which it has received this template and
only discard the template if all of those streams have failed?

-- david

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