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Internet-Draft ARA August 1997 Expiration Date: February 1998 File name: draft-ietf-ospf-ara-00.txt The OSPF Address Resolution Advertisement Option Rob Coltun FORE Systems (301) 571-2521 rcoltun@fore.com Juha Heinanen Telecom Finland +358 400 500 958 jh@tele.fi Status Of This Memo This document is an Internet-Draft. Internet-Drafts are working docu- ments of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute work- ing documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress". Coltun, Heinanen [Page 1] Internet-Draft ARA August 1997 To learn the current status of any Internet-Draft, please check the "1id-abstracts.txt" listing contained in the Internet- Drafts Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). Coltun, Heinanen [Page 2] Internet-Draft ARA August 1997 Table Of Contents 1.0 Abstract ................................................. 5 2.0 Overview ................................................. 5 2.1 Acknowledgments .......................................... 5 3.0 A Brief Comparison Of Address Resolution Models .......... 6 4.0 ARA Associations ......................................... 7 5.0 Examples ................................................. 8 5.1 Example 1: Intra-Area .................................... 8 5.2 Example 2: Inter-Area .................................... 9 6.0 Description Of ARA Packet Formats ........................ 10 6.1 Vertex Types And Vertex Identifiers ...................... 11 7.0 Distribution Of ARA Information .......................... 11 8.0 ARA Routing Table Extensions ............................. 13 8.1 Adding ARA Routing Table Extensions ...................... 13 8.1.1 Modifications To The Intra-Area Route Calculation ...... 14 8.1.2 Modifications To The Inter-Area Route Calculations ..... 15 8.1.3 Modifications To The AS External Route Calculations .... 15 9.0 Receiving ARAs ........................................... 16 10.0 Additional Data Structures And APIs ..................... 17 Appendix A: ARA Data Formats ................................. 17 A.1 ARA Formats .............................................. 17 A.1.1 The ARA Header ......................................... 18 A.1.2 Router ARAs ............................................ 20 A.1.3 Network ARAs ........................................... 20 Coltun, Heinanen [Page 3] Internet-Draft ARA August 1997 A.1.4 Vertex Association ..................................... 22 A.1.5 Resolution Information ................................. 23 A.1.6 ATM Address ............................................ 24 References ................................................... 26 Coltun, Heinanen [Page 4] Internet-Draft ARA August 1997 1.0 Abstract This document defines an OSPF option which enables routers to distri- bute IP to link-layer address resolution information. An OSPF Address Resolution Advertisement (ARA) may include link-layer specific func- tionality such as a multipoint-to-point connection identifier along with the address resolution information. The ARA option can be used to support router-to-router inter-subnet shortcut architectures such as those described in [HEIN] 2.0 Overview Along with the evolution of switched layer 2 technologies comes the ability to provide inter-subnet shortcut and cut-through data switch- ing (bypassing router intervention). Before the ingress devices is able to dynamically set up the switched path it must have the link- layer address of the egress device. Acquisition of the egress device's link-layer address may be through configuration or through a discovery mechanism which resolves an IP address (or an IP end-point identifier) to a link-layer address. This document introduces a method for IP to link-layer address resolu- tion to support router-to-router and router-to-network inter-subnet shortcuts. The ARA option supports both topology-derived and data- driven shortcuts architectures with simple extensions to OSPF. Dis- tribution of address resolution information is performed using stan- dard OSPF flooding mechanisms. This document does not define an architecture but is meant to be used with architectures such as those defined in [HEIN]. The ARA option is designed to support the follow- ing operations. Shortcuts between core or access routers within ISP Backbones. Shortcuts in enterprise networks between routers in the same OSPF area, between OSPF internal routers and autonomous system border routers (ASBR) and between routers and servers. Distributed router architectures. Interoperation with ION NHRP and MPOA. Inter-subnet multicast shortcuts using LIJ or Point-to-MultiPoint procedures. 2.1 Acknowledgments Coltun, Heinanen [Page 5] Internet-Draft ARA August 1997 The author would like to thank Lou Berger, John Moy and Yiqun Cai, and the rest of the OSPF Working Group for the ideas and support they have given to this project. 