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Versions: 00 01 02 03 04 05 06 07 draft-ietf-bfd-on-lags

Network Working Group                                     M. Bhatia, Ed.
Internet-Draft                                            Alcatel-Lucent
Intended status: Standards Track                            M. Chen, Ed.
Expires: December 3, 2012                            Huawei Technologies
                                                         S. Boutros, Ed.
                                                    M. Binderberger, Ed.
                                                           Cisco Systems
                                                            J. Haas, Ed.
                                                        Juniper Networks
                                                            June 1, 2012

Bidirectional Forwarding Detection (BFD) on Link Aggregation Group (LAG)


   This document proposes a mechanism to run BFD on Link Aggregation
   Group (LAG) interfaces.  It does so by running an independent
   Asynchronous mode BFD session on every LAG member link.

   This mechanism allows the verification of member link connectivity,
   either in combination with, or in absence of, LACP.  It provides a
   shorter detection time than what LACP offers.  The connectivity check
   can also cover elements of layer 3 bidirectional forwarding.

   This mechanism utilizes a well-known UDP port distinct from that of
   single-hop BFD over IP.  This new UDP port removes the ambiguity of
   BFD over LAG packets from BFD over single-hop IP.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months

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   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."

   This Internet-Draft will expire on December 3, 2012.

Copyright Notice

   Copyright (c) 2012 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
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 4
   2.  BFD on LAG member links . . . . . . . . . . . . . . . . . . . . 4
     2.1.  Micro BFD session address family  . . . . . . . . . . . . . 5
     2.2.  Micro BFD session negotiation . . . . . . . . . . . . . . . 5
   3.  LAG Management Module . . . . . . . . . . . . . . . . . . . . . 6
     3.1.  BFD in the presence of LACP . . . . . . . . . . . . . . . . 6
     3.2.  BFD in the absence of LACP  . . . . . . . . . . . . . . . . 7
     3.3.  Handling Exceptions . . . . . . . . . . . . . . . . . . . . 7
   4.  BFD on LAG members and layer-3 applications . . . . . . . . . . 7
   5.  Detecting a member link failure . . . . . . . . . . . . . . . . 7
   6.  Security Consideration  . . . . . . . . . . . . . . . . . . . . 8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 8
   9.  Contributing authors  . . . . . . . . . . . . . . . . . . . . . 8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 9
     10.1. Normative References  . . . . . . . . . . . . . . . . . . . 9
     10.2. Informative References  . . . . . . . . . . . . . . . . . . 9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9

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1.  Introduction

   The Bidirectional Forwarding Detection (BFD) protocol [RFC5880]
   provides a mechanism to detect faults in the bidirectional path
   between two forwarding engines, including interfaces, data link(s),
   and to the extent possible the forwarding engines themselves, with
   potentially very low latency.  The BFD protocol also provides a fast
   mechanism for detecting communication failures on any data links and
   the protocol can run over any media and at any protocol layer.

   Link aggregation (LAG) as defined in [IEEE802.1AX] provides
   mechanisms to combine multiple physical links into a single logical
   link.  This logical link provides higher bandwidth and better
   resiliency since if one of the physical member links fails the
   aggregate logical link can continue to forward traffic over the
   remaining operational physical member links.

   Currently, the Link Aggregation Control Protocol (LACP) is used to
   detect failures on a per physical member link.  However, the use of
   BFD for failure detection would (1) provide a faster detection (2)
   provide detection in the absence of LACP (3) and would be able to
   verify L3 connectivity per member link.

   Running a single BFD session over the aggregation without internal
   knowledge of the member links would make it impossible for BFD to
   guarantee detection of the physical member link failures.

   The goal is to verify link connectivity for every member link.

   The approach taken in this document is to run a Asynchronous mode BFD
   session over each member link and make BFD control whether the member
   link should be part of the L2 Loadbalance table of the LAG virtual
   port in the presence or the absence of LACP.

   This document describes how to establish an Asynchronous mode BFD
   session per physical member link of the LAG virtual port.

   While there are native Ethernet mechanisms to detect failures
   (802.1ax, .3ah) that could be used for LAG, the solution proposed in
   this document enables operators who have already deployed BFD over
   different technologies (e.g.  IP, MPLS) to use a common failure
   detection mechanism.

