Re: [Lsr] clarification of locator block and locator node in draft-ietf-spring-srv6-network-programming and draft-ietf-lsr-isis-srv6-extensions

[Chris Bowers <[e-mail]>]

Ketan,

See inline [CB].

On Wed, Mar 4, 2020 at 12:36 AM Ketan Talaulikar (ketant) <[e-mail]>
wrote:

> Hi Chris,
>
>
>
> You are right in that there is no assumption that all SRv6 locators in a
> domain are allocated from the same block. Therefore knowing the blocks used
> in the domain is useful.
>

[CB] Since you refer to "blocks" (plural) in this sentence, are you saying
that in the scenario where all SRv6 locators in a domain are not allocated
from the same block, you would expect different routers in the same domain
to advertise different values of B and N?  For example, assume we have a
network where all SRv6 locators in a domain are not allocated from the same
block.  Router A advertises an SRv6 Locator TLV with locator = 2000::/64,
and an SRv6 End SID sub-TLV with some endpoint behavior.  Router B
advertises an SRv6 Locator TLV with locator = 3000::/64, and an SRv6 End
SID sub-TLV with some endpoint behavior. What should routers A and B
advertise as the values of B and N in their SRv6 SID Structure Sub-Sub-TLVs
?


>
>
> The IGP drafts covers the advertisement of the B and N parts of the
> locally configured locator on the node via IGPs. On the receiver side, the
> IGP may not really do much with this information, however it enables
> propagation of this information from all nodes in the network to be
> advertised out via BGP-LS (or other mechanisms) as part of the topology
> feed. Once this is part of the topology feed, it enables use-cases on
> controllers to perform network wide validation of the SRv6 SID block
> provisioning and can also help in automation of the security aspects
> described in
> https://tools.ietf.org/html/draft-ietf-6man-segment-routing-header-26#section-5
>
>
>
[CB] If an ISIS speaker is not expected to do anything with B and N, then I
think the text in draft-ietf-lsr-isis-srv6-extensions needs to clarify
this.  I have a similar observation about Fun. Length and Arg. Length in
the SRv6 SID Structure Sub-Sub-TLV .  As far as I can tell, none of the
endpoint behaviors that are currently specified to be carried in ISIS End,
End.X, and LAN End.X SIDs sub-TLVs uses an Argument, so there is never a
case where an SRv6 SID Structure Sub-Sub-TLV should have a non-zero value
for Arg. Length. What should an ISIS speaker do if it receives a non-zero
value of the Arg. Length for an endpoint behavior that doesn't use an
argument?  Are there any use cases envisioned where an ISIS speaker needs
to know the Arg. Length ?