3.0 A Brief Comparison Of Address Resolution Models Current models of inter-subnet address resolution have taken the form of a query/response protocol as in the case of [NHRP]. In this model the ingress device originates a resolution request which is forwarded hop-by-hop through a series of NHRP servers towards the destination IP address contained in the request. The the last-hop server (the one that is closest to the destination) responds to the request with the link-layer address that it associates with the requested IP address. The returned address may be the address of the requested host system or the address of a router which is on the path to the destination. Upon receiving a response to its request, the ingress device sets up a shortcut path to be used for data transfer. The resolution request mechanism has the following characteristics. o Routers and hosts may participate in the request mechanism. The participating devices are discovered through polling. o The request mechanism requires polling by the ingress device to detect topology and reachability changes. Changes in the topology could result in packet loss for the polling interval. Stable routing loops may form as a result of topology changes (given a limited set of failure conditions and topologies). o Requests are unreliable and are subject to packet loss. o It is recommended that the request mechanism be limited to intra- area shortcuts (although with correctly designed topologies this limi- tation may be over restrictive). o The target of a request may be a host or network addresses (exclud- ing class D (multicast) networks). o The response to the request allows the requesting entity to set up a point-to-point shortcut. Given the above characteristics, the query-response protocol may not be the optimal mechanism for particular applications such as the one described in [HEIN]. The ARA option has the following characteristics. o Only routers participate in the ARA option. Participation in the Coltun, Heinanen [Page 6] Internet-Draft ARA August 1997 ARA option is discovered through address resolution advertisements. o The ARA option does not require polling by the ingress device to detect topology and reachability changes. Changes in the topology and system reachability may result in packet loss (or transient loops) for the OSPF convergence time. Additionally, since topology changes are determined as a result of OSPF's SPF calculation (which results in loop-free paths), shortcuts derived from the ARA option will never result in stable routing loops. o Address resolution distribution is reliable and is not subject to packet loss. o The target of ARA derived shortcuts may be routers and and their connected networks within an OSPF area. Inter-area shortcuts are sup- ported when the destination is associated with an OSPF AS boundary router advertisement (e.g., networks external to the OSPF autonomous system). o The ARA option allows the requesting entity to set up point-to-point shortcuts as well as shortcuts that join point-to-multipoint and multipoint-to-point trees. o Routers that run the ARA option can interoperate with systems run- ning NHRP. o The ARA option may easily be extended to support inter-subnet multi- cast shortcuts. 4.0 ARA Associations The ARA option defines three types of advertisements. These include 1) intra-area router associations, 2) intra-area network associations, and 3) inter-area ASBR associations. Associations correspond to a piece of the OSPF topology. Intra-area router associations correspond to link-layer reachability of a router within the local area, intra- area network associations correspond to link-layer reachability of a router's directly connected networks (also within the local area), and inter-area ASBR associations correspond to ASBRs that may be in the local or in a remote area. An ingress router can use these associa- tions as follows. Intra-area router associations are used to setup shortcuts to routers within the local area. Data sent over the shortcut will be forwarded to destinations local to and beyond the router including ones that are in the local area, in a remote area or external to the autonomous system. A destination that is "beyond Coltun, Heinanen [Page 7] Internet-Draft ARA August 1997 the router" is determined by the OSPF topology map. Intra-area network associations (which may advertise a host, net- work or IP multicast address) are used to setup a shortcuts to systems whose address fall within the range of the advertised network. Inter-area ASBR associations are used to setup shortcuts to ASBRs that are in the local or remote area. These shortcuts are used to send data to destinations that are external to the autonomous system and reachable via the ASBR. The ARA option maintains a list of all association for a specific ver- tex and vertex type in an ARA Association Table. The lookup keys to an entry in the table include the vertex type, vertex ID and, if the scope is area-local, the area ID. Associations are added to the routing table during the OSPF routing table calculation (see the section entitled Adding ARA Routing Table Extensions below). So, in addition to the standard information fields contained in the routing table (i.e., IP network number, IP mask, next-hop interface, etc.), the routing table is extended to contain link-layer associations (via a reference to the ARA Association Table). The use of the extensions are ARA user application specific and beyond the scope of this document. See [HEIN] for an example of an ARA user application. 