Re: [OSPF] Gen-ART and OPS-Dir review of draft-ietf-ospf-node-admin-tag-06 - Editorial comments and nits

"Black, David" <david.black@emc.com> Wed, 07 October 2015 14:50 UTC

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From: "Black, David" <david.black@emc.com>
To: Shraddha Hegde <shraddha@juniper.net>, Rob Shakir <rjs@rob.sh>, "as@cisco.com" <as@cisco.com>, "bruno.decraene@orange.com" <bruno.decraene@orange.com>, "ops-dir@ietf.org" <ops-dir@ietf.org>, "General Area Review Team (gen-art@ietf.org)" <gen-art@ietf.org>, "lizhenbin@huawei.com" <lizhenbin@huawei.com>
Thread-Topic: Gen-ART and OPS-Dir review of draft-ietf-ospf-node-admin-tag-06 - Editorial comments and nits
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Subject: Re: [OSPF] Gen-ART and OPS-Dir review of draft-ietf-ospf-node-admin-tag-06 - Editorial comments and nits
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Most of the nits/editorial comments are fine.  Two follow-ups:

> -- 3.1.  TLV format
> 
>    Type : TBA, Suggested value 10
> 
> Please add an RFC Editor Note asking the RFC Editor to replace this with the
> actual IANA-assigned value.
> <Shraddha> Does the RFC Editor Note go as part of this document.

Yes, e.g.:

**RFC Editor: Please replace above TBA with the actual IANA-assigned value.

> -- 4.5.  Explicit routing policy

The discussion of this example appears to warrant revision to reflect
the preference vs. prohibition discussion around Major Issue [1].

Thanks,
--David

> -----Original Message-----
> From: Shraddha Hegde [mailto:shraddha@juniper.net]
> Sent: Wednesday, October 07, 2015 3:08 AM
> To: Black, David; Rob Shakir; as@cisco.com; bruno.decraene@orange.com; ops-
> dir@ietf.org; General Area Review Team (gen-art@ietf.org);
> lizhenbin@huawei.com
> Cc: acee@cisco.com; ospf@ietf.org; ietf@ietf.org
> Subject: RE: Gen-ART and OPS-Dir review of draft-ietf-ospf-node-admin-tag-06
> 
> David,
> 
> Thanks a lot for your detailed review and comments.
> 
> Here are the details of responses. I have also attached the updated document.

[... snip ...]

