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Network Working Group                                           E. Chen
Internet Draft                                                  N. Shen
Intended Status: Informational                            Cisco Systems
Expiration Date: January 17, 2018                             R. Raszuk
                                                           Bloomberg LP
                                                           July 16, 2017



              Unsolicited BFD for Sessionless Applications
                   draft-chen-bfd-unsolicited-00.txt


Status of this Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on January 17, 2018.

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Abstract

   For operational simplification of "sessionless" applications using
   BFD, in this document we present procedures for "unsolicited BFD"
   that allow a BFD session to be initiated by only one side, and be
   established without explicit per-session configuration or
   registration by the other side (subject to certain per-interface or
   per-router policies).


1. Introduction

   The current implementation and deployment practice for BFD ([RFC5880]
   and [RFC5881]) usually requires BFD sessions be explicitly configured
   or registered on both sides. This requirement is not an issue when an
   application like BGP [RFC4271] has the concept of a "session" that
   involves both sides for its establishment.  However, this requirement
   can be operationally challenging when the prerequisite "session" does
   not naturally exist between two endpoints in an application.
   Simultaneous configuration and coordination may be required on both
   sides for BFD to take effect. For example:

      o When BFD is used to keep track of the "liveness" of the nexthop
        of static routes. Although only one side may need the BFD
        functionality, currently both sides need to be involved in
        specific configuration and coordination and in some cases
        static routes are created unnecessarily just for BFD.

      o When BFD is used to keep track of the "liveness" of the
        third-pary nexthop of BGP routes received from the Route Server
        [RFC7947] at an Internet Exchange Point (IXP).  As the
        third-party nexthop is different from the peering address of
        the Route Server, for BFD to work, currently two routers peering
        with the Route Server need to have routes and nexthops from each
        other (although indirectly via the Router Server), and the
        nexthop of each router must be present at the same time. These
        issues are discussed in detail in [RS-BFD].

   Clearly it is beneficial and desirable to reduce or eliminate
   unnecessary configurations and coordination in these "sessionless"
   applications using BFD.

   In this document we present procedures for "unsolicited BFD" that
   allow a BFD session to be initiated by only one side, and be
   established without explicit per-session configuration or



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   registration by the other side (subject to certain per-interface or
   per-router policies).

   With "unsolicited BFD" there is potential risk for excessive resource
   usage by BFD. To mitigate such risks, several mechanisms are
   recommended in the Security Considerations section.

   Compared to the "Seamless BFD" [RFC7880], this proposal involves only
   minor procedural enhancements to the widely deployed BFD itself.  It
   does not require the exchange of BFD discriminators over an out-of-
   band channel before the BFD session bring-up.  Thus we believe that
   it is a much simpler solution to the issues discussed.

   When BGP Add-Path [RFC7911] is deployed at an IXP using the Route
   Server, the alternate BGP paths can be made available to the clients
   of the Router Server. The "unsolicited BFD" can be used in BGP route
   selection by these clients to eliminate paths with "inaccessible
   nexthops".


1.1. Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


2. Procedures for Unsolicited BFD

   With "unsolicited BFD", one side takes the "Active role" and the
   other side takes only the "Passive role" as described in [RFC5880].

   On the passive side, the "unsolicited BFD" SHOULD be configured
   explicitly on an interface. The BFD parameters can be either per-
   interface or per-router based. It MAY also choose to use the
   parameters that the active side uses in its BFD Control packets.  The
   "Discriminator", however, MUST be chosen to allow multiple
   unsolicited BFD sessions.

   The active side initiates the BFD Control packets as specified in
   [RFC5880].  The passive side does not initiates the BFD Control
   packets.

   When the passive side receives a BFD Control packet from the active
   side with 0 as the "remote-discriminator", and it does not find an
   existing session with the same source address as in the packet and
   "unsolicited BFD" is allowed on the interface by local policy, it
   SHOULD then create a matching BFD session toward the active side



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   (based on the source address and destination address in the BFD
   Control packet) as if the session were locally registered.  It would
   then start sending the BFD Control packets and perform necessary
   procedure for bringing up, maintaining and tearing down the BFD
   session.  If the BFD session fails to get established within certain
   specified time, or if an established BFD session goes down, the
   passive side would stop sending BFD Control packets and delete the
   BFD session created until the BFD Control packets is initiated by the
   active side again.

   The "Passive role" may change to the "Active role" when a local
   client registers for the same BFD session, and from the "Active role
   " to the "Passive role " when there is no longer any locally
   registered client for the BFD session.


3. IANA Considerations

   This documents makes no IANA requests.


4. Security Considerations

   The same security considerations as those described in [RFC5880] and
   [RFC5881] apply to this document.  With "unsolicited BFD" there is
   potential risk for excessive resource usage by BFD. To mitigate such
   risks, the following measures are RECOMMENDED:

      o Limit the feature to a single-hop BFD with "TTL=255" [RFC5082],
        and to specific interfaces.

      o Apply "access control" to allow BFD packets only from certain
        subnets or hosts.

      o Deploy the feature only in an environment with certain level of
        "trust".

      o Use BFD authentication.

      o Limit the number of "unsolicited BFD" sessions.











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5. Acknowledgments

   TBD


6. References


6.1. Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC5082]  Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and
              C. Pignataro, "The Generalized TTL Security Mechanism
              (GTSM)", RFC 5082, October 2007.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <http://www.rfc-editor.org/info/rfc5880>.

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
              DOI 10.17487/RFC5881, June 2010,
              <http://www.rfc-editor.org/info/rfc5881>.


6.2. Informative References

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <http://www.rfc-editor.org/info/rfc4271>.

   [RFC7880]  Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
              Pallagatti, "Seamless Bidirectional Forwarding Detection
              (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
              <http://www.rfc-editor.org/info/rfc7880>.

   [RFC7911]  Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", RFC 7911,
              DOI 10.17487/RFC7911, July 2016,
              <http://www.rfc-editor.org/info/rfc7911>.

   [RFC7947]  Jasinska, E., Hilliard, N., Raszuk, R., and N. Bakker,
              "Internet Exchange BGP Route Server", RFC 7947,



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              DOI 10.17487/RFC7947, September 2016,
              <http://www.rfc-editor.org/info/rfc7947>.

   [RS-BFD]   Bush, R., J. Haas, J. Scudder, A. Nipper, and T. King,
              "Making Route Servers Aware of Data Link Failures at
              IXPs", Work in Progress, draft-ietf-idr-rs-bfd-02, March
              2017.


7. Authors' Addresses

   Enke Chen
   Cisco Systems
   560 McCarthy Blvd.
   Milpitas, CA 95035
   USA

   Email: enkechen@cisco.com

   Naiming Shen
   Cisco Systems
   560 McCarthy Blvd.
   Milpitas, CA 95035
   USA

   Email: naiming@cisco.com

   Robert Raszuk
   Bloomberg LP
   731 Lexington Ave
   New York City, NY 10022
   USA

   Email:robert@raszuk.net

















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