5.0 Examples 5.1 Example 1: Intra-Area Consider the sample single-area topology in Figure 1 below. In this example RT1, RT2 and RT5 support the ARA option (by definition they also support the Opaque LSA option) and RT4 supports the Opaque LSA option only (this is necessary so that RT4 redistributes the ARAs ori- ginated by RT1, RT2 and RT5). RT2 and RT5 have each originated an ARA with an intra-area router association and RT5 has originated an ARA with an intra-area network association for N5. As a result of running the routing table calculation, RT1 would have entries for N1-N8 in its routing table. The entry for N2 would refer- ence the link-layer associations distributed in RT2's R-ARA, the entries for N3, N4, N6, N7, N8 would reference the link-layer associa- tions distributed in RT5's R-ARA and the entry for N5 would reference the link-layer associations distributed in RT5's intra-area N-ARA. Coltun, Heinanen [Page 8] Internet-Draft ARA August 1997 + ARA | +---+ N3 N5 N1|--|RT1|\ \ N4 / | +---+ \ \ | / + \ \|/ \+---+ +---+ |RT4|------------|RT5|ARA +---+ +---+ + ARA / | N7 | +---+ / | / N2|--|RT2|/ | / | +---+ +---+ +---+/ + |RT3|-----------|RT6|----N8 +---+ +---+ | | +---------+ N6 Figure 1: Sample Single-Area Toplogy 5.2 Example 2: Inter-Area Consider the sample 2-area topology in Figure 2 below. In this exam- ple RT1, RT2, RT3, RT4 and RT6 support the ARA option and RT5 supports the Opaque option. N3-N7 are AS external routes and RT5 and RT6 are ASBRs. RT4 is an area-border router and originates LS Type-4 LSAs on behalf of RT5 and RT6 and a LS Type-3 LSA for N8 into area 1.1.1.1. RT1, RT2, RT3 and RT4 have originated intra-area R-ARAs, and RT6 has originated an inter-area R-ARA. As a result of running the routing table calculation, RT1 would have entries for N1-N8 in its routing table. The entry for N2 would refer- ence the link-layer associations distributed in RT3's R-ARA, the entries for N3, N4, N5 and N8 would reference the link-layer associa- tions distributed in RT4's intra-area R-ARA (i.e., R1 can't see link- layer information beyond the area border router) and the entries for N6 and N7 would reference the link-layer associations distributed in RT6's inter-area R-ARA. Coltun, Heinanen [Page 9] Internet-Draft ARA August 1997 | + ARA ARA | | +---+ +---+ | N3 N5 N1|--|RT1|----|RT2|\ | \ N4 / | +---+ +---+ \ | \ | / + \ ARA \|/ \+---+ +---+ |RT4|------|RT5| +---+ +---+ + ARA / | | N6 | +---+ / | | / N2|--|RT3|/ | ARA / | +---+ | +---+/ + | |RT6|----N7 | +---+ | | | | | +---+ | |RT7| | +---+ | | | +-----+ | N8 | | | Area 1.1.1.1 | OSPF Backbone ------------------------|------------------------- Figure 2: Sample Area Toplogy 6.0 Description Of ARA Packet Formats ARA LSAs (ARAs) include the information necessary to associate an IP entity (i.e., a router, network or host) with a link-layer address. The ARA option allows further refinement so that an association may additionally include information about QoS control services and link- layer functionality (e.g., for Point-to-MultiPoint and MultiPoint-to- point connections). ARA advertisements may also include a logical network identifier field, which is to be used when more than one vir- tual overlay network is present within the OSPF domain. The ARA format allows more than one equivalent association to been advertised by a router for a specific vertex. The association can include a preference which identifies the advertising router's Coltun, Heinanen [Page 10] Internet-Draft ARA August 1997 relative preference for the equivalent associations. Equivalent asso- ciations are ones that have identical link service type, integrated service type and logical network identifier fields. ARA information is encapsulated in Opaque LSAs. Three LS Types (LS Type 9, 10 and 11) constitute the Opaque class of link-state adver- tisements. Each of the three Opaque link-state types have a scope associated with them so that distribution of the information may be limited appropriately by the originator of the LSA. Opaque LSAs have a sub-type which identifies the specific information that is carried within the LSA. The ARA Opaque types are Opaque-type 1 and 2. The flooding scope for specific vertex types is realized by embedding the association in the appropriate Opaque LSA type. 6.1 Vertex Types And Vertex Identifiers The Vertex Type identifies the piece of IP topology that the link- layer information is being associated with. The Vertex Type may be a router or a network (a host is considered a network with a mask of 255.255.255.255). Vertex type 1 ARAs advertise router address resolution associations. These associations are used to advertise the router's link-layer attachments. A Vertex Type of 1 is identified by an Opaque type of 1. The vertex identifier for a Router ARA (R-ARA) is the advertising router field of the ARA header. Intra-area vertex type-1 advertise- ments are included in Opaque Type-10 LSAs (their flooding scope is area-local). Inter-area vertex type-1 advertisements are included in Opaque Type-11 LSAs (their flooding scope is domain-wide). Inter-area vertex type-1 advertisements are originated by