Re: [netmod] questions about draft-rtgyangdt-rtgwg-device-model-00

Nadeau Thomas <tnadeau@lucidvision.com> Wed, 19 August 2015 12:49 UTC

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Subject: Re: [netmod] questions about draft-rtgyangdt-rtgwg-device-model-00
From: Nadeau Thomas <tnadeau@lucidvision.com>
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Date: Wed, 19 Aug 2015 08:48:28 -0400
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To: Berger Lou <lberger@labn.net>
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Cc: Routing WG <rtgwg@ietf.org>, Andy Bierman <andy@yumaworks.com>, netmod WG <netmod@ietf.org>, draft-rtgyangdt-rtgwg-device-model@ietf.org
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> On Aug 18, 2015:9:38 PM, at 9:38 PM, Lou Berger <lberger@labn.net>; wrote:
> 
> [Adding authors and RTG WG.]
> 
> Hi Andy,
>    I'm not sure who you are looking to hear from as you addressed this
> mail to the netmod list. I'm happy to give my opinion as it seems you
> might have been aiming this at the draft authors.  (but then again
> perhaps not.) 
> 
> On 8/18/2015 8:01 PM, Andy Bierman wrote:
>> Hi,
>> 
>> I assume this draft is what we should be reviewing and not
>> the obsolete openconfig draft?
> 
> My personal view / hope is that the openconfig draft will be revised to
> cover requirements

	Can you be specific about which requirements you feel are not covered ?

