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." Xu, et al. Expires August 14, 2014 [Page 1] Internet-Draft FIB Reduction in Virtual Subnet February 2014 The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 14, 2014. Copyright Notice Copyright (c) 2013 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. 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 Xu, et al. Expires August 14, 2014 [Page 2] Internet-Draft FIB Reduction in Virtual Subnet February 2014 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 | +------------+---------+--------+------+ +------------+---------+--------+------+ Xu, et al. Expires August 14, 2014 [Page 3] 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 Xu, et al. Expires August 14, 2014 [Page 4] Internet-Draft FIB Reduction in Virtual Subnet February 2014 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 Xu, et al. Expires August 14, 2014 [Page 5] Internet-Draft FIB Reduction in Virtual Subnet February 2014 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 Xu, et al. Expires August 14, 2014 [Page 6]