[MBONED] Eric Rescorla's Discuss on draft-ietf-mboned-mtrace-v2-22: (with DISCUSS and COMMENT)

Eric Rescorla <ekr@rtfm.com> Thu, 18 January 2018 15:34 UTC

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Date: Thu, 18 Jan 2018 07:34:59 -0800
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Subject: [MBONED] Eric Rescorla's Discuss on draft-ietf-mboned-mtrace-v2-22: (with DISCUSS and COMMENT)
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Eric Rescorla has entered the following ballot position for
draft-ietf-mboned-mtrace-v2-22: Discuss

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----------------------------------------------------------------------
DISCUSS:
----------------------------------------------------------------------

The security considerations of this document are inadequate. My review
turns up at least the following potential issues which do
not seem to be addressed or even discussed:

- Amplification: this protocol does not appear to verify that the
  sender of the query actually owns the IP it claims. Because
  responses are much larger than queries, this allows for an amplification
  attack, especially if the client is able to send a query that elicits
  multiple replies. One defense here would be to fill the rest of the packet
  with zeroes, thus somewhat reducing the amplification factor. Access
  control would also help.

- Forgery of responses: because the query id is so short, an attacker
  can generally produce a message which has a nontrivial chance of
  corresponding to an extant query. This could be addressed by having
  a query ID that was large and random.

- Anyone on-path can forge responses.

In addition, Section 9.4 seems inadequate. Isn't it generally the case that
who is sending to who is sensitive? This seems like a fairly serious privacy
obstacle to using this protocol at all.

It seems like many of the issues I raise above would be fixed or at
least mitigated by having some sort of access control mechanism.  I
understand why it might be the case that it's not practical to have
full communication security between the links (though it would of
course be desirable), but it's not clear to me why arbitrary people
should be allowed to instantiate queries.


----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------

S 1.
   When an Mtrace2 client initiates a multicast trace, it sends an
   Mtrace2 Query packet to the LHR or RP for a multicast group and,

This seems a bit confusing as there are multiple LHRs for the group.
Can you rephrase?


S 2.1.
   ALL-[protocol]-ROUTERS group
      It is a link-local multicast address for multicast routers to

This is grammatically funny. Perhaps remove "It is"


S 3.
   additional information associated with the message.  If an
   implementation receives an unknown TLV type for the first TLV in a
   message (i.e., the header TLV), it SHOULD ignore and silently discard
   the entire packet.  If an implementation receives an unknown TLV type
   for a subsequent TLV within a message, it SHOULD ignore and silently
   discard the entire packet.

ISTM that these cases are handled identically so is there a reason
not just to remove the first sentence and change the second one to
"for any TLV"/



S 3.2.1
   An Mtrace2 Query is usually originated by an Mtrace2 client which
   sends an Mtrace2 Query message to the LHR.  When tracing towards the
   source or the RP, the intermediate routers MUST NOT modify the Query
   message except the Type field.

I'm not sure I follow this. Don't routers either (a) not touch this at all
or (b) if they are the LHR, change Type from Query -> Request and then
add a response block? This text seems to not really capture either case.


S 3.2.4.
      Note that Mtrace2 does not require all the routers on the path to
      have synchronized clocks in order to measure one-way latency.

It's not clear to me how one does this. Can you expand?


S 3.2.6.

          0x01    # of the returned Standard Response Blocks

Nit: Do you want to say 0x0001

Also, an example of the case covered by this section would help, I think.



S 4.4.
It might be clearer to move this up a bit in the text as it sort of
summarizes some cases you already covered before. It would be easier
if it provided an overview instead.


S 5.9.

   In this case, the Mtrace2
   client may receive multiple Mtrace2 Replies from different routers
   along the path.  When this happens, the client MUST treat them as a
   single Mtrace2 Reply message.

Can you please describe how the client reassembles multiple messages
into one. I think I may know how to do this, but the document should
tell me.

S 8.
   The following new registries are to be created and maintained under
   the "RFC Required" registry policy as specified in [4].

Why did you choose RFC Required rather than Specification Required?
This just seems to unduly put load on the ISE.