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Versions: (draft-nishida-tsvwg-sctp-failover) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 7829

Network Working Group                                         Y. Nishida
Internet-Draft                                        GE Global Research
Intended status: Experimental                               P. Natarajan
Expires: September 3, 2014                                 Cisco Systems
                                                                 A. Caro
                                                        BBN Technologies
                                                                 P. Amer
                                                  University of Delaware
                                                              K. Nielsen
                                                                Ericsson
                                                           March 2, 2014


                    Quick Failover Algorithm in SCTP
                 draft-ietf-tsvwg-sctp-failover-03.txt

Abstract

   One of the major advantages of SCTP is supporting multi-homed
   communication.  If a multi-homed end-point has a redundant network
   connections, the SCTP associations have a good chance to survive
   network failures by migrating traffic from inactive networks to
   active ones.  However, if the SCTP standard is followed, there can be
   a significant delay during the migration.  During this period, SCTP
   might not be able to transmit much data to the peer.  This issue
   drastically impairs the usability of SCTP in some situations.  This
   memo describes the issue of the SCTP failover mechanism and specifies
   an alternative failover procedure for SCTP that improves its
   performance during and after failover.  The procedures require only
   minimal modifications to the current specification.

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
   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 September 3, 2014.




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Copyright Notice

   Copyright (c) 2014 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.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions and Terminology  . . . . . . . . . . . . . . . . .  4
   3.  Issues with the SCTP Path Management . . . . . . . . . . . . .  5
   4.  Existing Solutions for Smooth Failover . . . . . . . . . . . .  6
     4.1.  Reduce Path.Max.Retrans (PMR)  . . . . . . . . . . . . . .  6
     4.2.  Adjust RTO related parameters  . . . . . . . . . . . . . .  6
   5.  SCTP with Potentially-Failed Destination State (SCTP-PF) . . .  8
     5.1.  SCTP-PF Description  . . . . . . . . . . . . . . . . . . .  8
     5.2.  Effect of Path Bouncing  . . . . . . . . . . . . . . . . . 10
     5.3.  Permanent Failover . . . . . . . . . . . . . . . . . . . . 10
   6.  Socket API Considerations  . . . . . . . . . . . . . . . . . . 12
     6.1.  Support for the Potentially Failed Path State  . . . . . . 12
     6.2.  Peer Address Thresholds (SCTP_PEER_ADDR_THLDS) Socket
           Option . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     6.3.  Exposing the Potentially Failed Path State
           (SCTP_EXPOSE_POTENTIALLY_FAILED_STATE) Socket Option . . . 14
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 17
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19











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1.  Introduction

   The Stream Control Transmission Protocol (SCTP) as specified in
   [RFC4960] supports multihoming at the transport layer -- an SCTP
   association can bind to multiple IP addresses at each endpoint.
   SCTP's multihoming features include failure detection and failover
   procedures to provide network interface redundancy and improved end-
   to-end fault tolerance.

   In SCTP's current failure detection procedure, the sender must
   experience Path.Max.Retrans (PMR) number of consecutive failed
   retransmissions on a destination before detecting a path failure.
   The sender fails over to an alternate active destination only after
   failure detection.  Until detecting the failover, the sender
   continues to transmit data on the failed path, which degrades the
   SCTP performance.  Concurrent Multipath Transfer (CMT) [IYENGAR06] is
   an extension to SCTP and allows the sender to transmit data on
   multiple paths simultaneously.  Research [NATARAJAN09] shows that the
   current failure detection procedure worsens CMT performance during
   failover and can be significantly improved by employing a better
   failover algorithm.

   This document specifies an alternative failure detection procedure
   for SCTP (and CMT) that improves the SCTP (and CMT) performance
   during a failover.

   Also the operation after a failover impacts the performance of the
   protocol.  With [RFC4960] procedures, SCTP will, after a failover
   from the primary path, switch back to use the primary path for data
   transfer as soon as this path becomes available.  From a performance
   perspective, as confirmed in research [CARO02], such a switchback of
   the data transmission path is not optimal in general.  As an
   alternative option to the switchback operation of [RFC4960], this
   document specifies the support the Permanent Failover switchover
   procedures proposed by [CARO02].
















