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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-12) exists of draft-ietf-lsr-ospf-prefix-originator-04 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 LSR Working Group A. Wang 3 Internet-Draft China Telecom 4 Intended status: Standards Track Z. Hu 5 Expires: April 26, 2020 Huawei Technologies 6 October 24, 2019 8 Prefix Unreachable Announcement for SRv6 Fast Convergence 9 draft-wang-lsr-prefix-unreachable-annoucement-00 11 Abstract 13 This document describes the mechanism that can be used to announce 14 the unreachable prefixes for SRv6 fast convergence. 16 Status of This Memo 18 This Internet-Draft is submitted in full conformance with the 19 provisions of BCP 78 and BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF). Note that other groups may also distribute 23 working documents as Internet-Drafts. The list of current Internet- 24 Drafts is at https://datatracker.ietf.org/drafts/current/. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 This Internet-Draft will expire on April 26, 2020. 33 Copyright Notice 35 Copyright (c) 2019 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (https://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. Code Components extracted from this document must 44 include Simplified BSD License text as described in Section 4.e of 45 the Trust Legal Provisions and are provided without warranty as 46 described in the Simplified BSD License. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 51 2. Conventions used in this document . . . . . . . . . . . . . . 2 52 3. Scenario Description . . . . . . . . . . . . . . . . . . . . 3 53 4. Inter-area prefix unreachable solution . . . . . . . . . . . 3 54 5. Intra-area prefix unreachable solution . . . . . . . . . . . 4 55 6. Implementation Consideration . . . . . . . . . . . . . . . . 4 56 7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 57 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 58 9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 5 59 10. Normative References . . . . . . . . . . . . . . . . . . . . 5 60 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 62 1. Introduction 64 OSPF and IS-IS have the summary route and default route mechanism on 65 area border router or L1L2 border router, which can be used to 66 increase the scalability of these IGP protocols. Such summary 67 mechanism can also reduce the SPF calculation time when the link 68 oscillation occurs in another area. 70 The summary route and the default route may cover the host route or 71 link prefixes of intra area or inter area. But in some situations, 72 the router needs to know the exact reachability information about 73 prefix in other area, especially when the prefix is unreachable but 74 it is located within the summary range. 76 With the introduction of SRv6, more and more services are migrated 77 from the MPLS data plane to the IPv6 data plane. The biggest 78 difference between IPv6 and MPLS is that IPv6 has aggregation 79 ability, so we need to reconsider how to know the prefix reachability 80 in the case of aggregation. 82 This document introduces the mechanism that can be used in such 83 situation, to announce the unreachable prefixes which are located in 84 the summary address range. 86 2. Conventions used in this document 88 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 89 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 90 document are to be interpreted as described in [RFC2119] . 92 3. Scenario Description 94 Figure1 illustrates the topology scenario when OSPF is running in 95 multi-area. R0-R4 are routers in backbone area, S1-S4,T1-T4 are 96 internal routers in area 1 and area 2 respectively. R1 and R3 are 97 area border routers between area 0 and area 1. R2 and R4 are area 98 border routers between area 0 and area 2. Ps2 is the host address of 99 S2 and Pt2 is the host address T2. 101 +---------------------+------+--------+-----+--------------+ 102 | +--+ +--+ ++-+ ++-+ +-++ + -+ +--+| 103 | |S1+--------+S2+---+R1+---|R0+----+R2+---+T1+--------+T2|| 104 | +-++ Ps2+-++ ++-+ +--+ +-++ ++++ Pt2 +-++| 105 | | | | | || | | 106 | | | | | || | | 107 | +-++ +-++ ++-+ +-++ ++++ +-++| 108 | |S4+--------+S3+---+R3+-----------+R4+---+T3+--------+T4|| 109 | +--+ +--+ ++-+ +-++ ++-+ +--+| 110 | | | | 111 | | | | 112 | Area 1 | Area 0 | Area 2 | 113 +---------------------+---------------+--------------------+ 115 Figure1: OSPF Inter-Area Prefix Unreachable Announcement Scenario 117 If the area border router R1/R3 and R2/R4 does the summary action, 118 then one summary address that cover the prefixes of area 0, area 1 119 and area 2 will be announced to area 1 and area 2, instead of the 120 detail address. When the node S2 is down, Ps2 become unreachable. 121 But there will be no change to the summary prefix. Except the border 122 router R1/R3, the other routers within area 0 and area 2 do not know 123 the unreachable status of this prefix. When these routers send 124 traffic to prefix Ps2, the traffic will be dropped. 