idnits 2.17.1 draft-ietf-ospf-dc-06.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** Looks like you're using RFC 2026 boilerplate. This must be updated to follow RFC 3978/3979, as updated by RFC 4748. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- ** The document seems to lack a 1id_guidelines paragraph about Internet-Drafts being working documents. ** The document seems to lack a 1id_guidelines paragraph about 6 months document validity. == No 'Intended status' indicated for this document; assuming Proposed Standard == The page length should not exceed 58 lines per page, but there was 4 longer pages, the longest (page 2) being 60 lines == It seems as if not all pages are separated by form feeds - found 0 form feeds but 5 pages Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack an Introduction section. ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) Miscellaneous warnings: ---------------------------------------------------------------------------- -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (February 2003) is 7735 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: 'RFC2328' is defined on line 193, but no explicit reference was found in the text Summary: 5 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Sira Panduranga Rao 3 Internet Draft UTA 4 Expiration Date: September 2003 Alex Zinin 5 File name: draft-ietf-ospf-dc-06.txt Alcatel 6 Abhay Roy 7 Cisco Systems 9 February 2003 11 Detecting Inactive Neighbors over OSPF Demand Circuits 12 draft-ietf-ospf-dc-06.txt 14 Status of this Memo 16 This document is an Internet-Draft and is in full conformance with 17 all provisions of Section 10 of RFC2026. 19 Internet Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its Areas, and its Working Groups. Note that other 21 groups may also distribute working documents as Internet Drafts. 23 Internet Drafts are draft documents valid for a maximum of six 24 months. Internet Drafts may be updated, replaced, or obsoleted by 25 other documents at any time. It is not appropriate to use Internet 26 Drafts as reference material or to cite them other than as a "working 27 draft" or "work in progress". 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 Abstract 37 OSPF is a link-state intra-domain routing protocol used in IP 38 networks. OSPF behavior over demand circuits is optimized in RFC1793 39 to minimize the amount of overhead traffic. A part of OSPF demand 40 circuit extensions is the Hello suppression mechanism. This technique 41 allows a demand circuit to go down when no interesting traffic is 42 going through the link. However, it also introduces a problem, where 43 it becomes impossible to detect a OSPF-inactive neighbor over such a 44 link. This memo addresses the above problem by the neighbor probing 45 mechanism. 47 1. Motivation 49 In some situations, when operating over demand circuits, the remote 50 neighbor may be unable to run OSPF, and, as a possible result, unable 51 to route application traffic. Possible scenarios include: 53 o The OSPF process might have died on the remote neighbor. 55 o Oversubscription (Section 7 of [RFC1793]) may cause a 56 continuous drop of application data at the link level. 58 The problem here is that the local router cannot identify the 59 problems such as this, since Hello exchange is suppressed on demand 60 circuits. If the topology of the network is such that other routers 61 cannot communicate their knowledge about the remote neighbor via 62 flooding, the local router and all routers behind it will never know 63 about the problem, so application traffic may continue being 64 forwarded to the OSPF-incapable router. 66 This memo describes a backward-compatible neighbor probing mechanism 67 based on the details of the standard flooding procedure followed by 68 OSPF routers. 70 2. Proposed Solution 72 The solution this document proposes uses the link-state update 73 packets to detect whether the OSPF process is operational on the 74 remote neighbor. We call this process "Neighbor probing". The idea 75 behind this technique is to allow either of the two neighbors 76 connected over a demand circuit to test the remote neighbor at any 77 time (see Section 2.1). 79 The routers across the demand circuit can be connected by either a 80 point-to-point link, a virtual link, or a point-to-multipoint 81 interface. The case of routers connected by broadcast networks or 82 NBMA is not considered, since Hello suppression is not used in these 83 cases (Section 3.2 [RFC1793]). 85 The neighbor probing mechanism is used as follows. After a router 86 has synchronized the LSDB with its neighbor over the demand circuit, 87 the demand circuit may be torn down if there is no more application 88 traffic. When application traffic starts going over the link, the 89 link is brought up, and the routers may probe each other. The routers 90 may also periodically probe each other any time the link is up (could 91 be implemented as a configurable option) with the caution that OSPF 92 packets sent as part of neighbor probing are not considered as 93 interesting traffic and do not cause the demand circuit to remain up 94 (relevant details of implementation are outside of the scope of this 95 document). 