Re: [trill] Eric Rescorla's Discuss on draft-ietf-trill-arp-optimization-08: (with DISCUSS and COMMENT)

[Donald Eastlake <[e-mail]>]

Hi Eric,

I realize that most of the delay has been on the TRILL WG end but I hope
you don't mind if I ping you again on looking at the -09 revision of this
draft...

Thanks,
Donald
===============================
 Donald E. Eastlake 3rd   [phone] (cell)
 155 Beaver Street, Milford, MA 01757 USA
 [e-mail]

On Mon, Oct 9, 2017 at 7:05 PM, Donald Eastlake <[e-mail]> wrote:

> Hi Eric,
>
> A -09 version of draft-ietf-trill-arp-optimization has been posted. Could
> you look at it to see if it resolves your comments?
>
> Thanks,
> Donald
> ===============================
>  Donald E. Eastlake 3rd   [phone] <(508)%20333-2270> (cell)
>  155 Beaver Street, Milford, MA 01757 USA
>  [e-mail]
>
> On Mon, Oct 2, 2017 at 2:12 PM, Eric Rescorla <[e-mail]> wrote:
>
>>
>>
>> On Mon, Oct 2, 2017 at 4:54 PM, Donald Eastlake <[e-mail]> wrote:
>>
>>> Hi Eric,
>>>
>>> My apologies for the delay in response. (For part of the time I was on
>>> a cruise...)
>>>
>>> It looks like we are in agreement on most items.
>>>
>>> See below.
>>>
>>> On Fri, Sep 22, 2017 at 9:18 AM, Eric Rescorla <[e-mail]> wrote:
>>> >
>>> >
>>> > On Wed, Aug 23, 2017 at 12:38 PM, Donald Eastlake <[e-mail]>
>>> wrote:
>>> >>
>>> >> Hi Eric,
>>> >>
>>> >> On Wed, Jul 5, 2017 at 7:38 AM, Eric Rescorla <[e-mail]> wrote:
>>> >> > Eric Rescorla has entered the following ballot position for
>>> >> > draft-ietf-trill-arp-optimization-08: Discuss
>>> >> >
>>> >> > ------------------------------------------------------------
>>> ----------
>>> >> > DISCUSS:
>>> >> > ------------------------------------------------------------
>>> ----------
>>> >>
>>> >> As a general comment, the Security Consideration section could use
>>> >> clarification and some expansion.
>>> >>
>>> >> Although one can imagine various mixed modes, to the first
>>> approximation
>>> >> there are two ways of doing the optimization of various
>>> multi-destination
>>> >> messages discussed in this document:
>>> >>
>>> >> + Using data plane learning by observing ARP/ND and similar messages
>>> (in
>>> >> addition to the learning of MAC addresses from the data plane which is
>>> >> enabled by default in TRILL). As described in this document, such
>>> data plane
>>> >> learning by TRILL switches can be used to sometimes optimize
>>> >> ARP/ND/RARP/unknown-destination messages. But the result isn't
>>> particularly
>>> >> more or less secure than it is when this data plane learning is done
>>> by end
>>> >> stations rather than by TRILL switches (or bridges or other kinds of
>>> >> switches) in the middle doing some optimization of the relevant
>>> >> multi-destination messages. Interface address information learned
>>> through
>>> >> data plane learning by edge TRILL switches can also be propagated via
>>> the
>>> >> control plane but this is not significantly different from
>>> propagating that
>>> >> information via the multi-destination messages that are being
>>> optimized to
>>> >> unicast or optimized away.
>>> >> + Using a complete, trusted directory as might be based on an
>>> orchestration
>>> >> system in a data center. Since the messages between TRILL switches
>>> doing
>>> >> ARP/ND/RARP/unknown-destination optimization can be secured and the
>>> TRILL
>>> >> switches can be configured to ignore data plane learning, this
>>> enables TRILL
>>> >> switches to provide answers that are "correct" in that they
>>> correspond to
>>> >> the data in this complete, trusted directory. However, there can
>>> still be
>>> >> various forged messages/addresses on a local link between end
>>> station(s) and
>>> >> edge TRILL switches. Such a local link can, with TRILL, be a bridged
>>> LAN, so
>>> >> such forgeries emitted by an end station may be seen by other end
>>> stations
>>> >> and cause incorrect learning from the data plane.