2.  BFD on LAG member links

   The mechanism proposed for a fast detection of LAG member link
   failure is to run Asynchronous mode BFD sessions on every LAG member

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   link.  We call these per LAG member link BFD sessions "micro BFD
   sessions" in the remainder of this document.

2.1.  Micro BFD session address family

   Only one address family MUST be used for all micro BFD sessions
   running on all LAG member links.  I.e. all member link micro BFD
   sessions MUST either use IPv4 or IPv6.

2.2.  Micro BFD session negotiation

   A single micro BFD session runs on each member link of the LAG.  The
   micro BFD session's negotiation MUST follow the same procedures
   defined in [RFC5880] and [RFC5881].

   Only Asynchronous mode BFD is considered in this document; the use of
   the BFD echo function is outside the scope of this document.  At
   least one system MUST take the Active role (possibly both).  The
   micro BFD sessions on the member links are independent BFD sessions:
   They use their own unique local discriminator values, maintain their
   own set of state variables and have their own independent state
   machines.  Timer values MAY be different, even among the micro BFD
   sessions belonging to the same aggregation, although it is expected
   that micro BFD sessions belonging to the same aggregation will use
   the same timer values.

   The demultiplexing of a received BFD packet is solely based on the
   Your Discriminator field, if this field is nonzero.  For the initial
   Down BFD packets of a BFD session this value MAY be zero.  In this
   case demultiplexing MUST be based on some combination of other fields
   which MUST include the interface information of the member link.

   The procedure for the Reception of BFD Control Packets in Section
   6.8.6 of [RFC5880] is amended as follows for per member link micro
   BFD over LAG sessions: "If the Your Discriminator field is non-zero
   and a micro BFD over LAG session is found, the interface on which the
   micro BFD control packet arrived on MUST correspond to the interface
   associated with that session."

   The BFD Control packets for each micro BFD session are IP/UDP
   encapsulated as defined in [RFC5881], but with a new UDP destination
   port "BfdBndlPort" (to be assigned by IANA).  Control packets use a
   destination IP address that is the peer's remote IP address.  The
   details of how this destination IP address is learned is outside the
   scope of this document.

   On Ethernet-based LAG member links the destination MAC is a dedicated
   MAC address (to be assigned by IANA according to [RFC5342]) to be the

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   immediate next hop.  This dedicated MAC address MUST be used for the
   initial BFD packets of a micro BFD session when in the Down/AdminDown
   state.  When sending BFD packets for the micro BFD session in the
   Init and Up state, the MAC address from the received BFD packets for
   the session MUST be used.

   On Ethernet-based LAG member links the source MAC SHOULD be the MAC
   address of the port transmitting the packet.

   This mechanism helps to reduce the use of additional MAC addresses,
   which reduces the required resources on the Ethernet hardware on the
   receiving port.

3.  LAG Management Module

   The LAG Management Module (LMM) could be envisaged as a client of
   BFD; i.e. the LMM requests a micro BFD session per member link.  The
   LMM then uses the micro BFD session state, in addition to LACP state,
   to monitor the health of the individual members links of the LAG.

   The micro BFD session for a particular port MUST be requested when
   the port is attached to an aggregator.  The session MUST be deleted
   when the port is detached from the aggregator.

   The LMM uses the status of the BFD session to determine whether the
   member link should be included in the LAG L2 load balance table.  In
   other words, even when LACP is used and considers the member link to
   be ready to forward traffic, the member link is only used by the
   traffic load balancer when the micro BFD session is Up.

3.1.  BFD in the presence of LACP

   Prior to LACP coming up, the micro BFD session is Passive and does
   not send BFD control packets.  Once LACP has determined that a link
   is suitable for aggregation within its selected LAG and has completed
   negotiations with the partner device so as to bring that link to
   Distributing state, the micro BFD session can be made Active and the
   session started on the link.

   BFD, as a layer 3 protocol, is viewed as running across the LAG, with
   load balancing constraints ensuring particular BFD micro sessions are
   effectively bound to particular member links.

   Although the link is in LACP Distributing state, it should not be
   used for carrying traffic other than the micro BFD session.  BFD is
   used to verify that a link is ready to be an active member of its LAG
   for the purpose of carrying LAG level data traffic.  Only when the

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   micro BFD session is up should the link become active for forwarding
   general traffic over the bundle.

