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Henderickx 11 Alcatel-Lucent 12 February 29, 2016 14 FIB Reduction in Virtual Subnet 15 draft-ietf-bess-virtual-subnet-fib-reduction-02 17 Abstract 19 Virtual Subnet is a BGP/MPLS IP VPN-based subnet extension solution 20 which is intended for building Layer3 network virtualization overlays 21 within and/or between data centers. This document describes a 22 mechanism for reducing the FIB size of PE routers in the Virtual 23 Subnet context. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on September 1, 2016. 42 Copyright Notice 44 Copyright (c) 2016 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 61 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 62 3. Solution Description . . . . . . . . . . . . . . . . . . . . 3 63 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 64 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 65 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 66 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 67 7.1. Normative References . . . . . . . . . . . . . . . . . . 5 68 7.2. Informative References . . . . . . . . . . . . . . . . . 5 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 71 1. Introduction 73 Virtual Subnet [I-D.ietf-bess-virtual-subnet] is a BGP/MPLS IP VPN 74 [RFC4364] -based subnet extension solution which is intended for 75 building Layer3 network virtualization overlays within and/or across 76 data centers. In the Virtual Subnet context, since CE host routes of 77 a given VPN instance need to be exchanged among PE routers 78 participating in that VPN instance, the resulting forwarding table 79 (a.k.a. FIB) size of PE routers may become a big concern in large- 80 scale data center environment where they may need to install a huge 81 amount of host routes into their forwarding tables. In some cases 82 where host routes need to be maintained on the control plane, it 83 needs a method to reduce the FIB size of PE routers without any 84 change to the RIB and the routing table. Therefore, this document 85 proposes a very simple mechanism for reducing the FIB size of PE 86 routers. The basic idea of this mechanism is: Those host routes 87 learnt from remote PE routers are selectively installed into the FIB 88 while the remaining routes including local CE host routes are 89 installed into the FIB by default as before. 91 1.1. Requirements Language 93 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 94 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 95 document are to be interpreted as described in RFC 2119 [RFC2119]. 97 2. Terminology 99 This memo makes use of the terms defined in [RFC4364]. 101 3. Solution Description 103 +----------+ 104 +----+PE/RR(APR)+----+ 105 +------------------+ | +----------+ | +---------------_--+ 106 |VPN_A:192.0.2.1/24| | | |VPN_A:192.0.2.1/24| 107 | \ | | | | / | 108 | +------+ \ ++---+-+ +-+---++/ +------+ | 109 | |Host A+------_+ PE-1 | | PE-2 +------+Host B| | 110 | +------+\ ++-+-+-+ +-+-+-++ /+------+ | 111 | 192.0.2.2/24 | | | | | | 192.0.2.3/24 | 112 | | | | | | | | 113 | DC West | | | IP/MPLS Backbone | | | DC East | 114 +------------------+ | | | | +------------------+ 115 | +--------------------+ | 116 | | 117 VRF: V VRF:V 118 +--------------+---------+--------+------+ +--------------+---------+--------+------+ 119 | Prefix | Nexthop |Protocol|In_FIB| | Prefix | Nexthop |Protocol|In_FIB| 120 +--------------+---------+--------+------+ +--------------+---------+--------+------+ 121 |192.0.2.1/32 |127.0.0.1| Direct | Yes | |192.0.2.1/32 |127.0.0.1| Direct | Yes | 122 +--------------+---------+--------+------+ +--------------+---------+--------+------+ 123 |192.0.2.2/32 |192.0.2.2| Direct | Yes | |192.0.2.2/32 | PE-1 | IBGP | No | 124 +--------------+---------+--------+------+ +--------------+---------+--------+------+ 125 |192.0.2.3/32 | PE-2 | IBGP | No | |192.0.2.3/32 |192.0.2.3| Direct | Yes | 126 +--------------+---------+--------+------+ +--------------+---------+--------+------+ 127 |192.0.2.0/25 | APR | IBGP | Yes | |192.0.2.0/25 | APR | IBGP | Yes | 128 +--------------+---------+--------+------+ +--------------+---------+--------+------+ 129 |192.0.2.128/25| APR | IBGP | Yes | |192.0.2.128/25| APR | IBGP | Yes | 130 +--------------+---------+--------+------+ +--------------+---------+--------+------+ 131 |192.0.2.0/24 |192.0.2.1| Direct | Yes | |192.0.2.0/24 |192.0.2.1| Direct | Yes | 132 +--------------+---------+--------+------+ +--------------+---------+--------+------+ 134 Figure 1: Selective FIB Installation Example 136 To reduce the FIB size of PE routers, the selective FIB installation 137 concept as described in [I-D.ietf-grow-va] can be leveraged in the 138 Virtual Subnet context. Take the VPN instance demonstrated in 139 Figure 1 as an example, the FIB reduction procedures are described as 140 follows: 142 1. Multiple more specific prefixes (e.g., 192.0.2.0/25 and 143 192.0.2.128/25) corresponding to an extended subnet (i.e., 144 192.0.2.0/24) are specified as Virtual Prefixes (VPs). 