Thanks,
>
> Ketan
>
>
>
> *From:* Chris Bowers <[e-mail]>
> *Sent:* 02 March 2020 23:39
> *To:* Ketan Talaulikar (ketant) <[e-mail]>
> *Cc:* Ketan Talaulikar (ketant) <ketant=[e-mail]>;
> [e-mail]; SPRING WG List <[e-mail]>;
> draft-ietf-spring-srv6-network-programming <
> [e-mail]>; Peter Psenak
> (ppsenak) <[e-mail]>; Bruno Decraene <[e-mail]>
> *Subject:* Re: [Lsr] clarification of locator block and locator node in
> draft-ietf-spring-srv6-network-programming and
> draft-ietf-lsr-isis-srv6-extensions
>
>
>
> Ketan,
>
>
>
> Based on current documents, allocating all SRv6 locators used in a domain
> from a single block is optional.
>
>
>
> However, assuming for the moment that a network operator has chosen to
> allocate all SRv6 locators used in a domain from a single block, so that
> there is a well-defined value of B and N across a domain, what is the use
> of having a router advertise its own understanding of these two values?
> And what is a receiver supposed to do with this information?
>
>
>
> Thanks,
>
> Chris
>
>
>
> On Fri, Feb 28, 2020 at 8:23 AM <[e-mail]> wrote:
>
> Hi Ketan,
>
>
>
> Thanks fort the follow up.
>
> Clarification inline [Bruno]
>
>
>
> *From**:* Ketan Talaulikar (ketant) [mailto:[e-mail]]
> *Sent:* Friday, February 28, 2020 11:11 AM
> *To:* DECRAENE Bruno TGI/OLN; Ketan Talaulikar (ketant); Chris Bowers
> *Cc:* [e-mail]; SPRING WG List;
> draft-ietf-spring-srv6-network-programming; Peter Psenak (ppsenak)
> *Subject:* RE: [Lsr] clarification of locator block and locator node in
> draft-ietf-spring-srv6-network-programming and
> draft-ietf-lsr-isis-srv6-extensions
>
>
>
> Hi Bruno,
>
>
>
> I believe the description and usage of Locator is very well described and
> covered in the net-pgm draft as also the corresponding IGP extensions. Is
> the question is more about the “block” part of it (what is not in the block
> part is in the node part as per the text in the net-pgm draft)?
>
>
>
> The “block” is again not a new thing. Please check the following:
>
> Under
> https://tools.ietf.org/html/draft-ietf-6man-segment-routing-header-26#section-5
> … look for “block”
>
> https://tools.ietf.org/html/rfc8402#section-2 … look under SRGB for SRv6
>
>
>
> [Bruno]
>
> To clarify, my question was not specific to “block” but related to the
> usage, by the receiver, of the following piece of information:
>
>
>
>       LB Length: SRv6 SID Locator Block length
>
>       LN Length: SRv6 SID Locator Node length
>
>       Fun. Length: SRv6 SID Function length
>
>       Arg. Length: SRv6 SID Arguments length
>
>
>
>
>
> So perhaps I don’t get Chris’s point and would wait for him to clarify.
>
> [Bruno] I’ll leave this to Chris.
>
>
>
> Thanks,
>
> Ketan
>
>
>
> *From:* Lsr <[e-mail]> *On Behalf Of *
> [e-mail]
> *Sent:* 28 February 2020 14:34
> *To:* Ketan Talaulikar (ketant) <ketant=[e-mail]>;
> Chris Bowers <[e-mail]>
> *Cc:* [e-mail]; SPRING WG List <[e-mail]>;
> draft-ietf-spring-srv6-network-programming <
> [e-mail]>; Peter Psenak
> (ppsenak) <[e-mail]>
> *Subject:* Re: [Lsr] clarification of locator block and locator node in
> draft-ietf-spring-srv6-network-programming and
> draft-ietf-lsr-isis-srv6-extensions
>
>
>
> Hi Ketan,
>
>
>
>
>
>
>
> *From:* Lsr [mailto:[e-mail] <[e-mail]>] *On
> Behalf Of *Ketan Talaulikar (ketant)
> *Sent:* Friday, February 28, 2020 6:30 AM
>
>
>
> Hi Chris,
>
>
>
> I agree with Peter and I would suggest to drop LSR since this is not a
> protocol specific thing.
>
>
>
> I believe the text in draft-ietf-spring-srv6-network-programming clears
> says what locator block and locator node are. What more details do you
> think are required?
>
>
>
> [Bruno] Speaking as an individual, the draft could possibly clarify the
> usage of these information/fields by the receiver. Possibly using the same
> name/term (e.g. SRv6 SID Locator Block length) to ease the references
> between both drafts.
>
>
>
> Thanks,
>
> --Bruno
>
>
>
> Thanks,
>
> Ketan
>
>
>
> *From:* Lsr <[e-mail]> *On Behalf Of *Chris Bowers
> *Sent:* 27 February 2020 22:46
> *To:* [e-mail]; SPRING WG List <[e-mail]>
> *Cc:* Peter Psenak (ppsenak) <[e-mail]>
> *Subject:* [Lsr] clarification of locator block and locator node in
> draft-ietf-spring-srv6-network-programming and
> draft-ietf-lsr-isis-srv6-extensions
>
>
>
> SPRING and LSR WGs,
>
>
>
> I think that we need a much more detailed description of the locator block
> and locator node in either draft-ietf-spring-srv6-network-programming or
> draft-ietf-lsr-isis-srv6-extensions.  See original email below.
>
>
>
> Thanks,
>
> Chris
>
>
>
> On Thu, Feb 27, 2020 at 11:08 AM Peter Psenak <[e-mail]> wrote:
>
> Hi Chris,
>
> On 27/02/2020 17:54, Chris Bowers wrote:
> > LSR WG,
> >
> > Section 9 of draft-ietf-lsr-isis-srv6-extensions-05 defines the  SRv6
> > SID Structure Sub-Sub-TLV. In particular, it defines encoding for the
> > locator block length and the locator node length.  The text refers to
> > [I-D.ietf-spring-srv6-network-programming] for the definition of these
> > concepts.
> >
> > As far as I can tell, the only reference to locator block and locator
> > node in draft-ietf-spring-srv6-network-programming-10 is section 3.1
> > which has the following text:
> >
> >     A locator may be represented as B:N where B is the SRv6 SID block
> >     (IPv6 subnet allocated for SRv6 SIDs by the operator) and N is the
> >     identifier of the parent node instantiating the SID..
> >
> > I think that we need a much more detailed description of the locator
> > block and locator node.
>
> sure, but that would be in the
> draft-ietf-spring-srv6-network-programming-10, not in
> draft-ietf-lsr-isis-srv6-extensions, as these are not a protocol
> specific constructs.
>
> thanks,
> Peter
>
> >
> > Thanks,
> >
> > Chris
> >
>
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