[Nsi-wg] Topology Abstract sent to Terena

[Jerry Sobieski]

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.
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