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Versions: (draft-beeram-teas-rsvp-te-scaling-rec) 00 01 02 03 04 05 06 07 08 09 RFC 8370

TEAS Working Group                                  Vishnu Pavan Beeram
Internet Draft                                         Juniper Networks
Intended status: Proposed Standard                            Ina Minei
                                                            Google, Inc
                                                             Rob Shakir
                                                            Google, Inc
                                                          Dante Pacella
                                                                Verizon
                                                             Tarek Saad
                                                          Cisco Systems

Expires: April 30, 2017                                October 30, 2016


   Implementation Recommendations to Improve the Scalability of RSVP-TE
                                Deployments
                  draft-ietf-teas-rsvp-te-scaling-rec-03


Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on April 30, 2017.

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   Copyright (c) 2016 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
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   (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
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Abstract

   The scale at which RSVP-TE Label Switched Paths (LSPs) get deployed
   is growing continually and the onus is on RSVP-TE implementations
   across the board to keep up with this increasing demand.

   This document makes a set of implementation recommendations to help
   RSVP-TE deployments push the envelope on scaling and advocates the
   use of a couple of techniques - "Refresh Interval Independent RSVP
   (RI-RSVP)" and "Per-Peer flow-control" - for improving scaling.

Conventions used in this document

   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 RFC-2119 [RFC2119].


Table of Contents

   1. Introduction...................................................3
   2. Recommendations................................................3
      2.1. "RFC2961 specific" Recommendations........................3
         2.1.1. Basic Pre-Requisites.................................4
         2.1.2. Making Acknowledgements mandatory....................4
         2.1.3. Clarifications on reaching Rapid Retry Limit (Rl)....4
      2.2. Refresh Interval Independent RSVP.........................5
         2.2.1. Capability Advertisement.............................6
         2.2.2. Compatibility........................................6
      2.3. Per-Peer RSVP Flow Control................................6
         2.3.1. Capability Advertisement.............................7
         2.3.2. Compatibility........................................7
   3. Security Considerations........................................8
   4. IANA Considerations............................................8
      4.1. Capability Object Values..................................8
   5. References.....................................................8
      5.1. Normative References......................................8
      5.2. Informative References....................................9


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   6. Acknowledgments................................................9
   Appendix A. Recommended Defaults..................................9
   Contributors.....................................................10
   Authors' Addresses...............................................10

1. Introduction

   The scale at which RSVP-TE [RFC3209] Label Switched Paths (LSPs) get
   deployed is growing continually and there is considerable onus on
   RSVP-TE implementations across the board to keep up with this
   increasing demand in scale.

   The set of RSVP Refresh Overhead Reduction procedures [RFC2961]
   serves as a powerful toolkit for RSVP-TE implementations to help
   cover a majority of the concerns about soft-state scaling. However,
   even with these tools in the toolkit, analysis of existing
   implementations [RFC5439] indicates that the processing required
   under certain scale may still cause significant disruption to an
   LSR.

   This document builds on the scaling work and analysis that has been
   done so far and makes a set of concrete implementation
   recommendations to help RSVP-TE deployments push the envelope
   further on scaling - push higher the threshold above which an LSR
   struggles to achieve sufficient processing to maintain LSP state.

   This document advocates the use of a couple of techniques - "Refresh
   Interval Independent RSVP (RI-RSVP)" and "Per-Peer flow-control" -
   for significantly cutting down the amount of processing cycles
   required to maintain LSP state. "RI-RSVP" helps completely eliminate
   RSVP's reliance on refreshes and refresh-timeouts while "Per-Peer
   Flow-Control" enables a busy RSVP speaker to apply back pressure to
   its peer(s). In order to reap maximum scaling benefits, it is
   strongly RECOMMENDED that implementations support both the
   techniques, but it is possible for an implementation to support just
   one but not the other.

