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Andersson 3 Internet-Draft Bronze Dragon Consulting 4 Intended status: Informational May 10, 2021 5 Expires: November 11, 2021 7 MPLS Open Design Team Questions 8 draft-andersson-mpls-open-dt-questions-01 10 Abstract 12 This document is a living document, meaning that during the life 13 timme of the MPLS Open Design Team we will put additonal questions/ 14 issues into the document. When we find an answer amd a way to 15 document the issu it will be removed from this document. 17 Ideally when the Design Team is closed this document will be empty, 18 or maybe we just add a pointer to where the answer to quesstion is 19 documented. Thus this document will never go on to become an RFCc. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on November 11, 2021. 38 Copyright Notice 40 Copyright (c) 2021 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (https://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 1.1. Requirement Language . . . . . . . . . . . . . . . . . . 2 57 2. Open DT Question List . . . . . . . . . . . . . . . . . . . . 3 58 2.1. Below the BoS . . . . . . . . . . . . . . . . . . . . . . 3 59 2.1.1. Limitations to the ability of LSR's to scan the Label 60 Stack . . . . . . . . . . . . . . . . . . . . . . . . 3 61 2.1.2. Does flooding om maximum scanning depth of an LSR 62 scale? . . . . . . . . . . . . . . . . . . . . . . . 3 63 2.1.3. Placeholder, due to duplicate to another section . . 4 64 2.1.4. First Nibble . . . . . . . . . . . . . . . . . . . . 4 65 2.1.5. More then on ACH after the BoS . . . . . . . . . . . 4 66 2.1.6. More then one indicator? . . . . . . . . . . . . . . 4 67 2.1.7. Multiple types of Indicators in the same stack . . . 4 68 2.1.8. Comfortable Readable Label Depth . . . . . . . . . . 4 69 2.2. Above the BoS . . . . . . . . . . . . . . . . . . . . . . 5 70 2.2.1. Resuse the ELI . . . . . . . . . . . . . . . . . . . 5 71 2.2.2. Using any bSPL . . . . . . . . . . . . . . . . . . . 5 72 2.2.3. Use of Extended SPLs . . . . . . . . . . . . . . . . 5 73 2.2.4. Generalized Action Indicator . . . . . . . . . . . . 5 74 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 75 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 76 5. Normative References . . . . . . . . . . . . . . . . . . . . 6 77 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 79 1. Introduction 81 "Living Documents" are not commonly used in the IETF, but we have 82 considered it to be a good way of documenting the state of the issues 83 worked on by the design team. 85 1.1. Requirement Language 87 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 88 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 89 "OPTIONAL" in this document are to be interpreted as described in BCP 90 14 [RFC2119] [RFC8174] when, and only when, they appear in all 91 capitals, as shown here. 93 For a document that is not intended to become and RFC on the 94 Standards Track it might seem moot to have the requirement language 95 included, however it might be that a question or an answer to one of 96 the questions might use the BCP 14 language, so to avoid ambiguity we 97 left it in 99 2. Open DT Question List 101 2.1. Below the BoS 103 As we start working on this document we just add new questions as we 104 define them. It is possible that later we will try to find a 105 grouping af questions based more on technical commonalities. 107 2.1.1. Limitations to the ability of LSR's to scan the Label Stack 109 Several LSRs have limitations how deep it is possible to scan the 110 label stack looking for certain information. If the info that are 111 being looked for is below this depth, is it possible to use these 112 LSRs for manadatoy actions? 114 The inormation needed for the mandatory action will never be found. 116 2.1.2. Does flooding om maximum scanning depth of an LSR scale? 118 A remedy for the issues in Section 2.1.1 has been suggested, the 119 maximum scanning depth for each LSR in the network should be flooded 120 to all othr LSRs and used as a constraint when setting up LSPs. 122 Would that scasle satisfactorily. 124 Tentative answer: 126 Stewart: It is one additional capability field (no more than a byte) 127 to flood and I find it hard to imagine that it would not scale. 129 The IGPs will need to be slightly updated, RFC 8491 will be a good 130 starting point. 132 Loa: Flooding will be done by an IGP, which is a small update to the 133 IGP. For networks that is controlled by a network management system 134 (centralized controller), the NMS will both knew the scanning 135 limitations and establish the LSP. 137 Conclusion: Unless we see any further comments, this question is 138 closed. 140 2.1.3. Placeholder, due to duplicate to another section 142 Duplicate entry, in order to keep section number the duplicate has 143 ben replaced by a placeholder. 145 2.1.4. First Nibble 147 We have indications that when we started to snoop the first nibble 148 after the LSE that has the BoS set to find out if the packet carried 149 IP (v4 or v6), there was also an agreement that "we" would never put 150 anything but 0b0000 or 0b0001 in that first nibble. 152 It is off couurse intresting to try to understand the definition of 153 "we" but since the aggreement were between the Internet Area and the 154 PWE3 working group, it is likely that it will be considered binding 155 for the Routing Area. 157 Stewart: Can you try to find out more about this and where we stand 158 today. 160 2.1.5. More then on ACH after the BoS 162 Is it possible to have more than one ACH after the BoS. 164 If currently not possible do we want to add it? 166 How are the ACH's separated and related to the indicator in the label 167 stack? 169 2.1.6. More then one indicator? 171 What happens when you find the first indicator? 173 If an LSR is scanning "the entire stack", what happens when the first 174 indicator is found? Is the scanning aborted. 176 If an GAL is below an FAI in the stack will it be found? 178 2.1.7. Multiple types of Indicators in the same stack 180 Is it possible to have multiple types of indicators in the same label 181 stack, e.g. FAI and GAL? 183 2.1.8. Comfortable Readable Label Depth 185 What is the Readable Label Depth (RLD) that we are comforable with. 187 This is a question that was voiced at a DT meeting, but there were 188 not real discussion. 190 Here we take the question to mean "What is the minimum RLD that we 191 can count on by any LSR when we design functions that need to detect 192 action indicators in the label stack?" 194 2.2. Above the BoS 196 - 198 2.2.1. Resuse the ELI 200 When using bSPLs for multipurpose - "the useless bit in the bSPL" - 201 it was sometimes talked about reusing the ELI (unless this was 202 misunderstood). 204 Is this still on the agenda? 206 2.2.2. Using any bSPL 208 Is it possible to use the "useless bits" in any bSPL to indicate 209 actions? 211 If we do will the corresponding bits. e.g. MSB in the TTL, mean the 212 same thing regardless of in which bSPL it is found? 214 2.2.3. Use of Extended SPLs 216 Is it possible to use the "useless bits" in an eSPL/cSPL? It would 217 give use more bits to play with. If the answer to the question in 218 Section 2.2.2 is yes the useless bits in the XL would be interpreted 219 as in any other indicator, but you have at least 11 new bits in the 220 eSPL. 222 Maybe allocate an extended FAI-2 from the extended range? 224 2.2.4. Generalized Action Indicator 226 Could we generalize the FAI (+ FAI-2 ?) to be general mechanism for 227 indicating presence of "stuff" after the BoS? 229 3. IANA Considerations 231 This document does not make any allocations of code points from IANA 232 registries. 234 4. Acknowledgements 236 - 238 - 240 5. Normative References 242 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 243 Requirement Levels", BCP 14, RFC 2119, 244 DOI 10.17487/RFC2119, March 1997, 245 . 247 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 248 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 249 May 2017, . 251 Author's Address 253 Loa Andersson 254 Bronze Dragon Consulting 256 Email: loa@pi.nu