Re: Benjamin Kaduk's Discuss on draft-ietf-bfd-yang-16: (with DISCUSS and COMMENT)

["Reshad Rahman (rrahman)" <[e-mail]>]

Revision 17 has been uploaded.

On 2018-08-01, 5:28 PM, "Reshad Rahman (rrahman)" <[e-mail]> wrote:

    I'm integrating Benjamin's proposal in the next rev.
    
    Regards,
    Reshad.
    
    On 2018-07-30, 4:45 PM, "PFFC JHAAS" <[e-mail]> wrote:
    
        Benjamin,
        
        Your proposal would be fine. It basically says be mindful of the relationship. 
        
        Jeff
        
        > On Jul 30, 2018, at 10:41, Benjamin Kaduk <[e-mail]> wrote:
        > 
        > Hi Reshad,
        > 
        >> On Thu, Jul 26, 2018 at 12:16:05AM +0000, Reshad Rahman (rrahman) wrote:
        >> Hi Benjamin and Jeff,
        >> 
        >> Following our discussion in Montreal, would the following, or something along these lines, be OK with you in the Security Considerations section.
        >> 
        >>   When BFD clients are used to modify BFD configuration (as described
        >>   in Section 2.1), any authentication and authorization for the BFD
        >>   configuration changes have to take place in the BFD clients.  For
        >>   example, if the BFD client is an IGP then the IGP SHOULD be
        >>   authenticated. Also, consideration should be given to the access control of
        >>   the BFD clients.
        > 
        > I can't speak for Jeff, but I think this is edging closer to the bits he
        > doesn't like.  (It seems to capture the topics I had in mind just fine,
        > though.)
        > 
        >> From our discussion in Montreal, it seemed like we might end up at
        > something more like:
        > 
        > When BFD clients are used to modify BFD configuration (as described
        > in Section 2.1), the BFD clients need to be included in an analysis of
        > the security properties of the BFD-using system (e.g., when considering the
        > authentication and authorization of control actions).  In many cases, BFD
        > is not the most vulnerable portion of such a composite system, since BFD is
        > limited to generating well-defined traffic at a fixed rate on a given path;
        > in the case of an IGP as BFD client, attacking the IGP could cause more
        > broad-scale disruption than (de)configuring a BFD session could cause.
        > 
        > -Benjamin
        > 
        > 
        >> On 2018-07-15, 9:05 AM, "Benjamin Kaduk" <[e-mail]> wrote:
        >> 
        >>>    On Wed, Jul 11, 2018 at 11:32:18AM -0400, Jeffrey Haas wrote:
        >>> Benjamin,
        >>> 
        >>>> On Wed, Jul 11, 2018 at 10:02:41AM -0500, Benjamin Kaduk wrote:
        >>>> "may be overkill in some circumstances" sounds exactly like an RFC 2119
        >>>> SHOULD, does it not?
        >>> 
        >>> Putting it slightly a different way, I am always wary of trying to embed too
        >>> much operational and security wisdom in documents for the following reasons:
        >>> - What's wise in one set of circumstances may not be in another.  By being
        >>>  proscriptive, you may lead to implementations that lack necessary
        >>>  flexibility.
        >> 
        >>    In my opinion, including guidance with the supporting motivation suffices
        >>    to leave flexibility for unanticipated future cases with differing needs.
        >> 
        >>> - You're imposing a level of fate binding between mechanisms that may
        >>>  contravene desired behaviors from some operators that have split
        >>>  operational roles.
        >> 
        >>    If the stated motivation does not apply to operators with such split roles,
        >>    do we not think they are smart enough to see that the prerequisite is not
        >>    met and ignore the advice?
        >> 
        >>> [...]
        >>>> To frame the same idea in a different fashion, we have this nice security
        >>>> considerations boilerplate for YANG modules, talking about how the usual
        >>>> access methods are NETCONF/RESTCONF, with MTI secure transport of ssh/TLS.
        >>>> The scheme being described here is effectively providing a new access
        >>>> mechanism (IGP) for a subset of the YANG module,
        >>> 
        >>> This is perhaps my personal disconnect.
        >>> 
        >>> Much of the point of providing a common configuration grouping for BFD for
        >>> client protocols was to encapsulate, "I'm a client of BFD, here's my
        >>> parameters".  An implementation is free to use the "please use bfd with
        >>> these parameters for my protocol" or perhaps ignore them.  But in
        >>> circumstances that an operator may wish to limit access to protocol BFD
        >>> behavior, it has the existing ability in NACM to enforce its policy on those
        >>> BFD nodes within the protocol tree.
        >>> 
        >>> What I feel you're saying is we need to call special attention to these
        >>> instantiations that may be imported by some module.  
        >>> 
        >>> What I'm confused about is why such an import is any more special than any
        >>> other import from another module.
        >> 
        >>    I've been trying to wrap my head around your explanation for the past few
        >>    days, and I'm not sure I'm succeeding at it.  The only reason I'm raising
        >>    this point with this document is because there is text in the document like
        >>    "[f]or example, when a new IGP peer is discovered, the IGP would create a
        >>    BFD session to the newly discovered peer and similarly when an IGP peer
        >>    goes away, the IGP would remove the BFD session to that peer."  Imagine if
        >>    I was writing a document about a device that controls a physical door, and
        >>    the usual way to operate the device is to manually enter a PIN while
        >>    physically in front of the door.  If I also said "some people expose this
        >>    door-unlocking device to the internet and accept unlock requests over
        >>    HTTP", that would be incredibly unresponsible of me unless I added some
        >>    extra qualifier.  Perhaps it would be "and these people are crazy", or
        >>    perhaps "but HTTP itself is insecure, so in such situations TLS ought to be
        >>    used with mutual authentication, authorization checks for the party
        >>    requesting unlocking, and the best practices from RFC 7525".
        >> 
        >>    So, in my head, I see this document as using a not-quite-throwaway example
        >>    to make a point about the limitations of the main focus of the document,
        >>    and should properly qualify the different security properties of that
        >>    example.  Your description above still reads to me as if it's focusing on
        >>    YANG modules not specified in this document but that also use the same BFD
        >>    grouping.  In such a case, when the NACM applies, isn't that still going
        >>    through normal management paths for that respective YANG module?  I'm still
        >>    trapped in a rut thinking about "received IGP packet from the network that
        >>    instantiates a new IGP session; as a side effect instantiate a BFD session
        >>    as well", where the incoming IGP packet is just the IGP implementation and
        >>    not a "management function" per se.
        >> 
        >>    -Benjamin
        >> 
        >> 
        
        
    
    

--- Begin Message ---

A new version of I-D, draft-ietf-bfd-yang-17.txt
has been successfully submitted by Reshad Rahman and posted to the
IETF repository.

Name:		draft-ietf-bfd-yang
Revision:	17
Title:		YANG Data Model for Bidirectional Forwarding Detection (BFD)
Document date:	2018-08-01
Group:		bfd
Pages:		79
URL:            https://www.ietf.org/internet-drafts/draft-ietf-bfd-yang-17.txt
Status:         https://datatracker.ietf.org/doc/draft-ietf-bfd-yang/
Htmlized:       https://tools.ietf.org/html/draft-ietf-bfd-yang-17
Htmlized:       https://datatracker.ietf.org/doc/html/draft-ietf-bfd-yang
Diff:           https://www.ietf.org/rfcdiff?url2=draft-ietf-bfd-yang-17

Abstract:
   This document defines a YANG data model that can be used to configure
   and manage Bidirectional Forwarding Detection (BFD).

   The YANG modules in this document conform to the Network Management
   Datastore Architecture (NMDA).

                                                                                  


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