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Versions: (draft-xu-l3vpn-virtual-subnet-fib-reduction) 00 01 02 03 04

Network Working Group                                              X. Xu
Internet-Draft                                                    Huawei
Intended status: Informational                              C. Jacquenet
Expires: February 4, 2017                                         Orange
                                                                T. Boyes
                                                            Bloomberg LP
                                                                  B. Fee
                                                        Extreme Networks
                                                           W. Henderickx
                                                                   Nokia
                                                          August 3, 2016


                    FIB Reduction in Virtual Subnet
            draft-ietf-bess-virtual-subnet-fib-reduction-04

Abstract

   Virtual Subnet is a BGP/MPLS IP VPN-based subnet extension solution
   which is intended for building Layer3 network virtualization overlays
   within and/or between data centers.  This document describes a
   mechanism for reducing the FIB size of PE routers in the Virtual
   Subnet context.

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 February 4, 2017.

Copyright Notice

   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
   Provisions Relating to IETF Documents



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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 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Solution Description  . . . . . . . . . . . . . . . . . . . .   3
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Virtual Subnet [RFC7814] is a BGP/MPLS IP VPN [RFC4364] -based subnet
   extension solution which is intended for building Layer3 network
   virtualization overlays within and/or across data centers.  In the
   Virtual Subnet context, since CE host routes of a given VPN instance
   need to be exchanged among PE routers participating in that VPN
   instance, the resulting forwarding table (a.k.a.  FIB) size of PE
   routers may become a big concern in large-scale data center
   environment where they may need to install a huge amount of host
   routes into their forwarding tables.  In some cases where host routes
   need to be maintained on the control plane, it needs a method to
   reduce the FIB size of PE routers without any change to the RIB and
   the routing table.  Therefore, this document proposes a very simple
   mechanism for reducing the FIB size of PE routers.  The basic idea of
   this mechanism is: Those host routes learnt from remote PE routers
   are selectively installed into the FIB while the remaining routes
   including local CE host routes are installed into the FIB by default
   as before.

1.1.  Requirements Language

   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].




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2.  Terminology

   This memo makes use of the terms defined in [RFC4364].

3.  Solution Description

                            +----------+
                       +----+PE/RR(APR)+----+
+------------------+   |    +----------+    |   +------------------+
|VPN_A:192.0.2.1/24|   |                    |   |VPN_A:192.0.2.1/24|
|              \   |   |                    |   |  /               |
|  +------+     \ ++---+-+                +-+---++/     +------+   |
|  |Host A+------_+ PE-1 |                | PE-2 +------+Host B|   |
|  +------+\      ++-+-+-+                +-+-+-++     /+------+   |
|   192.0.2.2/24   | | |                    | | |   192.0.2.3/24   |
|                  | | |                    | | |                  |
|     DC West      | | |  IP/MPLS Backbone  | | |      DC East     |
+------------------+ | |                    | | +------------------+
                     | +--------------------+ |
                     |                        |
VRF:                 V                    VRF:V
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|   Prefix     | Nexthop |Protocol|In_FIB| |   Prefix     | Nexthop |Protocol|In_FIB|
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|192.0.2.1/32  |127.0.0.1| Direct |  Yes | |192.0.2.1/32  |127.0.0.1| Direct |  Yes |
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|192.0.2.2/32  |192.0.2.2| Direct |  Yes | |192.0.2.2/32  |  PE-1   |  IBGP  |  No  |
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|192.0.2.3/32  |   PE-2  |  IBGP  |  No  | |192.0.2.3/32  |192.0.2.3| Direct |  Yes |
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|192.0.2.0/25  |   APR   |  IBGP  |  Yes | |192.0.2.0/25  |   APR   |  IBGP  |  Yes |
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|192.0.2.128/25|   APR   |  IBGP  |  Yes | |192.0.2.128/25|   APR   |  IBGP  |  Yes |
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|192.0.2.0/24  |192.0.2.1| Direct |  Yes | |192.0.2.0/24  |192.0.2.1| Direct |  Yes |
+--------------+---------+--------+------+ +--------------+---------+--------+------+

             Figure 1: Selective IPv4 FIB Installation Example













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                              +----------+
                         +----+PE/RR(APR)+----+
+--------------------+   |    +----------+    |   +----------------+
|VPN_A:              |   |                    |   |VPN_A:          |
|2001:db8::1/64      |   |                    |   |2001:db8::1/64  |
|              \     |   |                    |   |  /             |
|  +------+     \ ++---+-+                +-+---++/     +------+   |
|  |Host A+------_+ PE-1 |                | PE-2 +------+Host B|   |
|  +------+\      ++-+-+-+                +-+-+-++     /+------+   |
| 2001:db8::2/64   | | |                    | | | 2001:db8::3/64   |
|                  | | |                    | | |                  |
|     DC West      | | |  IP/MPLS Backbone  | | |      DC East     |
+------------------+ | |                    | | +------------------+
                     | +--------------------+ |
                     |                        |
VRF:                 V                    VRF:V
+----------------+-----------+--------+------+ +----------------+-----------+--------+------+
|    Prefix      |  Nexthop  |Protocol|In_FIB| |    Prefix      |  Nexthop  |Protocol|In_FIB|
+----------------+-----------+--------+------+ +----------------+-----------+--------+------+
|2001:db8::1/64  |    ::1    | Direct |  Yes | |2001:db8::1/64  |    ::1    | Direct |  Yes |
+----------------+-----------+--------+------+ +----------------+-----------+--------+------+
|2001:db8::2/64  |2001:db8::2| Direct |  Yes | |2001:db8::2/64  |   PE-1    |  IBGP  |  No  |
+----------------+-----------+--------+------+ +----------------+-----------+--------+------+
|2001:db8::3/64  |    PE-2   |  IBGP  |  No  | |2001:db8::3/64  |2001:db8::3| Direct |  Yes |
+----------------+-----------+--------+------+ +----------------+-----------+--------+------+
|2001:db8::0/63  |    APR    |  IBGP  |  Yes | |2001:db8::0/63  |    APR    |  IBGP  |  Yes |
+----------------+-----------+--------+------+ +----------------+-----------+--------+------+
|2001:db8::128/63|    APR    |  IBGP  |  Yes | |2001:db8::128/63|    APR    |  IBGP  |  Yes |
+----------------+-----------+--------+------+ +----------------+-----------+--------+------+
|2001:db8::0/64  |2001:db8::1| Direct |  Yes | |2001:db8::0/64  |2001:db8::1| Direct |  Yes |
+----------------+-----------+--------+------+ +----------------+-----------+--------+------+

