Re: [spring] solicit feedback on draft-dunbar-sr-sdwan-over-hybrid-networks-02 proposing SD-WAN source node using UDP port to indicate to SR ingress node how to map to appropriate Binding SID

[Robert Raszuk <[e-mail]>]

Hi Lou,

>  *allocation* of resources (i.e., configuration of data plane queuing and
even per flow shaping and policing).

I will continue this topic as I do think it is quite important to be on the
same page in this WG and beyond. I guess we are at the fudamental question
what does it mean to "allocate or reserve a resource".

Clearly configuration of shaping and policing does not fall under such
definition.

Also as stated already sizing the queues is basic diffserv. Remember that
diffserv does not hard reserve anything too. It prioritizes traffic and I
have not seen any implementation which would automatically adjust queue
depths based on the reception of RSVP-RESV msg.

To me "resource allocation" brings memory of SDH containers and TDM
networks which is a bit misleading if someone even remotely tries to map it
to diffserv.

And since this is SPRING SR since day one claims full support for diffserv
both in SR-MPLS as well as SRv6 architectures.

Best,
R.


On Tue, Jul 3, 2018 at 3:53 PM, Lou Berger <[e-mail]> wrote:

> Hi Robert,
>
>
> On 7/3/2018 4:07 AM, Robert Raszuk wrote:
>
>> Hello Jeff,
>>
>>     “What exactly do you call by "resource allocation" in WAN ?” –
>>     anything that is not “best effort”, BW reservation, protection
>>     type, number of hops, latency, you name it…
>>
>>     Somehow, between ATM and now
>>
>>     *​​*
>>     *we managed to build a technology that would work in both, control
>>     and data planes* 😉
>>
>>     TE with BW reservation is a working technology, with all the bugs,
>>     whether done as a soft state on a device and enforced in FW, aka
>>     RSVP-TE or computed on a controller and enforced by policing
>>     configuration out of band. We also know pretty well how to compute
>>     a constrain path that is loop free and with the constrains. Either
>>     way, working stuff.
>>
>>
>>
>> ​It has been nearly 20 years and it seems that some marketing slides from
>> vendors are still in minds of many many people ...
>>
> I think this is *quite* true. There's also quiet a bit of marketing
> documents on what constitutes QoS (vs CoS).
>
>
>> MPLS-TE does *NOT* do any data plane reservations nor any data plane
>> resource allocation. It is all control plane game. Let me shock you even
>> more today ... what we call "Guaranteed Bandwidth TE" also does *NOT*
>> perform any data plane reservations. This up to current days is the most
>> misunderstood element (or hidden secret) of one of the technologies which
>> has been made available during the last two decades.
>>
>> This *completely* depends on which vendor and platform you choose.
>
> From the IETF perspective, the RFCs certainly support both reservation
> (i.e., book keeping) and *allocation* of resources, (i.e., configuration of
> data plane queuing and even per flow shaping and policing).   This is
> something that continues to be included in all TE related RFCs to date.
>
> If you signal MPLS TE LSP with 5M "reservation" to check if such a path in
>> your network can be established such check is *ONLY* done at the control
>> plane (RP/RE) pools of available bandwidth (per priority level) registers
>> and physical interfaces nor any data plane queues are never aware of it.
>>
>
> again, this depends on the vendor and the platform.  Informed users
> understand this and those that care, buy equipment that satisfy their
> requirements.  I have worked on projects on both sides (vendors and
> users/providers) and some care quite a bit about the queuing behavior
> associated with TE, others are perfectly happy with TE as a path
> selection/distribution/pinning tool.
>
>
>> Now what is a direct consequence of this is if you like to really do
>> control plane reservations and think of it as actual data plane you must do
>> it in 1:1 fashion - again all done in control plane. That means that two
>> fundamental conditions must be met:
>>
>> A) All traffic must be sent over MPLS-LSPs - be it IPv4, IPv6, multicast
>> etc ... - even if I have seen 3 networks trying to do that for IPv4 no one
>> did it for all traffic types.
>>
>> B) All traffic entering your network must be subject to very strict
>> admission control and excess shaped or dropped which is very hard thing to
>> do considering statistical multiplexing gains you count on in any IP
>> network (Explanation: On any single ingress node you must apply strict CAC
>> as you are not aware about what traffic is coming from other ingress nodes.
>> So you may be dropping or shaping traffic which could flow through your
>> network just fine end to end due to absence of competing class from
>> different ingress).
>> ​
>> ​All RSVP-TE does is traffic steering in normal steady state or during
>> protection. That's all. In the WAN's data plane it is all back to basic
>> Diff Serve at each router's data plane.
>>
>> The only technology which does provide interface data plane reservation
>> is RSVP IntServ - but I doubt anyone here or Linda in her draft meant to
>> use such tool.
>>
>
> While this statement may be true for certain vendors, it is not true a
> *technology* or standards perspective.
>
>
>> Why am I jumping on this here in SPRING WG list ... Well few months ago I
>> have witnessed a discussion where someone was arguing that SR is much worse
>> then MPLS-TE as it does not provide any data plane reservations. When I
>> tried to nicely and politely explain how confused the person is the look I
>> got was comparable to those green folks walking down from just arrived UFO.
>>
>>
> While I certainly accept that for some vendors SR-TE is just as good as
> MPLS-TE, if SR-TE is defined as only supporting path control this will be
> the first instance of a TE RFC/definition (at least that I'm aware of) that
> won't support resource allocation, i.e., *any* form of traffic treatment
> (queue) control.
>
>
> So to conclude SR just like MPLS-TE does a good job in packet steering via
>> your domain. (SR can do actually more via embedded functions/apps). But the
>> fundamental difference is that SR does that steering without necessity of
>> number of control plane protocols and their required extensions - so does
>> simplify control plane significantly. Neither of those do any data plane
>> reservations and all bandwidth contentions need to be resolved via classic
>> QoS.
>>
>
> There is a major difference here in what you characterize here, i.e.,
> SR-TE, and how the 'TE' term is used in the existing set of RFCs.  I don't
> know how we (the IETF) want to denote this difference - I suspect this will
> depend on which WG is asked.  In this group it seems that  some (perhaps
> many) are perfectly happy to have SR-TE *not* include actual resource
> allocation and traffic treatment (queue) control - I personally would
> prefer that it be included so that the part of the market that cares about
> such can be supported albeit with the need for users to evaluate actual
> vendor TE implementations as is done today.
>
> Lou
>
>>
>> Cheers,
>> R.
>>
>>
>>
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