	—Tom


> while the DT draft  leads to an agreed upon approach
> to addressing those requirements.  Again, just stating my view, not the
> view of the DT, co-authors or OC draft authors.
> 
>> 
>> 
>> https://tools.ietf.org/html/draft-rtgyangdt-rtgwg-device-model-00
>> 
>> 
>> Q1) scope
>> 
>> 
>> sec 2:
>> 
>>   The model organization can itself be thought of as a "meta-model",
>>   in that it describes the relationships between individual models.  We
>>   choose to represent it also as simple YANG model consisting of lists
>>   and containers to serve as anchor points for the corresponding
>>   individual models.
>> 
>>   As shown below, our model is rooted at a "device", which represents a
>>   network router, switch, or similar network element.  
>> 
>> 
>> Why is this a meta-model?
> because the aim to to show how other models inter-relate rather than
> define the details of all models. As stated in the intro:
> 
>   This document aims to provide an extensible structure that can be
>   used to tie together other models. It allows for existing, emerging,
>   and future models. The overall structure can be constructed using
>   YANG augmentation and imports.
> 
> 
>> It looks like a real YANG data model where ad-hoc classification is
>> being done
>> using container names.
> 
> Sure, we're using YANG, or at least trying, to document our proposal. 
> Do you think there's a better way to formally document the work?
> 
>> 
>> If vendors augment this tree with their own ad-hoc hierarchy, then how
>> is this
>> any better than what we have now?
>> 
> This goes to requirements which is really in the scope of
> draft-openconfig-netmod-model-structure.  From my perspective it comes
> down to how much information is needed from an actual device in order to
> come up with its yang-based configuration, and the principle that there
> is benefit in this being minimized.  For example, consider the case
> where a config is generated before a specific device is fielded or
> perhaps even purchased/selected. But again, this more of a requirements
> discussion.
> 
>> What is the scope of this work?
> see slide 7 of
> https://www.ietf.org/proceedings/93/slides/slides-93-rtgwg-3.pdf
> 
>> It appears to be only for "routers switches or similar network elements".
>> 
>> From the slide:
>   From DT charter: An overall architecture for
>   “the protocols and functionality contained inside the Routing Area”
> 
>> The hierarchy seems quite router-centric.
> It is intended to be network device centric, routers, switches,
> firewalls, etc.
> 
>> Is the expectation that all YANG-based devices will use this
>> data hierarchy, or only some devices?
> The proposal is to provide a framework for any device that supports a
> protocol or other mechanism defined within the routing area.  (Or at
> least that's our understanding of what we were asked to do.)
> 
>> 
>> Is the expectation that all YANG modules will use this
>> data hierarchy, or only some modules? 
> 
> I personally think there will be siblings to /device, e.g., /service -
> but this is beyond the scope of this draft.
> 
>> Is it just
>> for IETF routing modules or more than that?
>> 
> I think this is the same question and answer as above.
> 
>> Q2) interfaces
>> 
>>   The interface model is taken from [RFC7223 <https://tools.ietf.org/html/rfc7223>] and includes possible
>>   technology-specific augmentations using example technologies defined
>>   in [RFC7277 <https://tools.ietf.org/html/rfc7277>].
>>  +--rw interfaces
>>      |  +--rw interface* [name]
>>      |     +--rw name                       string
>>      |     +--rw bind-network-element-id?   uint8
>>      |     +--rw ethernet
>>      |     |  +--rw bind-networking-instance-name?   string
>>      |     |  +--rw aggregates
>>      |     |  +--rw rstp
>>      |     |  +--rw lldp
>>      |     |  +--rw ptp
>>      |     +--rw vlans
>>      |     +--rw tunnels
>>      |     +--rw ipv4
>>      |     |  +--rw bind-networking-instance-name?   string
>>      |     |  +--rw arp
>>      |     |  +--rw icmp
>>      |     |  +--rw vrrp
>>      |     |  +--rw dhcp-client
>>      |     +--rw ipv6
>>      |        +--rw bind-networking-instance-name?   string
>>      |        +--rw vrrp
>>      |        +--rw icmpv6
>>      |        +--rw nd
>>      |        +--rw dhcpv6-client
>> 
>> 
>> Actually the interface model is quite different than the one in RFC 7223.
>> Seems rather ethernet-centric.  I notice the "type" leaf was removed,
>> along with everything else.  Is the plan to toss out RFC 7223,
>> recharter the interfaces work, and start over?
>> 
> 
> So this may be our/my inexperience at play here.  I didn't think it
> appropriate for a document that is augmenting an existing model to
> redefine the current model - I actually thought this was part of the
> power of YANG augmentation.  Are you saying we should have included the
> whole 7223 model to augment it, or something different?
> 
> Also not the text says:
>        ... possible technology-specific augmentations  using example
> technologies ..
> and
> 
>   The interfaces container includes a number of commonly used
>   components as examples:
> 
>> Q3) virtual devices
>> 
>>   The model supports the potentially independent system management
>>   functions and configuration per logical network element. This
>>   permits, for example, different users to manage either the whole
>>   device or just the associated logical network element. 
>> 
>> Sec 2.2.1 shows the system management tree but it is wrong.
> 
> Yes, good catch of a cut-and-past bug. thankfully it is correct both
> immediately before in the section intro and the details
> 
>> The following tree is what the YANG model defines:
>> +--rw device
>>          +--rw logical-network-elements
>>               -rw logical-network-element* [network-element-id]
>>                   +--rw network-element-id                  uint8
>>                   +--rw network-element-name?               string
>>                   +--rw default-networking-instance-name?   string
>>                   +--rw system-management
>>                   |  +--rw device-view?                      boolean
>>                   |  +--rw syslog
>>                   |  +--rw dns
>>                   |  +--rw ntp
>>                   |  +--rw statistics-collection
>>                   |  +--rw ssh
>>                   |  +--rw tacacs
>>                   |  +--rw snmp
>>                   |  +--rw netconf
>> What about devices that do not have logical network elements?
> It would have only a single network-element-id
> 
>> This hierarchy may be appropriate for very large routers
>> but nothing else.
> The intent is to cover all implementations independent of vendors.  We
> had a good range of view points both in the DT and in the RTGWG
> discussion.  Not saying there was full agreement, just that we have a
> proposed starting  point.
> 
>> How can this tree represent both the physical view and the virtual view?
> Are you referring to section 2.3?  If so, I think we all agree (and said
> as much in Prague) that this section could be clearer.  We/I tried to
> explain it in the Prague slide 25 (for this you may want to see the
> animation in
> https://www.ietf.org/proceedings/93/slides/slides-93-rtgwg-3.pptx)
> 
> Basically the amount of information provided depends on the
> logical-network-element context used to access this information.  So if
> a model is "retrieved" via an IP address associated with a
> network-element-id  with device-view=true (e.g., the left side of slide
> 25), then the device's full view is provided.  And when a model is
> "retrieved" via an IP address associated with a network-element-id  with
> device-view=false (e.g., the ride side of slide 25, either color) only
> information related to the network-element-id is provided.
> 
>> It seems to assume this is the "root user physical view".
>> Please explain how device-type=VIRTUAL is used.
> 
> This is a bit different and hasn't been a major point of discussion in
> the WG -- we brought this over from the openconfig draft.  I read this
> as being pretty uninteresting and simply set based on if the device is
> running on dedicated special purpose h/w (e.g, a classic
> "name-your-vendor" router) or as a VM (aka NFV).  I'll defer to the OC
> or other DT folks if their opinion differs.
> 
> Thanks for the comments/discussion!
> 
> Lou
> 
>> Andy
>> 
>> 
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> 
> 
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