as AS boundary routers. Vertex type 2 ARAs advertise IP network address resolution associa- tions (the network may be a IP multicast (class D) network). These associations are used to advertise the link-layer associations for a router's directly connected network. Vertex Type 2 advertisements are be included in area-local (LS Type 10) advertisements. A Vertex Type of 2 is identified by an Opaque type of 2. The vertex identifier (the network and mask) for a Network ARA (N-ARA) is contained in the body of the advertisement. A N-ARA may only identify a single network (i.e., lists of networks are not permitted). If a router wishes to advertise several associations for a single ver- tex it has two options. It may originate multiple (N or R) ARAs each containing different associations or it may originate a single (N or R) ARA containing a list of associations. 7.0 Distribution Of ARA Information Coltun, Heinanen [Page 11] Internet-Draft ARA August 1997 In general, OSPF is composed of two components. It's transport com- ponent deals with adjacency formation and reliable distribution of topology information. The second component tracks topology informa- tion changes and organizes the topology information that has gathered from other routers into to a topology map which is used to build the router's routing table. The ARA option uses both the OSPF transport component and of the topology map component. ARA uses the OSPF Opaque LSA as defined in [OPAQ] for distribution of resolution information. The Opaque LSA is an optional mechanism to allow for distribution of information. This information may be used directly by OSPF or by other protocols and mechanisms such as the ARA option. Opaque LSAs use standard OSPF link-state database flooding mechanisms for distribution. Each of the three Opaque types (LS Types 9, 10 and 11) have a scope associated with them so that distribution of the information throughout the OSPF topology may be limited if appropriate. ARA information has topology-specific scopes (i.e., dif- ferent Opaque types) depending on the ARA vertex type (see the section entitled Vertex Types and Vertex Identifiers). The ARA option uses the topology map component of OSPF to validate the information that is received by the distribution mechanism and to install the associations into the routing table. Validation is needed because topology information contained in the OSPF link-state database may be stale (i.e., the originator of the information is no longer reachable). It is envisioned that an implementor designs an ARA user application interface to which facilitates 1) flooding of ARA information to other routers in the OSPF network, 2) receiving ARA information from other routers in the OSPF network and 3) determining the validity (and change of validity) of ARA information. For the realization of 1 above, an implementation must provide an API which allows the ARA user application to have its local OSPF entity distribute resolution information in the ARA defined format (if the scope is area-local, the area must also be supplied). In addition, the API must support the purging of associations that were previously originated by the router if they are no longer valid and send out new versions when the association information has changed. For the realization of 2 and 3 above, this document extends the rout- ing table to include the associations that have been advertised by the ARA capable routers. (i.e,. the routing table provides the API for the ARA user application). That is, in addition to the standard information fields contained in the routing table (i.e., IP network number, IP mask, next-hop interface, etc.), the routing table is extended to contain link-layer associations. The associations are Coltun, Heinanen [Page 12] Internet-Draft ARA August 1997 added to the routing table during the OSPF routing table calculation (see the section on Adding ARA Routing Table Extensions below). The use of the extensions are ARA user application specific and beyond the scope of this document. See [HEIN] for an example of an ARA user application. The following section defines the mechanism to calculate the ARA rout- ing table extensions. 8.0 ARA Routing Table Extensions OSPF determines reachability and topology changes by performing the algorithms described in the section entitled "Calculation of the rout- ing table" (see section 16 of [OSPF]). ARAs are included in this cal- culation for the purpose of binding link-layer associations to IP routing table entries. A link-layer association consists of the list of link-layer addresses, link-layer service types and other link-layer objects such as Point- to-MultiPoint call identifiers and QoS service specific information. (See section Appendix A for a more complete description of the specific link-layer information distributed in ARAs). The associa- tions that are bound to a routing table entry are the associations that are closest to the originator of the routing table's network entry. The closest associations are determined during to the construc- tion of the OSPF topology map. The associations that are bound to the routing table entries are subsequently used by the ARA user applica- tion