>>> >>
>>> >> The existing Security Considerations section is a bit sketchy and
>>> >> concentrates more on the data plane case, as that is the one with the
>>> >> greatest security challenges.
>>> >
>>> > Yes, this seems like a reasonable assessment. Alia, does someone have
>>> the
>>> > action item to make it less sketchy?
>>>
>>> We are working on a draft revision to reflect the above thinking to a
>>> greater extent and decrease sketchiness.
>>>
>>> >> > It's not clear to me how the security properties of this mechanism
>>> >> > compare to existing TRILL. The text says:
>>> >> >
>>> >> >    Unless Secure ND (SEND [RFC3971]) is used, ARP and ND messages
>>> can be
>>> >> >    easily forged. Therefore the learning of MAC/IP addresses by
>>> RBridges
>>> >> >    from ARP/ND should not be considered as reliable. See Section
>>> 4.1 for
>>> >> >    SEND Considerations.
>>> >> >
>>> >> > "not considered as reliable" seems suboptimal. You need to cover how
>>> >> > this mechanism compares to the non-use of this mechanism.
>>> >>
>>> >> As above, the optimization mechanisms do not make any significant
>>> >> difference to the inherent insecurities of data plane learning but
>>> when used
>>> >> with a complete, trusted directory, it improves considerably over
>>> data plane
>>> >> learning..
>>> >
>>> > That had kind of been my impression, but then I don't understand what
>>> "not
>>> > considered as reliable" is doing here. I'm supposed to be doing
>>> something
>>> > with it, so while it may be non-secure, I'm still relying on it, no?
>>>
>>> Well, at some level some elements of your protocol stack are "relying"
>>> on it or "trusting" it or whatever term you want, but it's trivially
>>> forged unless you use additional security protocols so I guess we
>>> could say something about that. TRILL supports different link
>>> technologies but if you are using an Ethernet link, I suppose you
>>> could use 802.1AE to improve trust in MAC addresses at layer 2. It
>>> wouldn't hurt to mention that but it has very little to do with ARP/ND
>>> optimization or TRILL.
>>>
>>
>> I think if you just sort of say "you are using it, but it's not
>> trustworthy and here's why" you have it covered.
>>
>> -Ekr
>>
>>
>>> >> > This document seems very sketchy on what you do when you get
>>> duplicate
>>> >> > IPs.
>>> >>
>>> >> Why should what you do when you notice a duplicate IP address be
>>> >> significantly different just because some multi-destination messages
>>> are
>>> >> being optimized? Why shouldn't you just do whatever you do now and
>>> why is
>>> >> that any of TRILL's business?
>>> >
>>> > Because you're getting the information via different vector, TRILL
>>> needs to
>>> > specify what you do,
>>> > if only to say "do what you would do otherwise".
>>>
>>> OK.
>>>
>>> >> >    In the case where the former owner replies, a Duplicate Address
>>> has
>>> >> >    been detected. In this case the querying RBridge SHOULD log the
>>> >> >    duplicate so that the network administrator can take appropriate
>>> >> >    action.
>>> >> >
>>> >> > How does logging solve the problem?
>>> >>
>>> >> It doesn't but it seems better than not logging.
>>> >>
>>> >> > What do you reply to ARPs with and/or propagate to other nodes?
>>> >>
>>> >> If you are asking how you reply to ARPs if the IP address being ARPed
>>> for
>>> >> has been found to be duplicated, there are the two cases outlined
>>> above. If
>>> >> you are using a complete, trusted directory, you give the presumed
>>> correct
>>> >> answer provided by that directory. If you are using data plane
>>> learning, you
>>> >> use whatever you last learned from the data plane (which could have
>>> been a
>>> >> forgery over writing good information or good information over
>>> writing a
>>> >> forgery or a forgery overwriting a different forgery or ...).
