Re: [Lsr] AD Review of draft-ietf-ospf-ospfv2-hbit-06

[Padmadevi Pillay Esnault <[e-mail]>]

Dear Alvaro

Thank you for your review.

We will go through the comments and work on them.

Thanks
Padma on behalf of my co-authors

On 11/28/18, 7:53 AM, "Alvaro Retana" <[e-mail]> wrote:

    Dear authors:
    
    I just finished reading this document.  Even though it is relatively short,
    I have significant concerns and I think it needs more work.  Please take a
    look at the detailed comments in-line below -- I'm highlighting some of the
    issues here.
    
    (1) What is the Update to rfc2328?  Please be specific in both the Abstract
    and the Introduction to indicate how rfc2328 is Updated.  Also, see my
    question about rfc6987 in §6.
    
    (2) Operational/Deployment Considerations.  There are several places
    (specially in §3) where the specification offers a choice (e.g. by using
    MAY).  Some of those choices would be better informed if there was a
    discussion of the considerations behind them.  Please take a look at
    rfc5706 (specially §2).  Either a discussion close to where the behavior is
    specified or a separate section is ok.  Please also keep migration in mind
    (see comments in §5).
    
    (3) Both the IANA and Security Considerations sections need more details.
    
    
    I will wait for them to be addressed before starting the IETF Last Call.
    
    Thanks!
    
    Alvaro.
    
    
    [The line numbers come from idnits.]
    
    ...
    11                        H-bit Support for OSPFv2
    12                     draft-ietf-ospf-ospfv2-hbit-06
    
    [nit] Please make the title more descriptive.  "non-transit router", "host
    mode", etc. come to mind.
    
    
    14 Abstract
    
    16   OSPFv3 defines an option bit for router-LSAs known as the R-bit in
    17   RFC5340.  If the R-bit is clear, an OSPFv3 router can participate in
    18   OSPF topology flooding, however it will not be used as a transit
    19   router.  In such cases, other routers in the OSPFv3 routing domain
    20   only install routes to allow local traffic delivery.  This document
    21   defines the H-bit functionality to prevent other OSPFv2 routers from
    22   using the router for transit traffic in OSPFv2 routing domains as
    23   described in RFC 2328.  This document updates RFC 2328.
    
    [minor] Describing the functionality in terms of OSPFv2 would have been
    nice.  IOW, there's no need (in the Abstract) to force the reader to go
    figure out what OSPFv3 already did to decide if it's worth reading this
    document or not.
    
    [major] What is the Update to rfc2328?  Please be specific, both here and
    in the Introduction: don't just mention the section updated, but (more
    important) what is the update about.  "This document updates rfc2328 by
    assigning a bit...changing the SPF process...creating a registry..."
     All/none/something else?
    
    Note that the answer to "what is the update?" doesn't have to be all.  I
    think that the registry creation is a must.  But Updating because of the
    SPF changes means that you expect an rfc2328 implementation to consider the
    H-bit when running SPF.  I think you really mean that implementations of
    this document (i.e. not all rfc2328 implementations) have to use the
    modified SPF.  That is my guess...please consider the answer carefully.
    
    
    ...
    42 Copyright Notice
    
    44   Copyright (c) 2018 IETF Trust and the persons identified as the
    45   document authors.  All rights reserved.
    
    47   This document is subject to BCP 78 and the IETF Trust's Legal
    48   Provisions Relating to IETF Documents
    49   (https://trustee.ietf.org/license-info) in effect on the date of
    50   publication of this document.  Please review these documents
    51   carefully, as they describe your rights and restrictions with respect
    52   to this document.  Code Components extracted from this document must
    53   include Simplified BSD License text as described in Section 4.e of
    54   the Trust Legal Provisions and are provided without warranty as
    55   described in the Simplified BSD License.
    
    57   This document may contain material from IETF Documents or IETF
    58   Contributions published or made publicly available before November
    59   10, 2008.  The person(s) controlling the copyright in some of this
    60   material may not have granted the IETF Trust the right to allow
    61   modifications of such material outside the IETF Standards Process.
    62   Without obtaining an adequate license from the person(s) controlling
    63   the copyright in such materials, this document may not be modified
    64   outside the IETF Standards Process, and derivative works of it may
    65   not be created outside the IETF Standards Process, except to format
    66   it for publication as an RFC or to translate it into languages other
    67   than English.
    