to setup shortcut paths. Because a link-layer association may be bound to more than one entry in the routing table, an ARA implementa- tion keeps a table of ARA derived link-layer associations which is referenced by the routing table entry. An entry in the ARA Associa- tion Table consists of a list of all association for a specific vertex and vertex type. The lookup keys to an entry in the table include the vertex type, vertex ID and, if the scope is area-local, the area ID. 8.1 Adding ARA Routing Table Extensions Section 16 of the OSPF specification is modified for the purpose of adding the ARA routing table extensions. Transit vertex data struc- tures and the internal representation of Type-3, Type-4 and Type-5 LSAs are extended to be able to reference a list of link-layer associ- ations (i.e., they have a reference to the ARA Association Table). The vertex and LSA's list of link-layer associations are added to the routing table along with the entry. Coltun, Heinanen [Page 13] Internet-Draft ARA August 1997 8.1.1 Modifications To The Intra-Area Route Calculation The intra-area route calculation is enhanced (specifically section 16.1 step 3) as follows. o Call the vertex that is about to be added to the SPF tree ver- tex M. If vertex M was originated by the calculating router skip this procedure. o If vertex M is a transit network vertex lookup the link-layer association entry in the ARA Association Table. This entry's vertex type will be type-2, the vertex identifier will consist of a network and mask which are equivalent to those found in vertex M and its area ID will be the one that is associated with the shortest-path calculation. o If an entry is found reference this entry in vertex M's link- layer association field. o If vertex M is a router vertex lookup the an entry in the ARA Association Table. This entry's vertex type will be type-1, the vertex identifier will be vertex M's advertising router and its area ID will be the one that is associated with the shortest-path calculation. o If an entry is found reference this entry in vertex M's link- layer association field. o If no link-layer association entries are found, and vertex M's parent vertex has link-layer association information, vertex M inherits it's parent vertex's information (else the information field is left blank). o When vertex M is added to the routing table, copy vertex M's link-layer association list into the routing table entry's link- layer association field. The following describes the enhancements to section 16.1 step 2 of [OSPF] which adds intra-area stub networks to the routing table. o Before adding the stub network to the routing table lookup the entry in the ARA Association Table. This entry's vertex type will be type-2, the vertex identifier will consist of a network and mask which are equivalent to those found in the stub network and its area ID will be the one that is associated with the shortest-path calculation. Coltun, Heinanen [Page 14] Internet-Draft ARA August 1997 o If an entry is found copy the entry's association information into the routing table entry's link-layer association field. o If an entry is not found and the stub network's advertising router vertex has link-layer association information, the routing table entry will use the advertising router's information (else the information field is left blank). 8.1.2 Modifications To The Inter-Area Route Calculations The following describes the enhancements to OSPF sections 16.2, 16.3, 16.5 which calculate inter-area routes. Before the destination associ- ated with the LSA is added to the routing table the following is per- formed. o If the LSA is a Type-3 summary LSA, locate the area border router (ABR) that originated the advertisement. If link-layer association information is available for the ABR entry, copy the contents of the ABR's link-layer association information field into the routing table entry's link-layer association field. o If the LSA is a Type-4 summary LSA, lookup the entry in the ARA Association Table. This entry's vertex type will be type-1, the vertex identifier will the Type-4's Link-State ID (the link-state ID identifies the ASBR) the area ID will not be used (the ARAs have domain-wide scope). o If an entry is found copy the entry's association information into the routing table entry's link-layer association field. o If an entry is not found locate the area border router (ABR) that originated the Type-4 advertisement. Copy the contents of the ABR's link-layer association information field into the rout- ing table entry's link-layer association field. 