Re: [Netconf] a joint discussion on dynamic subscription

"Eric Voit (evoit)" <evoit@cisco.com> Wed, 13 June 2018 22:01 UTC

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From: "Eric Voit (evoit)" <evoit@cisco.com>
To: Tianran Zhou <zhoutianran@huawei.com>, Alexander Clemm <alexander.clemm@huawei.com>, "Zhengguangying (Walker)" <zhengguangying@huawei.com>, Martin Bjorklund <mbj@tail-f.com>, "netconf@ietf.org" <netconf@ietf.org>
Thread-Topic: a joint discussion on dynamic subscription
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Date: Wed, 13 Jun 2018 22:01:06 +0000
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Subject: Re: [Netconf] a joint discussion on dynamic subscription
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Hi Tianran,

> From: Tianran Zhou, June 12, 2018 11:47 PM
> 
> Hi Eric,
> 
> When we are discussing the draft-ietf-netconf-udp-pub-channel, we find a
> conflict with current dynamic subscription design.
> 1. The dynamic subscription requires notification to use the same channel as
> the subscription.

This is true when you look at the NETCONF transport draft.  However this is *not* required by the base subscribed-notification draft.  And in fact, the HTTP transport draft might not use the same logical channel.  E.g., see how the URI is returned within:
https://github.com/netconf-wg/notif-restconf/blob/master/draft-ietf-netconf-restconf-notif-05.txt 

So if you wanted to define some transport session independence for a UDP transport, subscribed-notifications should permit that.   And if you believe there is something in the text which prohibits this, let me know.

> 2. The RPC does not have the input information about the receiver because the
> above assumption.
> 
> However, when we talk about the distributed data collection (multi data
> originators), the publication channel is always different from the subscription
> channel.

While it likely isn't what you want, even with NETCONF, the single NETCONF session doesn't means that distributed line card generation of the notification messages is impossible.  For example, the inclusion of the header object message-generator-id (as defined within draft-ietf-netconf-notification-messages) allows the notification message generation to be distributed onto linecards even if the messages themselves are still driven back to a central transport session.  Note that I am not recommending this, but the specifications would support this.

> So either the distributed data collection does not support dynamic
> subscription, or current dynamic subscription definition may need
> modification.

I think for UDP, you will want to define a way to bind the lifecycle of the dynamic subscription's channels across multiple line cards.  This will require some thinking as well as coordination within the publisher.

Perhaps returning multiple URIs (one for each linecard) might be something which could make this easier.  If you go down this path, you still will need to fate-share the lifecycle of the subscription across all of those line cards.

Eric
 
> What's your thoughts?
> 
> Regards,
> Tianran