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

Eric Rescorla <ekr@rtfm.com> Mon, 09 July 2018 13:55 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Mon, 9 Jul 2018 06:54:54 -0700
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To: Hitoshi Asaeda <asaeda@ieee.org>
Cc: Kerry Meyer <kerry.meyer@me.com>, draft-ietf-mboned-mtrace-v2@ietf.org, The IESG <iesg@ietf.org>, MBONED WG <mboned@ietf.org>, mboned-chairs@ietf.org
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Subject: Re: [MBONED] Eric Rescorla's Discuss on draft-ietf-mboned-mtrace-v2-22: (with DISCUSS and COMMENT)
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On Mon, Jul 9, 2018 at 6:51 AM, Hitoshi Asaeda <asaeda@ieee.org>; wrote:

> Eric,
>
> > >> Section 4.2.1, however (see below), prohibits processing of a Request
> that is not sent from an adjacent router. Also, it is worth considering
> that this problem hypothesis supposes that a DoS attack is launched from a
> trusted router address. Even for this scenario, however, the document does
> provide protection. The normative descriptions to which the quote above
> refers are:
> > >>
> > >> -  The previous paragraph from section 9.2 (requirement for use of
> ACLs; slightly reworded later in this email to the new proposed text):
> > >>
> > >> ----------
> > >>   A router MUST support an access control list (ACL) mechanism to
> > >>   filter out Queries from clients and Requests from peer router
> > >>   addresses that are unauthorized or that are beyond a specified
> > >>   administrative boundary.  This filtering could, for example, be
> > >>   specified via a list of allowed/disallowed client and peer addresses
> > >>   or subnets for the Mtrace2 protocol port.  If a Query or Request is
> > >>   received from an unauthorized address or one beyond the specified
> > >>   administrative boundary, the Query/Request MUST NOT be processed.
> > >>   The router MAY, however, perform rate limited logging of such
> events.
> > >> ----------
> > >>
> > >> and
> > >>
> > >>  - Section 4.2.1 (required validity checks to force rejection of a
> Request message from a source that is not an adjacent router):
> > >>
> > >> ----------
> > >> 4.2.1.  Request Packet Verification
> > >>
> > >>   If the Mtrace2 Request does not come from an adjacent router, or if
> > >>   the Request is not addressed to this router, or if the Request is
> > >>     addressed to a multicast group which is not a link-scoped group
> > >>   (i.e., 224.0.0.0/24 for IPv4, FFx2::/16 [3] for IPv6), it MUST be
> > >>   silently ignored.  The Generalized TTL Security Mechanism (GTSM)
> [14]
> > >>   SHOULD be used by the router to determine whether the router is
> > >>   adjacent or not.
> > >> ----------
> > >
> > > Unless I'm missing something, this just restricts things to a *node*
> which is adjacent. But if I'm a device that's on the same LAN as a router
> (which isn't a crazy proposition, ISTM), then why can't I mount this attack?
> >
> > Only an adjacent *multicast router* can send requests, because a request
> is transformed from a query initiated by a downstream node/device and
> forwarded toward the source/RP
> >
> > But the difference between a request and a response is just some bits in
> the packet.
>
> I cannot understand this comment.
> It is very common to design protocol messages using the TLV format and
> differentiate the messages by the different type values.
>

Yes. That's why it's important to have the receiver check.



> > And so what stops some other host on the LAN from sending something that
> claims to be a request.
>
> We cannot stop someone from sending packets, but can
> ignore/drop/rate-limit the packets if something wrong.
>

Yes.


> > In your example, you are a valid *user (or device)* and send Request,
> and can attack someone. But in our definition, you cannot send any Requests
> because you are not a valid *multicast router*.
> >
> > Yes, but that needs to be technically enforced, not just stated.
>
> Right. That's why we propose a new type of ACLs as follows.
>



>
> > The problem you may think here is that the ACLs in general do not
> validate the Request is traversed from valid (or invalid) routers as the
> message types cannot be specified in ACLs, right?
> > If we define a *particular* ACL entry to specify accepted/non-accepted
> IP addresses (or ranges) or admin boundaries for each of three mtrace
> message types, Query/Request/Reply, will your concern be disappeared?
> >
> > I think so, if you require its use.
>
> Ok, fine. I'll explain this ACL extension in the upcoming meeting.
>
> > To protect against spoofing of Request packet, as Kerry said,
> > > > NOTE:  To protect against spoofing of Request packets by a trusted
> host, some authentication mechanism such as use of an Authentication Header
> (AH) between routing peers should be also considered. However, discussion
> of such external authentication mechanisms is out of the scope of this
> document.
> >
> > Also, router validation is in general defined in the routing protocol
> specifications and routers can run the authentication mechanisms. We do not
> provide an mtrace unique/specific authentication mechanism for routers in
> this document. But as the example, we can describe the PIM case to verify
> adjacent PIM neighbor routers, if it's helpful.
> >
> > I don't follow this.
>
> Is some point unclear for you?
> Let's see PIM-SM (multicast routing protocol). PIM-SM has a way to
> verify/recognize a valid PIM neighbor. If you need such adjacent router
> verification, we can mention this routing protocol's verification
> mechanism.
>
> > > Given that we're a week from Montreal, it might be easier to just try
> to meet there. What say you?
> >
> > Although Kerry may not, I'll be there.
> > I asked a slot to report the current situation in the Mboned WG meeting.
> Please come to the meeting.
> >
> > I have to be at RTCWEB.
>
> Hmm.. Then we won't be able to reach any consensus in the meeting...
>
> > But before the f2f discussions or the meeting, I need to understand and
> clarify problems you have been thinking.
> >
> > The point of the F2F discussion is to clarify the issue.
>
> I'll then personally contact you to meet next week.
>

That's fine, but if you send me proposed new text beforehand, I can also
review it.

>
> Regards,
>
> Hitoshi
>
>
>
> > -Ekr
> >
> >
> > Regards,
> >
> > Hitoshi
> >
> > (snip a lot)
>
>