Re: [secdir] Secdir review of draft-ietf-trill-multilevel-unique-nickname-05

"Zhangmingui (Martin)" <zhangmingui@huawei.com> Mon, 05 March 2018 03:49 UTC

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From: "Zhangmingui (Martin)" <zhangmingui@huawei.com>
To: Donald Eastlake <d3e3e3@gmail.com>, Roman Danyliw <rdd@cert.org>
CC: "iesg@ietf.org" <iesg@ietf.org>, "secdir@ietf.org" <secdir@ietf.org>, "draft-ietf-trill-multilevel-unique-nickname.all@ietf.org" <draft-ietf-trill-multilevel-unique-nickname.all@ietf.org>
Thread-Topic: Secdir review of draft-ietf-trill-multilevel-unique-nickname-05
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Date: Mon, 5 Mar 2018 03:49:47 +0000
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Subject: Re: [secdir] Secdir review of draft-ietf-trill-multilevel-unique-nickname-05
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Hi Donald, Roman,

Thanks a lot for the review! The comments have been incorporated in the 06 version which has been uploaded.

Thanks,
Mingui

> -----Original Message-----
> From: Donald Eastlake [mailto:d3e3e3@gmail.com]
> Sent: Monday, March 05, 2018 2:58 AM
> To: Roman Danyliw <rdd@cert.org>;
> Cc: iesg@ietf.org; secdir@ietf.org;
> draft-ietf-trill-multilevel-unique-nickname.all@ietf.org
> Subject: Re: Secdir review of draft-ietf-trill-multilevel-unique-nickname-05
> 
> Hi Roman,
> 
> Thanks for doing a review. See responses below.
> 
> On Fri, Mar 2, 2018 at 9:00 PM, Roman Danyliw <rdd@cert.org>; wrote:
> > Reviewer: Roman Danyliw
> > Review result: Ready with nits
> >
> > I have reviewed this document as part of the security directorate's ongoing
> effort to review all IETF documents being processed by the IESG.  These
> comments were written primarily for the benefit of the security area directors.
> Document editors and WG chairs should treat these comments just like any
> other last call comments.
> >
> > The summary of the review is Ready with nits.
> >
> > My feedback is as follows:
> >
> > (1) Section 4.1, Multilevel TRILL Basics, Page 8
> >
> > Thus Level 1 link state
> > information stays within a Level 1 area and Level 2 link state
> > information stays in Level 2 unless there are specific provisions for
> > leaking (copying) information between levels.
> >
> > ** What are these provisions where such leakage of information should occur
> beyond expected routing behavior?
> 
> Typically "link state" information stays within a Level 1 area or within the Level
> 2 routers. Occasionally there is information that it is desirable to  flood
> throughout the domain at both Level 1 and Level 2. IS-IS "link state"
> information is in the form of TLVs. Typically this domain wide flooding is
> accomplished by using two flags in the value portion of the TLV. One flag
> indicates the the TLV is to be flooded domain wide while the other is initially
> zero and is set when the TLV is flooded from Level 2 to Level 1 -- this second flag
> is to stop a TLV from being flooded from Level 2 to Level 1 and then back to
> Level 2 again resulting in TLV looping. See, for example, the IS-IS Router
> Capabilities TLV D and S flags as specified in Section 2 of RFC 7981.  This is all
> standard IS-IS machinery that someone familiar with IS-IS would know -- there
> is nothing TRILL specific about it.
> 
> > (2) Section 4.2, Nickname Allocation, Page 8-9.
> >
> > Level 2 RBridges contend for nicknames in the range from 0xF000
> > through 0xFBFF the same way as specified in [RFC6325], using Level 2
> > LSPs. The highest priority border router for a Level 1 area should
> > contend with others in Level 2 for smallish blocks of nicknames for
> > the range from 0x0001 to 0xEFFF. Blocks of 64 aligned on multiple of
> > 64 boundaries are RECOMMENDED in this document.
> >
> > ** This text provides guidance to allocate nicknames from the range 0x0001 -
> 0xFBFF (0x0001 - 0xEFFF and 0xF000 - 0xFBFF); and Section 3.7 of RFC6325 says
> that 0xFFC0 - 0xFFFF and 0x0 are reserved.  Collectively, these two documents
> leave the range of 0xFC00 - 0xFFBF unspecified.  If that's intentional, describe
> how these values should be handled. Or, perhaps there a typo and L2 Rbridges
> should allocate from 0xF000 - 0xFFBF (i.e., s/0xFBFF/0xFFBF/)?
> 
> I believe it's a typo and is should by 0xF000 - 0xFFBF.
> 
> > ** (Editorial) The language "smallish blocks of nicknames" seems imprecise.
> 
> I think we could just delete the word "smallish".
> 
> > (3) Section 6, Security Considerations, Page 12.
> >
> > With TRILL multilevel, flooding of control traffic for link state
> > information of Level 1 and Level 2 is separated. This addresses the
> > TRILL scalability issues as specified in Section 2 of [RFC8243] and
> > also confines the effective scope of possible malicious events.
> >
> > ** Per the sentence "With TRILL ... is separated", I recommend
> > clarifying the language on what and in what way there is separation
> 
