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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 Pradosh Mohapatra 5 Expiration Date: July 2013 David Smith 6 Cisco 7 January 22, 2013 9 Revised Validation Procedure for BGP Flow Specifications 10 draft-ietf-idr-bgp-flowspec-oid-01 12 Abstract 14 This document describes a modification to the validation procedure 15 defined in RFC 5575 for the dissemination of BGP flow specifications. 16 RFC 5575 requires that the originator of the flow specification 17 matches the originator of the best-match unicast route for the 18 destination prefix embedded in the flow specification. This allows 19 only BGP speakers within the data forwarding path (such as autonomous 20 system border routers) to originate BGP flow specifications. Though 21 it is possible to disseminate such flow specifications directly from 22 border routers, it may be operationally cumbersome in an autonomous 23 system with a large number of border routers having complex BGP 24 policies. The modification proposed herein enables flow 25 specifications to be originated from a centralized BGP route 26 controller. 28 Status of this Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF), its areas, and its working groups. Note that 35 other groups may also distribute working documents as Internet- 36 Drafts. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 The list of current Internet-Drafts can be accessed at 44 http://www.ietf.org/ietf/1id-abstracts.txt. 46 The list of Internet-Draft Shadow Directories can be accessed at 47 http://www.ietf.org/shadow.html. 49 This Internet-Draft will expire on July 1, 2013. 51 Copyright Notice 53 Copyright (c) 2013 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (http://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the Simplified BSD License. 66 Table of Contents 68 1 Specification of Requirements ...................... 2 69 2 Motivation ......................................... 3 70 3 Introduction ....................................... 5 71 4 Revised Validation Procedure ....................... 6 72 5 Security Considerations ............................ 7 73 6 IANA Considerations ................................ 7 74 7 Normative References ............................... 7 75 8 Acknowledgements ................................... 8 76 9 Authors' Addresses ................................. 8 78 1. Specification of Requirements 80 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 81 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 82 document are to be interpreted as described in [RFC2119]. 84 2. Motivation 86 Step (a) of the validation procedure in [RFC5575], section 6 is 87 defined with the underlying assumption that the flow specification 88 NLRI traverses the same path, in the inter-domain and intra-domain 89 route distribution graph, as that of the longest-match unicast route 90 for the destination prefix embedded in the flow specification. 92 In the case of inter-domain traffic filtering, for example, the flow 93 specification originator at the egress border routers of ASN1 (RTR-D 94 and RTR-E in figure 1) matches the EBGP neighbor that advertised the 95 longest match destination prefix (RTR-F and RTR-G respectively). 96 Similarly, at the ingress border routers of ASN1 (RTR-A and RTR-B in 97 figure 1), the flow specification originator matches the egress IBGP 98 border routers that had advertised the unicast route for the best- 99 match destination prefix (RTR-D and RTR-E respectively). This is true 100 even when ingress border routers select paths from different egress 101 border routers as best path based upon IGP distance (as an example, 102 RTR-A chooses RTR-D's path as best; RTR-B chooses RTR-E as the best 103 path). 105 / - - - - - - - - - - - - - - 106 | ASN1 | 107 +-------+ +-------+ 108 | | | | | | 109 | RTR-A | | RTR-B | 110 | | | | | | 111 +-------+ +-------+ 112 | \ / | 113 IBGP \ / IBGP 114 | \ / | 115 +-------+ 116 | | | | 117 | RTR-C | 118 | | RC | | 119 +-------+ 120 | / \ | 121 / \ 122 | IBGP / \ IBGP | 123 +-------+ +-------+ 124 | | RTR-D | | RTR-E | | 125 | | | | 126 | | | | | | 127 +-------+ +-------+ 128 | | | | 129 - - -|- - - - - - - - -|- - -/ 130 | EBGP EBGP | 131 - - -|- - - - - - - - -|- - -/ 132 | | | | 133 +-------+ +-------+ 134 | | | | | | 135 | RTR-F | | RTR-G | 136 | | | | | | 137 +-------+ +-------+ 138 | ASN2 | 139 / - - - - - - - - - - - - - - 141 Figure 1 143 It is highly desirable that each ASN is able to protect itself 144 independently from network security attacks using the BGP