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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group James Uttaro 2 Internet Draft AT&T 3 Updates: 5575 Clarence Filsfils 4 Intended Status: Proposed Standard David Smith 5 Expiration Date: September 21, 2016 Juan Alcaide 6 Cisco 7 Pradosh Mohapatra 8 Sproute Networks 9 March 21, 2016 11 Revised Validation Procedure for BGP Flow Specifications 12 draft-ietf-idr-bgp-flowspec-oid-03 14 Abstract 16 This document describes a modification to the validation procedure 17 defined in RFC 5575 for the dissemination of BGP flow specifications. 18 RFC 5575 requires that the originator of the flow specification 19 matches the originator of the best-match unicast route for the 20 destination prefix embedded in the flow specification. This allows 21 only BGP speakers within the data forwarding path (such as autonomous 22 system border routers) to originate BGP flow specifications. Though 23 it is possible to disseminate such flow specifications directly from 24 border routers, it may be operationally cumbersome in an autonomous 25 system with a large number of border routers having complex BGP 26 policies. The modification proposed herein enables flow 27 specifications to be originated from a centralized BGP route 28 controller. 30 Status of this Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF), its areas, and its working groups. Note that 37 other groups may also distribute working documents as Internet- 38 Drafts. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 44 The list of current Internet-Drafts can be accessed at 45 http://www.ietf.org/ietf/1id-abstracts.txt. 47 The list of Internet-Draft Shadow Directories can be accessed at 48 http://www.ietf.org/shadow.html. 50 This Internet-Draft will expire on September 21, 2016. 52 Copyright Notice 54 Copyright (c) 2016 IETF Trust and the persons identified as the 55 document authors. All rights reserved. 57 This document is subject to BCP 78 and the IETF Trust's Legal 58 Provisions Relating to IETF Documents 59 (http://trustee.ietf.org/license-info) in effect on the date of 60 publication of this document. Please review these documents 61 carefully, as they describe your rights and restrictions with respect 62 to this document. Code Components extracted from this document must 63 include Simplified BSD License text as described in Section 4.e of 64 the Trust Legal Provisions and are provided without warranty as 65 described in the Simplified BSD License. 67 Table of Contents 69 1 Specification of Requirements ...................... 3 70 2 Motivation ......................................... 3 71 3 Introduction ....................................... 5 72 4 Revised Validation Procedure ....................... 6 73 5 Security Considerations ............................ 7 74 6 IANA Considerations ................................ 7 75 7 Normative References ............................... 7 76 8 Acknowledgements ................................... 8 77 9 Authors' Addresses ................................. 8 79 1. Specification of Requirements 81 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 82 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 83 document are to be interpreted as described in [RFC2119]. 85 2. Motivation 87 Step (a) of the validation procedure in [RFC5575], section 6 is 88 defined with the underlying assumption that the flow specification 89 NLRI traverses the same path, in the inter-domain and intra-domain 90 route distribution graph, as that of the longest-match unicast route 91 for the destination prefix embedded in the flow specification. 93 In the case of inter-domain traffic filtering, for example, the flow 94 specification originator at the egress border routers of ASN1 (RTR-D 95 and RTR-E in figure 1) matches the EBGP neighbor that advertised the 96 longest match destination prefix (RTR-F and RTR-G respectively). 97 Similarly, at the ingress border routers of ASN1 (RTR-A and RTR-B in 98 figure 1), the flow specification originator matches the egress IBGP 99 border routers that had advertised the unicast route for the best- 100 match destination prefix (RTR-D and RTR-E respectively). This is true 101 even when ingress border routers select paths from different egress 102 border routers as best path based upon IGP distance (as an example, 103 RTR-A chooses RTR-D's path as best; RTR-B chooses RTR-E as the best 104 path). 