>>> >>
>>> >> > Do you tell the originator of the advertisement you have a
>>> duplicate?
>>> >>
>>> >> As far as I know there is no standardized way to tell a station that
>>> you
>>> >> think it has an IP address that is duplicated locally and I don't
>>> think it
>>> >> is the job of TRILL to provide such a mechanism. Certainly this
>>> document
>>> >> does not propose anything of that sort.
>>> >
>>> > OK.
>>> >
>>> >
>>> >> >    When a newly connected end-station exchanges messages with a DHCP
>>> >> >    [RFC2131] server an edge RBridge should snoop them (mainly the
>>> >> >    DHCPAck message) and store IP/MAC mapping information in its
>>> ARP/ND
>>> >> >    cache and should also send the information out through the TRILL
>>> >> >    control plane using ESADI.
>>> >> >
>>> >> > What happens if the attacker sets up a fake DHCP server and pretends
>>> >> > to assign addresses to himself? It seems like maybe that's the same
>>> >> > as fake ARPs but maybe not.
>>> >>
>>> >> This snooping on DHCP messages only applies to the data plane learning
>>> >> case. In the case of a complete, trusted directory, edge RBridges
>>> already
>>> >> know the right answer, so to speak. With data plane learning, if
>>> there are
>>> >> forged DHCP messages, things are likely to get all screwed up. Of
>>> course,
>>> >> you could run DHCP over IPsec but, partly due to the localized nature
>>> of
>>> >> DHCP, I don't think very many people do that. There is also RFC 3118
>>> which
>>> >> can be used to authenticate DHCP messages, but that assumes the
>>> distribution
>>> >> of keying information.
>>> >>
>>> >> There isn't much difference between the various multi-destination
>>> messages
>>> >> (ARP / DHCP) advertising the addresses and point of attachment of
>>> >> interfaces. But, overall, I'm not sure why a document that is just
>>> >> describing ways to optimize the distribution of various
>>> multi-destination
>>> >> messages needs to analyze the security of the protocols implemented
>>> by those
>>> >> multi-destination when, as in the data plane learning case, it is not
>>> >> significantly changing that security.
>>> >
>>> > Well, in this case, you have a new threat vector: DHCP. Even if it is
>>> the
>>> > same kind of threats, it's still a new threat vector.
>>> > More generally documents need to contain complete security
>>> considerations
>>> > sections. If the security considerations
>>> > are the same as with some other document, then they need to say that.
>>>
>>> OK.
>>>
>>> >> > In general, the security considerations need a complete threat
>>> >> > analysis per 3552.
>>> >>
>>> >> I don't think there is that much new in this document. While the
>>> Security
>>> >> Considerations section needs clarification and some expansion, I
>>> don't think
>>> >> it is, for example, the job of this document to do a threat analysis
>>> of the
>>> >> ARP protocol as long as it can make a reasonable case that the
>>> security of
>>> >> ARP is not significantly changed by the optimizations specified.
>>> >
>>> > Sure, but it also doesn't make that case.
>>>
>>> I'll see what we can do.
>>>
>>> >> > ------------------------------------------------------------
>>> ----------
>>> >> > COMMENT:
>>> >> > ------------------------------------------------------------
>>> ----------
>>> >>
>>> >> For completeness, I've cut and pasted below the COMMENT responses I
>>> sent
>>> >> to you a while ago.
>>> >>
>>> >> Thanks,
>>> >> Donald
>>> >> ===============================
>>> >>  Donald E. Eastlake 3rd   [phone] (cell)
>>> >>  155 Beaver Street, Milford, MA 01757 USA
>>> <https://maps.google.com/?q=155+Beaver+Street,+Milford,+MA+01757+USA&entry=gmail&source=g>
>>> >>  [e-mail]
>>> >>
>>> >> > S 2.