8.1.3 Modifications To The AS External Route Calculations The following describes the enhancements to OSPF sections 16.4 and 16.6 which calculate AS external routes. Before the destination asso- ciated with the LSA is added to the routing table the following is performed. o If the LSA has a forwarding address, look up the forward address in the routing table (this will be an internal OSPF Coltun, Heinanen [Page 15] Internet-Draft ARA August 1997 route). Copy the contents of the route's link-layer association information field into the external route's routing table entry's link-layer association field. o If the LSA does not have a forwarding address, copy the con- tents of the advertising ASBR's link-layer association informa- tion field into the routing table entry's link-layer association field. Note that the ASBR's association information may have been added from an intra-area or domain-wide R-ARAs. 9.0 Receiving ARAs After the ARA has been processed according to section 13 of [OSPF] the ARA has been determined to be 1) a newer invocation of with the same contents, 2) a newer invocation with different contents, 3) a new ARA or 4) a newer invocation that is being flushed by the ARA's origina- tor. Actions need to be taken if the ARA is new, the ARA is being purged or the contents of the ARA has changed. o Lookup the ARA's vertex in the ARA Association Table. If the ARA is a LS Type-10, the table entry will reference the ARA's associated area. If the ARA is Type-11 the table entry will not be associated with an area. o If the ARA is new and there is an existing entry, add the asso- ciations found in the newly received ARA to the entry. The ARA application must be informed that new associations have been added. o If there is no existing entry, create one which contains the associations found in the ARA. Reschedule the SPF calculation. o If the ARA's contents have changed, modify the existing entry and inform the ARA application that there has been a change to the contents of the link-layer association entry for the speci- fied vertex. o If the ARA is being flushed and there is an existing entry, remove the associations from the link-layer entry that were included in the ARA. If the contents of the entry is now empty, remove the entry from the table and reschedule the SPF calcula- tion. If the entry still contains associations inform the ARA user application that there has been a change to the contents of the entry. Coltun, Heinanen [Page 16] Internet-Draft ARA August 1997 10.0 Additional Data Structures And APIs This section lists the additional data structures and APIs needed to support the OSPF ARA option. o The implementation must support the Opaque LSA option as defined in [OPAQ]. o Configuration flag to enable the OSPF ARA option. o A ARA Association Table is added. An entry in this table con- tains the list of link-layer associations for a specific vertex and vertex type. The lookup keys to an entry in the table include the vertex type, vertex ID and, if the scope is area-local, the area ID. The table is referenced by the routing table and the data structures used in the SPF calculation. o Transit vertex data structures and the internal representation of Type-3, Type-4 and Type-5 LSAs are extended to contain a reference to the an entry in the ARA Association Table. o The routing table is extended to contain a reference to the an entry in the ARA Association Table. o To be able to flood ARA information to other ARA capable routers an implementation must provide an API which allows the ARA user application to have its local OSPF entity distribute resolution information in ARA format (if the scope is area-local, a reference to the area must also be supplied). Additionally the API must be able to purge the associations that were previously distributed when they are no longer valid and send out new ver- sions when the associations information has changed. A.1 ARA Formats This document defines three different types of Address Resolution Advertisements. Each type of ARA begins with a standard 20-byte Opaque LSA header [OPAQ]. This header is described in section A.1.1. Subse- quent sections describe the specific advertisements and their content (i.e., the formats of the resolution information). Each ARA describes a link-layer association for a piece of the OSPF routing domain. Any router may originate intra-area router ARAs and network ARAs. These ARAs are distributed throughout the local area. ASBRs may originate domain-wide router ARAs. An ARA capable router Coltun, Heinanen [Page 17] Internet-Draft ARA August 1997 may use the ARAs to build shortcut paths to other ARA capable routers. A.1.1 The ARA Header All ARAs begin with a common 20-byte header. This header contains enough information to uniquely identify the ARA. The header, which is a subset of the standard LSA header, includes the ARA Vertex Type and distribution scope. The Vertex Type is derived from the Opaque Type field. The vertex identifier for a Router ARA (R-ARA) is the advertising router field of the ARA header. The vertex identifier for a Network ARA (N-ARA) is contained in the body of the advertisement. A N-ARA may only identify a single network (i.e., lists of networks are not per- mitted). A router may originate multiple (N or R) ARAs each contain- ing different associations or may originate a single (N or R) ARA con- taining a list of associations. