Re: WGLC for BFD Multipoint documents (last round)

"Reshad Rahman (rrahman)" <> Sat, 03 February 2018 18:01 UTC

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From: "Reshad Rahman (rrahman)" <>
To: Greg Mirsky <>
CC: "Carlos Pignataro (cpignata)" <>, "" <>
Subject: Re: WGLC for BFD Multipoint documents (last round)
Thread-Topic: WGLC for BFD Multipoint documents (last round)
Date: Sat, 3 Feb 2018 18:01:14 +0000
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Hi Greg,

While OOB mechanism would improve security, my personal opinion is that we should try to improve security without requiring an OOB mechanism. I think we can add text to the security considerations to address the concerns below, e.g. A tail SHOULD prevent the number of MultipointTail sessions from exceeding the number of expected streams.  The concern expressed in b) cannot be fixed by what I proposed because of multiple streams.  So just preventing the number of MultipointTail sessions from exceeding the number of expected streams should be good enough.


From: Rtg-bfd <>; on behalf of Greg Mirsky <>;
Date: Thursday, February 1, 2018 at 10:23 PM
To: "Reshad Rahman (rrahman)" <>;
Cc: "Carlos Pignataro (cpignata)" <>;, ""; <>;
Subject: Re: WGLC for BFD Multipoint documents (last round)

Hi Reshad,
thank you for your patience and support.
To address your questions a) and b) we may recommend that an implementation creates MultipointTail session only if provisioned with My Discriminator value for the given pair of MultipointHead and multicast tree via out-of-band control or management plane. Discussion of exact mechanisms is outside the scope of this document. And then the text will continue to discuss measures for implementations that create MultipointTail session dynamically for any known combination of head and multicast tree that has Multipoint BFD enabled.


On Wed, Jan 31, 2018 at 6:44 AM, Reshad Rahman (rrahman) <<>> wrote:
Hi Greg,

Thanks for addressing the changes so promptly. I’d like to hear from the WG on the 2 security concerns below, i.e. whether they need to be addressed and if yes, then how. I believe if we address a) below we also address b)?


: a) We should have the ability, e.g. via configuration, to prevent the number
: of MultipointTail sessions from exceeding the number of expected streams.
: Otherwise 1 misbehaving head could use up all the MultipointTail session
: resources on a tail.
: b) A misbehaving head which changes My Discriminator for a MultipointHead
: session will cause tails to create many MultipointTail sessions (4.13.2). We
: should consider adding a check to see if we have a MultipointTail session
: based on source address and the identify of the of the multipoint tree with a
: different discriminator?

7.  Security Considerations

   The same security considerations as those described in [RFC5880]
   apply to this document.  Additionally, implementations that create
   MultpointTail sessions dynamically upon receipt of Multipoint BFD
   Control packets MUST implement protective measures to prevent
   infinite number of MultipointTail sessions being created.  Below are
   listed some points to be considered in such implementations.

      If a Multipoint BFD Control packet did not arrive on a multicast
      tree (e.g. on expected interface, with expected MPLS label, etc),
      then a MultipointTail session should not be created.

      If redundant streams are expected for a given multicast stream,
      then the implementations should not create more MultipointTail
      sessions than the number of streams.  Additionally, when the
      number of MultipointTail sessions exceeds the number of expected
      streams, then the implementation should generate an alarm to users
      to indicate the anomaly.

Katz, et al.             Expires August 3, 2018                [Page 16]

Internet-Draft         BFD for Multipoint Networks          January 2018

      The implementation should have a reasonable upper bound on the
      number of MultipointTail sessions that can be created, with the
      upper bound potentially being computed based on the number of
      multicast streams that the system is expecting.

On 2018-01-30, 10:23 PM, "Greg Mirsky" <<>> wrote:

    Hi Reshad,<>,
    I've uploaded the new version of the draft:

    A New Internet-Draft is available from the on-line Internet-Drafts directories.
    This draft is a work item of the Bidirectional Forwarding Detection WG
    of the IETF.

            Title           : BFD for Multipoint Networks
            Authors         : Dave Katz
                              Dave Ward
                              Santosh Pallagatti
                              Greg Mirsky
            Filename        : draft-ietf-bfd-multipoint-13.txt
            Pages           : 18
            Date            : 2018-01-30

       This document describes extensions to the Bidirectional Forwarding
       Detection (BFD) protocol for its use in multipoint and multicast

    The IETF datatracker status page for this draft is:

    There are also htmlized versions available at:

    A diff from the previous version is available at:

    Will respond to your comments on the Active Tails shortly.


    On Mon, Jan 29, 2018 at 11:47 AM, Reshad Rahman (rrahman)
    <<>> wrote:
    > Greg, these changes are good with me.
    > Regards,
    > Reshad.
    > From: Greg Mirsky <<>>
    > Date: Monday, January 29, 2018 at 1:04 PM
    > To: "Reshad Rahman (rrahman)" <<>>
    > Cc: "Carlos Pignataro (cpignata)" <<>>, Jeffrey Haas
    > <<>>, "<>" <<>>
    > Subject: Re: WGLC for BFD Multipoint documents (last round)
    > Hi Reshad,
    > nits fixed and the new text below:
    > OLD TEXT
    > A number of values of the state variable are added to the base BFD…
    > NEW TEXT
    > A number of new values of the state variable bfd.SessionType are added to
    > the base BFD…
    > Would you accept this update?
    > Regards,
    > Greg
    > On Mon, Jan 29, 2018 at 5:52 AM, Reshad Rahman (rrahman) <<>>
    > wrote:
    > Hi Greg,
    > Section 4.2. s/The head has a session of type MultipointHead Section 4.4.1/
    > The head has a session of type MultipointHead, as defined in Section 4.4.1,
    > /
    > Section 4.4.1. “A number of values of the state variable are added to the
    > base BFD…”. That sentence needs rewording IMO but maybe I’m just missing
    > what it’s trying to convey.
    > Section 4.6. s/Active role , / Active role, /
    > Section 4.10. “MUST send packets with P bit set.”. Did we agree on “MUST
    > send packets with the P bit set.”?
    > Regards,
    > Reshad.
    > <snip>