> This is basic to multilevel IS-IS and anyone familiar with that would understand.
> We could add a reference to IS-IS.
> 
> > ** Per the follow-up sentence, "... also confines the effective scope of
> possible malicious events", I recommend discussing in more detail how the
> scope of malicious events is reduced with this approach.
> 
> I suggest the following replacement text:
> 
>    Since TRILL multilevel uses the existing IS-IS multilevel facilities [IS-IS],
> flooding of control traffic for link state information is automatically confined to
> a Level 1 area or to Level 2 except (for limited types of information that can be
> specifically flagged for wider flooding). This addresses the TRILL scalability
> issues as specified in Section 2 of [RFC8243] and also, except of the wider
> flooding case, this confines the scope of the effects of malicious events that
> could be communicated through the link state.
> 
> > (4) Section 6, Security Considerations, Page 12.
> >
> > However, due to the nature that unique nickname areas share a unique
> > nickname space, border RBridges still have to leak nickname
> > information between levels. For this purpose, border RBridges need to
> > fabricate the nickname announcements as specified in Section 4.3.
> >
> > ** As it is raised as an issue with a mitigation, I recommend articulating the
> implication of leaking nicknames across levels.
> 
> Since nicknames must be unique across the multi-level domain, and nicknames
> in TRILL are auto-allocated, clearly RBridges inside an area need to know what
> nicknames are in use, which is the effect and purpose of leaking nickname claim
> information across levels. I suggest the following wording:
> 
>     However, due to the nature that unique nickname areas share a common
> nickname space, border RBridges still have to leak nickname information
> between levels. Such leaking means that nickname related events in one area
> can affect other areas. For this purpose, border RBridges need to fabricate the
> nickname announcements as specified in Section 4.3.
> 
> > (5) Section 6, Security Considerations, Page 12.
> >
> > Malicious devices may also fake the NickBlockFlags APPsub-TLV to
> > announce a range of nicknames. By doing this, the attacker can attract
> > TRILL data packets that are originally to reach a bunch of other
> > RBridges.
> >
> > ** Recommend articulating the implications of a rogue device changing the
> path -- it might deny service, expose traffic to inspection, etc.
> 
> This is not that much different from an RBridge announcing low cost to some
> MAC address to attract data packets. It is typical that all routers in some
> routing domain have to be, to a reasonable extent, trusted since there is a
> large variety of information they could maliciously announce to cause problems.
> If a rogue router makes false announcements to attract traffic, typically the
> traffic goes to that router and not to the intended destination. Anyone familiar
> with common routing techniques would be aware of this.
> 
> > ** (Editorial) Recommend alternate language for the colloquial "... bunch of
> other RBridges"
> 
> bunch -> number
> 
> > (6) Section 6, Security Considerations, Page 12.
> >
> > For this reason, RBridges SHOULD be configured to include the IS-IS
> > Authentication TLV (10) in the IS-IS PDUs that contains the
> > NickBlockFlags APPsub-TLV, so that IS-IS security ([RFC5304]
> > [RFC5310]) can be used to secure the network.
> >
> > ** Should a preference be expressed for RFC5310 over RFC5304?  To quote
> RFC5310, "[while at the time of this writing there are no openly published
> attacks on the HMAC-MD5 mechanism, some reports ([Dobb96a], [Dobb96b])
> create concern about the ultimate strength of the MD5 cryptographic hash
> function."
> 
> I would agree that RFC 5310 security is superior to RFC 5304 security.
> Perhaps references to 5304 can be removed.
> 
> > ** Recommend being more specific with the language "to secure the
> network".  Perhaps "For this reason, RBridges SHOULD authenticate their
> peer by using the IS-IS Authentication TLV (10) in the IS-IS PDUs that contains
> the NickBlockFlags APPsub-TLV."
> 
> Suggest replacing "to secure the network" with "to authenticate those PDUs
> and discard them if they are forged."
> 
> > (7) Section 6, Security Considerations, Page 12.
> >
> > If border RBridges do not prune multi-destination distribution tree
> > traffic in Data Labels that are configured to be area local, then
> > traffic that should have been contained within an area might be
> > wrongly delivered to end stations in that Data Label in other areas.
> > This would generally violate security constraints.
> >
> > ** Recommend being more specific on the security constraints being
> > violated
> 
> OK.
> 
> Thanks,
> Donald
> ===============================
>  Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
>  155 Beaver Street, Milford, MA 01757 USA  d3e3e3@gmail.com