Re: [irs-discuss] Comments on Topology API use case document

Thomas Nadeau <> Wed, 03 October 2012 12:10 UTC

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Date: Wed, 3 Oct 2012 08:10:16 -0400
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To: Shane Amante <>
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Subject: Re: [irs-discuss] Comments on Topology API use case document
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On Oct 3, 2012:12:56 AM, at 12:56 AM, Shane Amante <> wrote:

> Hi Joel,
> Thanks for your review.  Please see below.
> On Oct 2, 2012, at 8:38 PM, Joel M. Halpern <> wrote:
>> Overall, this looks very helpful.
>> In the terminology section, two things struck me:
>> First, we probably need to consistently qualify the term "Policy Manager".  What is described in this document as the "Policy Manager" is a very interesting and powerful function.  it is a policy function.  But it is no more the entire policy manager than a security policy manager is the entire policy manager.  It seems to me that this is a discipline we need to acquire early, or we will forever find ourselves arguing about the meaning of terms when we actually agree.  (The later description of the Policy Manager edges into the broader perspective, but isn't really the same.)
> We'll look at making the text in terminology section better align with the broader definition of a Policy Manager in Section 3.3. 
> Indeed, a "Policy Management" function is indeed critical.  Arguably, it's in the top two most critical elements of this work, IMO.  And, you're right that we need to align on definitions for what it is for fear or forever qualifying it.  The reason we chose "Policy Manager" is that it seemed the closest match to what are (likely) considered routine functions in networking today, namely, "routing policies" (cf: BGP), "security policies" (cf: ACL preventing/allowing packets through), etc.  Is that part clear?  Note, at this stage, we're depicting this as a single "Policy Manager" function; however, if this work evolves it's likely this will get broken down into sub-components (security, routing, etc.) to more precisely define their domain-specific attributes.
>> I have to disagree with the definition of Multi-Layer Topology.  I agree that topologies are layered.  However, the OSI topology abstraction is absolutely wrong.  As was pointed out to me many years ago, and has become more prevalent ever sine, w run L2 VPN services on MPLS infrastructure on IP infrastructure, which is in term supported by Ethernet, some which may actually be emulated Ethernet on MPLS on ...
> Hrm.  Ultimately, what I think you're describe is a perfect example of building a specific hierarchical network.  The problem is, today, we *DO NOT* have any (standards-based) way to represent the reality of those hierarchical relationships /outside of/ the data-plane and control-plane[1].  Over the years, we've clearly engineered such hierarchy directly into the routing (and, forwarding) planes of network equipment.  In addition, we've barely enumerated some attributes of *individual* protocols or network components, (cf: SNMP MIB's), but they are entirely /standalone/.  Instead, we need to take the next step.  Specifically, we need to fully enumerate attributes and, more importantly, metadata of individual control & data-plane protocols (and, related network components) using a common, standards-based *vocabulary*.  Only once we do that will it be possible to:
> a) Define hierarchical relationships between network components (protocols, services, etc.), using the aforementioned attributes/metadata as filtering/selection criteria, as appropriate; and,
> b) Summarize all of this vocabulary into schemas/data-models that can then be exchanged between systems that *DO NOT* (cannot *and* will not) directly participate in routing & forwarding.
> Ultimately, this is the core essence of SDN/IRS.
> [1] BGP recursing to an IGP for next-hop; LDP relying on IGP to determine shortest-path, etc.

	Just to add to this. Joel, while I agree with you RE: the "OSI topology", we are not trying to enumerate EVERYTHING in the network nor are we out to incarnate those theoretical layers. Ultimately what we want is to represent different abstractions of topology that are used for routing/switching. This is really a matter of grouping links/ports/nodes, their facets, and then connecting or relating them together. This then can represent active and inactive topological elements in arbitrary ways, but more importantly, how they really exist within one's network versus a theoretical model (i.e.: OSI). 

>> While I appreciate the importance of the Inventory function in evaluating SRLGs, I think the document should probably point out that this often depends upon physical realities not visible to any automated system.  (The number of stories of operators failing to meet diversity guarantees are legion.)
> Really!?!?  ;-)
> More seriously, I thought this was made clear in the first two paragraphs of Section 4.1.1, "Capacity Planning and Traffic Engineering":
> ---snip---
>   [...] Due to this inefficiency, the
>   underlying physical network inventory information, (containing SRLG
>   and corresponding critical network asset information), used by the
>   IP/MPLS Capacity Planning and TE applications is not updated
>   frequently, thus exposing the network to, at minimum, inefficient
>   utilization and, at worst, critical impairments.
> ---snip---
>> I find it strange that this draft describes change application using a different paradigm than the other IRS drafts.  Is this deliberate, indicating that these use cases need a different mechanism than is elsewhere described?  (I wold have simply indicated that the Topology manager will need to apply changes, and left it there as far as this document is concerned.
> I'm not sure I understand the above comment.  Can you elaborate?

	I agree; I am confused. The draft does not (intentionally) describe any specific mechanisms; the aim was to describe how normalized topology could be used.  We have a forth coming requirements draft that further elaborates on what components need to exist in order for these use cases to work.


> -shane
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