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2.  Conventions and Terminology

   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].














































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3.  Issues with the SCTP Path Management

   SCTP can utilize multiple IP addresses for a single SCTP association.
   Each SCTP endpoint exchanges the list of its usable addresses during
   initial negotiation with its peer.  Then the endpoints select one
   address from the peer's list and define this as the primary
   destination.  During normal transmission, SCTP sends all user data to
   the primary destination.  Also, it sends heartbeat packets to all
   idle destinations at a certain interval to check the reachability of
   the path.  Idle destinations normally include all non-primary
   destinations.

   If a sender has multiple active destination addresses, it can
   retransmit data to secondary destination address, when the
   transmission to the primary times out.

   When a sender receives an acknowledgment for DATA or HEARTBEAT chunks
   sent to one of the destination addresses, it considers that
   destination to be active.  If it fails to receive acknowledgments,
   the error count for the address is increased.  If the error counter
   exceeds the protocol parameter 'Path.Max.Retrans', SCTP endpoint
   considers the address to be inactive.

   The failover process of SCTP is initiated when the primary path
   becomes inactive (error counter for the primary path exceeds
   Path.Max.Retrans).  If the primary path is marked inactive, SCTP
   chooses a new destination address from one of the active destinations
   and start using this address to send data to.  If the primary path
   becomes active again, SCTP uses the primary destination for
   subsequent data transmissions and stop using non-primary one.

   One issue with this failover process is that it usually takes
   significant amount of time before SCTP switches to the new
   destination.  Let's say the primary path on a multi-homed host
   becomes unavailable and the RTO value for the primary path at that
   time is around 1 second, it usually takes over 60 seconds before SCTP
   starts to use the secondary path.  This is because the recommended
   value for Path.Max.Retrans in the standard is 5, which requires 6
   consecutive timeouts before failover takes place.  Before SCTP
   switches to the secondary address, SCTP keeps trying to send packets
   to the primary and only retransmitted packets are sent to the
   secondary can be reached at the receiver.  This slow failover process
   can cause significant performance degradation and will not be
   acceptable in some situations.

   Another issue is that once the primary path is active again, the
   traffic is switched back.  This is not optimal in general.




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4.  Existing Solutions for Smooth Failover

   The following approaches are conceivable for the solutions of this
   issue.

4.1.  Reduce Path.Max.Retrans (PMR)

   Smaller values for Path.Max.Retrans shorten the failover duration.
   In fact, this is recommended in some research results [JUNGMAIER02]
   [GRINNEMO04] [FALLON08].  For example, if when Path.Max.Retrans=0,
   SCTP switches to another destination on a single timeout.  However,
   smaller value for Path.Max.Retrans also results in spurious failover.
   In addition, smaller Path.Max.Retrans values also affect
   'Association.Max.Retrans' values.  When the SCTP association's error
   count (sum of error counts on all ACTIVE paths) exceeds
   Association.Max.Retrans threshold, the SCTP sender considers the peer
   endpoint unreachable and terminates the association.  Therefore,
   Section 8.2 in [RFC4960] recommends that Association.Max.Retrans
   value should not be larger than the summation of the Path.Max.Retrans
   of each of the destination addresses, else the SCTP sender considers
   its peer reachable even when all destinations are INACTIVE.  To avoid
   such inconsistent behavior an SCTP implementation SHOULD reduce
   Association.Max.Retrans accordingly whenever it reduces
   Path.Max.Retrans.  However, smaller Association.Max.Retrans value
   increases chances of association termination during minor congestion
   events.

   Another issue is that the interval of heartbeat packet: 'HB.interval'
   could be in the order of seconds (recommended value is 30 seconds).
   When the primary path becomes inactive, the next HB can be
   transmitted only seconds later.  Meanwhile, the primary path may have
   recovered.  In such situations, post failover, an endpoint is forced
   to wait on the order of seconds before the endpoint can resume
   transmission on the primary path.

   The advantage of tuning Path.Max.Retrans is that it requires no
   modification to the current standard.  However, as we discuss above
   tuning Path.Max.Retrans ignores several recommendations in [RFC4960].
   In addition, some research results indicate path bouncing caused by
   spurious failover does not cause serious problems.  We discuss the
   effect of path bouncing in Section 5.2.

4.2.  Adjust RTO related parameters

   As several research results indicate, we can also shorten the
   duration of failover process by adjusting RTO related parameters
   [JUNGMAIER02] [FALLON08].  During failover process, RTO keeps being
   doubled.  However, if we can choose smaller value for RTO.max, we can



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   stop the exponential growth of RTO at some point.  Also, choosing
   smaller values for RTO.initial or RTO.min can contribute to keep RTO
   value small.