146 Meanwhile, one or more PE routers (or route reflectors) are 147 configured as Aggregation Point Routers (APR) for each VP. The 148 APRs for a given VP would install a null route to that VP while 149 propagating a route to that VP via the L3VPN signaling. 151 2. For a given host route in the routing table which is learnt from 152 any remote PE router, PE routers which are non-APRs for any VP 153 covering this host route would not install it into the FIB by 154 default. In contrast, PE routers (or route reflectors) which are 155 APRs for any VP covering that host route would install it into 156 the FIB. If one or more particular remote host routes need to be 157 installed by non-APR PE routers by default as well for whatever 158 reasons, the best way to realize such goal is to attach a special 159 extended communities attribute to those particular host routes 160 either by originating PE routers or by route reflectors. Upon 161 receiving any host routes attached with the above extended 162 communities attribute, non-APR PE routers SHOULD install them by 163 default. 165 3. Upon receiving a packet destined for a given remote CE host, if 166 no host route for that CE host is found in the FIB, the ingress 167 PE router would forward the packet to a given APR according to 168 the longest-matching VP route, which in turn forwards the packet 169 to the final egress PE router. In this way, the FIB size of 170 those non-APR PE routers can be greatly reduced at the potential 171 cost of path stretch. 173 In order to forward packets destined for remote CE hosts directly to 174 the final egress PE routers without the potential path stretch 175 penalty, non-APR PE routers could perform on-demand FIB installation 176 for remote host routes which are available in the routing table. For 177 example, upon receiving an ARP request or Neighbor Solicitation (NS) 178 message from a local CE host, the non-APR PE router would perform a 179 lookup in the routing table. If a corresponding host route for the 180 target host is found but not yet installed into the FIB, it would be 181 installed into the FIB. Another possible way to trigger on-demand 182 FIB installation is as follows: when receiving a packet whose 183 longest-matching FIB entry is a particular VP route learnt from any 184 APR, a copy of this packet would be sent to the control plane while 185 this original packet is forwarded as normal. The above copy sent to 186 the control plane would trigger a lookup in the routing table. If a 187 corresponding host route is found but not yet installed into the FIB, 188 it would be installed into the FIB. To provide robust protection 189 against DoS attacks on the control plane, rate-limiting of the above 190 packets sent to the control plane MUST be enabled. Those FIB entries 191 for remote CE host routes which are on-demand installed on non-APR PE 192 routers would expire if not used for a certain period of time. 194 4. Acknowledgements 196 The authors would like to thank Susan Hares, Yongbing Fan, Robert 197 Raszuk and Bruno Decraene for their valuable suggestions on this 198 document. 200 5. IANA Considerations 202 The type value for the Extended Communities Attributes as described 203 in this doc is required to be allocated by the IANA. 205 6. Security Considerations 207 Those security considerations as described in 208 [I-D.ietf-bess-virtual-subnet] are applicable to this document. This 209 document does not introduce any new security risk. 211 7. References 213 7.1. Normative References 215 [I-D.ietf-bess-virtual-subnet] 216 Xu, X., Jacquenet, C., Raszuk, R., Boyes, T., and B. Fee, 217 "Virtual Subnet: A BGP/MPLS IP VPN-based Subnet Extension 218 Solution", draft-ietf-bess-virtual-subnet-07 (work in 219 progress), December 2015. 221 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 222 Requirement Levels", BCP 14, RFC 2119, 223 DOI 10.17487/RFC2119, March 1997, 224 . 226 [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private 227 Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 228 2006, . 230 7.2. Informative References 232 [I-D.ietf-grow-va] 233 Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and 234 L. Zhang, "FIB Suppression with Virtual Aggregation", 235 draft-ietf-grow-va-06 (work in progress), December 2011. 237 Authors' Addresses 238 Xiaohu Xu 239 Huawei 241 Email: xuxiaohu@huawei.com 243 Christian Jacquenet 244 Orange 246 Email: christian.jacquenet@orange.com 248 Truman Boyes 249 Bloomberg LP 251 Email: tboyes@bloomberg.net 253 Brendan Fee 254 Extreme Networks 256 Email: bfee@enterasys.com 258 Wim Henderickx 259 Alcatel-Lucent 261 Email: wim.henderickx@alcatel-lucent.com