>>> >> >
>>> >> >    plane on the edge RBridges, it should be possible to completely
>>> >> >    suppress flooding of ARP/ND messages in a TRILL Campus, When all
>>> end-
>>> >> >    station MAC addresses are similarly known, it should be possible
>>> to
>>> >> >    suppress unknown unicast flooding by dropping any unknown unicast
>>> >> >    received at an edge RBridge.
>>> >> >
>>> >> > Are these "should be possibles" normative? Descriptive?
>>> >>
>>> >> Section 2 of this document is a general discussion of the optimization
>>> >> problem which, while it does mention a couple of possible facets of
>>> >> potential solutions, is not intended to be normative.
>>> >>
>>> >>
>>> >> > S 4.
>>> >> > This is a sequence of steps, so it would be nice to preface them
>>> with
>>> >> > a list of the steps. It's also odd to have SEND considerations right
>>> >> > in the middle here.
>>> >>
>>> >> Sorry, I don't understand exactly what you are pointing at as a
>>> >> sequence of steps. All of Section 4? Just the text between the Section
>>> >> 4 heading and the Section 4.1 heading? Something else?
>>> >
>>> > Sorry, my point is that if I read this correctly, I do 4.3, then 4.4,
>>> etc.
>>> > It would be nice if they were listed ahead of this as "this is what
>>> you do,
>>> > now read the sections"
>>>
>>> OK. We can add some clarifying material to Section 4 before the 4.1
>>> heading.
>>>
>>> >> > 4.3 Get Sender's IP/MAC Mapping Information for Non-zero IP
>>> >> >
>>> >> > Please explain what a non-zero IP is and why it's relevant.
>>> >> > This graf also needs an introductory sentence or something before
>>> >> > the bullets.
>>> >>
>>> >> Here is a copy of the response that was sent to a similar comment in
>>> >> Dale Worley's GENART review:
>>> >>
>>> >> This section is talking about getting and handling the IP/MAC
>>> >> mapping information for a local end station by an edge RBridge. An
>>> >> ARP/ND from such a local end station might show a zero source IP
>>> >> address if the end station does not have one or is probing for
>>> >> duplicates.
>>> >>
>>> >> Perhaps the title for the Section should be something like
>>> >>
>>> >>    4.3 Extracting Local End Station IP/MAC Mapping Information
>>> >>
>>> >> and a new first paragraph could be added something like
>>> >>
>>> >>    Edge RBridges extract and use information about the correspondence
>>> >> between local end station IP and MAC addresses from the ARP/ND
>>> >> messages those end stations send as described below. An apparent zero
>>> >> source IP address means that the end station is probing for duplicate
>>> >> IP addresses and messages with such a zero source IP address are not
>>> >> used for the extraction of IP/MAC address mapping information
>>> >
>>> > LGTM
>>> >
>>> >
>>> >> > S 4.4.
>>> >> >    It is not essential that all RBridges use the same strategy for
>>> which
>>> >> >    option to select for a particular ARP/ND query. It is up to the
>>> >> >    implementation.
>>> >> >
>>> >> > This seems inconsistent with the MUST in arm (b) below, because I
>>> >> > can just take some other arm. It's also kind of surprising to be
>>> this
>>> >> > non-prescriptive.
>>> >>
>>> >> The wording needs to be clarified. Which lettered item listed below
>>> >> applies is determined by the circumstances; however, which of the
>>> >> numbered strategies associated with these items is followed is an
>>> >> implementation choice in handeling any particular ARP/ND.
>>> >
>>> > OK.
>>> >
>>> >
>>> >> > S 8.
>>> >> >    some other location (MAC/VM Mobility) and gets connected to egde-
>>> >> >
>>> >> > Nit: edge is mispelled.
>>> >>
>>> >> OK.
>>>
>>> Thanks,
>>> Donald
>>> ===============================
>>>  Donald E. Eastlake 3rd   [phone] (cell)
>>>  155 Beaver Street, Milford, MA 01757 USA
>>> <https://maps.google.com/?q=155+Beaver+Street,+Milford,+MA+01757+USA&entry=gmail&source=g>
>>>  [e-mail]
>>>
>>
>>
>