   Similar to reducing Path.Max.Retrans, the advantage of this approach
   is that it requires no modification to the current specification,
   although it needs to ignore several recommendations described in the
   Section 15 of [RFC4960].  However, this approach requires to have
   enough knowledge about the network characteristics between end
   points.  Otherwise, it can introduce adverse side-effects such as
   spurious timeouts.








































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5.  SCTP with Potentially-Failed Destination State (SCTP-PF)

5.1.  SCTP-PF Description

   SCTP-PF stems from the following two observations about SCTP's
   failure detection procedure:

   o  In order to minimize performance impact during failover, the
      sender should avoid transmitting data to the failed destination as
      early as possible.  In the current SCTP path management scheme,
      the sender stops transmitting data to a destination only after the
      destination is marked Failed.  Thus, a smaller PMR value is ideal
      so that the sender transitions a destination to the Failed state
      quicker.

   o  Smaller PMR values increase the chances of spurious failure
      detection where the sender incorrectly marks a destination as
      Failed during periods of temporary congestion.  Larger PMR values
      are preferable to avoid spurious failure detection.

   From the above observations it is clear that tweaking the PMR value
   involves the following tradeoff -- a lower value improves performance
   but increases the chances of spurious failure detection, whereas a
   higher value degrades performance and reduces spurious failure
   detection in a wide range of path conditions.  Thus, tweaking the
   association's PMR value is an incomplete solution to address
   performance impact during failure.

   This proposal introduces a new "Potentially-failed" (PF) destination
   state in SCTP's path management procedure.  The PF state was
   originally proposed to improve CMT performance [NATARAJAN09].  The PF
   state is an intermediate state between Active and Failed states.
   SCTP's failure detection procedure is modified to include the PF
   state.  The new failure detection algorithm assumes that loss
   detected by a timeout implies either severe congestion or failure en-
   route.  After a number of consecutive timeouts on a path, the sender
   is unsure, and marks the corresponding destination as PF.  A PF
   destination is not used for data transmission except in special cases
   (discussed below).  The new failure detection algorithm requires only
   sender-side changes.  Details are:

   1.  The sender maintains a new tunable parameter called Potentially-
       failed.Max.Retrans (PFMR).  The recommended value of PFMR = 0
       when quick failover is used.  When PFMR is larger or equal to
       PMR, quick failover is turned off.

   2.  Each time the T3-rtx timer expires on an active destination, the
       error counter of that destination address will be incremented.



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       When the value in the error counter exceeds PFMR, the endpoint
       should mark the destination transport address as PF.

   3.  The sender SHOULD avoid data transmission to PF destinations.
       When all destinations are in either PF or Inactive state, the
       sender MAY either move the destination from PF to Active state
       (and transmit data to the active destination) or the sender MAY
       transmit data to a PF destination.  In the former scenario, (i)
       the sender MUST NOT notify the ULP about the state transition,
       and (ii) MUST NOT clear the destination's error counter.  It is
       recommended that the sender picks the PF destination with least
       error count (fewest consecutive timeouts) for data transmission.
       In case of a tie (multiple PF destinations with same error
       count), the sender MAY choose the last active destination.

   4.  Only heartbeats MUST be sent to PF destination(s) once per RTO.
       This means the sender SHOULD ignore HB.interval for PF
       destinations.  If an heartbeat is unanswered, the sender
       increments the error counter and exponentially backs off the RTO
       value.  If error counter is less than PMR, the sender SHOULD
       transmit another heartbeat immediately after T3-timer expiration.

   5.  When the sender receives an heartbeat ACK from a PF destination,
       the sender clears the destination's error counter and transitions
       the PF destination back to Active state.  The sender should
       perform slow-start as specified in Section 7.2.1 of [RFC4960]
       when it sends data on this destination.

   6.  Additional (PMR - PFMR) consecutive timeouts on a PF destination
       confirm the path failure, upon which the destination transitions
       to the Inactive state.  As described in [RFC4960], the sender (i)
       SHOULD notify ULP about this state transition, and (ii) transmit
       heartbeats to the Inactive destination at a lower frequency as
       described in Section 8.3 of [RFC4960].

   7.  When all destinations are in the Inactive state, the sender picks
       one of the Inactive destinations for data transmission.  This
       proposal recommends that the sender picks the Inactive
       destination with least error count (fewest consecutive timeouts)
       for data transmission.  In case of a tie (multiple Inactive
       destinations with same error count), the sender MAY choose the
       last active destination.

