Re: [mpls] Requesting WG LC for draft-ietf-mpls-rsvp-shared-labels

[Alexander Okonnikov <[e-mail]>]

Hi Panav,

From section 7:


	"If the label type is a delegation label, then the stacking procedure stops at that delegation hop."
	
It is OK for "Stack to Reach Delegation Hop" approach, but it doesn't work for "Stack to Reach Egress", isn't it?

Also, regarding FRR support. Section 1 says:

	"Functionalities such as bandwidth admission control, LSP priorities, preemption, 
	auto-bandwidth and Fast Reroute continue to work with this forwarding plane."
	
It seems that shared labels approach supports only facility bypass link-protection. It doesn't support one-to-one link- and node-protection, per my understanding. Facility bypass node-protection is not supported as well (as mentioned in Section 8). Hence, FRR support is very limited, and section 1 needs correction.

Thank you.

> 13 сент. 2018 г., в 20:28, Alexander Okonnikov <[e-mail]> написал(а):
> 
> Hi Panav,
> 
> Questions regarding ETLD:
> 
> The draft is not clear about signaling of ETLD attribute. It says that ETLD is conveyed as per-hop attribute. Is my understanding correct that it is conveyed as RRO Hop attribute? Probably it could be cleaned to avoid confusion whether ERO or RRO Hop attribute mechanism is used.
> 
> Next, the draft says that:
> 
> 	"... If a node is reached where the ETLD set from the previous hop is 1, then that
> 	node MUST select itself as the delegation hop.  If a node is reached and it is 
> 	determined that this hop cannot receive more than one transport label, then that node 
> 	MUST select itself as the delegation hop. ..."
> 
> What is purpose of the second sentence/rule?
> 
> Next:
> 
> 	"If there is a node or a sequence of nodes along the path of the LSP that do not 
> 	support ETLD, then the immediate hop that supports ETLD MUST select itself as the 
> 	delegation hop."
> 
> If some node (consecutive nodes) doesn't support ETLD then it doesn't support TE labels. Hence, that node (regular RSVP-TE LSR) will do SWAP and not POP. As a result non-decremented ETLD is OK and immediate hop that supports ETLD not necessary should become delegation hop?
> 
> Also, from Section 9.7:
> 
> "The ETLD field specifies the maximum number of transport labels that this hop can potentially send to its downstream hop.  It MUST be set to a non-zero value."
> 
> Strictly speaking it is not correct. ETLD reflects decrementing counter and not capability of some transit node. I.e. if we consider LSP R1-R2-R3, R1 puts value 5 in ETLD,and R2 supports imposing of 2 labels, it doesn't mean that R2 should rewrite ETLD with value 2. It just should decrement value 5. Correct?
> 
> Also, per my understanding it is supposed that in fact ETLD value will not be just decremented, but it will be copied from previous RRO Hop attributes subobject into being inserted RRO Hop attributes subobject with decrementing. May be it would be better to signal ETLD value in LSP Attributes object (and each capable node decrements ETLD value there), while signaling support of ETLD itself in RRO Hop attributes subobject?
> 
> Thank you.
> 
>> 13 сент. 2018 г., в 20:22, Alexander Okonnikov <[e-mail] <mailto:[e-mail]>> написал(а):
>> 
>> Hi Pavan,
>> 
>> I'm sorry for delay with answer.
>> 
>> If ingress uses regular Path MTU discovery mechanism, it could produce value of MTU lower than actual one. This is because ingress doesn't know MTU per each hop. Let's consider case with four routers: R1 - R2 - R3 - R4. MTU for R1-R2 link is 2000, MTU for R2-R3 is 1600 and MTU for R3-R4 is 2000. By virtue of regular Path MTU discovery mechanism R1 will derive from FLOWSPEC that path MTU is 1600. As soon as R1 doesn't know how many labels in the stack will be on the lowest MTU hop, it can only set LSP MTU to most conservative value (1600 - 4 - 4 = 1592, provided that R4 has advertised implicit null label). In fact actual path MTU is 1596 (1600 - 4 on R2-R3 hop). Of course, it could be acceptable, but calculated LSP MTU as more lower than actual as longer LSP path. For correct path MTU discovery ingress needs to know MTU per each hop.
>> 
>> Thank you.
>> 
>>> 6 сент. 2018 г., в 18:27, Vishnu Pavan Beeram <[e-mail] <mailto:[e-mail]>> написал(а):
>>> 
>>> Alexander, Hi!
>>>  
>>> I apologize for the delayed response.
>>>  
>>> This draft does not propose any changes to the standard RSVP MTU signaling procedures (Int Serv object specific signaling procedures). After the initial signaling sequence is complete, an ingress implementation (RFC3209) would typically take the path MTU learnt via signaling, run it through some local logic and then arrive at an MTU value that can be assigned to the LSP. This local logic typically involves deducting the number of bytes in the label stack used for the LSP from the path MTU learnt via signaling. The ingress implementation supporting this draft will rely on the Resv RRO to accurately determine the max-number of labels pushed along the path of the LSP (note that with delegation, downstream hops can impose label stacks) and account for it in the local logic used to arrive at the MTU value assigned to the LSP.
>>>  
>>> I hope this addresses your question.
>>>  
>>> Regards,
>>> -Pavan
>>> 
>>> On Tue, Aug 7, 2018 at 12:22 PM Alexander Okonnikov <[e-mail] <mailto:[e-mail]>> wrote:
>>> Hi Pavan,
>>> 
>>> 
>>> Regular RSVP-TE LSPs use standard RSVP path MTU discovery mechanism. That one cannot be used "as is" for approach described in the draft, and the draft doesn't address path MTU identification. Is it to be considered?
>>> 
>>> Thank you.
>>> 
>>> 26.07.2018 06:07, Vishnu Pavan Beeram пишет:
>>>> Chairs, Hi!
>>>> 
>>>> As mentioned (in our presentation) in last week's WG session, we believe that the draft is sufficiently baked and ready to progress to the next stage. We would like to formally request this draft to be considered for WG LC.
>>>> 
>>>> Regards,
>>>> - Pavan (on behalf of the authors)
>>>> 
>>>> 
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>> 
>