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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IDR Workgroup M. Zheng 3 Internet-Draft Ciena 4 Intended status: Standards Track A. Lindem 5 Expires: May 5, 2021 Cisco Systems 6 J. Haas 7 Juniper Networks, Inc. 8 A. Fu 9 Bloomberg L.P. 10 November 1, 2020 12 BGP BFD Strict-Mode 13 draft-ietf-idr-bgp-bfd-strict-mode-04 15 Abstract 17 This document specifies extensions to RFC4271 BGP-4 that enable a BGP 18 speaker to negotiate additional Bidirectional Forwarding Detection 19 (BFD) extensions using a BGP capability. This BFD capability enables 20 a BGP speaker to prevent a BGP session from being established until a 21 BFD session is established. It is referred to as BGP BFD "strict- 22 mode". BGP BFD strict-mode will be supported when both the local 23 speaker and its remote peer are BFD strict-mode capable. 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 https://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 May 5, 2021. 42 Copyright Notice 44 Copyright (c) 2020 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 (https://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 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 61 3. BFD Strict-Mode Capability . . . . . . . . . . . . . . . . . 3 62 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3 63 5. Manageability Considerations . . . . . . . . . . . . . . . . 4 64 6. Security Considerations . . . . . . . . . . . . . . . . . . . 4 65 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 66 8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 4 67 9. Normative References . . . . . . . . . . . . . . . . . . . . 5 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 70 1. Introduction 72 Bidirectional Forwarding Detection BFD [RFC5882] enables routers to 73 monitor data plane connectivity and to detect faults in the 74 bidirectional forwarding path between them. This capability is 75 leveraged by routing protocols such as BGP [RFC4271] to rapidly react 76 to topology changes in the face of path failures. 78 The BFD interaction with BGP is specified in Section 10.2 of 79 [RFC5882]. When BFD is enabled for a BGP neighbor, faults in the 80 bidirectional forwarding detected by BFD result in session 81 termination. It is possible in some failure scenarios for the 82 network to be in a state such that a BGP session may be established 83 but a BFD session cannot be established. In some other scenarios, it 84 may be possible to establish a BGP session, but a degraded or poor- 85 quality link may result in the corresponding BFD session going up and 86 down frequently. 88 To avoid situations which result in routing churn and to minimize the 89 impact of network interruptions, it will be beneficial to disallow 90 BGP to establish a session until BFD session is successfully 91 established and has stabilized. We refer to this mode of operation 92 as BGP BFD "strict-mode". However, always using "strict-mode" would 93 preclude BGP operation in an environment where not all routers 94 support BFD strict-mode or have BFD enabled. This document defines 95 BGP "strict-mode" operation as preventing BGP session establishment 96 until both the local and remove speakers have a stable BFD session. 98 The document also specifies the BGP protocol extensions for BGP 99 capability [RFC5492] for announcing BFD parameters including a BGP 100 speaker's support for "strict-mode", i.e., requiring a BFD session 101 for BGP session establishment. 103 2. Requirements Language 105 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 106 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 107 "OPTIONAL" in this document are to be interpreted as described in BCP 108 14 [RFC2119] [RFC8174] when, and only when, they appear in all 109 capitals, as shown here. 111 3. BFD Strict-Mode Capability 113 The BGP Strict-Mode Capability [RFC5492] will allow a BGP speaker's 114 to advertise this capability. The capability is defined as follows: 116 Capability code: TBD 118 Capability length: 0 octets 120 4. Operation 122 A BGP speaker which supports capabilities advertisement and has BFD 123 strict-mode enabled MUST include the BFD strict-mode capability. 