Re: [lisp] Rtgdir last call review of draft-ietf-lisp-gpe-04

Fabio Maino <fmaino@cisco.com> Wed, 15 August 2018 18:15 UTC

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To: Adrian Farrel <adrian@olddog.co.uk>, rtg-dir@ietf.org
Cc: lisp@ietf.org, ietf@ietf.org, draft-ietf-lisp-gpe.all@ietf.org
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From: Fabio Maino <fmaino@cisco.com>
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Subject: Re: [lisp] Rtgdir last call review of draft-ietf-lisp-gpe-04
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Hi Adrian,
thanks for such a detailed review.

I went through your comments and I can incorporate all of them into a 
new version of the draft.

Wrt the reduction in size of the Map-Versioning and Nonce fields, I 
could add in Section 3, right after the definition of the encoding of 
those fields, the following:

> The encoding of the Nonce field in LISP-GPE, compared with the one 
> used in RFC6830bis for the LISP data plane encapsulation, reduces the 
> length of the nonce from 24 to 16 bits. As per RFC6830bis, ITRs are 
> required to generate different nonces when sending to different RLOCs, 
> but the same nonce can be used for a period of time when encapsulating 
> to the same ETR. The use of 16 bits nonces still allows  an ITR to 
> determine to and from reachability for up to 64k RLOCs at the same time.
>
> Similarly, the encoding of the Source and Dest Map-Version fields, 
> compared with RFC6830bis, is reduced from 12 to 8 bits. This still 
> allows to associate 256 different versions to each EID-to-RLOC mapping 
> to inform commmunicating ITRs and ETRs about modifications of the 
> mapping.
>


Either Deborah, Joel, or Luigi: if you could please confirm that it is 
ok to publish a new version of the draft at this point, I'll update it 
right away.