97 The case when one or more of the router's links are oversubscribed 98 (see section 7 of [RFC1793]) should be considered by the 99 implementations. In such a situation even if the link status is up 100 and application data is being sent on the link, only a limited number 101 of neighbors is really reachable. To make sure temporarily 102 unreachable neighbors are not mistakenly declared down, Neighbor 103 probing should be restricted to those neighbors that are actually 104 reachable (i.e., there is a circuit established with the neighbor at 105 the moment the probing procedure needs to be initiated). This check 106 itself is also considered an implementation detail. 108 2.1 Neighbor Probing 110 The neighbor probing method described in this section is completely 111 compatible with standard OSPF implementations, because it is based on 112 standard behavior that must be followed by OSPF implementations in 113 order to keep their LSDBs synchronized. 115 When a router needs to verify OSPF capability of a neighbor reachable 116 through a demand circuit, it should flood to the neighbor any LSA in 117 its LSDB that would normally be sent to the neighbor during the 118 initial LSDB synchronization process (it most cases such an LSA must 119 have already been flooded to the neighbor by the time the probing 120 procedure starts). For example, the router may flood its own router- 121 LSA (without originating a new version), or the neighbor's own 122 router-LSA. If the neighbor is still alive and OSPF-capable, it 123 replies with a link state acknowledgement or a link state update (an 124 implied acknowledgement) and the LSA is removed from the neighbor's 125 retransmission list. The implementations should limit the number of 126 times an LSA can be retransmitted when used for neighbor probing. If 127 no acknowledgement (explicit or implicit) is received for a 128 predefined period of time, the probing router should treat this as 129 evidence of the neighbor's unreachability (proving wrong the 130 assumption of reachability used in [RFC1793]) and should bring the 131 adjacency down. 133 Note that when the neighbor being probed receives such a link state 134 update packet, the received LSA has the same contents as the LSA in 135 the neighbor's LSDB, and hence should normally not cause any 136 additional flooding. However, since LSA refreshes are not flooded 137 over demand circuits, the received LSA may have a higher Sequence 138 Number. This will result in the first probe LSA being flooded further 139 by the neighbor. Note that if the current version of the probe LSA 140 has already been flooded to the neighbor, it will not be propagated 141 any further by the neighbor. Also note that in any case subsequent 142 (non-first) probe LSAs will not effect further flooding until the 143 LSA's sequence number is incremented. 145 Again, the implementation should insure (through internal mechanisms) 146 that OSPF link state update packets sent over the demand circuit for 147 the purpose of neighbor probing do not prevent that circuit from 148 being torn down. 150 3. Support of Virtual Links and Point-to-multipoint Interfaces 152 Virtual links can be treated analogous to point-to-point links and so 153 the techniques described in this memo are applicable to virtual links 154 as well. The case of point-to-multipoint interface running as demand 155 circuit (section 3.5 [RFC1793]) can be treated as individual point- 156 to-point links, for which the solution has been described in section 157 2. 159 4. Compatibility issues 161 All mechanisms described in this document are backward-compatible 162 with standard OSPF implementations. 164 5. Considerations 166 In addition to the lost functionality mentioned in Section 6 of 167 [RFC1793], there is an added overhead in terms of the amount of data 168 (link state updates and acknowledgements) being transmitted due to 169 neighbor probing whenever the link is up and thereby increasing the 170 overall cost. 172 6. Acknowledgements 174 The original idea of limiting the number of LSA retransmissions on 175 demand circuits (used as part of the solution described in this 176 document) and its implementation belong to Padma Pillay-Esnault and 177 Derek Yeung. 179 The authors would like to thank John Moy, Vijayapal Reddy Patil, SVR 180 Anand, and Peter Psenak for their comments on this work. 182 A significant portion of Sira's work was carried out as part of the 183 HFCL-IISc Research Project (HIRP), Bangalore, India. He would like to 184 thank the team for their insightful discussions. 186 7. Security Considerations 188 The mechanism described in this document does not modify security 189 aspects of the OSPF routing protocol. 191 8. Normative References 193 [RFC2328] 194 Moy, J., "OSPF Version 2", RFC 2328, April 1998. 196 [RFC1793] 197 Moy, J., "Extending OSPF to Support Demand Circuits", RFC 1793, 198 April 1995. 200 Appendix A. Configurable Parameters 202 This memo defines the following additional configuration parameters 203 for OSPF interfaces. 205 ospfIfDemandNbrProbe 206 Indicates whether or not neighbor probing is enabled to deter- 207 mine whether or not the neighbor is inactive. Neighbor probing 208 is disabled by default. 210 ospfIfDemandNbrProbeRetxLimit 211 The number of consecutive LSA retransmissions before the 212 neighbor is deemed inactive and the neighbor adjacency is 213 brought down. Sample value is 10 consecutive LSA retransmis- 214 sions. 216 ospfIfDemandNbrProbeInterval 217 Defines how often the neighbor will be probed. Sample value is 218 2 minutes. 220 Authors' addresses 222 Sira Panduranga Rao Alex Zinin 223 The University of Texas at Arlington Alcatel 224 Arlington, TX 76013 Sunnyvale, CA 225 Email: siraprao@hotmail.com E-mail: zinin@psg.com 227 Abhay Roy 228 Cisco Systems 229 170 W. Tasman Dr. 230 San Jose,CA 95134 231 USA 232 E-mail: akr@cisco.com