125 A BGP speaker which supports the BFD Strict-Mode capability, examines 126 the list of capabilities present in the capabilities that the speaker 127 receives from its peer. If both the local and remote BGP speakers 128 include the BFD strict-mode capability, the BGP finite state machine 129 does not transition to the Established state from OpenSent or 130 OpenConfirm state [RFC4271] until the BFD session is in the Up state 131 (see below for AdminDown state). This means that a KEEPALIVE message 132 is not sent nor is the KeepaliveTimer set. 134 If the BFD session does not transition to the Up state, and the 135 HoldTimer has been negotiated to a non-zero value, the BGP FSM will 136 close the session appropriately. If the HoldTimer has been 137 negotiated to a zero value, the session should be closed after a time 138 of X. This time X is referred as "BGP BFD Hold time". The proposed 139 default BGP BFD Hold time value is 30 seconds. The BGP BFD Hold time 140 value is configurable. 142 If BFD session is in the AdminDown state, then the BGP finite state 143 machine will proceed normally without input from BFD. This means 144 that BFD session "AdminDown" state WILL NOT prevent the BGP state 145 transition to Established state from OpenConfirm. 147 Once the BFD session has transitioned to the Up state, the BGP FSM 148 may proceed to transition to the Established state from the OpenSent 149 or OpenConfirm state appropriately. I.e. a KEEPALIVE message is 150 sent, and the KeepaliveTimer is started. 152 If either BGP peer has not advertised the BFD Strict-Mode Capability, 153 then a BFD session WILL NOT be required for the BGP session to reach 154 Established state. This does not preclude usage of BFD after BGP 155 session establishment [RFC5882]. 157 If BFD is disabled for a BGP peer and the BGP session state is being 158 held in OpenSent or OpenConfirm state, then the BGP will close 159 session, and start a new TCP connect. 161 5. Manageability Considerations 163 Auto-configuration is possible for the enabling BGP BFD Strict-Mode. 164 However, the configuration automation is out of the scope of this 165 document. 167 A BGP NOTIFICATION message Subcode indicating BFD Hold timer 168 expiration may be required for network management. (To be discussed 169 in the next revision of this document.) 171 6. Security Considerations 173 The mechanism defined in this document interacts with the BGP finite 174 state machine when so configured. The security considerations of BFD 175 thus, become considerations for BGP-4 [RFC4271] so used. Given that 176 a BFD session is required for a BGP session, a Denial-of-Service 177 (DoS) attack on BGP can now be mounted by preventing a BFD session 178 between the BGP peers from being established or interrupting an 179 existing BFD session. The use of the BFD Authentication mechanism 180 defined in [RFC5880] is thus RECOMMENDED when used to protect BGP-4 181 [RFC4271]. 183 7. IANA Considerations 185 This document defines a new BGP capability - BFD Capability. The 186 Capability Code for BFD Capability is TBD. 188 8. Acknowledgement 190 The authors would like to acknowledge the review and inputs from 191 Shyam Sethuram, Mohammed Mirza, Bruno Decraene, Carlos Pignataro, and 192 Enke Chen. 194 9. Normative References 196 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 197 Requirement Levels", BCP 14, RFC 2119, 198 DOI 10.17487/RFC2119, March 1997, 199 . 201 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 202 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 203 DOI 10.17487/RFC4271, January 2006, 204 . 206 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 207 with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February 208 2009, . 210 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 211 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 212 . 214 [RFC5882] Katz, D. and D. Ward, "Generic Application of 215 Bidirectional Forwarding Detection (BFD)", RFC 5882, 216 DOI 10.17487/RFC5882, June 2010, 217 . 219 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 220 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 221 May 2017, . 223 Authors' Addresses 225 Mercia Zheng 226 Ciena 227 3939 N. 1st Street 228 San Jose, CA 95134 229 UNITED STATES 231 Email: merciaz.ietf@gmail.com 233 Acee Lindem 234 Cisco Systems 235 301 Midenhall Way 236 GARY, NC 27513 237 UNITED STATES 239 Email: acee@cisco.com 240 Jeffrey Haas 241 Juniper Networks, Inc. 242 1133 Innovation Way 243 SUNNYVALE, CALIFORNIA 94089 244 UNITED STATES 246 Email: jhaas@juniper.net 248 Albert Fu 249 Bloomberg L.P. 251 Email: afu14@bloomberg.net