2. Recommendations

2.1. "RFC2961 specific" Recommendations

   The implementation recommendations discussed in this section are
   based on the proposals made in [RFC2961] and act as pre-requisites
   for implementing either or both of the techniques discussed in
   Sections 2.2 and 2.3.



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2.1.1. Basic Pre-Requisites

   An implementation that supports either or both of the techniques
   discussed in Sections 2.2 and 2.3:

   - SHOULD indicate support for RSVP Refresh Overhead Reduction
     extensions (as specified in Section 2 of [RFC2961]) by default,
     with the ability to override the default via configuration.

   - MUST support reliable delivery of Path/Resv and the corresponding
     Tear/Err messages using the procedures specified in [RFC2961].

   - MUST support retransmit of all RSVP-TE messages using exponential-
     backoff, as specified in Section 6 of [RFC2961].


2.1.2. Making Acknowledgements mandatory

   The reliable message delivery mechanism specified in [RFC2961]
   states that "Nodes receiving a non-out of order message containing a
   MESSAGE_ID object with the ACK_Desired flag set, SHOULD respond with
   a MESSAGE_ID_ACK object."

   In an implementation that supports either or both of the techniques
   discussed in Sections 2.2 and 2.3, nodes receiving a non-out of
   order message containing a MESSAGE ID object with the ACK-Desired
   flag set, MUST respond with a MESSAGE_ID_ACK object. This
   improvement to the predictability of the system in terms of reliable
   message delivery is key for being able to take any action based on a
   non-receipt of an ACK.

2.1.3. Clarifications on reaching Rapid Retry Limit (Rl)

   According to section 6 of [RFC2961] "The staged retransmission will
   continue until either an appropriate MESSAGE_ID_ACK object is
   received, or the rapid retry limit, Rl, has been reached." The
   following clarifies what actions, if any, a router should take once
   Rl has been reached.

   If it is the retransmission of Tear/Err messages and Rl has been
   reached, the router need not take any further actions. If it is the
   retransmission of Path/Resv messages and Rl has been reached, then
   the router starts periodic retransmission of these messages. The
   retransmitted messages MUST carry MESSAGE_ID object with ACK_Desired
   flag set. This periodic retransmission SHOULD continue until an
   appropriate MESSAGE_ID ACK object is received indicating


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   acknowledgement of the (retransmitted) Path/Resv message. The
   configurable periodic retransmission interval SHOULD be less than
   the regular refresh interval. A default periodic retransmission
   interval of 30 seconds is RECOMMENDED by this document.

2.2. Refresh Interval Independent RSVP

   The RSVP protocol relies on periodic refreshes for state
   synchronization between RSVP neighbors and for recovery from lost
   RSVP messages. It relies on refresh timeout for stale state cleanup.
   The primary motivation behind introducing the notion of "Refresh
   Interval Independent RSVP" (RI-RSVP) is to completely eliminate
   RSVP's reliance on refreshes and refresh timeouts. This is done by
   simply increasing the refresh interval to a fairly large value.
   [RFC2961] and [RFC5439] do talk about increasing the value of the
   refresh-interval to provide linear improvement on transmission
   overhead, but also point out the degree of functionality that is
   lost by doing so. This section revisits this notion, but also
   proposes sufficient recommendations to make sure that there is no
   loss of functionality incurred by increasing the value of the
   refresh interval.

   An implementation that supports RI-RSVP:

   - MUST support all the recommendations made in Section 2.1

   - MUST make the default value of the configurable refresh interval
     be a large value (10s of minutes). A default value of 20 minutes
     is RECOMMENDED by this document.

   - MUST implement coupling the state of individual LSPs with the
     state of the corresponding RSVP-TE signaling adjacency. When an
     RSVP-TE speaker detects RSVP-TE signaling adjacency failure, the
     speaker MUST act as if the all the Path and Resv state learnt via
     the failed signaling adjacency has timed out.

