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Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group R. Ogier 2 Internet-Draft SRI International 3 Updates: 5614 May 5, 2013 4 Intended status: Experimental 5 Expires: November 6, 2013 7 Use of OSPF-MDR in Single-Hop Broadcast Networks 8 draft-ietf-ospf-manet-single-hop-mdr-02.txt 10 Abstract 12 RFC 5614 (OSPF-MDR) extends OSPF to support mobile ad hoc networks 13 (MANETs) by specifying its operation on the new OSPF interface of type 14 MANET. This document describes the use of OSPF-MDR in a single-hop 15 broadcast network, which is a special case of a MANET in which each 16 router is a (one-hop) neighbor of each other router. Unlike an OSPF 17 broadcast interface, such an interface can have a different cost 18 associated with each neighbor. The document includes configuration 19 recommendations and simplified mechanisms that can be used in single-hop 20 broadcast networks. 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 Copyright Notice 39 Copyright (c) 2013 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 1. Introduction 54 OSPF-MDR [RFC5614] specifies an extension of OSPF [RFC2328, RFC5340] 55 to support mobile ad-hoc networks (MANETs) by specifying its 56 operation on the new OSPF interface of type MANET. OSPF-MDR 57 generalizes the Designated Router (DR) to a connected dominating set 58 (CDS) consisting of a typically small subset of routers called MANET 59 Designated Routers (MDRs). Similarly, the Backup Designated Router 60 (BDR) is generalized to a subset of routers called Backup MDRs 61 (BMDRs). MDRs achieve scalability in MANETs similar to the way DRs 62 achieve scalability in broadcast networks: 64 o MDRs have primary responsibility for flooding LSAs. Backup MDRs 65 provide backup flooding when MDRs temporarily fail. 67 o MDRs allow the number of adjacencies to be dramatically reduced, 68 by requiring adjacencies to be formed only between MDR/BMDR 69 routers and their neighbors. 71 In addition, OSPF-MDR has the following features: 73 o MDRs and BMDRs are elected based on information obtained from 74 modified Hello packets received from neighbors. 76 o If adjacency reduction is used (the default), adjacencies are 77 formed between MDRs so as to form a connected subgraph. 78 An option (AdjConnectivity = 2) allows for additional adjacencies 79 to be formed between MDRs/BMDRs to form a biconnected subgraph. 81 o Each non-MDR router becomes adjacent with an MDR called its 82 Parent, and optionally (if AdjConnectivity = 2) becomes adjacent 83 with another MDR or BMDR called its Backup Parent. 85 o Each router advertises connections to its neighbor routers as 86 point-to-point links in its router-LSA. Network-LSAs are not used. 88 o In addition to full-topology LSAs, partial-topology LSAs may be 89 used to reduce the size of router-LSAs. Such LSAs are formatted 90 as standard LSAs, but advertise links to only a subset of 91 neighbors. 93 o Optionally, differential Hellos can be used, which reduce 94 overhead by reporting only changes in neighbor states. 96 This document describes the use of OSPF-MDR in a single-hop broadcast 97 network, which is a special case of a MANET in which each router is a 98 (one-hop) neighbor of each other router. Unlike an OSPF broadcast 99 interface, such an interface can have a different cost associated 100 with each neighbor. An example use case is when the underlying radio 101 system performs layer-2 routing, but has a different number of 102 (layer-2) hops to (layer-3) neighbors. 104 Section 2 describes the operation of OSPF-MDR in a single-hop 105 broadcast network with recommended parameter settings. Section 3 106 describes an alternative procedure which may be used to decide which 107 neighbors on a single-hop broadcast network to advertise in the 108 router-LSA. Section 4 describes a simplified version of the MDR 109 selection algorithm for single-hop networks. 111 The alternative procedure of Section 3 and the simplified algorithm 112 of Section 4 are optional and MUST NOT be used if it is possible for 113 two routers in the network to be more than one hop from each other. 115 1.1. Terminology 117 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 118 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 119 document are to be interpreted as described in [RFC2119]. 121 2. Operation in a Single-Hop Broadcast Network 123 When OSPF-MDR is used in a single-hop broadcast network, the 124 following parameter settings and options (defined in [RFC5614]) 125 should be used: 127 o AdjConnectivity SHOULD be equal to 2 (biconnected), MAY be equal 128 to 1 (uniconnected), and SHOULD NOT be equal to 0 (full topology). 130 o An adjacency SHOULD be eliminated if neither the router nor 131 the neighbor is an MDR or BMDR (see Section 7.3 of [RFC5614]). 133 o LSAFullness MUST be equal to 4 or 5 if full-topology LSAs are 134 required. (The value 5 is defined in Section 3 of this document.) 136 o LSAFullness MAY be equal to 1 (min-cost LSAs) if full-topology 137 LSAs are not required. This option reduces the number of 138 advertised links while still providing shortest paths. 140 If AdjConnectivity equals 1 or 2 and full-topology LSAs are used, 141 OSPF-MDR running on a single-hop broadcast network has the following 142 properties: 144 o A single MDR is selected, which becomes adjacent with every other 145 router, as in an OSPF broadcast network. 147 o Two BMDRs are selected. This occurs because the MDR selection 148 algorithm ensures that the MDR/BMDR backbone is biconnected. 149 If AdjConnectivity = 2, every non-MDR/BMDR router becomes adjacent 150 with one of the BMDRs in addition to the MDR. 152 o When all adjacencies are fully adjacent, the router-LSA for each 153 router includes point-to-point (type 1) links to all bidirectional 154 neighbors (in state 2-Way or greater). 