    [major] As far as I can tell, the first version of
    draft-keyupate-ospf-ospfv2-hbit (the predecessor of this document) was
    published in 2015.  So the copyright text above doesn't apply.  Are we
    missing other predecessors?
    
    If not, then this issue should be easy to fix.  In at least the XML editor
    that I use, there's an option to indicate pre-RFC5378 work, or not.  In
    this case it seems like it should be No.
    
    
    ...
    85 1.  Introduction
    
    [minor] Same comment as for the Abstract: describing the functionality in
    terms of OSPFv2 would have been nicer.  You can still make the reference to
    the R-bit at the end, if you really want to.
    
    87   OSPFv3 [RFC5340] defines an option bit for router-LSAs known as the
    88   R-bit.  If the R-bit is clear, an OSPFv3 router can participate in
    89   OSPFv3 topology flooding without acting as a transit router.  In such
    90   cases, other routers in the OSPFv3 routing domain only install routes
    91   used for local traffic.
    
    93   This functionality is particularly useful for BGP Route Reflectors,
    94   known as virtual Route Reflectors (vRRs), that are not in the
    95   forwarding path but are in central locations such as data centers.
    96   Such Route Reflectors typically are used for route distribution and
    97   are not capable of forwarding transit traffic.  However, they need to
    98   learn the OSPF topology for:
    
    100   1.  SPF computation for Optimal Route Reflection functionality as
    101       defined in [I-D.ietf-idr-bgp-optimal-route-reflection]
    
    103   2.  Reachability resolution for its Route Reflector Clients.
    
    [nit] Clearly route reflection is not the only motivation for this work.
    The justification only related to RRs seems gratuitous.  Just a nit...
    
    105   This document defines the R-bit functionality equivalent for OSPFv2
    106   defined in [RFC2328] by introducing a new router-LSA bit known as the
    107   "H-bit".  This document updates appendix A.4.2 of RFC 2328.
    
    [nit] s/OSPFv2 defined in [RFC2328]/OSPFv2 [RFC2328]  It sounds as if "the
    R-bit functionality equivalent for OSPFv2" is already in rfc2328.
    
    [major] Please be specific about what the Update is.
    
    
    ...
    117 3.  H-bit Support
    
    119   This document defines a new router-LSA bit known as the Host Bit or
    120   the H-bit.  An OSPFv2 router advertising a router-LSA with the H-bit
    121   set indicates to other OSPFv2 routers in the area supporting the
    122   functionality that it MUST NOT be used as a transit router.  The bit
    123   value usage of the H-bit is reversed from the R-bit defined in OSPFv3
    124   [RFC5340] to support backward compatibility.  The modified OSPFv2
    125   router-LSA format is:
    
    [minor] "...MUST NOT be used as a transit router"  Put a forward reference
    to §4.
    
    [nit] The text keeps making reference to the R-bit.  Even though there is a
    relationship, the H-bit is an independent feature.  IOW, I don't think
    there's a need to explain the relationship to OSPFv3.
    
    [minor] On the same topic:  The comparison to OSPFv3 is made and the
    "reverse" bit setting is justified "to support backward compatibility", but
    that is not explained anywhere.  I was hoping that §5 (Auto Discovery and
    Backward Compatibility) would say something, but it doesn't.
    
    127        0                   1                   2                   3
    128        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
    129       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    130       |            LS age             |     Options   |       1       |
    131       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    132       |                        Link State ID                          |
    133       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    134       |                     Advertising Router                        |
    135       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    136       |                     LS sequence number                        |
    137       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    138       |         LS checksum           |             length            |
    139       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    140       |H|0|0|N|W|V|E|B|        0      |            # links            |
    141       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    142       |                          Link ID                              |
    143       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    144       |                         Link Data                             |
    145       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    146       |     Type      |     # TOS     |            metric             |
    147       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    148       |                              ...                              |
    149       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    150       |      TOS      |        0      |          TOS  metric          |
    151       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    152       |                          Link ID                              |
    153       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    154       |                         Link Data                             |
    155       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    156       |                              ...                              |
    
    158      bit H
    159          When set, an OSPFv2 router is a non-transit router and is
    160          incapable of forwarding transit traffic.
    
