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Linden 4 Intended status: Standards Track Cisco Systems 5 Expires: September 12, 2019 March 11, 2019 7 BGP BFD Strict-Mode 8 draft-merciaz-ietf-idr-bgp-bfd-strict-mode-00 10 Abstract 12 This document specifies extensions to RFC4271 BGP-4 that enable a BGP 13 speaker to signal additional Bidirectional Forwarding Detection (BFD) 14 extensions using an optional parameter BFD capability. This BFD 15 capability enables a BGP speaker to prevent a BGP session from being 16 established until a BFD session is established. It is referred to as 17 BGP BFD "strict-mode". BGP BFD strict-mode will be supported when 18 both the local speaker and its remote peer are BFD strict-mode 19 capable, Otherwise, a BGP speaker and its peer should not require a 20 BFD session for BGP session establishment. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at https://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on September 12, 2019. 39 Copyright Notice 41 Copyright (c) 2019 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (https://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 3. 3. BGP BFD Capability . . . . . . . . . . . . . . . . . . . . 3 59 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 5. Backward Compatibility . . . . . . . . . . . . . . . . . . . 4 61 6. Security Considerations . . . . . . . . . . . . . . . . . . . 4 62 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 63 8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 5 64 9. Informative References . . . . . . . . . . . . . . . . . . . 5 65 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 67 1. Introduction 69 Bidirectional Forwarding Detection BFD [RFC5882] enables routers to 70 monitor data plane connectivity and to detect faults in the 71 bidirectional forwarding path between them. This capability is 72 leveraged by routing protocols such as BGP [RFC4271] to rapidly react 73 to topology changes in the face of path failures. 75 The BFD interaction with BGP is specified in Section 10.2 of 76 [RFC5882]. When BFD is enabled for a BGP neighbor, faults in the 77 bidirectional forwarding detected by BFD result in session 78 termination. It is possible in some failure scenarios for the 79 network to be in a state such that a BGP session may be established 80 but a BFD session cannot be established. In some other scenarios, it 81 may be possible to establish a BGP session, but a degraded or poor- 82 quality link may result in the corresponding BFD session going up and 83 down frequently. 85 To avoid situations which result in routing churn and to minimize the 86 impact of network interruptions, it will be beneficial to disallow 87 BGP to establish a neighbor session until BFD session is successfully 88 established and has stabilized. We refer to this mode of operation 89 as BGP BFD "strict-mode". However, always using strict-mode" would 90 preclude BGP operation in an environment where not all routers 91 support BFD strict-mode or have BFD enabled. This document defines 92 BGP "strict-mode" operation as preventing BGP session establishment 93 until both the local and remove speakers have a stable BFD session. 94 The document also specifies the BGP protocol extensions for BGP 95 capability [BGP-CAP] for announcing BFD parameters including a BGP 96 speaker's support for "strict-mode", i.e., requiring a BFD session 97 for BGP session establishment. 99 2. Terminology 101 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 102 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 103 document are to be interpreted as described in [RFC2119] . 105 3. 3. BGP BFD Capability 107 The BGP Capability [RFC5492] for BFD parameters will allow a BGP 108 speaker's BFD capabilities including its support for BFD strict-mode. 109 This capability is defined as follows: 111 Capability code: TBD 113 Capability length: 1 octet 115 Capability value: Consists of 1 octet BFD flags as follows: 117 +--------------------------------------------------+ 118 | BFD Flags (8 bits) | 119 +--------------------------------------------------+ 121 The use and meaning of the fields are as follows: 123 BFD Flags: This field contains bit flags relating to BFD. 125 0 1 2 3 4 5 6 7 126 +-+-+-+-+-+-+-+-+ 127 |S| Reserved | 128 +-+-+-+-+-+-+-+-+ 130 The most significant bit is defined as state of Strict-Mode ("Strict- 131 Mode", or "S") bit, which can be used by a BGP speaker to signal its 132 support for BFD Strict-mode. When set (value 1), this bit indicates 133 that the BGP speaker has the BFD "Strict-mode" enabled. If both 134 local BGP speaker and its peer are enabled with BFD strict-mode, then 135 BGP session establishment will be disallowed until a BFD session is 136 established. A BGP speaker with BFD strict-mode enabled MUST 137 advertise the BFD capability with "S" bit value 1. 