Re: [Lsr] Last Call: <draft-ietf-lsr-isis-srv6-extensions-14.txt> (IS-IS Extension to Support Segment Routing over IPv6 Dataplane) to Proposed Standard

[Shraddha Hegde <[e-mail]>]

Les,

I don't agree with mandating prefix attributes sub-TLV in locator TLV at this stage of publication
when there are multiple implementations that don't originate it.
There are usecases that can be deployed without prefix attributes sub-TLV.

I propose that we clarify the specific usecases that require prefix attributes sub-TLVs to be associated with locator TLV. For example, we should add the TI-LFA with leaked locators across multiple levels that Gunter pointed out,
and add a statement that prefix attributes sub-tlv SHOULD be originated in locator TLV
for this usecase to be supported.

Rgds
Shraddha


Juniper Business Use Only
From: Les Ginsberg (ginsberg) <ginsberg=[e-mail]>
Sent: Wednesday, May 12, 2021 3:59 AM
To: Shraddha Hegde <[e-mail]>; Alvaro Retana <[e-mail]>; Peter Psenak (ppsenak) <[e-mail]>; [e-mail]; Gengxuesong (Geng Xuesong) <[e-mail]>
Cc: [e-mail]; [e-mail]; Van De Velde, Gunter (Nokia - BE/Antwerp) <[e-mail]>
Subject: RE: [Lsr] Last Call: <draft-ietf-lsr-isis-srv6-extensions-14.txt> (IS-IS Extension to Support Segment Routing over IPv6 Dataplane) to Proposed Standard

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Shraddha/ Xuesong -

Since Prefix Attributes sub-TLV is required for correct operation when a Locator is leaked, would it be safe to assume that your implementations either do not leak Locators or you advise your customers not to deploy this feature with multiple levels?

The problem with allowing the sub-TLV to be optional is that if the sub-TLV is omitted you cannot tell whether the Locator has been leaked - so you don't know whether you have a problem or not.

The safest thing to do is require prefix-attributes sub-TLV always - then you can guarantee that if the prefix is leaked the necessary information will be present.
Anything else leaves us vulnerable.

We all appreciate interoperability considerations, but frankly this is a gap that needs to be closed to support correct operation.

   Les

From: Lsr <[e-mail]<mailto:[e-mail]>> On Behalf Of Shraddha Hegde
Sent: Tuesday, May 11, 2021 8:21 AM
To: Alvaro Retana <[e-mail]<mailto:[e-mail]>>; Peter Psenak (ppsenak) <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Cc: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; Van De Velde, Gunter (Nokia - BE/Antwerp) <[e-mail]<mailto:[e-mail]>>
Subject: Re: [Lsr] Last Call: <draft-ietf-lsr-isis-srv6-extensions-14.txt> (IS-IS Extension to Support Segment Routing over IPv6 Dataplane) to Proposed Standard

Juniper has an  implementation of SRv6 that does not support Prefix attributes sub-tlv in locator TLV.
We would prefer not to change the optional sub-TLV to MUST.

Rgds
Shraddha




Juniper Business Use Only
From: Lsr <[e-mail]<mailto:[e-mail]>> On Behalf Of Alvaro Retana
Sent: Friday, May 7, 2021 7:23 PM
To: Peter Psenak <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Cc: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; Van De Velde, Gunter (Nokia - BE/Antwerp) <[e-mail]<mailto:[e-mail]>>
Subject: Re: [Lsr] Last Call: <draft-ietf-lsr-isis-srv6-extensions-14.txt> (IS-IS Extension to Support Segment Routing over IPv6 Dataplane) to Proposed Standard

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On May 3, 2021 at 5:17:58 AM, Peter Psenak wrote:

> Technically I agree with you and if everybody agrees, I'm fine to
> enforce the presence of the Prefix Attribute Flags TLV in the Locator TLV.

So...what does everyone else think?

We need to close on this point before the IESG evaluates the document.  I'm requesting it to be put on the May/20 telechat, which means that we should have a resolution and updated draft by the end of next week.


Thanks!

Alvaro.



On May 3, 2021 at 5:17:58 AM, Peter Psenak ([e-mail]<mailto:[e-mail]>) wrote:
Hi Gunter,

Prefix Attribute Flags Sub-TLV has been defined as an optional Sub-TLV.
The problem you describe is not specific to Locator TLV, same applies to
regular IPv4/v6 prefixes (forget SR MPLS for a while) - if the Prefix
Attribute Flags TLV is not included, one can not tell whether the prefix
has been propagated (L1->L2) or generated as a result of the local
interface attached on the originator. Same applies to redistribution and
R-flag for IPv4 prefix TLVs.

SRv6 Locator TLV has been defined a while back and the Prefix Attribute
Flags Sub-TLV has always been an optional Sub-TLV of it. I'm not sure we
can start to mandate the Prefix Attribute Flags TLV at this point.

Technically I agree with you and if everybody agrees, I'm fine to
enforce the presence of the Prefix Attribute Flags TLV in the Locator TLV.

thanks,
Peter


On 03/05/2021 10:45, Van De Velde, Gunter (Nokia - BE/Antwerp) wrote:
> Hi Peter, All,
>
> Could we update to "draft-ietf-lsr-isis-srv6-extensions" that the prefix-attribute tlv is mandatory when a locator is redistributed?
>
> Why?
> *When calculating a LFA for an SRv6 End.SID we better know if the locator has been redistributed or not for a correct operation.
>
> Reasoning:
> * A locator has the D bit. This one is set when we redistribute from L2 to L1.
> ** So this end-sid will not be used as we know that it is redistributed.
>
> * In the other direction (L1-L2), we only know that a locator is redistributed from L1 to L2 if the prefix-attribute sub-tlv is advertised.
> ** This means if the operator does not configure advertisement of the prefix-attribute tlv, ISIS could potentially use an end-sid which does not terminate on the expected node.
>
> * Compared to sr-mpls, a prefix-sid has the R flag indicating it is redistributed.
> * We don't have that for locator end-sids.
>
> Relevant snip from " draft-ietf-lsr-isis-srv6-extensions"
>
> 7.1. SRv6 Locator TLV Format
>
> The SRv6 Locator TLV has the following format:
>
> 0 1 2 3
> 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | Type | Length |R|R|R|R| MT ID |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
> Type: 27
>
> Length: variable.
>
> R bits: reserved for future use. They MUST be
> set to zero on transmission and MUST be ignored on receipt.
>
> MT ID: Multitopology Identifier as defined in [RFC5120].
> Note that the value 0 is legal.
>
> Followed by one or more locator entries of the form:
>
> 0 1 2 3
> 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | Metric |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | Flags | Algorithm |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | Loc Size | Locator (variable)...
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> | Sub-TLV-len | Sub-TLVs (variable) . . . |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>
> Metric: 4 octets. As described in [RFC5305].
>
> Flags: 1 octet. The following flags are defined
>
> 0
> 0 1 2 3 4 5 6 7
> +-+-+-+-+-+-+-+-+
> |D| Reserved |
> +-+-+-+-+-+-+-+-+
>
> where:
> D-flag: Same as described in section 4.1. of [RFC5305].
>
>
> G/
>