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS age | Options | LS Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opaque Type | Opaque ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LS age The time in seconds since the ARA was originated. Options The optional capabilities supported by the described portion of the routing domain. OSPF's optional capabilities are documented in Section A.2 of [OSPF]. LS Type The type of the LSA. Each LSA type has a separate Coltun, Heinanen [Page 18] Internet-Draft ARA August 1997 advertisement format. The AR LSA as defined in this docu- ment may be Type-10 (for N-ARAs and R-ARAs with intra-area scope) or Type-11 (for ASBR R-ARA with inter-domain scope). Opaque Type The link-state ID of the Opaque LSA is divided into an Opaque Type field (the first 8 bits) and an Opaque ID (the remaining 24 bits). The Address Resolution Advertisements are Opaque-types 1 and 2. Opaque-type 1 advertisements are Router Address Resolution Advertisements and contain associ- ations for the advertising router. R-ARAs may be encapsu- lated in type-10 (Opaque) LSAs when the associations are to be distributed within the area or encapsulated in type-11 (Opaque) LSAs when the associations are to be coordinated with inter-area ASBR (LS Type-4) advertisements (i.e., the router is an ASBR). Opaque-type 2 advertisements area Network Address Resolution Advertisements and contain associations for one of the advertising router's directly connected IP networks (or hosts). N-ARAs are encapsulated in LS Type-10 (Opaque) LSAs (i.e., their scope is area local). Opaque ID A 24-bit semantic-less LSA identifier which serves to dif- ferentiate between multiple LSAs originated by the same router. The Opaque ID must be unique for an advertising router within the advertising scope of the LSA. Advertising Router The Router ID of the router that originated the ARA. For R-ARAs the Advertising Router also serves as the ARA vertex identifier. LS sequence number Detects old or duplicate ARAs. Successive instances of an ARA is given successive LS sequence numbers. See Section 12.1.6 of [OSPF] for more details. LS checksum The Fletcher checksum of the complete contents of the ARA, including the ARA header but excluding the LS age field. See Section 12.1.7 of [OSPF] for more details. Length The length in bytes of the LSA. This includes the 20 byte ARA header. Coltun, Heinanen [Page 19] Internet-Draft ARA August 1997 A.1.2 Router ARAs Opaque-type 1 advertisements are Router Address Resolution Advertise- ments and contain associations for the advertising router. R-ARAs may be encapsulated in LS Type-10 (Opaque) LSAs when the associations are to be distributed within the area or encapsulated in LS Type-11 (Opaque) LSAs when the associations are to be coordinated with inter- area ASBR (LS Type-4) advertisements (i.e., the router is an ASBR). All of the router's associations may be described in a single R-LSA or they may distributed over several R-LSAs. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS age | Options | 10 or 11 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | Opaque ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+ Vertex Association +-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+ Vertex Association +-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The body of the R-ARA consists of a list of associations for the advertising router. Each Vertex Association begins with a common 6- byte header (described in Section A.1.4) followed by association- specific resolution information (described in Section A.1.5). A.1.3 Network ARAs Coltun, Heinanen [Page 20] Internet-Draft ARA August 1997 Opaque-type 2 advertisements area Network Address Resolution Adver- tisements and contain associations for one of the advertising router's directly connected IP networks (or hosts). N-ARAs are encapsulated in LS Type-10 (Opaque) LSAs (i.e., their scope is area local). 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS age | Options | 10 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 2 | Opaque ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP Network Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP Network Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+ Vertex Association +-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+ Vertex Association +++ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IP Network Number One of the router's directly connect network. This number represents an IP network/subnet/supernet. IP Network Mask A 32-bit number indicating the range of IP addresses resid- ing on a single IP network/subnet/supernet. The body of the N-ARA consists of a list of associations for this IP Coltun, Heinanen [Page 21] Internet-Draft ARA August 1997 Network Number. Each Vertex Association begins with a common 6-byte header (described in Section A.1.4) followed by association-specific resolution information (described in Section A.1.5). A.1.4 Vertex Association The Vertex Association field consists of the link service type, IntServ service name, administrative weight, association length, logi- cal network ID followed by the association-specific resolution infor- mation. