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Versions: 00 01 02 draft-ietf-bess-virtual-subnet-fib-reduction

Network working group                                              X. Xu
Internet Draft                                                    Huawei
Category: Informational
                                                                S. Hares

                                                                  Y. Fan
                                                           China Telecom

                                                            C. Jacquenet
                                                                  Orange

                                                                T. Boyes
                                                            Bloomberg LP

                                                                   B Fee
                                                        Extreme Networks

Expires: August 2014                                   February 14, 2014


                      FIB Reduction in Virtual Subnet

               draft-xu-l3vpn-virtual-subnet-fib-reduction-00


Abstract

   Virtual Subnet is a L3VPN-based subnet extension solution which can
   be used to build Layer3 network virtualization overlays within and/or
   across 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), 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."





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Internet-Draft       FIB Reduction in Virtual Subnet      February 2014

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   described in the Simplified BSD License.

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. Solution Overview ........................................... 3
   3. Security Considerations ..................................... 5
   4. IANA Considerations ......................................... 5
   5. Acknowledgements ............................................ 5
   6. References .................................................. 5
      6.1. Normative References ................................... 5
      6.2. Informative References ................................. 5
   Authors' Addresses ............................................. 5









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1. Introduction

   Virtual Subnet [VS] is a L3VPN-based subnet extension solution which
   can be used to build Layer3 network virtualization overlays within
   and/or across data centers. Since host routes of a given VPN instance
   are usually exchanged among PE routers participating in that VPN
   instance in the context of Virtual Subnet, the forwarding table
   (a.k.a. FIB) size of PE routers may become a scaling concern once
   they need to install a huge amount of host routes into their
   forwarding tables, especially in the particular cloud data center
   interconnect scenario where millions of host routes are there.

   To address the above FIB scaling concern, 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 installed into the FIB on demand, while the remaining
   routes including local host routes are installed into the FIB by
   default as before.

2. Solution Overview
                                        +--------+
                                  +-----+PE-3/APR+-----+
            +-----------------+   |     +--------+     |   +-----------------+
            |VPN_A:1.1.1.1/24 |   |                    |   |VPN_A:1.1.1.1/24 |
            |              \  |   |                    |   |  /              |
            |  +------+     \++---+-+                +-+---++/     +------+  |
            |  |Host A+------+ PE-1 |                | PE-2 +------+Host B|  |
            |  +------+\     ++-+-+-+                +-+-+-++     /+------+  |
            |   1.1.1.2/24    | | |                    | | |    1.1.1.3/24   |
            |                 | | |                    | | |                 |
            |     DC West     | | |  IP/MPLS Backbone  | | |      DC East    |
            +-----------------+ | |                    | | +-----------------+
                                | +--------------------+ |
                                |                        |
        VRF_A :                 V                VRF_A : V
      +------------+---------+--------+------+ +------------+---------+--------+------+
      |   Prefix   | Nexthop |Protocol|In_FIB| |   Prefix   | Nexthop |Protocol|In_FIB|
      +------------+---------+--------+------+ +------------+---------+--------+------+
      | 1.1.1.1/32 |127.0.0.1| Direct |  Yes | | 1.1.1.1/32 |127.0.0.1| Direct |  Yes |
      +------------+---------+--------+------+ +------------+---------+--------+------+
      | 1.1.1.2/32 | 1.1.1.2 | Direct |  Yes | | 1.1.1.2/32 |  PE-1   |  IBGP  |  No  |
      +------------+---------+--------+------+ +------------+---------+--------+------+
      | 1.1.1.3/32 |   PE-2  |  IBGP  |  No  | | 1.1.1.3/32 | 1.1.1.3 | Direct |  Yes |
      +------------+---------+--------+------+ +------------+---------+--------+------+
      | 1.1.1.0/25 |   APR   |  IBGP  |  Yes | | 1.1.1.0/25 |   APR   |  IBGP  |  Yes |
      +------------+---------+--------+------+ +------------+---------+--------+------+
      |1.1.1.128/25|   APR   |  IBGP  |  Yes | |1.1.1.128/25|   APR   |  IBGP  |  Yes |
      +------------+---------+--------+------+ +------------+---------+--------+------+
      | 1.1.1.0/24 | 1.1.1.1 | Direct |  Yes | | 1.1.1.0/24 | 1.1.1.1 | Direct |  Yes |
      +------------+---------+--------+------+ +------------+---------+--------+------+


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Internet-Draft       FIB Reduction in Virtual Subnet      February 2014

                      Figure 1: FIB Reduction Example

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

   1) Multiple more specific prefixes (e.g., 1.1.1.0/25 and 1.1.1.128/25)
      corresponding to an extended subnet (i.e., 1.1.1.0/24) are
      specified as Virtual Prefixes (VPs). Meanwhile, one or more PE
      routers are configured as Aggregation Point Routers (APR) for each
      VP. The 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 which are APRs for any VP covering
      that host route would install it into the FIB.

   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




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   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.

3. Security Considerations

   This document doesn't introduce additional security risk to BGP/MPLS
   IP VPN, nor does it provide any additional security feature for
   BGP/MPLS IP VPN.

4. IANA Considerations

   There is no requirement for any IANA action.

5. Acknowledgements

   Thanks Robert Raszuk for his review and suggestions on this document.

6. References

6.1. Normative References

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

   [VS] Xu, X et al., "Virtual Subnet: A L3VPN-based Subnet Extension
             Solution", draft-xu-l3vpn-virtual-subnet-03 (Work in
             Progress), January 2014.

6.2. Informative References

   [RFC4364] Rosen. E and Y. Rekhter, "BGP/MPLS IP Virtual Private
             Networks (VPNs)", RFC 4364, February 2006.

   [VA] Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and
             L. Zhang, "Virtual Aggregation", draft-ietf-grow-va-05.txt,
             (Work in Progress), December 2011.

Authors' Addresses

   Xiaohu Xu
   Huawei Technologies,
   Beijing, China.
   Phone: +86 10 60610041
   Email: xuxiaohu@huawei.com

   Susan Hares
   Email: shares@ndzh.com



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   Yongbing Fan
   Guangzhou Institute, China Telecom
   Guangzhou, China.
   Phone: +86 20 38639121
   Email: fanyb@gsta.com

   Christian Jacquenet
   Orange
   Rennes France
   Email: christian.jacquenet@orange.com

   Truman Boyes
   Bloomberg LP
   Phone: +1 2126174826
   Email: tboyes@bloomberg.net

   Brendan Fee
   Extreme Networks
   9 Northeastern Blvd.
   Salem, NH, 03079
   Email: bfee@enterasys.com



























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