flow 145 specification NLRI for intra-domain purposes only. Network operators 146 often deploy a dedicated Security Operations Center (SOC) within 147 their ASN to monitor and detect such security attacks. To mitigate 148 attacks in a scalable intra-domain manner, operators require the 149 ability to originate intra-domain flow specification NLRIs from a 150 central BGP route controller (or router reflector per [RFC4456]) that 151 is not within the data forwarding plane. In this way, operators can 152 direct border routers within their ASN with specific attack 153 mitigation actions (drop the traffic, forward to a clean-pipe center, 154 etc.). To originate a flow specification NLRI, a central BGP route 155 controller (or route reflector) must set itself as the originator in 156 the flowspec NLRI. This is necessary given the route controller is 157 originating the flow specification not reflecting it, and to avoid 158 the complexity of having to determine the egress border router whose 159 path was chosen as the best in each of the ingress border routers. It 160 thus becomes necessary to modify step (a) of the RFC 5575 validation 161 procedure such that an IBGP peer that is not within the data 162 forwarding plane may originate flow specification NLRIs. 164 3. Introduction 166 RFC 5575 defined a new BGP capability that can be used to distribute 167 traffic flow specifications amongst BGP speakers in support of 168 traffic filtering. The primary intention of RFC 5575 is to enable 169 downstream autonomous systems to signal traffic filtering policies to 170 upstream autonomous systems. In this way, traffic is filtered closer 171 to the source and the upstream autonomous system(s) avoid carrying 172 the traffic to the downstream autonomous system only to be discarded. 173 RFC 5575 also enables more granular traffic filtering based upon 174 upper layer protocol information (e.g., protocol port numbers) as 175 opposed to coarse IP destination prefix-based filtering. Flow 176 specification NLRIs received from a BGP peer are subject to validity 177 checks before being considered feasible and subsequently installed 178 within the respective Adj-RIB-In. The validation procedure defined 179 within RFC 5575 requires that the originator of the flow 180 specification NLRI matches the originator of the best-match unicast 181 route for the destination prefix embedded in the flow specification. 182 This allows only BGP speakers [RFC4271] within the data forwarding 183 path (such as autonomous system border routers) to originate BGP flow 184 specification NLRIs. Though it is possible to disseminate such flow 185 specification NLRIs directly from border routers, it may be 186 operationally cumbersome in an autonomous system with a large number 187 of border routers having complex BGP policies. This document 188 describes a modification to the RFC 5575 validation procedure 189 allowing flow specification NLRIs to be originated from a centralized 190 BGP route controller within the local autonomous system that is 191 neither in the data forwarding path nor serving as a BGP route 192 reflector [RFC4456]. While the proposed modification cannot be used 193 for inter-domain coordination of traffic filtering, it greatly 194 simplifies distribution of intra-domain traffic filtering policies in 195 an autonomous system with a large number of border routers having 196 complex BGP policies. By relaxing the validation procedure for IBGP, 197 the proposed modification allows flow specifications to be 198 distributed in a standard and scalable manner throughout an 199 autonomous system. 201 4. Revised Validation Procedure 203 Step (a) of the validation procedure specified in RFC 5575, section 6 204 is redefined as follows: 206 a) One of the following conditions MUST hold true: 207 o The originator of the flow specification matches the 208 originator of the best-match unicast route for the 209 destination prefix embedded in the flow specification. 210 o The AS_PATH and AS4_PATH attribute of the flow 211 specification are empty. 212 o The AS_PATH and AS4_PATH attribute of the flow 213 specification does not contain AS_SET and AS_SEQUENCE 214 segments. 