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Fu 5 Expires: September 20, 2018 Bloomberg 6 March 19, 2018 8 BFD Encapsulated in Large Packets 9 draft-haas-bfd-large-packets-00 11 Abstract 13 The Bidirectional Forwarding Detection (BFD) protocol is commonly 14 used to verify connectivity between two systems. BFD packets are 15 typically very small. It is desirable in some circumstances to know 16 that not only is the path between two systems reachable, but also 17 that it is capable of carrying a payload of a particular size. This 18 document discusses thoughts on how to implement such a mechanism 19 using BFD in Asynchronous mode. 21 Requirements Language 23 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 24 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to 25 be interpreted as described in [RFC2119] only when they appear in all 26 upper case. They may also appear in lower or mixed case as English 27 words, without normative meaning. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at http://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on September 20, 2018. 46 Copyright Notice 48 Copyright (c) 2018 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 64 2. BFD Encapsulated in Large Packets . . . . . . . . . . . . . . 3 65 3. Implementation and Deployment Considerations . . . . . . . . 3 66 4. Security Considerations . . . . . . . . . . . . . . . . . . . 3 67 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 68 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 6.1. Normative References . . . . . . . . . . . . . . . . . . 4 70 6.2. Informative References . . . . . . . . . . . . . . . . . 4 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 73 1. Introduction 75 The Bidirectional Forwarding Detection (BFD) [RFC5880] protocol is 76 commonly used to verify connectivity between two systems. However, 77 some applications may require that the Path MTU [RFC1191] between 78 those two systems meets a certain minimum criteria. When the Path 79 MTU decreases below the minimum threshold, those applications may 80 wish to consider the path unusable. 82 BFD may be encapsulated in a number of transport protocols. An 83 example of this is single-hop BFD [RFC5881]. In that case, the link 84 MTU configuration is typically enough to guarantee communication 85 between the two systems for that size MTU. BFD Echo mode 86 (Section 6.4 of [RFC5880]) is sufficient to permit verification of 87 the Path MTU of such directly connected systems. Previous proposals 88 ([I-D.haas-xiao-bfd-echo-path-mtu]) have been made for testing Path 89 MTU for such directly connected systems. However, in the case of 90 multi-hop BFD [RFC5883], this guarantee does not hold. 92 The encapsulation of BFD in multi-hop sessions is a simple UDP 93 packet. The BFD elements of procedure (Section 6.8.6 of [RFC5880]) 94 covers validating the BFD payload. However, the specification is 95 silent on the length of the encapsulation that is carrying the BFD 96 PDU. While it is most common that the transport protocol payload 97 (i.e. UDP) length is the exact size of the BFD PDU, this is not 98 required by the elements of procedure. This leads to the possibility 99 that the transport protocol length may be larger than the contained 100 BFD PDU. 102 2. BFD Encapsulated in Large Packets 104 Support for BFD between two systems is typically configured, even if 105 the actual session may be dynamically created by a client protocol. 106 A new BFD variable is defined in this document: 108 bfd.PaddedPduSize 109 The BFD transport protocol payload size is increased to this 110 value. The contents of this additional payload MUST be zero. 111 The minimum size of this variable MUST NOT be smaller than 112 permitted by the element of BFD procedure; 24 or 26 - see 113 Section 6.8.6 of [RFC5880]. 115 The Don't Fragment bit (Section 2.3 of [RFC0791]) of the IP payload, 116 when using IP encapsulations, MUST be set. 118 3. Implementation and Deployment Considerations 120 While this document proposes no change to the BFD protocol, 121 implementations may not permit arbitrarily padded transport PDUs to 122 carry BFD packets. While Section 6 of [RFC5880] warns against 123 excessive pedantry, implementations may not work with this mechanism 124 without additional support. Additional changes to the base BFD 125 protocol may be required to permit negotiation of this functionality 126 and the padding value. 128 It is also worthy of note that even if an implementation can function 129 with larger transport PDUs, that additional packet size may have 130 impact on BFD scaling. 132 This mechanism also can be applied to other forms of BFD, including 133 S-BFD [RFC7880]. 135 4. Security Considerations 137 This document does not change the underlying security considerations 138 of the BFD protocol or its encapsulations. 140 5. IANA Considerations 142 This document introduces no additional considerations to IANA. 144 6. References 146 6.1. Normative References 148 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 149 DOI 10.17487/RFC0791, September 1981, . 152 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 153 Requirement Levels", BCP 14, RFC 2119, 154 DOI 10.17487/RFC2119, March 1997, . 157 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 158 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 159 . 161 [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 162 (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, 163 DOI 10.17487/RFC5881, June 2010, . 166 [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 167 (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883, 168 June 2010, . 170 [RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S. 171 Pallagatti, "Seamless Bidirectional Forwarding Detection 172 (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016, 173 . 175 6.2. Informative References 177 [I-D.haas-xiao-bfd-echo-path-mtu] 178 Haas, J. and M. Xiao, "Application of the BFD Echo 179 function for Path MTU Verification or Detection", draft- 180 haas-xiao-bfd-echo-path-mtu-01 (work in progress), July 181 2011. 183 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 184 DOI 10.17487/RFC1191, November 1990, . 187 Authors' Addresses 189 Jeffrey Haas 190 Juniper Networks, Inc. 191 1133 Innovation Way 192 Sunnyvale, CA 94089 193 US 195 Email: jhaas@juniper.net 197 Albert Fu 198 Bloomberg 200 Email: afu14@bloomberg.net