Re: [Idr] draft-ietf-idr-segment-routing-te-policy Policy Name Sub-TLV considerations

Nandan Saha <nandan@arista.com> Thu, 12 March 2020 15:37 UTC

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From: Nandan Saha <nandan@arista.com>
Date: Thu, 12 Mar 2020 21:07:19 +0530
Message-ID: <CAE+itjccvXbCsQSDOrRdK2hBkg-Kp15ca-qQ6-GNWTeRFpEavA@mail.gmail.com>
To: Andrew Alston <Andrew.Alston@liquidtelecom.com>
Cc: "Ketan Talaulikar (ketant)" <ketant=40cisco.com@dmarc.ietf.org>, idr wg <idr@ietf.org>
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Subject: Re: [Idr] draft-ietf-idr-segment-routing-te-policy Policy Name Sub-TLV considerations
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On a slight tangent, can we please call the sub tlv "Candidate path name"
or some such. It's more accurate than "policy name" since the candidate
path is signalled in bgp, not a policy.

On Thu, Mar 12, 2020 at 5:57 PM Andrew Alston <
Andrew.Alston@liquidtelecom.com> wrote:

> I would be quite happy to stick to ascii here – it makes writing
> implementations simpler – and while I’ve seen one hardware vendor that had
> an entire cli in Cyrillic -  I’m not entirely sure that it justifies such a
> change.
>
>
>
> Then again – I’m a native English speaker so I’m biased – and the
> preference here isn’t really strong on my side.
>
>
>
> Andrew
>
>
>
>
>
> *From:* spring <spring-bounces@ietf.org> *On Behalf Of *Ketan Talaulikar
> (ketant)
> *Sent:* Thursday, 12 March 2020 15:22
> *To:* idr@ietf.org; spring@ietf.org
> *Cc:* Jeffrey Haas <jhaas@pfrc.org>rg>;
> draft-ietf-idr-segment-routing-te-policy@ietf.org; Alvaro Retana <
> aretana.ietf@gmail.com>
> *Subject:* Re: [spring] draft-ietf-idr-segment-routing-te-policy Policy
> Name Sub-TLV considerations
>
>
>
> Hello,
>
> Would like to bring back this topic for discussion and inputs from the IDR
> & SPRING WGs.
>
> We need to ask if the "SR Policy Name" object is something that needs
> localization (i.e. we change the encoding from ASCII to UTF-8).
>
> According to rfc6365 "Localization is the act of tailoring an application
> for a different language or script or culture." The question then arises:
> would someone want to define a policy name in something other than a
> language supported by ASCII? English is supported, but there are other
> languages which are not.
>
> This object traces it roots to the
> draft-ietf-spring-segment-routing-policy document which indicates the use
> of "printable ASCII characters" :
> https://tools.ietf.org/html/draft-ietf-spring-segment-routing-policy-06#section-2.1
> So any changes to the encoding would need to be reflected in this document
> (and other protocols and Yang models as an extension).
>
> Further on, the equivalent object in PCEP has been already defined as
> using ASCII in the now published
> https://tools.ietf.org/html/rfc8231#section-7.3.2
>
> Based on the WG inputs, we can determine the next course of action.
>
> Thanks,
> Ketan
>
> -----Original Message-----
> From: Ketan Talaulikar (ketant)
> Sent: 13 February 2020 23:38
> To: Jeffrey Haas <jhaas@pfrc.org>rg>;
> draft-ietf-idr-segment-routing-te-policy@ietf.org; idr@ietf.org
> Subject: RE: draft-ietf-idr-segment-routing-te-policy Policy Name Sub-TLV
> considerations
>
> Hi Jeff,
>
> I agree with you about the limits on the policy name size.
>
> I am not aware of any IETF standard that mandates the use of UTF-8 for
> encoding of string for names. The similar object in PCEP is encoded in
> ASCII - https://tools.ietf.org/html/rfc8231#section-7.3.2
>
> Thanks,
> Ketan
>
> -----Original Message-----
> From: Jeffrey Haas <jhaas@pfrc.org>
> Sent: 12 February 2020 15:17
> To: draft-ietf-idr-segment-routing-te-policy@ietf.org; idr@ietf.org
> Subject: draft-ietf-idr-segment-routing-te-policy Policy Name Sub-TLV
> considerations
>
> Authors,
>
> In draft-ietf-idr-segment-routing-te-policy-08, Section 2.4.6 we have a
> TLV for Policy Name. Its text is:
>
> : 2.4.6. Policy Name Sub-TLV
> :
> : An operator MAY set the Policy Name sub-TLV to attach a symbolic name
> : to the SR Policy candidate path.
> :
> : Usage of Policy Name sub-TLV is described in section 2 in
> : [I-D.ietf-spring-segment-routing-policy].
> :
> : The Policy Name sub-TLV may exceed 255 bytes length due to long
> : policy name. Therefore a 2-octet length is required. According to
> : [I-D.ietf-idr-tunnel-encaps], the first bit of the sub-TLV codepoint
> : defines the size of the length field. Therefore, for the Policy Name
> : sub-TLV a code point of 128 or higher is used.
> :
> : The Policy Name sub-TLV is optional and it MUST NOT appear more than
> : once in the SR Policy TLV.
> :
> : The Policy Name sub-TLV has 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 | RESERVED |
> : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> : // Policy Name //
> : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> :
> : Where:
> :
> : Type: 129.
> :
> : Length: Variable.
> :
> : RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
> : transmission and MUST be ignored on receipt.
> :
> : Policy Name: Symbolic name for the policy. It SHOULD be a string
> : of printable ASCII characters, without a NULL terminator.
>
> draft-ietf-spring-segment-routing-policy-06, Section 2.1 discusses this
> Sub-TLV:
>
> : An implementation MAY allow assignment of a symbolic name comprising
> : of printable ASCII characters to an SR Policy to serve as a user-
> : friendly attribute for debug and troubleshooting purposes. Such
> : symbolic names may identify an SR Policy when the naming scheme
> : ensures uniqueness.
>
> There are two observations I'd like to make:
> 1. A 65K length isn't very likely in BGP. :-) I suggest that greater
> guidance for shorter names should be offered. For example, perhaps limit
> the length to 1K. Alternatively, offer advice such as: "Implementations may
> choose to truncate long Policy Names".
>
> 2. The guidance about "printable ASCII" is rather old-style and likely to
> run askance of IESG review for internationalization considerations.. I'd
> suggest that the field be encoded in UTF-8 and make reference to
> print-safety similar to RFC 8203 (BGP Administrative Shutdown) in its
> Security Considerations.
>
> -- Jeff
>
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