             Figure 2: Selective IPv6 FIB Installation Example

   To reduce the FIB size of PE routers, the selective FIB installation
   concept as described in [I-D.ietf-grow-va] can be leveraged in the
   Virtual Subnet context.  Take the VPN instance demonstrated in
   Figure 1 or Figure 2 as an example, the FIB reduction procedures are
   described as follows:

   1.  Multiple more specific prefixes (e.g., 192.0.2.0/25 and
       192.0.2.128/25 in IPv4 example, or 2001:db8::0/63 and
       2001:db8::128/63 in IPv6 example ) corresponding to an extended
       subnet (i.e., 192.0.2.0/24 in IPv4 example, or 2001:db8::0/64 in
       IPv6 example) are specified as Virtual Prefixes (VPs).
       Meanwhile, one or more PE routers (or route reflectors) are
       configured as Aggregation Point Routers (APR) for each VP.  The




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       APRs for a given VP would install a null route to that VP while
       propagating a route to that VP via the L3VPN signaling.

   2.  For a given host route in the routing table which is learnt from
       any remote PE router, PE routers which are non-APRs for any VP
       covering this host route would not install it into the FIB by
       default.  In contrast, PE routers (or route reflectors) which are
       APRs for any VP covering that host route would install it into
       the FIB.  If one or more particular remote host routes need to be
       installed by non-APR PE routers by default as well for whatever
       reasons, the best way to realize such goal is to attach a special
       extended communities attribute to those particular host routes
       either by originating PE routers or by route reflectors.  Upon
       receiving any host routes attached with the above extended
       communities attribute, non-APR PE routers SHOULD install them by
       default.

   3.  Upon receiving a packet destined for a given remote CE host, if
       no host route for that CE host is found in the FIB, the ingress
       PE router would forward the packet to a given APR according to
       the longest-matching VP route, which in turn forwards the packet
       to the final egress PE router.  In this way, the FIB size of
       those non-APR PE routers can be greatly reduced at the potential
       cost of path stretch.

   In order to forward packets destined for remote CE hosts directly to
   the final egress PE routers without the potential path stretch
   penalty, non-APR PE routers could perform on-demand FIB installation
   for remote host routes which are available in the routing table.  For
   example, upon receiving an ARP request or Neighbor Solicitation (NS)
   message from a local CE host, the non-APR PE router would perform a
   lookup in the routing table.  If a corresponding host route for the
   target host is found but not yet installed into the FIB, it would be
   installed into the FIB.  Another possible way to trigger on-demand
   FIB installation is as follows: when receiving a packet whose
   longest-matching FIB entry is a particular VP route learnt from any
   APR, a copy of this packet would be sent to the control plane while
   this original packet is forwarded as normal.  The above copy sent to
   the control plane would trigger a lookup in the routing table.  If a
   corresponding host route is found but not yet installed into the FIB,
   it would be installed into the FIB.  To provide robust protection
   against DoS attacks on the control plane, rate-limiting of the above
   packets sent to the control plane MUST be enabled.  Those FIB entries
   for remote CE host routes which are on-demand installed on non-APR PE
   routers would expire if not used for a certain period of time.






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4.  Acknowledgements

   The authors would like to thank Susan Hares, Yongbing Fan, Robert
   Raszuk, Bruno Decraene and Fred Baker for their valuable suggestions
   on this document.

5.  IANA Considerations

   The type value for the Extended Communities Attributes as described
   in this doc is required to be allocated by the IANA.

6.  Security Considerations

   Those security considerations as described in [RFC7814] are
   applicable to this document.  This document does not introduce any
   new security risk.

7.  References

7.1.  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>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <http://www.rfc-editor.org/info/rfc4364>.

   [RFC7814]  Xu, X., Jacquenet, C., Raszuk, R., Boyes, T., and B. Fee,
              "Virtual Subnet: A BGP/MPLS IP VPN-Based Subnet Extension
              Solution", RFC 7814, DOI 10.17487/RFC7814, March 2016,
              <http://www.rfc-editor.org/info/rfc7814>.

7.2.  Informative References

   [I-D.ietf-grow-va]
              Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and
              L. Zhang, "FIB Suppression with Virtual Aggregation",
              draft-ietf-grow-va-06 (work in progress), December 2011.

Authors' Addresses

   Xiaohu Xu
   Huawei

   Email: xuxiaohu@huawei.com



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   Christian Jacquenet
   Orange

   Email: christian.jacquenet@orange.com


   Truman Boyes
   Bloomberg LP

   Email: tboyes@bloomberg.net


   Brendan Fee
   Extreme Networks

   Email: bfee@extremenetworks.com


   Wim Henderickx
   Nokia

   Email: wim.henderickx@nokia.com





























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