   8.  ACKs for retransmissions do not transition a PF destination back
       to Active state, since a sender cannot disambiguate whether the
       ack was for the original transmission or the retransmission(s).





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   9.  SCTP shall provide the means to expose the PF state of its
       destinations as well as SCTP SHOULD notify the ULP of the state
       transitions from Active to PF and from PF to Active state.  SCTP
       can provide the means to suppress exposure of PF state and
       association state transitions and in this case the ULP MAY make
       SCTP suppress exposure of PF state to ULP.  In this case the ULP
       will rely solely on the [RFC4960] state machine even if quick
       failover function is activated in SCTP.

5.2.  Effect of Path Bouncing

   The methods described above can accelerate the failover process.
   Hence, they might introduce the path bouncing effect where the sender
   keeps changing the data transmission path frequently.  This sounds
   harmful to the data transfer, however several research results
   indicate that there is no serious problem with SCTP in terms of path
   bouncing effect [CARO04] [CARO05].

   There are two main reasons for this.  First, SCTP is basically
   designed for multipath communication, which means SCTP maintains all
   path related parameters (CWND, ssthresh, RTT, error count, etc) per
   each destination address.  These parameters cannot be affected by
   path bouncing.  In addition, when SCTP migrates the data transfer to
   another path, it starts with the minimal or the initial CWND.  Hence,
   there is little chance for packet reordering or duplicating.

   Second, even if all communication paths between the end-nodes share
   the same bottleneck, the quick failover results in a behavior already
   allowed by [RFC4960].

5.3.  Permanent Failover

   Post failover then, by [RFC4960] behavior, an SCTP sender migrates
   the traffic back to the original primary destination once this
   destination becomes active anew.  As the CWND towards the original
   primary destination has to be rebuilt once data transfer resumes, the
   switch back to use the original primary path is not always optimal.
   Indeed [CARO02] shows that the switch over to the original primary
   may degrade SCTP performance compared to continuing data transmission
   on the same path, especially, but not only, in scenarios where this
   path's characteristics are better.  In order to mitigate this
   performance degradation, Permanent Failover operation was proposed in
   [CARO02].  When SCTP changes the destination due to failover,
   Permanent Failover marks it as new primary.  This means Permanent
   Failover allows SCTP sender to continue data transmission to the path
   even after the old primary destination becomes active again.  This is
   achieved by having SCTP perform a switchover of the primary path to
   an alternative working path rather than having SCTP switch back data



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   transfer to the (previous) primary path.

   The manner of switchover operation that is most optimal in a given
   scenario depends on the relative quality of a set primary path versus
   the quality of alternative paths available as well as it depends on
   the extent to which it is desired for the mode of operation to
   enforce traffic distribution over a number of network paths.  I.e.,
   load distribution of traffic from multiple SCTP associations may be
   sought to be enforced by distribution of the set primary paths with
   [RFC4960] switchback operation.  However as [RFC4960] switchback
   behavior is suboptimal in certain situations, especially in scenarios
   where a number of equally good paths are available, it is recommended
   for SCTP to support also, as alternative behavior, the Permanent
   Failover modes of operation where forced switch back to a previously
   failed primary path is not always performed.  The Permanent Failover
   operation requires only sender side changes.  Details, as originally
   outlined in [CARO02], are:

   1.  The sender maintains a new tunable parameter, called
       Primary.Switchover.Max.Retrans (PSMR).  When the path error
       counter on a set primary path exceeds PSMR, the SCTP
       implementation autonomously selects and sets a new primary path.

   2.  The primary path selected by the SCTP implementation shall be the
       path which at the given time would be chosen for data transfer.
       A previously failed primary path may come in use as data transfer
       path as per normal path selection when the present data transfer
       path fails.

   3.  The recommended value of PSMR is PFMR when Permanent failover is
       used.  This means that no forced switchback to a previously
       failed primary path is performed.

   4.  It must be possible to disable the Permanent Failover and obtain
       the standard switchback operation of [RFC4960].

   We recommend that SCTP-PF should stick to the standard RFC4960
   behavior as default, i.e., switch back to the old primary destination
   once the destination becomes active again.  However, implementors MAY
   implement Permanent Failover and MAY enable it based on network
   configurations or users' requests.










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6.  Socket API Considerations

   This section describes how the socket API defined in [RFC6458] is
   extended to provide a way for the application to control and observe
   the quick failover behavior.