   - MUST make use of Node-ID based Hello Session ([RFC3209],
     [RFC4558]) for detection of RSVP-TE signaling adjacency failures;
     A default value of 9 seconds is RECOMMENDED by this document for
     the configurable node hello interval (as opposed to the 5ms
     default value proposed in Section 5.3 of [RFC3209]).

   - MUST indicate support for RI-RSVP via the CAPABILITY object in
     Hello messages.




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2.2.1. Capability Advertisement

   An implementation supporting the RI-RSVP recommendations MUST set a
   new flag "RI-RSVP Capable" in the CAPABILITY object signaled in
   Hello messages.

   The new flag that will be introduced to CAPABILITY object is
   specified below.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Length             | Class-Num(134)|  C-Type  (1)  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Reserved                      |I|T|R|S|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   I bit

   Indicates that the sender supports RI-RSVP.

   Any node that sets the new I-bit in its CAPABILITY object MUST also
   set Refresh-Reduction-Capable bit in common header of all RSVP-TE
   messages.

2.2.2. Compatibility

   The RI-RSVP functionality MUST be activated only between peers that
   indicate their support for this functionality.

2.3. Per-Peer RSVP Flow Control

   The set of recommendations discussed in this section provide an RSVP
   speaker with the ability to apply back pressure to its peer(s) to
   reduce/eliminate RSVP-TE control plane congestion.

   An implementation that supports "Per-Peer RSVP Flow Control":

   - MUST support all the recommendations made in Section 2.1

   - MUST use lack of ACKs from a peer as an indication of peer's RSVP-
     TE control plane congestion. If congestion is detected, the local
     system MUST throttle RSVP-TE messages to the affected peer. This
     MUST be done on a per-peer basis. (Per-peer throttling MAY be
     implemented by a traffic shaping mechanism that proportionally


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     reduces the RSVP signaling packet rate as the number of
     outstanding Acks increases. And when the number of outstanding
     Acks decreases, the send rate would be adjusted up again.)

   - SHOULD use a Retry Limit (Rl) value of 7 (Section 6.2 of
     [RFC2961], suggests using 3).

   - SHOULD prioritize Tear/Error over trigger Path/Resv (messages that
     bring up new LSP state) sent to a peer when the local system
     detects RSVP-TE control plane congestion in the peer.

   - MUST indicate support for all recommendations in this section via
     the CAPABILITY object in Hello messages.


2.3.1. Capability Advertisement

   An implementation supporting the "Per-Peer Flow Control"
   recommendations MUST set a new flag "Per-Peer Flow Control Capable"
   in the CAPABILITY object signaled in Hello messages.

   The new flag that will be introduced to CAPABILITY object is
   specified below.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Length             | Class-Num(134)|  C-Type  (1)  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Reserved                    |F|I|T|R|S|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   F bit

   Indicates that the sender supports Per-Peer RSVP Flow Control

   Any node that sets the new I-bit in its CAPABILITY object MUST also
   set Refresh-Reduction-Capable bit in common header of all RSVP-TE
   messages.

2.3.2. Compatibility

   The "Per-Peer Flow Control" functionality MUST be activated only if
   both peers support it. If a peer hasn't indicated that it is capable
   of participating in "Per-Peer Flow Control", then it is risky to


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   assume that the peer would always acknowledge a non-out of order
   message containing a MESSAGE ID object with the ACK-Desired flag
   set.

3. Security Considerations

   This document does not introduce new security issues. The security
   considerations pertaining to the original RSVP protocol [RFC2205]
   and RSVP-TE [RFC3209] and those that are described in [RFC5920]
   remain relevant.

4. IANA Considerations

4.1. Capability Object Values

   IANA maintains all the registries associated with "Resource
   Reservation Protocol (RSVP) Paramaters" (see
   http://www.iana.org/assignments/rsvp-parameters/rsvp-
   parameters.xhtml). "Capability Object Values" Registry (introduced
   by [RFC5063]) is one of them.

