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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: 3 November 2022 Cisco Systems 6 J. Haas 7 Juniper Networks, Inc. 8 A. Fu 9 Bloomberg L.P. 10 2 May 2022 12 BGP BFD Strict-Mode 13 draft-ietf-idr-bgp-bfd-strict-mode-07 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 3 November 2022. 42 Copyright Notice 44 Copyright (c) 2022 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 (https://trustee.ietf.org/ 49 license-info) in effect on the date of publication of this document. 50 Please review these documents carefully, as they describe your rights 51 and restrictions with respect to this document. Code Components 52 extracted from this document must include Revised BSD License text as 53 described in Section 4.e of the Trust Legal Provisions and are 54 provided without warranty as described in the Revised BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 59 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 60 3. BFD Strict-Mode Capability . . . . . . . . . . . . . . . . . 3 61 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3 62 5. Manageability Considerations . . . . . . . . . . . . . . . . 4 63 6. Security Considerations . . . . . . . . . . . . . . . . . . . 4 64 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 65 8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 5 66 9. Normative References . . . . . . . . . . . . . . . . . . . . 5 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 69 1. Introduction 71 Bidirectional Forwarding Detection BFD [RFC5882] enables routers to 72 monitor data plane connectivity and to detect faults in the 73 bidirectional forwarding path between them. This capability is 74 leveraged by routing protocols such as BGP [RFC4271] to rapidly react 75 to topology changes in the face of path failures. 77 The BFD interaction with BGP is specified in Section 10.2 of 78 [RFC5882]. When BFD is enabled for a BGP neighbor, faults in the 79 bidirectional forwarding detected by BFD result in session 80 termination. It is possible in some failure scenarios for the 81 network to be in a state such that a BGP session may be established 82 but a BFD session cannot be established. In some other scenarios, it 83 may be possible to establish a BGP session, but a degraded or poor- 84 quality link may result in the corresponding BFD session going up and 85 down frequently. 87 To avoid situations which result in routing churn and to minimize the 88 impact of network interruptions, it will be beneficial to disallow 89 BGP to establish a session until BFD session is successfully 90 established and has stabilized. We refer to this mode of operation 91 as BGP BFD "strict-mode". However, always using "strict-mode" would 92 preclude BGP operation in an environment where not all routers 93 support BFD strict-mode or have BFD enabled. This document defines 94 BGP "strict-mode" operation as preventing BGP session establishment 95 until both the local and remove speakers have a stable BFD session. 96 The document also specifies the BGP protocol extensions for BGP 97 capability [RFC5492] for announcing BFD parameters including a BGP 98 speaker's support for "strict-mode", i.e., requiring a BFD session 99 for BGP session establishment. 101 2. Requirements Language 103 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 104 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 105 "OPTIONAL" in this document are to be interpreted as described in BCP 106 14 [RFC2119] [RFC8174] when, and only when, they appear in all 107 capitals, as shown here. 109 3. BFD Strict-Mode Capability 111 The BGP Strict-Mode Capability [RFC5492] will allow a BGP speaker's 112 to advertise this capability. The capability is defined as follows: 114 Capability code: TBD 116 Capability length: 0 octets 118 4. Operation 120 A BGP speaker which supports capabilities advertisement and has BFD 121 strict-mode enabled MUST include the BFD strict-mode capability. 123 A BGP speaker which supports the BFD Strict-Mode capability, examines 124 the list of capabilities present in the capabilities that the speaker 125 receives from its peer. If both the local and remote BGP speakers 126 include the BFD strict-mode capability, the BGP finite state machine 127 does not transition to the Established state from OpenSent or 128 OpenConfirm state [RFC4271] until the BFD session is in the Up state 129 (see below for AdminDown state). This means that a KEEPALIVE message 130 is not sent nor is the KeepaliveTimer set. 132 If the BFD session does not transition to the Up state, and the 133 HoldTimer has been negotiated to a non-zero value, the BGP FSM will 134 close the session appropriately. If the HoldTimer has been 135 negotiated to a zero value, the session should be closed after a time 136 of X. This time X is referred as "BGP BFD Hold time". The proposed 137 default BGP BFD Hold time value is 30 seconds. The BGP BFD Hold time 138 value is configurable. 140 If BFD session is in the AdminDown state, then the BGP finite state 141 machine will proceed normally without input from BFD. This means 142 that BFD session "AdminDown" state WILL NOT prevent the BGP state 143 transition to Established state from OpenConfirm. 145 Once the BFD session has transitioned to the Up state, the BGP FSM 146 may proceed to transition to the Established state from the OpenSent 147 or OpenConfirm state appropriately. I.e. a KEEPALIVE message is 148 sent, and the KeepaliveTimer is started. 150 If either BGP peer has not advertised the BFD Strict-Mode Capability, 151 then a BFD session WILL NOT be required for the BGP session to reach 152 Established state. This does not preclude usage of BFD after BGP 153 session establishment [RFC5882]. 155 If BFD is disabled for a BGP peer and the BGP session state is being 156 held in OpenSent or OpenConfirm state, then the BGP will close 157 session, and start a new TCP connect. 159 5. Manageability Considerations 161 Auto-configuration is possible for the enabling BGP BFD Strict-Mode. 162 However, the configuration automation is out of the scope of this 163 document. 165 A BGP NOTIFICATION message Subcode indicating BFD Hold timer 166 expiration may be required for network management. (To be discussed 167 in the next revision of this document.) 169 6. Security Considerations 171 The mechanism defined in this document interacts with the BGP finite 172 state machine when so configured. The security considerations of BFD 173 thus, become considerations for BGP-4 [RFC4271] so used. Given that 174 a BFD session is required for a BGP session, a Denial-of-Service 175 (DoS) attack on BGP can now be mounted by preventing a BFD session 176 between the BGP peers from being established or interrupting an 177 existing BFD session. The use of the BFD Authentication mechanism 178 defined in [RFC5880] is thus RECOMMENDED when used to protect BGP-4 179 [RFC4271]. 181 7. IANA Considerations 183 This document defines a new BGP capability - BFD Capability. The 184 Capability Code for BFD Capability is TBD. 186 8. Acknowledgement 188 The authors would like to acknowledge the review and inputs from 189 Shyam Sethuram, Mohammed Mirza, Bruno Decraene, Carlos Pignataro, and 190 Enke Chen. 192 9. Normative References 194 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 195 Requirement Levels", BCP 14, RFC 2119, 196 DOI 10.17487/RFC2119, March 1997, 197 . 199 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 200 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 201 DOI 10.17487/RFC4271, January 2006, 202 . 204 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 205 with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February 206 2009, . 208 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 209 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 210 . 212 [RFC5882] Katz, D. and D. Ward, "Generic Application of 213 Bidirectional Forwarding Detection (BFD)", RFC 5882, 214 DOI 10.17487/RFC5882, June 2010, 215 . 217 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 218 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 219 May 2017, . 221 Authors' Addresses 223 Mercia Zheng 224 Ciena 225 3939 N. 1st Street 226 San Jose, CA 95134 227 United States 228 Email: merciaz.ietf@gmail.com 229 Acee Lindem 230 Cisco Systems 231 301 Midenhall Way 232 GARY, NC 27513 233 United States 234 Email: acee@cisco.com 236 Jeffrey Haas 237 Juniper Networks, Inc. 238 1133 Innovation Way 239 SUNNYVALE, CALIFORNIA 94089 240 United States 241 Email: jhaas@juniper.net 243 Albert Fu 244 Bloomberg L.P. 245 Email: afu14@bloomberg.net