216 An empty AS_PATH and AS4_PATH attribute indicates per [RFC4271] that 217 the flow specification NLRI originated in the same autonomous system 218 as the local BGP speaker. Similarly, lack of AS_SET and AS_SEQUENCE 219 segments within an AS_PATH and AS4_PATH attribute that is not empty 220 indicates that the flow specification NLRI originated in the same 221 autonomous system as the local BGP speaker but that the autonomous 222 system includes a BGP confederation [RFC5065]. With this proposed 223 modification to the RFC 5575 validation procedure, it is now possible 224 for an IBGP peer that is not within the data forwarding path to 225 originate flow specification NLRIs. This applies with and without the 226 presence of a BGP confederation within the autonomous system. 228 Further, RFC 5575 states that "BGP (flow specification) 229 implementations MUST also enforce that AS_PATH attribute of a route 230 received via the External Border Gateway Protocol (eBGP) contains the 231 neighboring AS in the left-most position of the AS_PATH attribute". 232 This rule is not valid for all topologies. For example, it prevents 233 exchange of BGP flow specification NLRIs at Internet exchanges with 234 BGP route servers. Therefore, this document also redefines the RFC 235 5575 AS_PATH and AS4_PATH validation procedure referenced above as 236 follows. 238 BGP flow specification implementations MUST enforce that the last AS 239 added within the AS_PATH and AS4_PATH attribute of a EBGP learned 240 flow specification NLRI MUST match the last AS added within the 241 AS_PATH and AS4_PATH attribute of the best-match unicast route for 242 the destination prefix embedded in the flow specification. This 243 proposed modification enables the exchange of BGP flow specification 244 NLRIs at Internet exchanges with BGP route servers while at the same 245 time, for security reasons, prevents an EBGP peer from advertising an 246 inter-domain flow specification for a destination prefix that it does 247 not provide reachability information for. Note, comparing only the 248 last ASNs is sufficient for EBGP learned flow specification NLRIs. 249 Requiring a full AS_PATH and AS4_PATH match would limit origination 250 of inter-domain flow specifications to the origin (or first) AS of 251 the best-match unicast route for the destination prefix embedded in 252 the flow specification only. As such, a full AS_PATH and AS4_PATH 253 validity check may prevent transit ASNs from originating inter-domain 254 flow specifications which is not desirable. 256 5. Security Considerations 258 No new security issues are introduced by relaxing the validation 259 procedure for IBGP learned flow specifications. With this proposal, 260 the security characteristics of BGP flow specifications remain 261 equivalent to the existing security properties of BGP unicast 262 routing. Traffic flow specifications learned from IBGP peers are 263 trusted, hence, its not required to validate that the originator of 264 an intra-domain traffic flow specification matches the originator of 265 the best-match unicast route for the flow destination prefix. 266 Conversely, this proposal continues to enforce the validation 267 procedure for EBGP learned traffic flow specifications. In this way, 268 the security properties of RFC 5575 are maintained such that an EBGP 269 peer cannot cause a denial-of-service attack by advertising an 270 inter-domain flow specification for a destination prefix that it does 271 not provide reachability information for. 273 6. IANA Considerations 275 This document has no actions for IANA. 277 7. Normative References 279 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 280 Requirement Levels", BCP 14, RFC 2119, March 1997. 282 [RFC4271] Rekhter, Y., Li, T., and Hares, S., "A Border Gateway 283 Protocol 4 (BGP-4)", RFC 4271, January 2006. 285 [RFC4456] Bates, T., Chen, E., and Chandra, R., "BGP Route 286 Reflection: An Alternative to Full Mesh Internal BGP (IBGP)", RFC 287 4456, April 2006. 289 [RFC5065] Traina, P., McPherson, D., and Scudder, J., "Autonomous 290 System Confederations for BGP", August 2007. 292 [RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J., 293 and McPherson, D., "Dissemination of Flow Specification Rules", RFC 294 5575, August 2009. 296 8. Acknowledgements 298 The authors would like to thank Han Nguyen for his direction on this 299 work as well as Waqas Alam, Keyur Patel, Robert Raszuk, Eric Rosen 300 and Shyam Sethuram for their review comments. 302 9. Authors' Addresses 304 James Uttaro 305 AT&T 306 200 S. Laurel Avenue 307 Middletown, NJ 07748 308 USA 310 Email: ju1738@att.com 312 Clarence Filsfils 313 Cisco 314 Brussels 1000 315 BE 317 Email: cf@cisco.com 319 Pradosh Mohapatra 320 Cisco 321 170 W. Tasman Drive 322 San Jose, CA 95134 323 USA 325 Email: pmohapat@cisco.com 326 David J. Smith 327 Cisco 328 111 Wood Avenue South 329 Iselin, NJ 08830 330 USA 332 E-mail: djsmith@cisco.com