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Svc Type | IS Svc Name | Admin Weight | Assoc Length + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Logical Network ID | Resolution Information + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Remaining Octets of Resolution Information padded to 32-bits + | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Link Svc Type Identifies the link-layer functionality for this associa- tion. Link Service Types 1, 2 and 3 are defined by this specification. All other Link Service Types are reserved for definition by the IANA (iana@isi.edu). The current list of Link Service Types is described below in Table 1. Link Service Type Description ------------------------------------------------- 1 ATM Point-To-Point 2 ATM MultiPoint-To-Point 3 ATM Point-To-MultiPoint Coltun, Heinanen [Page 22] Internet-Draft ARA August 1997 Table 1 IS Svc Name The IntServ Service Name. Refer to [IS] as a reference for the IETF defined service specifications. Admin Weight When more than one equivalent association has been adver- tised for a specific vertex, this field is used to denote the advertising router's preference for each association. Equivalent associations are ones that have identical Link Service Type, IS Svc Name and Logical Network Identifier fields. Assoc Length The length in bytes of this association. Logical Network ID When more than one virtual overlay network is used to estab- lish shortcut paths within the OSPF domain, this number identifies a specific virtual overlay network. The router must have an active attachment to the specific logical net- work to use the associated resolution information. An ARA capable router is configured with a list of Logical Network IDs. The default value (i.e., only one virtual overlay net- work or too lazy to care) for the ID is 0. Resolution Information The resolution information field includes link-layer and service-type specific information. The contents of this field is defined in section A.1.5 of this document. The Vertex Association may include several resolution informa- tion items. A.1.5 Resolution Information The resolution information field is an extensible field that includes link-layer and service-type specific information. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Res Type | Res Length | Resolution Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | remaining octets of Resolution Value padded to 32-bits | Coltun, Heinanen [Page 23] Internet-Draft ARA August 1997 | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Res Type Identifies the resolution being advertised. Resolution Types 1 and 2 are defined by this specification. Resolution Type 1 is defined in A.1.6, Type 2 is defined in A.1.7. All other resolution types are reserved for definition by the IANA (iana@isi.edu). The current list of resolution types is described below in Table 2. Resolution Type Description ------------------------------------------------- 1 ATM Address 2 ATM LIJ Call Identifier Table 2 Res Length The total length in octets of this resolution information field This value includes the Res Type and Res Length fields. Resolution Value The resolution type-specific data. A.1.6 ATM Address An ATM address is the Resolution Type 1. This includes the type and length of ATM number (8 bits), the type and length of ATM subaddress (8 bits), the ATM number (x octets) and possibly the ATM subaddress (y octets). 8 7 6 5 4 3 2 1 +---+---+---+---+---+---+---+---+ | Type And Len Of ATM Number | +---+---+---+---+---+---+---+---+ Coltun, Heinanen [Page 24] Internet-Draft ARA August 1997 | Type And Len Of ATM Subaddr | +-----+-----+-----+-----+-----+-----+-----+-----+ | ATM Number... +-----+-----+-----+-----+-----+-----+-----+-----+ | ATM Subaddress... +-----+-----+-----+-----+-----+-----+-----+-----+ Format Of The ATM Address The Type and Length field of ATM number and ATM subaddress are encoded as follows. MSB 8 7 6 5 4 3 2 1 LSB +-----+-----+-----+-----+-----+-----+-----+-----+ | 0 | 1/0 | Octet length of address | +-----+-----+-----+-----+-----+-----+-----+-----+ Where: Bit(s) Description ------------------------------------------------- 8 Reserved = 0 (for future use) 7 Type = 0 ATM Forum NSAPA format = 1 E.164 format 6-1 Length = 6 bit unsigned octet length of address (MSB = bit.6, LSB = bit.1). Value range is from 0 to 20 (decimal). A non-existing ATM subaddress is indicated by setting the subaddress length to zero. If the subaddress length is zero, the corresponding type field MUST be ignored and the ATM subaddress field MUST NOT con- sume any octets in the packet. The ATM number and ATM subaddress fields are encoded as defined by the ATM Forum UNI 3.1 [AF] signalling specification. References Coltun, Heinanen [Page 25] Internet-Draft ARA August 1997 [AF] ATM Forum, "ATM User-Network Interface (UNI) Specification Version 3.1.", ISBN 0-13-393828-X, Prentice-Hall, Inc., Upper Saddle River, NJ, 07458, September, 1994. [HEIN] Heinanen, J., "Intra-area IP unicast among routers over legacy ATM", Internet Draft, July 1997, <draft-ietf-ion-intra-area-unicast-00.txt> [IS] S. Shenker and J. Wroclawski. "Network Element QoS Control Service Specification Template". Internet Draft, July 1996, <draft- ietf-intserv-svc-template-03.txt> [OPAQ] Coltun, R., "The OSPF Opaque LSA Option", Internet Draft May 1997, <draft-ietf-ospf-opaque-01.txt> [OSPF] Moy, J., "OSPF Version 2", RFC 2178, July 1997 [NHRP] Luciani, J., Katz, D., Piscitello, D., Cole, B., "NBMA Next-Hop Resolution Protocol", Internet Draft, March 1997, <draft-ietf-rolc-nhrp-11.txt> Coltun, Heinanen [Page 26]