106 / - - - - - - - - - - - - - - 107 | ASN1 | 108 +-------+ +-------+ 109 | | | | | | 110 | RTR-A | | RTR-B | 111 | | | | | | 112 +-------+ +-------+ 113 | \ / | 114 IBGP \ / IBGP 115 | \ / | 116 +-------+ 117 | | | | 118 | RTR-C | 119 | | RC | | 120 +-------+ 121 | / \ | 122 / \ 123 | IBGP / \ IBGP | 124 +-------+ +-------+ 125 | | RTR-D | | RTR-E | | 126 | | | | 127 | | | | | | 128 +-------+ +-------+ 129 | | | | 130 - - -|- - - - - - - - -|- - -/ 131 | EBGP EBGP | 132 - - -|- - - - - - - - -|- - -/ 133 | | | | 134 +-------+ +-------+ 135 | | | | | | 136 | RTR-F | | RTR-G | 137 | | | | | | 138 +-------+ +-------+ 139 | ASN2 | 140 / - - - - - - - - - - - - - - 142 Figure 1 144 It is highly desirable that each ASN is able to protect itself 145 independently from network security attacks using the BGP flow 146 specification NLRI for intra-domain purposes only. Network operators 147 often deploy a dedicated Security Operations Center (SOC) within 148 their ASN to monitor and detect such security attacks. To mitigate 149 attacks in a scalable intra-domain manner, operators require the 150 ability to originate intra-domain flow specification NLRIs from a 151 central BGP route controller (or router reflector per [RFC4456]) that 152 is not within the data forwarding plane. In this way, operators can 153 direct border routers within their ASN with specific attack 154 mitigation actions (drop the traffic, forward to a clean-pipe center, 155 etc.). To originate a flow specification NLRI, a central BGP route 156 controller (or route reflector) must set itself as the originator in 157 the flowspec NLRI. This is necessary given the route controller is 158 originating the flow specification not reflecting it, and to avoid 159 the complexity of having to determine the egress border router whose 160 path was chosen as the best in each of the ingress border routers. It 161 thus becomes necessary to modify step (a) of the RFC 5575 validation 162 procedure such that an IBGP peer that is not within the data 163 forwarding plane may originate flow specification NLRIs. 165 3. Introduction 167 RFC 5575 defined a new BGP capability that can be used to distribute 168 traffic flow specifications amongst BGP speakers in support of 169 traffic filtering. The primary intention of RFC 5575 is to enable 170 downstream autonomous systems to signal traffic filtering policies to 171 upstream autonomous systems. In this way, traffic is filtered closer 172 to the source and the upstream autonomous system(s) avoid carrying 173 the traffic to the downstream autonomous system only to be discarded. 174 RFC 5575 also enables more granular traffic filtering based upon 175 upper layer protocol information (e.g., protocol port numbers) as 176 opposed to coarse IP destination prefix-based filtering. Flow 177 specification NLRIs received from a BGP peer are subject to validity 178 checks before being considered feasible and subsequently installed 179 within the respective Adj-RIB-In. The validation procedure defined 180 within RFC 5575 requires that the originator of the flow 181 specification NLRI matches the originator of the best-match unicast 182 route for the destination prefix embedded in the flow specification. 183 This allows only BGP speakers [RFC4271] within the data forwarding 184 path (such as autonomous system border routers) to originate BGP flow 185 specification NLRIs. Though it is possible to disseminate such flow 186 specification NLRIs directly from border routers, it may be 187 operationally cumbersome in an autonomous system with a large number 188 of border routers having complex BGP policies. This document 189 describes a modification to the RFC 5575 validation procedure 190 allowing flow specification NLRIs to be originated from a centralized 191 BGP route controller within the local autonomous system that is 192 neither in the data forwarding path nor serving as a BGP route 193 reflector [RFC4456]. While the proposed modification cannot be used 194 for inter-domain coordination of traffic filtering, it greatly 195 simplifies distribution of intra-domain traffic filtering policies in 196 an autonomous system with a large number of border routers having 197 complex BGP policies. By relaxing the validation procedure for IBGP, 198 the proposed modification allows flow specifications to be 199 distributed in a standard and scalable manner throughout an 200 autonomous system. 202 4. Revised Validation Procedure 204 Step (a) of the validation procedure specified in RFC 5575, section 6 205 is redefined as follows: 207 a) One of the following conditions MUST hold true: 208 o The originator of the flow specification matches the 209 originator of the best-match unicast route for the 210 destination prefix embedded in the flow specification. 211 o The AS_PATH and AS4_PATH attribute of the flow 212 specification are empty. 213 o The AS_PATH and AS4_PATH attribute of the flow 214 specification does not contain AS_SET and AS_SEQUENCE 215 segments. 