   Please note that this section is informational only.

   A socket API implementation based on [RFC6458] is, by means of the
   existing SCTP_PEER_ADDR_CHANGE event, extended to provide the event
   notification when a peer address enters or leaves the potentially
   failed state as well as the socket API implementation is extended to
   expose the potentially failed state of a peer address in the existing
   SCTP_GET_PEER_ADDR_INFO structure.

   Furthermore, two new read/write socket options for the level
   IPPROTO_SCTP and the name SCTP_PEER_ADDR_THLDS and
   SCTP_EXPOSE_POTENTIALLY_FAILED_STATE are defined as described below.
   The first socket option is used to control the values of the PFMR and
   PSMR parameters described in Section 5.  The second one controls the
   exposition of the potentially failed path state.

   Support for the SCTP_PEER_ADDR_THLDS and
   SCTP_EXPOSE_POTENTIALLY_FAILED_STATE socket options need also to be
   added to the function sctp_opt_info().

6.1.  Support for the Potentially Failed Path State

   As defined in [RFC6458], the SCTP_PEER_ADDR_CHANGE event is provided
   if the status of a peer address changes.  In addition to the state
   changes described in [RFC6458], this event is also provided, if a
   peer address enters or leaves the potentially failed state.  The
   notification as defined in [RFC6458] uses the following structure:

   struct sctp_paddr_change {
     uint16_t spc_type;
     uint16_t spc_flags;
     uint32_t spc_length;
     struct sockaddr_storage spc_aaddr;
     uint32_t spc_state;
     uint32_t spc_error;
     sctp_assoc_t spc_assoc_id;
   }

   [RFC6458] defines the constants SCTP_ADDR_AVAILABLE,
   SCTP_ADDR_UNREACHABLE, SCTP_ADDR_REMOVED, SCTP_ADDR_ADDED, and
   SCTP_ADDR_MADE_PRIM to be provided in the spc_state field.  This
   document defines in addition to that the new constant



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   SCTP_ADDR_POTENTIALLY_FAILED, which is reported if the affected
   address becomes potentially failed.

   The SCTP_GET_PEER_ADDR_INFO socket option defined in [RFC6458] can be
   used to query the state of a peer address.  It uses the following
   structure:

   struct sctp_paddrinfo {
     sctp_assoc_t spinfo_assoc_id;
     struct sockaddr_storage spinfo_address;
     int32_t spinfo_state;
     uint32_t spinfo_cwnd;
     uint32_t spinfo_srtt;
     uint32_t spinfo_rto;
     uint32_t spinfo_mtu;
   };

   [RFC6458] defines the constants SCTP_UNCONFIRMED, SCTP_ACTIVE, and
   SCTP_INACTIVE to be provided in the spinfo_state field.  This
   document defines in addition to that the new constant
   SCTP_POTENTIALLY_FAILED, which is reported if the peer address is
   potentially failed.

6.2.  Peer Address Thresholds (SCTP_PEER_ADDR_THLDS) Socket Option

   Applications can control the quick failover behavior by getting or
   setting the number of consecutive timeouts before a peer address is
   considered potentially failed or unreachable and before the primary
   path is changed automatically.  This socket option uses the level
   IPPROTO_SCTP and the name SCTP_PEER_ADDR_THLDS.

   The following structure is used to access and modify the thresholds:

   struct sctp_paddrthlds {
     sctp_assoc_t spt_assoc_id;
     struct sockaddr_storage spt_address;
     uint16_t spt_pathmaxrxt;
     uint16_t spt_pathpfthld;
     uint16_t spt_pathcpthld;
   };

   spt_assoc_id:  This parameter is ignored for one-to-one style
      sockets.  For one-to-many style sockets the application may fill
      in an association identifier or SCTP_FUTURE_ASSOC.  It is an error
      to use SCTP_{CURRENT|ALL}_ASSOC in spt_assoc_id.






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   spt_address:  This specifies which peer address is of interest.  If a
      wildcard address is provided, this socket option applies to all
      current and future peer addresses.

   spt_pathmaxrxt:  Each peer address of interest is considered
      unreachable, if its path error counter exceeds spt_pathmaxrxt.

   spt_pathpfthld:  Each peer address of interest is considered
      potentially failed, if its path error counter exceeds
      spt_pathpfthld.

   spt_pathcpthld:  Each peer address of interest is not considered the
      primary remote address anymore, if its path error counter exceeds
      spt_pathcpthld.  Using a value of 0xffff disables the selection of
      a new primary peer address.  If an implementation does not support
      the automatically selection of a new primary address, it should
      indicate an error with errno set to EINVAL if a value different
      from 0xffff is used in spt_pathcpthld.

