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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 A. Lindem 4 Intended status: Standards Track Cisco Systems 5 Expires: September 12, 2019 March 11, 2019 7 BGP BFD Strict-Mode 8 draft-merciaz-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 http://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 (http://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. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 58 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. Normative 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 [RFC5492] 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. Requirements Language 101 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 102 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 103 "OPTIONAL" in this document are to be interpreted as described in BCP 104 14 [RFC2119] [RFC8174] when, and only when, they appear in all 105 capitals, as shown here. 107 3. BGP BFD Capability 109 The BGP Capability [RFC5492] for BFD parameters will allow a BGP 110 speaker's BFD capabilities including its support for BFD strict-mode. 111 This capability is defined as follows: 113 Capability code: TBD 115 Capability length: 1 octet 117 Capability value: Consists of 1 octet BFD flags as follows: 119 +--------------------------------------------------+ 120 | BFD Flags (8 bits) | 121 +--------------------------------------------------+ 123 The use and meaning of the fields are as follows: 125 BFD Flags: This field contains bit flags relating to BFD. 127 0 1 2 3 4 5 6 7 128 +-+-+-+-+-+-+-+-+ 129 |S| Reserved | 130 +-+-+-+-+-+-+-+-+ 132 The most significant bit is defined as state of Strict-Mode ("Strict- 133 Mode", or "S") bit, which can be used by a BGP speaker to signal its 134 support for BFD Strict-mode. When set (value 1), this bit indicates 135 that the BGP speaker has the BFD "Strict-mode" enabled. If both 136 local BGP speaker and its peer are enabled with BFD strict-mode, then 137 BGP session establishment will be disallowed until a BFD session is 138 established. A BGP speaker with BFD strict-mode enabled MUST 139 advertise the BFD capability with "S" bit value 1. 141 The remaining bits are reserved and SHOULD be set to zero by the 142 sender and MUST be ignored by the receiver. 144 4. Operation 146 A BGP speaker that supports capabilities advertisement sends an OPEN 147 message to its BGP peer, the message MAY include an Optional 148 Parameter, called Capabilities. The parameter lists the capabilities 149 supported by the speaker. By following BGP capabilities 150 advertisement procedures defined in [RFC5492], BFD capability 151 advertisement for strict-mode is advertised to BGP peers. 153 A BGP speaker which supports capabilities advertisement and has BFD 154 strict-mode enabled MUST include the BGP BFD capability with the "S" 155 Bit set in the BGP capabilities it advertises. 157 A BGP speaker which supports BFD capability advertisement, examines 158 the list of capabilities present in the Capabilities BFD Parameter 159 that the speaker receives from its peer. If both the local and 160 remote BGP speakers BFD strict-mode enabled, then BGP session 161 establishment will be prevented until a BFD session is up. If either 162 peer has not advertised the BFD Capability with strict-mode enabled, 163 then a BFD session SHOULD NOT be required prior to BGP session 164 establishment. This does not preclude usage of BFD after BGP session 165 establishment [RFC5882]. 167 A BGP speaker which does not support or recognize BFD capability 168 should ignore the BFD capability. If a BGP speaker advertising the 169 capability receives the Unsupported Capability NOTIFICATION message, 170 it MUST NOT be result in BGP session termination. 172 5. Backward Compatibility 174 The new BFD capability will introduce any backward compatibility if 175 the procedures defined in this document are followed. A BGP speaker 176 which does not support BFD capability MUST ignore this capability. 177 The Unsupported Capability NOTIFICATION message MUST NOT result in 178 session termination by the BGP speaker advertising the capability. 180 6. Security Considerations 182 This specification doesn't change the basic security model inherent 183 in [RFC4271]. To the extent [RFC4271] might be said to help defend 184 against denials of service by making the control plane more 185 resilient, this extension may modestly increase that resilience; 186 however, there are enough confounding and deployment-specific factors 187 that no general claims can be made. 189 7. IANA Considerations 191 This document defines a new BGP capability - BFD Capability. The 192 Capability Code for BFD Capability is TBD. 194 IANA is requested to establish a "BGP BFD Capability Flags" registry 195 within the "Border Gateway Protocol (BGP) Parameters" grouping. The 196 Registration Procedure should be Standards Action, the initial values 197 as follows: 199 +--------------+---------------+------------+---------------+ 200 | Bit Position | Name | Short Name | Reference | 201 +--------------+---------------+------------+---------------+ 202 | 0 | Strict-Mode | S | this document | 203 | 1-7 | Unassigned | | this document | 204 +--------------+---------------+------------+---------------+ 206 8. Acknowledgement 208 The authors would like to acknowledge the review and inputs from 209 Shyam Sethuram and Mohammed Mirza. 211 9. Normative References 213 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 214 Requirement Levels", BCP 14, RFC 2119, 215 DOI 10.17487/RFC2119, March 1997, . 218 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 219 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 220 DOI 10.17487/RFC4271, January 2006, . 223 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 224 with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February 225 2009, . 227 [RFC5882] Katz, D. and D. Ward, "Generic Application of 228 Bidirectional Forwarding Detection (BFD)", RFC 5882, 229 DOI 10.17487/RFC5882, June 2010, . 232 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 233 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 234 May 2017, . 236 Authors' Addresses 238 Mercia Zheng 239 Cisco Systems 240 821 Alder Drive, 241 MILPITAS, CALIFORNIA 95035 242 UNITED STATES 244 Email: merciaz@cisco.com 246 Acee Lindem 247 Cisco Systems 248 821 Alder Drive, 249 MILPITAS, CALIFORNIA 95035 250 UNITED STATES 252 Email: acee@cisco.com