Internet DRAFT - draft-chen-bfd-unsolicited

draft-chen-bfd-unsolicited









Network Working Group                                           E. Chen
Internet Draft                                                  N. Shen
Intended Status: Informational                            Cisco Systems
Expiration Date: February 4, 2019                             R. Raszuk
                                                           Bloomberg LP
                                                         August 3, 2018



              Unsolicited BFD for Sessionless Applications
                   draft-chen-bfd-unsolicited-03.txt


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on February 4, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



Chen, Shen & Raszuk                                             [Page 1]





Internet Draft      draft-chen-bfd-unsolicited-03.txt        August 2018


   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 also discussed in [I-D.ietf-idr-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



Chen, Shen & Raszuk                                             [Page 2]





Internet Draft      draft-chen-bfd-unsolicited-03.txt        August 2018


   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 from "unexpected" remote systems.  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.
   Thus we believe that this proposal is inherently simpler in the
   protocol itself and deployment.  As an example, it does not require
   the exchange of BFD discriminators over an out-of-band channel before
   the BFD session bring-up.

   When BGP Add-Path [RFC7911] is deployed at an IXP using the Route
   Server, multiple BGP paths (when exist) can be made available to the
   clients of the Router Server as described in [RFC7947].  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



Chen, Shen & Raszuk                                             [Page 3]





Internet Draft      draft-chen-bfd-unsolicited-03.txt        August 2018


   "unsolicited BFD" is allowed on the interface by local policy, it
   SHOULD then create a matching BFD session toward the active side
   (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 from "unexpected"
   remote systems.  To mitigate such risks, the following measures are
   RECOMMENDED:

      o Limit the feature to specific interfaces, and to a single-hop
        BFD with "TTL=255" [RFC5082]. In addition make sure the source
        address of an incoming BFD packet belongs to the subnet of the
        interface from which the BFD packet is received.

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

      o Deploy the feature only in certain "trustworthy" environment,
        e.g., at an IXP, or between a provider and its customers.

      o Adjust BFD parameters as needed for the particular deployment
        and scale.

      o Use BFD authentication.





Chen, Shen & Raszuk                                             [Page 4]





Internet Draft      draft-chen-bfd-unsolicited-03.txt        August 2018


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,



Chen, Shen & Raszuk                                             [Page 5]





Internet Draft      draft-chen-bfd-unsolicited-03.txt        August 2018


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

   [I-D.ietf-idr-rs-bfd]
              Bush, R., J. Haas, J. Scudder, A. Nipper, and T. King,
              "Making Route Servers Aware of Data Link Failures at
              IXPs", draft-ietf-idr-rs-bfd-03 (work in progress), July
              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
















Chen, Shen & Raszuk                                             [Page 6]