Thanks,
Fabio




On 8/9/18 9:05 AM, Adrian Farrel wrote:
> Reviewer: Adrian Farrel
> Review result: Has Issues
>
> Hello,
>
> I have been selected as the Routing Directorate reviewer for this draft. The
> Routing Directorate seeks to review all routing or routing-related drafts as
> they pass through IETF last call and IESG review, and sometimes on special
> request. The purpose of the review is to provide assistance to the Routing ADs.
> For more information about the Routing Directorate, please see
> ?http://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir
>
> Although these comments are primarily for the use of the Routing ADs, it would
> be helpful if you could consider them as normal review comments. I believe that
> this review comes between WG publication and the start of IETF last call - you
> may wish to discuss with your AD whether to treat these comments separately or
> as part of IETF last call.
>
> Document: draft-ietf-lisp-gpe-04.txt
>   Reviewer: Adrian Farrel
>   Review Date: 9-August-2018
>   IETF LC End Date: No known
>   Intended Status: Standards Track
>
> Summary
> I have significant concerns about this document and recommend that the Routing
> ADs discuss these issues further with the authors. The issues are not
> substantially technical in nature, but do indicate the need for significant
> reworking of the text. I have tried to make suggestions for new text.
>
> Comments:
>
> This document specifies an alternate LISP header format that can be used to
> allow LISP to carry payloads other than IP. A new capabilities flag is defined
> so that routers know whether this new format is supported, and a new flag in
> the header itself indicates when the new format is in use.
>
> The document is clear and readable, but has some issues of presentation that
> could close a few potential misunderstandings and thus improve implmentation
> prospects.
>
> No attempt is made in the document to explain how/why the reduction in size of
> some standard LISP header fields is acceptable. For example, if implementations
> of this spec can safely operate with a 16 bit Nonce or 8 bit Map-Versions, why
> does 6830/6830bis feel the need for 24 and 12 bit fields rspectively?
>
> ===Major Issues===
>
> Section 3 has a mix of minor and leess minor issues...
>
> OLD
>     This document defines the following changes to the LISP header in
>     order to support multi-protocol encapsulation:
>
>     P Bit:  Flag bit 5 is defined as the Next Protocol bit.  The P bit
>        MUST be set to 1 to indicate the presence of the 8 bit next
>        protocol field.
>
>        P = 0 indicates that the payload MUST conform to LISP as defined
>        in [I-D.ietf-lisp-rfc6830bis].  Flag bit 5 was chosen as the P bit
>        because this flag bit is currently unallocated.
>
>     Next Protocol:  The lower 8 bits of the first 32-bit word are used to
>        carry a Next Protocol.  This Next Protocol field contains the
>        protocol of the encapsulated payload packet.
>
>        LISP uses the lower 24 bits of the first word for either a nonce,
>        an echo-nonce, or to support map-versioning
>        [I-D.ietf-lisp-6834bis].  These are all optional capabilities that
>        are indicated in the LISP header by setting the N, E, and the V
>        bit respectively.
>
>        When the P-bit and the N-bit are set to 1, the Nonce field is the
>        middle 16 bits.
>
>        When the P-bit and the V-bit are set to 1, the Version field is
>        the middle 16 bits.
>
>        When the P-bit is set to 1 and the N-bit and the V-bit are both 0,
>        the middle 16-bits are set to 0.
>
>        This document defines the following Next Protocol values:
>
>        0x1 :  IPv4
>
>        0x2 :  IPv6
>
>        0x3 :  Ethernet
>
>        0x4 :  Network Service Header [RFC8300]
>
>          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
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |N|L|E|V|I|P|K|K|        Nonce/Map-Version      | Next Protocol |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |                 Instance ID/Locator-Status-Bits               |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>                                LISP-GPE Header
>
> NOTES
>     - It would be helpful to put the figure higher up
>     - The use of "MUST" for the P-bit is attenuated wrongly
>     - Need to be consistent on "P Bit" or "P-bit" or "P bit"
>     - There looks to be a problem in the case of map version. The base
>       spec has 12 bits each for source and dest map-version, so this doc
>       needs to describe how the reeduced 16 bits is split (presumably not
>       12 and 4).
>     - You need a pointer to the IANA registry for next protocol
> NEW
>     This document defines two changes to the LISP header in order to
>     support multi-protocol encapsulation: the introduction of the P-bit
>     and the definition of a Next Protocol field.  This is shown in
>     Figure 1 and described below.
>
>          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
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |N|L|E|V|I|P|K|K|        Nonce/Map-Version      | Next Protocol |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |                 Instance ID/Locator-Status-Bits               |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>                           Figure 1 : The LISP-GPE Header
>
>     P-Bit:  Flag bit 5 is defined as the Next Protocol bit.
>
>        If the P-bit is clear (0) the LISP header conforms to the
>        definition in [I-D.ietf-lisp-rfc6830bis].
>
>        The P-bit is set to 1 to indicate the presence of the 8 bit Next
