Re: [mpls] Eric Rescorla's Discuss on draft-ietf-mpls-tp-shared-ring-protection-05: (with DISCUSS and COMMENT)

Huub van Helvoort <huubatwork@gmail.com> Thu, 25 May 2017 09:36 UTC

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Reply-To: huubatwork@gmail.com
References: <149560689201.28401.2592268750185030462.idtracker@ietfa.amsl.com>
To: Eric Rescorla <ekr@rtfm.com>, The IESG <iesg@ietf.org>
Cc: draft-ietf-mpls-tp-shared-ring-protection@ietf.org, Eric Gray <Eric.Gray@Ericsson.com>, mpls-chairs@ietf.org, mpls@ietf.org
From: Huub van Helvoort <huubatwork@gmail.com>
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Date: Thu, 25 May 2017 11:36:07 +0200
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Subject: Re: [mpls] Eric Rescorla's Discuss on draft-ietf-mpls-tp-shared-ring-protection-05: (with DISCUSS and COMMENT)
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Hello Eric,

Thank you for reviewing the security aspects of our draft.

Please see my response in-line [Huub]

> Eric Rescorla has entered the following ballot position for
> draft-ietf-mpls-tp-shared-ring-protection-05: Discuss
>
> The document, along with other ballot positions, can be found here:
> https://datatracker.ietf.org/doc/draft-ietf-mpls-tp-shared-ring-protection/
>
> ----------------------------------------------------------------------
> DISCUSS:
> ----------------------------------------------------------------------
>
> The security considerations of this document seem unacceptably
> incomplete, as they basically just point to other documents.
>
>     The RPS protocol defined in this document is carried in the G-ACh
>     [RFC5586], which is a generalization of the Associated Channel
>     defined in [RFC4385].  The security considerations specified in
> these
>     documents apply to the proposed RPS mechanism.
>
> The security considerations of those documents don't seem that great
> either. However, I believe that they miss a new security issue raised
> by the mechanism in this draft, which is that a member of the ring
> appears to be able to forge reports of errors at other parts of the
> ring. Specifically, S 5.1.3.3 says:
>
>     When a node is in a pass-through state, it MUST transfer the
> received
>     RPS Request in the same direction.
>
>     When a node is in a pass-through state, it MUST enable the traffic
>     flow on protection ring tunnels in both directions.
>
> This seems not to involve any filtering, which suggests that node B
> can send a forged SF from C->D and from D->C, which at least
> potentially
> temporarily breaks the link there, causing traffic diversion.
>
> More generally, this system assumes that every node trusts every
> other node completely. That must at least be stated.
>
> Incidentally, the text above appears to contain a bug in that it
> doesn't talk about processing incoming RPS requests intended for
> the receiving node, but I may just have missed the section where
> it says that.
[Huub] your discuss is applicable to any OAM protocol where an
intermediate node can forge false OAM messages and affect traffic.

Regarding this draft, a forged SF may cause a protection switch if
the protocol does not detect a failure of protocol caused by a wrong
sequence or illegal combination of received RPS messages from the
clock-wise and the anti-clock-wise direction in the ring.
The protection switch itself will not cause a loss of traffic.

> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
>
> S 4.1.1.
>     protect these LSPs that traverse the ring, a clockwise working ring
>     tunnel (RcW_D) via E->F->A->B->C->D, and its anticlockwise
> protection
>     ring tunnel (RaP_D) via D->C->B->A->F->E->D are established, Also,
> an
>     anti-clockwise working ring tunnel (RaW_D) via C->B->A->F->E->D, and
>     its clockwise protection ring tunnel (RcP_D) via D->E->F->A->B->C->D
>
> Why does the protection tunnel include D on both ends whereas the
> working
> tunnel does not?

[Huub] the working ring tunnel should not be a closed loop. the
protection ring tunnel is closed until a protection switch is activated,
at that time the protection ring tunnel is opened at the appropriate
location to transport the protected traffic.

> S 4.2.
>     packets are periodically exchanged between each pair of MEPs to
>     monitor the link health.  Three consecutive lost CC packets will be
>     interpreted as a link failure.
>
> Is this a normative statement (i.e., does it need a MUST).

[Huub] he MUST is a requirement for the SF detection described in RFC6371
and ITU-T G.806 .

> S 4.3.2.1.
> Why do you ever not use short wrapping?

[Huub] wrapping is a mechanism that can be used in case an LSP is dropped
in several nodes (p-2-mp application).
Short wrapping can be used only in p-2-p application.

> S 5.1.4.1
>     A node MUST revert from pass-through state to the idle state when it
>     detects NR codes incoming from both directions.  Both directions
>     revert simultaneously from the pass-through state to the idle state.
>
> incoming within what time frame?

[Huub] this time depends on the propagation delay in the ring and the
RPS processing time in each node.
Because of the 50 ms switching objective a 100 ms timer could be used.

Best regards, Huub.


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