139 The remaining bits are reserved and SHOULD be set to zero by the 140 sender and MUST be ignored by the receiver. 142 4. Operation 144 A BGP speaker that supports capabilities advertisement sends an OPEN 145 message to its BGP peer, the message MAY include an Optional 146 Parameter, called Capabilities. The parameter lists the capabilities 147 supported by the speaker. By following BGP capabilities 148 advertisement procedures defined in [RFC5492], BFD capability 149 advertisement for strict-mode is advertised to BGP peers. 151 A BGP speaker which supports capabilities advertisement and has BFD 152 strict-mode enabled MUST include the BGP BFD capability with the "S" 153 Bit set in the BGP capabilities it advertises. 155 A BGP speaker which supports BFD capability advertisement, examines 156 the list of capabilities present in the Capabilities BFD Parameter 157 that the speaker receives from its peer. If both the local and 158 remote BGP speakers BFD strict-mode enabled, then BGP session 159 establishment will be prevented until a BFD session is up. If either 160 peer has not advertised the BFD Capability with strict-mode enabled, 161 then a BFD session SHOULD NOT be required prior to BGP session 162 establishment. This does not preclude usage of BFD after BGP session 163 establishment [RFC5882]. 165 A BGP speaker which does not support or recognize BFD capability 166 should ignore the BFD capability. If a BGP speaker advertising the 167 capability receives the Unsupported Capability NOTIFICATION message, 168 it MUST NOT be result in BGP session termination. 170 5. Backward Compatibility 172 The new BFD capability will introduce any backward compatibility if 173 the procedures defined in this document are followed. A BGP speaker 174 which does not support BFD capability MUST ignore this capability. 175 The Unsupported Capability NOTIFICATION message MUST NOT result in 176 session termination by the BGP speaker advertising the capability. 178 6. Security Considerations 180 This specification doesn't change the basic security model inherent 181 in [RFC4271]. To the extent [RFC4271] might be said to help defend 182 against denials of service by making the control plane more 183 resilient, this extension may modestly increase that resilience; 184 however, there are enough confounding and deployment-specific factors 185 that no general claims can be made. 187 7. IANA Considerations 189 This document defines a new BGP capability - BFD Capability. The 190 Capability Code for BFD Capability is TBD. 192 IANA is requested to establish a "BGP BFD Capability Flags" registry 193 within the "Border Gateway Protocol (BGP) Parameters" grouping. The 194 Registration Procedure should be Standards Action, the initial values 195 as follows: 197 +--------------+---------------+------------+---------------+ 198 | Bit Position | Name | Short Name | Reference | 199 +--------------+---------------+------------+---------------+ 200 | 0 | Strict-Mode | S | this document | 201 | 1-7 | Unassigned | | this document | 202 +--------------+---------------+------------+---------------+ 204 8. Acknowledgement 206 The authors would like to acknowledge the review and inputs from 207 Shyam Sethuram and Mohammed Mirza. 209 9. Informative References 211 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 212 Requirement Levels", BCP 14, RFC 2119, 213 DOI 10.17487/RFC2119, March 1997, 214 . 216 [RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 217 Specifications: ABNF", RFC 2234, DOI 10.17487/RFC2234, 218 November 1997, . 220 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 221 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 222 DOI 10.17487/RFC4271, January 2006, 223 . 225 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 226 with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February 227 2009, . 229 [RFC5882] Katz, D. and D. Ward, "Generic Application of 230 Bidirectional Forwarding Detection (BFD)", RFC 5882, 231 DOI 10.17487/RFC5882, June 2010, 232 . 234 Authors' Addresses 236 Mercia Zheng 237 Cisco Systems 238 821 Alder Drive, 239 MILPITAS, CALIFORNIA 95035 240 UNITED STATES 242 Email: merciaz@cisco.com 244 Acee Lindem 245 Cisco Systems 246 821 Alder Drive, 247 MILPITAS, CALIFORNIA 95035 248 UNITED STATES 250 Email: acee@cisco.com