3.2.  BFD in the absence of LACP

   Use of LACP for link aggregation is strictly optional.  It is equally
   possible to use no aggregation control protocol and to step directly
   from the layer 1 or layer 2 OAM state becoming operational to
   starting the micro BFD session.  In this case, the micro BFD sessions
   begin as Active.

3.3.  Handling Exceptions

   If the BFD over LAG feature were provisioned on an aggregated link
   member after the link was already active within a LAG, BFD session
   state SHOULD NOT influence link state until the BFD session state
   transitions to Up.  If the BFD session never transitions to Up but
   the LAG becomes inactive, the previously documented procedures would
   then normally apply.

   If the BFD over LAG feature were deprovisioned on an aggregate link
   member after the BFD session had transitioned to Up, BFD may indicate
   to the remote port that it should not take the port down or remove it
   from the aggregation by setting its BFD session state to AdminDown.

   Note that if one device is not operating a micro BFD session on a
   link, while the other device is and perceives the session to be Down,
   this will result in the two devices having a different view of the
   status of the link.  This would likely lead to traffic loss across
   the LAG.

   The use of another protocol to bootstrap BFD can detect such
   mismatched config, since the side that's not configured can send a
   rejection error.  Such bootstrapping mechanisms are outside the scope
   of this document.

4.  BFD on LAG members and layer-3 applications

   Layer 3 protocols, e.g.  OSPF, may use a micro BFD session to detect
   failures on the LAG virtual port, or may establish a new BFD session
   over the logical LAG virtual port.

5.  Detecting a member link failure

   When a micro BFD session goes down then this member link MUST be
   taken out of the LAG L2 load balance table.

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6.  Security Consideration

   This document does not introduce any additional security issues and
   the security mechanisms defined in [RFC5880] apply in this document.

7.  IANA Considerations

   The IANA is requested to assign a well-known port number for the UDP
   encapsulated micro BFD sessions.  IANA is also requested to assign a
   dedicated MAC address according to RFC 5342 [RFC5342].

8.  Acknowledgements

   We would like to thank Dave Katz, Alexander Vainshtein, Greg Mirsky
   and Jeff Tantsura for their comments.

   The initial event to start the current discussion was the
   distribution of draft-chen-bfd-interface-00.

9.  Contributing authors

   Paul Hitchen
   Email: paul.hitchen@bt.com

   George Swallow
   Cisco Systems
   Email: swallow@cisco.com

   Wim Henderickx
   Email: wim.henderickx@alcatel-lucent.com

   Nobo Akiya
   Cisco Systems
   Email: nobo@cisco.com

   Neil Ketley
   Cisco Systems
   Email: nketley@cisco.com

   Carlos Pignataro
   Cisco Systems
   Email: cpignata@cisco.com

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   Nitin Bahadur
   Juniper Networks
   Email: nitinb@juniper.net

   Zuliang Wang
   Huawei Technologies
   Email: liang_tsing@huawei.com

   Liang Guo
   China Telecom
   Email: guoliang@gsta.com

   Jeff Tantsura
   Email: jeff.tantsura@ericsson.com

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, June 2010.

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
              June 2010.

10.2.  Informative References

              IEEE Std. 802.1AX, "IEEE Standard for Local and
              metropolitan area networks - Link Aggregation",
              November 2008.

   [RFC5342]  Eastlake, D., "IANA Considerations and IETF Protocol Usage
              for IEEE 802 Parameters", BCP 141, RFC 5342,
              September 2008.

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Authors' Addresses

   Manav Bhatia (editor)
   Bangalore  560045

   Email: manav.bhatia@alcatel-lucent.com

   Mach(Guoyi) Chen (editor)
   Huawei Technologies
   Q14 Huawei Campus, No. 156 Beiqing Road, Hai-dian District
   Beijing  100095

   Email: mach@huawei.com

   Sami Boutros (editor)
   Cisco Systems

   Email: sboutros@cisco.com

   Marc Binderberger (editor)
   Cisco Systems

   Email: mbinderb@cisco.com

   Jeffrey Haas (editor)
   Juniper Networks

   Email: jhaas@juniper.net

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