217 An empty AS_PATH and AS4_PATH attribute indicates per [RFC4271] that 218 the flow specification NLRI originated in the same autonomous system 219 as the local BGP speaker. Similarly, lack of AS_SET and AS_SEQUENCE 220 segments within an AS_PATH and AS4_PATH attribute that is not empty 221 indicates that the flow specification NLRI originated in the same 222 autonomous system as the local BGP speaker but that the autonomous 223 system includes a BGP confederation [RFC5065]. With this proposed 224 modification to the RFC 5575 validation procedure, it is now possible 225 for an IBGP peer that is not within the data forwarding path to 226 originate flow specification NLRIs. This applies with and without the 227 presence of a BGP confederation within the autonomous system. 229 Further, RFC 5575 states that "BGP (flow specification) 230 implementations MUST also enforce that AS_PATH attribute of a route 231 received via the External Border Gateway Protocol (eBGP) contains the 232 neighboring AS in the left-most position of the AS_PATH attribute". 233 This rule is not valid for all topologies. For example, it prevents 234 exchange of BGP flow specification NLRIs at Internet exchanges with 235 BGP route servers. Therefore, this document also redefines the RFC 236 5575 AS_PATH and AS4_PATH validation procedure referenced above as 237 follows. 239 BGP flow specification implementations MUST enforce that the last AS 240 added within the AS_PATH and AS4_PATH attribute of a EBGP learned 241 flow specification NLRI MUST match the last AS added within the 242 AS_PATH and AS4_PATH attribute of the best-match unicast route for 243 the destination prefix embedded in the flow specification. This 244 proposed modification enables the exchange of BGP flow specification 245 NLRIs at Internet exchanges with BGP route servers while at the same 246 time, for security reasons, prevents an EBGP peer from advertising an 247 inter-domain flow specification for a destination prefix that it does 248 not provide reachability information for. Note, comparing only the 249 last ASNs is sufficient for EBGP learned flow specification NLRIs. 251 Requiring a full AS_PATH and AS4_PATH match would limit origination 252 of inter-domain flow specifications to the origin (or first) AS of 253 the best-match unicast route for the destination prefix embedded in 254 the flow specification only. As such, a full AS_PATH and AS4_PATH 255 validity check may prevent transit ASNs from originating inter-domain 256 flow specifications which is not desirable. 258 5. Security Considerations 260 No new security issues are introduced by relaxing the validation 261 procedure for IBGP learned flow specifications. With this proposal, 262 the security characteristics of BGP flow specifications remain 263 equivalent to the existing security properties of BGP unicast 264 routing. Traffic flow specifications learned from IBGP peers are 265 trusted, hence, its not required to validate that the originator of 266 an intra-domain traffic flow specification matches the originator of 267 the best-match unicast route for the flow destination prefix. 268 Conversely, this proposal continues to enforce the validation 269 procedure for EBGP learned traffic flow specifications. In this way, 270 the security properties of RFC 5575 are maintained such that an EBGP 271 peer cannot cause a denial-of-service attack by advertising an 272 inter-domain flow specification for a destination prefix that it does 273 not provide reachability information for. 275 6. IANA Considerations 277 This document has no actions for IANA. 279 7. Normative References 281 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 282 Requirement Levels", BCP 14, RFC 2119, March 1997. 284 [RFC4271] Rekhter, Y., Li, T., and Hares, S., "A Border Gateway 285 Protocol 4 (BGP-4)", RFC 4271, March 2006. 287 [RFC4456] Bates, T., Chen, E., and Chandra, R., "BGP Route 288 Reflection: An Alternative to Full Mesh Internal BGP (IBGP)", RFC 289 4456, April 2006. 291 [RFC5065] Traina, P., McPherson, D., and Scudder, J., "Autonomous 292 System Confederations for BGP", August 2007. 294 [RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J., 295 and McPherson, D., "Dissemination of Flow Specification Rules", RFC 296 5575, August 2009. 298 8. Acknowledgements 300 The authors would like to thank Han Nguyen for his direction on this 301 work as well as Waqas Alam, Keyur Patel, Robert Raszuk, Eric Rosen 302 and Shyam Sethuram for their review comments. 304 9. Authors' Addresses 306 James Uttaro 307 AT&T 308 200 S. Laurel Avenue 309 Middletown, NJ 07748 310 USA 312 Email: ju1738@att.com 314 Juan Alcaide 315 Cisco 316 7100 Kit Creek Road 317 Research Triangle Park, NC 27709 318 USA 320 Email: jalcaide@cisco.com 322 Clarence Filsfils 323 Cisco 324 Brussels 1000 325 BE 327 Email: cf@cisco.com 328 David Smith 329 Cisco 330 111 Wood Avenue South 331 Iselin, NJ 08830 332 USA 334 Email: djsmith@cisco.com 336 Pradosh Mohapatra 337 Sproute Networks 339 Email: mpradosh@yahoo.com