>        Protocol field.
>
>     Next Protocol:  The lower 8 bits of the first 32-bit word are used to
>        carry a Next Protocol.  This Next Protocol field contains the
>        protocol of the encapsulated payload packet.
>
>        In [I-D.ietf-lisp-6834bis], LISP uses the lower 24 bits of the
>        first word for a nonce, an echo-nonce, or to support map-
>        versioning.  These are all optional capabilities that are
>        indicated in the LISP header by setting the N, E, and V bits
>        respectively.
>
>        When the P-bit and the N-bit are set to 1, the Nonce field is the
>        middle 16 bits (i.e., encoded in 16 bits, not 24 bits).  Note that
>        the E-bit only has meaning when the N-bit is set.
>
>        When the P-bit and the V-bit are set to 1, the Version fields use
>        the middle 16 bits: the Source Map-Version uses the high-order 8
>        bits, and the Dest Map-Version uses the low-order 8 bits.
>
>        When the P-bit is set to 1 and the N-bit and the V-bit are both 0,
>        the middle 16-bits MUST be set to 0 on transmission and ignored on
>        receipt.
>
>        This document defines the following Next Protocol values:
>
>        0x1 :  IPv4
>
>        0x2 :  IPv6
>
>        0x3 :  Ethernet
>
>        0x4 :  Network Service Header [RFC8300]
>
>        The values are tracked in an IANA registry as described in Section
>        5.
>
> ---
>
> Section 4 must describe the error case when a LISP-GPE capable router
> sets the P-bit on a packet to a non LISP-GPE capable router. So...
>
> OLD
>     When encapsulating IP packets to a non LISP-GPE capable router the P
>     bit MUST be set to 0.
> NEW
>     When encapsulating IP packets to a non LISP-GPE capable router the P-
>     bit MUST be set to 0.  That is, the encapsulation format defined in
>     this document MUST NOT be sent to a router that has not indicated
>     that it supports this specification because such a router would
>     ignore the P-bit (as described in [I-D.ietf-lisp-rfc6830bis]) and so
>     would misinterpret the other LISP header fields possibly causing
>     significant errors.
> END
>
> ---
>
> 4.1
>
> Not your fault that RFC 8060 doesn't have a registry for bits in the
> LCAF, but now you really need one or else future orthogonal specs risk
> colliding with the g-bit.  A bit odd to add this in this document, but
> not worth a bis on 8060.
>
> ===Minor Issues ===
>
> Section 2
>
> OLD
>     The LISP header [I-D.ietf-lisp-rfc6830bis] contains a series of flags
>     (some defined, some reserved), a Nonce/Map-version field and an
>     instance ID/Locator-status-bit field.  The flags provide flexibility
>     to define how the various fields are encoded.  Notably, Flag bit 5 is
>     the last reserved bit in the LISP header.
>
>          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
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |N|L|E|V|I|R|K|K|            Nonce/Map-Version                  |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |                 Instance ID/Locator-Status-Bits               |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>                                  LISP Header
> NOTES
>     We need to be careful not to risk any confusion. At least, "some
>     reserved" is an over-statement. But also we should not show a repeat
>     of the Lisp header as that causes a duplicate definition.
> NEW
>     The LISP header is defined in [I-D.ietf-lisp-rfc6830bis] and contains
>     a series of flags of which one (bit 5) is shown in that document as
>     "reserved for future use".  The setting of the flag fields defined
>     how the subsequent header fields are interpretted.
> END
>
> ---
>
> 4.1
> I don't think you should reproduce the Multiple Data-Planes LCAF Type
> figue from 8060 here as it creates a duplicate definition.  The text
> explanation of which bit is the g-bit shold be enough.
>
> ===Nits===
>
> Abstract
> OLD
>     This document describes extending the Locator/ID Separation Protocol
>     (LISP) Data-Plane, via changes to the LISP header, to support multi-
>     protocol encapsulation.
> NEW
>     This document describes extentions to the Locator/ID Separation
>     Protocol (LISP) Data-Plane, via changes to the LISP header, to
>     support multi-protocol encapsulation.
> END
>
> ---
>
> 1.
> OLD
>     LISP Data-Plane, as defined in in [I-D.ietf-lisp-rfc6830bis], defines
>     an encapsulation format that carries IPv4 or IPv6 (henceforth
>     referred to as IP) packets in a LISP header and outer UDP/IP
>     transport.
> NEW
>     The LISP Data-Plane is defined in [I-D.ietf-lisp-rfc6830bis].  It
>     specifies an encapsulation format that carries IPv4 or IPv6 packets
>     (henceforth jointly referred to as IP) in a LISP header and outer
>     UDP/IP transport.
>
> ---
>
> 1.1
> Please use the new boilerplate...
>     The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
>     "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
>     "OPTIONAL" in this document are to be interpreted as described in BCP
>     14 [RFC2119] [RFC8174] when, and only when, they appear in all
>     capitals, as shown here.
>
> ---
>
> 1.2
> Nothwithstanding the text in this section, abbreviations need to be
> expanded either on first use or in this section.
> I see:
> - LCAF
> - ETR
> - ITR
> - RLOC
> - xTR
>
> ---
>
> 2.
> s/As described in the introduction/As described in Section 1/
> s/LISP is limited to carry IP payloads/LISP is limited to carrying IP payloads/
>
> ---
>
> 4.1
> s/field as g bit/field as the g-bit/
>
> ---
>
> 8.1
> Please add RFC 8174
>