6.3.  Exposing the Potentially Failed Path State
      (SCTP_EXPOSE_POTENTIALLY_FAILED_STATE) Socket Option

   Applications can control the exposure of the potentially failed path
   state in the SCTP_PEER_ADDR_CHANGE event and the
   SCTP_GET_PEER_ADDR_INFO as described in Section 6.1.  The default
   value is implementation specific.

   This socket option uses the level IPPROTO_SCTP and the name
   SCTP_EXPOSE_POTENTIALLY_FAILED_STATE.

   The following structure is used to control the exposition of the
   potentially failed path state:

   struct sctp_assoc_value {
     sctp_assoc_t assoc_id;
     uint32_t assoc_value;
   };

   assoc_id:  This parameter is ignored for one-to-one style sockets.
      For one-to-many style sockets the application may fill in an
      association identifier or SCTP_FUTURE_ASSOC.  It is an error to
      use SCTP_{CURRENT|ALL}_ASSOC in assoc_id.

   assoc_value:  The potentially failed path state is exposed if and
      only if this parameter is non-zero.






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7.  Security Considerations

   There are no new security considerations introduced in this document.
















































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8.  IANA Considerations

   This document does not create any new registries or modify the rules
   for any existing registries managed by IANA.















































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9.  References

9.1.  Normative References

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

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.

9.2.  Informative References

   [CARO02]   Caro Jr., A., Iyengar, J., Amer, P., Heinz, G., and R.
              Stewart, "A Two-level Threshold Recovery Mechanism for
              SCTP", Tech report, CIS Dept, University of Delaware ,
              7 2002.

   [CARO04]   Caro Jr., A., Amer, P., and R. Stewart, "End-to-End
              Failover Thresholds for Transport Layer Multihoming",
              MILCOM 2004 , 11 2004.

   [CARO05]   Caro Jr., A., "End-to-End Fault Tolerance using Transport
              Layer Multihoming", Ph.D Thesis, University of Delaware ,
              1 2005.

   [FALLON08]
              Fallon, S., Jacob, P., Qiao, Y., Murphy, L., Fallon, E.,
              and A. Hanley, "SCTP Switchover Performance Issues in WLAN
              Environments", IEEE CCNC 2008, 1 2008.

   [GRINNEMO04]
              Grinnemo, K-J. and A. Brunstrom, "Performance of SCTP-
              controlled failovers in M3UA-based SIGTRAN networks",
              Advanced Simulation Technologies Conference , 4 2004.

   [IYENGAR06]
              Iyengar, J., Amer, P., and R. Stewart, "Concurrent
              Multipath Transfer using SCTP Multihoming over Independent
              End-to-end Paths.", IEEE/ACM Trans on Networking 14(5),
              10 2006.

   [JUNGMAIER02]
              Jungmaier, A., Rathgeb, E., and M. Tuexen, "On the use of
              SCTP in failover scenarios", World Multiconference on
              Systemics, Cybernetics and Informatics , 7 2002.

   [NATARAJAN09]
              Natarajan, P., Ekiz, N., Amer, P., and R. Stewart,



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              "Concurrent Multipath Transfer during Path Failure",
              Computer Communications , 5 2009.

   [RFC6458]  Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
              Yasevich, "Sockets API Extensions for the Stream Control
              Transmission Protocol (SCTP)", RFC 6458, December 2011.













































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Authors' Addresses

   Yoshifumi Nishida
   GE Global Research
   2623 Camino Ramon
   San Ramon, CA  94583
   USA

   Email: nishida@wide.ad.jp


   Preethi Natarajan
   Cisco Systems
   510 McCarthy Blvd
   Milpitas, CA  95035
   USA

   Email: prenatar@cisco.com


   Armando Caro
   BBN Technologies
   10 Moulton St.
   Cambridge, MA  02138
   USA

   Email: acaro@bbn.com


   Paul D. Amer
   University of Delaware
   Computer Science Department - 434 Smith Hall
   Newark, DE  19716-2586
   USA

   Email: amer@udel.edu


   Karen E. E. Nielsen
   Ericsson
   Kistavaegen 25
   Stockholm,   164 80
   Sweden

   Email: karen.nielsen@tieto.com






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