Re: [netconf] [yang-doctors] Yangdoctors last call review of draft-ietf-netconf-subscribed-notifications-21

"Eric Voit (evoit)" <evoit@cisco.com> Fri, 25 January 2019 15:41 UTC

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From: "Eric Voit (evoit)" <evoit@cisco.com>
To: Martin Bjorklund <mbj@tail-f.com>
CC: "andy@yumaworks.com" <andy@yumaworks.com>, "Reshad Rahman (rrahman)" <rrahman@cisco.com>, "alexander.clemm@huawei.com" <alexander.clemm@huawei.com>, "yang-doctors@ietf.org" <yang-doctors@ietf.org>, "netconf@ietf.org" <netconf@ietf.org>, "draft-ietf-netconf-subscribed-notifications.all@ietf.org" <draft-ietf-netconf-subscribed-notifications.all@ietf.org>
Thread-Topic: [yang-doctors] Yangdoctors last call review of draft-ietf-netconf-subscribed-notifications-21
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Date: Fri, 25 Jan 2019 15:41:47 +0000
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Subject: Re: [netconf] [yang-doctors] Yangdoctors last call review of draft-ietf-netconf-subscribed-notifications-21
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> From: Martin Bjorklund, January 25, 2019 10:30 AM
> 
> "Eric Voit (evoit)" <evoit@cisco.com>; wrote:
> > > From: Martin Bjorklund, January 25, 2019 3:40 AM
> > >
> > > "Eric Voit (evoit)" <evoit@cisco.com>; wrote:
> > > > > "Eric Voit (evoit)" <evoit@cisco.com>; wrote:
> > > > > > > "Eric Voit (evoit)" <evoit@cisco.com>; wrote:
> > > > > > > > > From: Martin Bjorklund, January 24, 2019 9:40 AM
> > > > > > > > >
> > > > > > > > > "Eric Voit (evoit)" <evoit@cisco.com>; wrote:
> > > > > > > > > > > From: Martin Bjorklund, January 24, 2019 8:17 AM
> > >
> > > [...]
> > >
> > > > > > > > > > > Thinking some more, what is supposed to happen if
> > > > > > > > > > > the client on the same session sends first an
> > > > > > > > > > > establish-subscription with dscp 42, and then
> > > > > > > > > > > another
> > > > > > > > > > > establish-
> > > subscription with dscp 10?
> > > > > > > > > >
> > > > > > > > > > This would be allowed.
> > > > > > > > >
> > > > > > > > > On linux at least this is a sockopt, i.e., the option
> > > > > > > > > applies to the socket, which means all packets on the
> > > > > > > > > session.  So how is this supposed to be implemented if
> > > > > > > > > different messages on the session should have different
> > > > > > > > > dscp values?
> > > > > > > > > Or is the
> > > > > > > > > idea that you send the msg, flush all data from ssh/tls
> > > > > > > > > to tcp, then flush the tcp buffers (not that easy...)?
> > > > > > > > >
> > > > > > > > > Even if there's just one establish-subscription with a
> > > > > > > > > dscp value, since it applies to the session it means
> > > > > > > > > that all normal rpcs on this session will get the same dscp value.
> > > > > > > > > It is not clear that this is the intention?
> > > > >
> > > > > Did you miss these questions?
> > > >
> > > > With NETCONF, one DSCP will apply to single TCP session.  So there
> > > > is no
> > > issue.
> > >
> > > The problem is if a client sends two establish-subscriptions with
> > > different values for dscp on the same session.  Or even if the
> > > client sends one
> > > establish-
> > > subscription with som dscp value, then the dscp will be applied to
> > > all packets from other rpcs as well.
> > >
> > > ... and even worse, with SSH channels you can have multiple NETCONF
> > > session on the same TCP session, which means that the dscp value
> > > applies to all packets in all NETCONF sessions sharing the same TCP
> > > session.
> > >
> > > I don't know what the right thing to do is.  Probably first agree
> > > that this is in fact a problem, then maybe simply document this
> > > somehow.
> >
> > I hadn't thought about multiple NETCONF SSH channels.  I agree
> > something to guide developers is needed here.  The easiest fix is to
> > recommend not supporting feature "dscp" with NETCONF.  (It shouldn't
> > be absolutely prohibited as DSCP related RFC's such as RFC7657 embed
> > text like "a single DSCP should be used for all packets in a TCP
> > connection".)
> >
> > Here is the text I suggest is put into
> > draft-ietf-netconf-netconf-event-notifications, Section 5:
> >
> > "The feature "dscp" SHOULD NOT be supported over NETCONF.  This will
> > avoid the potential for out-of-order packet delivery of the set of all
> > traffic within the TCP session."
> 
> I think this is a bit too limiting.  For configured subscriptions it can be perfectly
> fine, since the server can ensure that there's a single TCP session to the receiver
> in this case.  (I know we don't support configured subscriptions at the moment).
> 
> Perhaps we can say in the SN document:
> 
>   If a server that supports the "dscp" feature cannot guarantee that
>   the only packets sent on an underlying transport session are from
>   the subscription, then it should reject the subscription with a
>   "dscp-unavailable" error.  This will avoid the potential for
>   out-of-order packet delivery of the set of all traffic within the
>   TCP session.

This works for me.    I will put this in Section 2.3, directly after the sentence: 

   If the publisher supports the "dscp" feature, then a subscription
   with a "dscp" leaf MUST result in a corresponding [RFC2474] DSCP
   marking being placed within the IP header of any resulting
   notification messages and subscription state change notifications.

 unless I hear any objections on this thread.

Eric
 
> I think such text belongs to the SN document, since it may apply to other
> transports than just NETCONF.
> 
> 
> /martin
> 
> 
> 
> > With this text, a RESTCONF publisher can support the feature dscp.
> > And if someone attempts to use dscp with a NETCONF subscription to the
> > same publisher, the error "dscp-unavailable" can be sent.
> >
> > Eric
> >
> >
> > ...
> > > /martin
> >