   IANA is requested to assign two new Capability Object Value bit
   flags as follows:

   Bit       Hex      Name                                Reference
   Number    Value
   --------------------------------------------------------------------
   TBA       TBA      RI-RSVP Capable (I)                 Section 2.2.1
   TBA       TBA      Per-Peer Flow Control Capable (F)   Section 2.3.1

5. References

5.1. Normative References

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

   [RFC2205]   Braden, R., "Resource Reservation Protocol (RSVP)",
               RFC 2205, September 1997.

   [RFC2961]   Berger, L., "RSVP Refresh Overhead Reduction
               Extensions", RFC 2961, April 2001.

   [RFC3209]   Awduche, D., "RSVP-TE: Extensions to RSVP for LSP
               Tunnels", RFC 3209, December 2001.



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   [RFC4558]   Ali, Z., "Node-ID Based Resource Reservation (RSVP)
               Hello: A Clarification Statement", RFC 4558, June 2006.

   [RFC5063]   Satyanarayana, A., "Extensions to GMPLS Resource
               Reservation Protocol Graceful Restart", RFC5063, October
               2007.

5.2. Informative References

   [RFC5439]   Yasukawa, S., "An Analysis of Scaling Issues in MPLS-TE
               Core Networks", RFC 5439, February 2009.

   [RFC5920]   Fang, L., "Security Framework for MPLS and GMPLS
               Networks", RFC5920, July 2010.


6. Acknowledgments

   The authors would like to thank Yakov Rekhter for initiating this
   work and providing valuable inputs. They would like to thank
   Raveendra Torvi and Chandra Ramachandran for participating in the
   many discussions that led to the recommendations made in this
   document. They would also like to thank Adrian Farrel for providing
   detailed review comments.

Appendix A. Recommended Defaults

   (a)  Refresh-Interval (R)- 20 minutes (Section 2.2)
   Given that an implementation supporting RI-RSVP doesn't rely on
   refreshes for state sync between peers, the RSVP refresh interval is
   sort of analogous to IGP refresh interval, the default of which is
   typically in the order of 10s of minutes. Choosing a default of 20
   minutes allows the refresh timer to be randomly set to a value in
   the range [10 minutes (0.5R), 30 minutes (1.5R)].

   (b)  Node Hello-Interval - 9 Seconds (Section 2.2)
   [RFC3209] defines the hello timeout as 3.5 times the hello interval.
   Choosing 9 seconds for the node hello-interval gives a hello timeout
   of 3.5*9 = 31.5 seconds. This puts the hello timeout value to be in
   the same ballpark as the IGP hello timeout value.

   (c)  Retry-Limit (Rl) - 7 (Section 2.3)
   Choosing 7 as the retry-limit results in an overall rapid retransmit
   phase of 31.5 seconds. This nicely matches up with the 31.5 seconds
   hello timeout.



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   (d)  Periodic Retransmission Interval - 30 seconds (Section 2.1.3)
   If the Retry-Limit (Rl) is 7, then it takes about 30 (31.5 to be
   precise) seconds for the 7 rapid retransmit steps to max out. (The
   last delay from message 6 to message 7 is 16 seconds). The 30
   seconds interval also matches the traditional default refresh time.

Contributors

   Markus Jork
   Juniper Networks
   Email: mjork@juniper.net

   Ebben Aries
   Juniper Networks
   Email: exa@juniper.net


Authors' Addresses

   Vishnu Pavan Beeram (Ed)
   Juniper Networks
   Email: vbeeram@juniper.net

   Ina Minei
   Google, Inc
   Email: inaminei@google.com

   Rob Shakir
   Google, Inc
   Email: rjs@rob.sh

   Dante Pacella
   Verizon
   Email: dante.j.pacella@verizon.com

   Tarek Saad
   Cisco Systems
   Email: tsaad@cisco.com










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