> --- Nits/editorial comments: ----
> 
> -- 1.  Introduction
> 
> The Abstract says that the tags are for "route and path selection"; the
> Introduction should
> 
> also say that.  Suggestion - at the end of this sentence in the first
> paragraph:
> 
>    It is useful to assign a per-node administrative tag to a router in
>    the OSPF domain and use it as an attribute associated with the node.
> 
> add the text "for route and path selection".  This will help with the second
> sentence in
> 
> the second paragraph:
> 
> <Shraddha>Modified as per suggestion.
> 
>    Path selection is a functional set
>    which applies both to TE and non-TE applications and hence new TLV
>    for carrying per-node administrative tags is included in Router
>    Information LSA [RFC4970] .
> 
> If "path selection" and "functional set" are specific terms with specialized
> meaning in
> 
> OSPF context, that sentence is fine as-is, otherwise it would read better if
> it began with:
> 
>    Route and path selection functionality applies to both ...
> 
> <Shraddha> Modified as per suggestion.
> 
> This document provides mechanisms to advertise per-node administrative
> tags in OSPF for route and path selection. Route and path selection
> functionality applies
> 
> to
> both to TE and non-TE applications and hence new TLV for carrying per-node
> administrative tags is included in Router Information LSA ...
> 
> 
> 
> -- 3.1.  TLV format
> 
>    Type : TBA, Suggested value 10
> 
> Please add an RFC Editor Note asking the RFC Editor to replace this with the
> actual IANA-
> 
> assigned value.
> <Shraddha> Does the RFC Editor Note go as part of this document.
> 
> -- 3.2.  Elements of procedure
> 
> While it's obvious that tag usage should be confined to the administrative
> domain that
> 
> understands the tag, it's worth stating.  At the end of this
> sentence:
> 
>    Interpretation of tag values is specific to the administrative domain
>    of a particular network operator.
> 
> I'd suggest adding:
> 
>    , and hence tag values SHOULD NOT be propagated outside the
>    administrative domain to which they apply.
> 
> <Shraddha> Modified as per suggestion
> 
> -- 4.4.  Mobile back-haul network service deployment
> 
> Please expand "eNodeB" acronym on first use.
> 
> <Shraddha> Added
> 
> -- 4.5.  Explicit routing policy
> 
> In Figure 3:
> - The link from the leftmost pair of A nodes to the pair of T nodes
>    do not have link weights.
> - The link from the left R node to the left T node does not have a
>    link weight
> - The following example of an explicitly routed policy:
> 
>       - Traffic from A nodes to I nodes must not go through R and T
>       	nodes
> 
>     prevents the leftmost pair of A nodes from sending traffic to the
>     I nodes.  Was this "black hole" intended as part of the example?
> 
> Also: "explicitly routed policies" -> "explicit routing policies"
> 
> <Shraddha> It's probably not intended.
> Bruno, can you pls confirm?
> 
> But, the example in itself is very much valid, with node admin tags operators
> can
> have policies to drop traffic if destined towards certain prefixes.
> As Rob and Bruno, this is nothing new as such an operation is possible today
> with routing policies.
> 
> - 5. Security considerations
> 
> I'd add discussion that advertisement of tag values for one administrative
> domain into
> 
> another risks misinterpretation of the tag values (if the two domains have
> assigned
> 
> different meanings to the same values), which may have undesirable and
> unanticipated side
> 
> effects.
> 
> <Shraddha> Added this point to security considerations.
> 
> In addition, injection of tag values from the outside (e.g., forge OSPF
> traffic that
> 
> appears to be from a node in the domain and carries administrative tag values)
> is at least
> 
> a possible denial-of-service attack vector, and could also be used for more
> nefarious
> 
> purposes (e.g., reroute otherwise unobservable [to the attacker] VPN traffic
> via a route
> 
> where the attacker can observe it).
> 
> <Shraddha> In the absence of authentication, such attacks are possible on
> existing
>            OSPF implementations and I  don't think it's a new risk added by
> this extension.
> 
> 
> idnits 2.13.02 did not find any nits.
> 
> ---- Selected RFC 5706 Appendix A Q&A for OPS-Dir review ----
> 
> A.1.2.  Has installation and initial setup been discussed?
> A.1.5.  Has the impact on network operation been discussed?
> A.1.6.  Have suggestions for verifying correct operation been discussed?
> 
> 	No - given the impact that these tags could have on route and path
> 		computation, likely implementations will be powerful "guns"
> 		with which network operators can readily shoot themselves
> 		in far more than just their "feet."  These
> 		considerations would have to be documented based on the
> 		specific uses made of these tags by specific implementations
> 		and deployments.  All of that appears to be outside the scope
> 		of this draft.
> 
> A.1.7.  Has management interoperability been discussed?
> 
> 	No - at a minimum, reporting of tag values ought to be defined
> 		via an OSPF MIB extension or analogous functionality.
> 		This is minor issue [D].
> 
> A.1.8.  Are there fault or threshold conditions that should be reported?
> 
> 	Yes, but they're implementation-specific - see response to