    [nit] Please label the figure: Figure 1...
    
    [minor] Even though it seems obvious from the figure, please be explicit in
    saying that the H-bit is the first bit (or however that bit is
    identified)...
    
    162   When the H-bit is set, an OSPFv2 router is a non-transit router and
    163   should not be used to forward transit traffic.  In this mode, the
    164   other OSPFv2 routers in the area SHOULD NOT use the originating
    165   OSPFv2 router for transit traffic, but MAY use the OSPFv2 router for
    166   local traffic destined to that OSPFv2 router.
    
    [minor] The first/second sentences seem redundant: "should not be used to
    forward transit traffic...SHOULD NOT use the originating OSPFv2 router for
    transit traffic".
    
    [major] When would the non-transit router be used for transit?  IOW, why
    use "SHOULD NOT" and not "MUST NOT"?
    
    [major] "MAY use the OSPFv2 router for local traffic destined to that
    OSPFv2 router"   I'm not sure what behavior is being specified here.  The
    text sounds as if it was optional to even consider the router as a traffic
    destination.  Is that the intent?  Why?  What would make a network operator
    decide one way or the other?
    
    168   An OSPFv2 router originating a router-LSA with the H-bit set SHOULD
    169   advertise all its non-local router links with a link cost of
    170   MaxLinkMetric as defined in Section 3 of [RFC6987].  This is to
    171   increase the applicability of the H-bit to partial deployments where
    172   it is the responsibility of the operator to ensure that OSPFv2
    173   routers not supporting the H-bit do not install routes causing
    174   routing loops.
    
    [major] When would a router not advertise MaxLinkMetric?  IOW, why use
    SHOULD and not MUST?
    
    [major] What are "non-local router links"?  I always thought of links to be
    local to the router...what am I missing?
    
    [nit] s/advertise all its non-local router links with a link cost of
    MaxLinkMetric as defined in Section 3 of [RFC6987]/advertise all its
    non-local router links with a link cost of MaxLinkMetric [RFC6987]
    
    176   When the H-bit is set, IPv4 prefixes associated with local interfaces
    177   in other areas MAY be advertised in summary LSAs.  Non-local IPv4
    178   prefixes, e.g., those advertised by other routers and installed
    179   during the SPF computation, MAY be advertised in summary-LSAs if
    180   configured by policy.  Likewise, when the H-bit is set, only IPv4
    181   prefixes associated with local interfaces MAY be advertised in AS-
    182   external LSAs.  Non-local IPv4 prefixes, e.g., those exported from
    183   other routing protocols, MUST NOT be advertised in AS-external-LSAs.
    184   Finally, when the H-bit is set, an Area Border Router (ABR) MUST
    185   advertise a consistent H-bit setting in its self-originated router-
    186   LSAs for all attached areas.
    
    [minor] Some of the behavior specified in this paragraph may be non
    intuitive -- for example: "When the H-bit is set, IPv4 prefixes associated
    with local interfaces in other areas MAY be advertised in summary LSAs."
     During normal operation (aka rfc2328), these prefixes are always
    advertised (assuming normal areas, etc.)...and given that these are local
    to the router, it can be argued that one is not using the router as
    transit...on the other hand, going to a different area can be interpreted
    as transit.  In either case, it would be nice if more was said about the
    optional nature of including these prefixes in the summary LSA.  What are
    the operational considerations?
    
    [minor] The same comment for "prefixes associated with local interfaces MAY
    be advertised in AS-external LSAs".
    
    [major] "Non-local IPv4 prefixes...MAY be advertised in summary-LSAs if
    configured by policy."  Doesn't advertising result in the router being
    transit?  Doesn't it defeats the purpose of setting the H-bit?  But there
    may be operational reasons to do so -- e.g. if the router is the only ABR..