[Nsi-wg] Topology Abstract sent to Terena

[Jeroen van der Ham]

Hi,

Jerry, please make shorter arguments. I think this is an important discussion, but I cannot dedicate all my time to reading your emails. Your point below could have been made a lot more succinctly.

Mapping different labels and/or layers (VLANs in this case) to different network representations has been studied before.[1] It has the advantage of making pathfinding somewhat simpler, at the cost of generating those representations. There are two problems with it:
- it makes the network representation a lot more complex, making it a lot harder to diagnose problems.
- you get multiple representations of the same link, which have an inter-dependency. You want to represent that the link can carry 10Gb, yet not all of the VLANs can carry 10Gb at the same time.

Jeroen.

[1]: Path selection in multi-layer networks, Fernando Kuipers, Freek Dijkstra:
http://staff.science.uva.nl/~fdijkstr/publications/multilayer-pathselection.pdf


On 11 Dec 2011, at 17:55, Jerry Sobieski wrote:

> Hi Jeroen-
> 
> See attached slides... (just two simple slides)
> 
> My point was that if you cannot ever swap between two particular endpoints (portx/vlan100 and porty/vlan101) then those two particular endpoints should not be advertised as being part a network service that says it can do "any to any" switching - it can't.   If you advertise this cross-connect capability (as we do implicitly), then you entice and invite remote agents to take advantage of that capability - one which internally you knew all the time was never possible - ever.   That seems dis-ingenuous to me at best, and malicious in some worst case.    Why not just advertise 1000 Gbps capability as well?    And this actually causes the "exhaustive search" problem.
> 
> This does not mean that the remaining flat vlan switching capability is not important and useful. Take StarLight for instance, it had four convergent physical links: JGN,KRL,NL, and ESN.  Each with the four VLANs.   Even though SL could not swap VLAN IDs in the process of switching VLANs, it could still switch VLANs nontheless.   So,  A VLAN 100 from JGN could in fact switch to either of the other three destinations KRL/vlan100, NL/vlan100, or ESN/vlan100 but it all cases it retains the same VLAN 100.   So a non-swapping switch still provides important conventional forwarding/crossconnect switching capability.   As it was, by advertising SL as a single physical Network rather than four separate Network Services we created the problem of 75% of advertised routes were impossible.
> 
> So we could have defined four VLAN planes SL80, SL81, SL82, SL83 -> each as a separate NSI Network, and each would have had four adjacencies.   And those established and advertised adjacencies (SDPs) will have been mapped apriori to the associated VLANs in both adjacent networks.  If the adjacent network is also "VLAN challenged" the dependencies would have already been expressed in their [internal] topology in a similar fashion as well.  If those adjacent networks were label swapping, then all four endpoints SL80:PS80, SL81:PS81, etc would have converged on the same NSI Network as they do now...indicating that the adjacent network can route the circuit between STPs with different VLAN IDs.
> 
> So in fact, just because a switch or a network cannot do VLAN swapping does not mean it cannot do switching - and there is still important value in this capability.    By subdividing the challenged Networks into the appropriate VLAN planes, we express the very topological routing information you want.  And it did not require any changes to the PFs in other networks - and it did not actually require knowledge of the particular VLANs labels or any physical technology information.
> 
> One last point:  The mingling of impossible cross-connects is externally indistinguishable from simple internal resource exhaustion.   In terms of asking for a Reservation, if the route is impossible or if there is just not enough bandwidth, we still just get a reject.   So the question is: If we run out of resources and some crossconnects become "highly improbable" (but not strictly impossible) should we revoke those advertisements on the same grounds that we don't advertise impossible crossconnects?   Possibly...:-)    How long time will the "improbable" cross connects remain "improbable"?  If a cross connect is highly unlikely (e.g. Someone has reserved all 10 Gbps on a 10G path for 6 months...) is it misleading to continue advertsing it?    This is where state updates become important and a grey area comes in...
> 
> Hope this helps.
> Jerry
> 
> 
> On 12/10/11 2:16 PM, Jeroen van der Ham wrote:
>> On 10 Dec 2011, at 20:13, Jeroen van der Ham wrote:
>>>> <tirade>
>>>> With respect to VLAN swapping...   Inability to swap VLANs is essentially saying your NSI network cannot cross connect - ever - certain STPs.   If you cannot *ever* cross connect certain STPs, there is no service!      I might as well advertise STPs that point to bananas -  I will never be able crossconnect them either but who cares?  Advertising capabilities that can never be met is a Bad Thing. It injects false and misleading topological information - it could be considered malicious(!)
>> Sorry, I'm calling bullshit on that one.
>> 
>> In the Automated GOLE topology we currently have 0 networks that are able to do VLAN swapping. Netherlight does have that capability, but due to how things are connected, it is not available for the Automated GOLE topology.
>> 
>> If we cannot even provide a connection service on an existing network, then we have no connection service.
>> 
>> Jeroen.
> <VLAN Planes.pptx>