126 In another situation, assume the BGP session is built between Node S2 127 and T2, via Ps2 and Pt2 respectively. If Node S2 within area 1 128 become unreachable, the unreachable information can't be advertised 129 to Node T2 because the summary behaviour on border router R1/R3. The 130 BGP session between S1 and T2 will be kept until the BGP keepalive 131 timeout or other detection mechanism takes effect. During this 132 period, the BGP traffic to Node S2 will be in black hole. 134 4. Inter-area prefix unreachable solution 136 [RFC7794] and [I-D.ietf-lsr-ospf-prefix-originator] both define one 137 sub-TLV "Prefix Source Router ID" to announce the originator router 138 information of one prefix. This TLV can be used to announce the 139 prefix unreachable information when the link or node is down. 141 According to the procedure described in section 5 of 142 [I-D.ietf-lsr-ospf-prefix-originator], the ABR has the responsibility 143 to add the prefix originator information when it receive the type 1 144 LSA from other routers in the same area. When the ABR does the 145 summary work and receives one updated LSA that omits the prefix 146 belong to failed link which is within the range of summary address, 147 the ABR should announce one new type 3 LSA, which includes the 148 information about this prefix, but with the prefix originator set to 149 NULL(all 0 address). 151 When one node in one area is down, the ABR has also the ability to 152 detect the missing neighbor from the neighbor list. It should then 153 announce one new type 3 LSA that includes the loopback addresses of 154 this node, with the prefix originator set also to NULL(all 0 155 address). 157 For IS-IS, the above procedure is similar. The level-1/2 router will 158 accomplish the above work when it judges that one prefix within the 159 summary address range is missing. 161 These LSA will be transported via the traditional flooding procedure. 163 When the routers in other area receives such LSA, they will generate 164 automatically one black-hole route, with the prefix as the 165 destination, and the next hop be set to Null. 167 5. Intra-area prefix unreachable solution 169 In the intra-area scenario, like S1 illustrated in Figure 1, it will 170 learn two types of prefixes, one is summary route, another is host 171 route. When node S2 is down, S2 will withdraw the host route. But 172 S1 can still match the summary route via the longest mask matching. 173 For this scenario, when node S2 is down, S1 needs to keep the S2 host 174 route for a period of time but updates S2 host route to black hole 175 route. S1 will match the black hole route via the longest mask 176 matching. Such mechanism can be used to trigger a SRv6 VPN for PE 177 switching, or SRv6 TE mid-point protection. 179 The period for keeping the black hole route should be configured, to 180 ensure the related protocols or services be converged. 182 6. Implementation Consideration 184 The above procedures will only be triggered under the following 185 conditions: 187 1. The ABR or Level 1/2 router do the summary work. 189 2. The link prefix within the summary address range become 190 unreachable. 192 3. The node whose loopback address is within the summary address 193 become unreachable. 195 The Summary LSA that includes the unreachable prefix, with the prefix 196 originator set to NULL value, will be announced across the ABR 197 router, reach the routers in other areas. It's behavior is still the 198 same as that defined in OSPFv2 [RFC2328] or OSPFv3 [RFC5340] 200 7. Security Considerations 202 Security concerns for OSPF are addressed in [RFC5709] 204 Advertisement of the additional information defined in this document 205 introduces no new security concerns 207 8. IANA Considerations 209 TBD 211 9. Acknowledgement 213 TBD 215 10. Normative References 217 [I-D.ietf-lsr-ospf-prefix-originator] 218 Wang, A., Lindem, A., Dong, J., Psenak, P., and K. 219 Talaulikar, "OSPF Prefix Originator Extension", draft- 220 ietf-lsr-ospf-prefix-originator-04 (work in progress), 221 September 2019. 223 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 224 Requirement Levels", BCP 14, RFC 2119, 225 DOI 10.17487/RFC2119, March 1997, 226 . 228 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 229 DOI 10.17487/RFC2328, April 1998, 230 . 232 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 233 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 234 . 236 [RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M., 237 Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic 238 Authentication", RFC 5709, DOI 10.17487/RFC5709, October 239 2009, . 241 [RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and 242 U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4 243 and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794, 244 March 2016, . 246 Authors' Addresses 248 Aijun Wang 249 China Telecom 250 Beiqijia Town, Changping District 251 Beijing 102209 252 China 254 Email: wangaj3@chinatelecom.cn 256 Zhibo Hu 257 Huawei Technologies 258 Huawei Bld., No.156 Beiqing Rd. 259 Beijing 100095 260 China 262 Email: huzhibo@huawei.com