> 		A.1.[2,5,6] above.
> 
> A.2.  Management Considerations
>    Do you anticipate any manageability issues with the specification?
> 
> 	Yes, manageability has been largely ignored.
> 
> A.3.  Documentation
> 
>    Is an operational considerations and/or manageability section part of
>    the document?
> 
> 	No.
> 
>    Does the proposed protocol have a significant operational impact on
>    the Internet?
> 
> 	Yes, the anticipated uses will.
> 
>    Is there proof of implementation and/or operational experience?
> 
> 	Nothing was stated in the draft or shepherd write-up.
> 
> As an OPS-Dir member, I'm concerned by the above RFC 5706 answers, and in
> particular
> 
> treating all operational issues as vendor- and/or operator-specific.  One
> possible
> 
> alternative would be to scope the draft down to interoperably specify what's
> needed for
> 
> LFA, as indicated by this answer from the Shepherd write-up:
> 
> (9) How solid is the WG consensus behind this document? Does it
>     represent the strong concurrence of a few individuals, with others
>     being silent, or does the WG as a whole understand and agree with it?
> 
>       There is consensus from the WG and others outside the WG that
>       this document can progress. It complements work done on LFA
>       manageability in the RTG Working Group.
> 
> Another alternative could be Experimental RFC status for the full tag
> mechanism (e.g., to
> 
> figure out what it'll be used for in practice, how and why) rather than
> Proposed Standard.
> 
> This is major issue [1].
> 
> -----Original Message-----
> From: Black, David [mailto:david.black@emc.com]
> Sent: Wednesday, October 07, 2015 4:41 AM
> To: Rob Shakir <rjs@rob.sh>sh>; as@cisco.com; bruno.decraene@orange.com; ops-
> dir@ietf.org; Shraddha Hegde <shraddha@juniper.net>et>; General Area Review Team
> (gen-art@ietf.org) <gen-art@ietf.org>rg>; lizhenbin@huawei.com
> Cc: acee@cisco.com; ospf@ietf.org; ietf@ietf.org; Black, David
> <david.black@emc.com>
> Subject: RE: Gen-ART and OPS-Dir review of draft-ietf-ospf-node-admin-tag-06
> 
> Rob,
> 
> I think something needs to be said on use of tags for preference in route
> selection vs. prohibition on use of routes, e.g., as Section 4.5 starts out
> with a discussion of preference and then supplies two example policies that
> are prohibitions.
> 
> While Section 4.5 appears to need some attention, that seems to be a bit late
> in the draft to cover this topic - perhaps this would be fodder for an
> "Operational Considerations" section, as suggested in my reply to Bruno.
> That could include a statement that route preference policies are a less risky
> use of tags by comparison to route prohibition policies.
> 
> Now that I have a better idea of what this draft is intended for, please
> ignore my suggestions to scope it to LFA or make it Experimental.
> 
> Thanks,
> --David
> 
> > -----Original Message-----
> > From: Rob Shakir [mailto:rjs@rob.sh]
> > Sent: Tuesday, October 06, 2015 1:22 PM
> > To: as@cisco.com; bruno.decraene@orange.com; Black, David;
> > ops-dir@ietf.org; shraddha@juniper.net; General Area Review Team
> > (gen-art@ietf.org); lizhenbin@huawei.com
> > Cc: acee@cisco.com; ospf@ietf.org; Black, David; ietf@ietf.org
> > Subject: RE: Gen-ART and OPS-Dir review of
> > draft-ietf-ospf-node-admin-tag-06
> >
> >
> > On October 6, 2015 at 17:46:41, Black, David (david.black@emc.com) wrote:
> > > Rob,
> > >
> > > > Given that we are really selecting candidates from within a set of
> > > > paths
> > that
> > > > have already been selected by OSPF as valid, and usable - then I’m
> > > > not
> > sure
> > > > that I can understand the logic behind this sentence from your review:
> > "There
> > > > appears to be more than enough enabled by this draft to wreak
> > > > serious operational havoc”.
> > >
> > > Perhaps, I'm not understanding something, but I thought I saw an
> > unreachability
> > > problem in the example in Section 4.5/Figure 3:
> > >
> > > - The following example of an explicitly routed policy:
> > >
> > > - Traffic from A nodes to I nodes must not go through R and T nodes
> > >
> > > prevents the leftmost pair of A nodes from sending traffic to the I
> > > nodes. Was this "black hole" intended as part of the example?
> > >
> > > Was that a mistake, and at least one path from the leftmost pair of
> > > A nodes to the I nodes will be selected despite that "explicitly routed
> policy”?
> >
> > If the operator chooses to deny prefixes being installed in the RIB
> > based on these tags, then yes, they could end up with unreachability
> > problems. However, an operator can do this today with any routing
> > policy (a number of implementations already have inbound route
> > filtering) - we should not prevent this kind of mechanism based on the
> > fact that an erroneous config might be problematic.
> >
> > In the case that the operator *preferences* things based on the tags,
> > then this would not be an unreachability problem - OSPF would still
> > correctly determine that there is a path between all nodes in the
> > pictured network - and this would be installed in the RIB as per normal
> operation.
> >
> > (My memory is not 100% clear on whether this is intended as part of
> > the example, if it is, then the text should be clarified I agree.)
> >
> > Kind regards,
> > r.