156 3. Originating Router-LSAs 158 A router running OSPF-MDR with LSAFullness = 4 includes in its 159 router-LSA point-to-point (type 1) links for all fully adjacent 160 neighbors, and for all bidirectional neighbors that are routable. A 161 neighbor is routable if the SPF calculation has produced a route to 162 the neighbor and a flexible quality condition is satisfied. 164 This section describes an alternative procedure which MAY be used 165 instead of the procedure described in Section 6 of [RFC5614], to 166 decide which neighbors on a single-hop broadcast network to advertise 167 in the router-LSA. The alternative procedure will correspond to 168 LSAFullness = 5, and is interoperable with the other choices for 169 LSAFullness. This procedure avoids the need to check whether a 170 neighbor is routable, and thus avoids having to update the set of 171 routable neighbors. 173 If LSAFullness = 5, then the Selected Advertised Neighbor Set (SANS) 174 is the same as specified for LSAFullness = 4, and the following steps 175 are performed instead of the first paragraph of Section 9.4 in 176 [RFC5614]. 178 (1) The MDR includes in its router-LSA a point-to-point (type 1) link 179 for each fully adjacent neighbor. (Note that the MDR becomes 180 adjacent with all of its neighbors.) 182 (2) Each non-MDR router includes in its router-LSA a point-to-point 183 link for each fully adjacent neighbor, and, if the router is 184 fully adjacent with the MDR, for each bidirectional neighbor j 185 such that the MDR's router-LSA includes a link to j. 187 To provide rationale for the above procedure, let i and j be two 188 non-MDR routers. Since the SPF calculation (Section 16.1 of 189 [RFC2328]) allows router i to use router j as a next hop only if 190 router j advertises a link back to router i, routers i and j must 191 both advertise a link to each other in their router-LSAs before 192 either can use the other as a next hop. Therefore, the above 193 procedure for non-MDR routers (Step 2) implies there must exist a 194 path of fully adjacent links between i and j (via the MDR) in 195 both directions before this can happen. The above procedure for 196 non-MDR routers is similar to one described in Section 4.6 of 197 [RFC6845] for non-DR routers. 199 4. MDR Selection Algorithm 201 The MDR selection algorithm of [RFC5614] simplifies as follows in 202 single-hop networks. The resulting algorithm is similar to the DR 203 election algorithm of OSPF, but is slightly different (e.g., two 204 Backup MDRs are selected). The following simplified algorithm is 205 interoperable with the full MDR selection algorithm. 207 Note that lexicographic order is used when comparing tuples of the 208 form (RtrPri, MDR Level, RID). Also note that each router will form 209 adjacencies with its parents and dependent neighbors. In the 210 following, the term "neighbor" refers to a bidirectional neighbor (in 211 state 2-Way or greater). 213 Phase 1 (creating the neighbor connectivity matrix) is not required. 215 Phase 2: MDR Selection 217 (2.1) The set of Dependent Neighbors is initialized to be empty. 219 (2.2) If the router has a larger value of (RtrPri, MDR Level, RID) 220 than all of its (bidirectional) neighbors: the router selects 221 itself as an MDR, selects its BMDR neighbors as Dependent 222 Neighbors if AdjConnectivity = 2, then proceeds to Phase 4. 224 (2.3) Otherwise, if the router's MDR Level is currently MDR, then it 225 is changed to BMDR before executing Phase 3. 227 Phase 3: Backup MDR Selection 229 (3.1) Let Rmax be the neighbor with the largest value of (RtrPri, MDR 230 Level, RID). 232 (3.2) Determine whether or not there exist two neighbors, other than 233 Rmax, with a larger value of (RtrPri, MDR Level, RID) than the 234 router itself. 236 (3.3) If there exist two such neighbors, then the router sets its MDR 237 Level to MDR Other. 239 (3.4) Else, the router sets its MDR Level to BMDR, and if 240 AdjConnectivity = 2, adds Rmax and its MDR/BMDR neighbors as 241 Dependent Neighbors. 243 (3.5) If steps 3.1 through 3.4 resulted in the MDR Level changing 244 from MDR Other to BMDR, then execute Step 2.2 again before 245 proceeding to Phase 4. (This is necessary because running Step 246 2.2 again can cause the MDR Level to change to MDR.) 248 Phase 4: Parent Selection 250 Each router selects a Parent and (if AdjConnectivity = 2) a Backup 251 Parent for the single-hop broadcast network. The Parent for a non- 252 MDR router will be the MDR. The Backup Parent for an MDR Other, if 253 it exists, will be a BMDR. Each non-MDR router becomes adjacent with 254 its Parent and its Backup Parent, if it exists. The parent selection 255 algorithm is already simple, so a simplified version is not given 256 here. 258 The Parent and Backup Parent are analogous to the Designated Router 259 and Backup Designated Router interface data items in OSPF. As in 260 OSPF, these are advertised in the DR and Backup DR fields of each 261 Hello sent on the interface. 263 5. Security Considerations 265 This document describes the use of OSPF-MDR in a single-hop broadcast 266 network, and raises no security issues in addition to those already 267 covered in [RFC5614]. 269 6. IANA Considerations 271 This document has no IANA considerations. 273 7. Normative References 275 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 276 Requirement Levels", BCP 14, RFC 2119, March 1997. 278 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. 280 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 281 for IPv6", RFC 5340, July 2008. 283 [RFC5614] Ogier, R. and P. Spagnolo, "Mobile Ad Hoc Network (MANET) 284 Extension of OSPF Using Connected Dominating Set (CDS) 285 Flooding", RFC 5614, August 2009. 287 8. Informative References 289 [RFC6845] Sheth, N., L. Wang, and J. Zhang, "OSPF Hybrid Broadcast 290 and Point-to-Multipoint Interface Type", RFC 6845, 291 January 2013. 293 Author's Address 295 Richard G. Ogier 296 Email: rich.ogier@earthlink.net