Network Working Group Peter Psenak Internet Draft Sina Mirtorabi Expiration Date: September 2005 Abhay Roy File name: draft-ietf-ospf-mt-02.txt Liem Nguyen Padma Pillay-Esnault Cisco Systems March 2005 Multi-Topology (MT) Routing in OSPF Status of This Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 22, 2005. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This draft describes an extension to OSPF in order to define independent IP topologies called Multi-Topologies (MTs). The MT extension can be used for computing different paths for unicast traffic, multicast traffic, different classes of service, or in-band network management. [M-ISIS] describes a similar mechanism for ISIS. An optional extension to exclude selected links from the default topology is also described. Psenak et al. [Page 1]
Internet Draft MT-OSPF September 2005 1. Introduction OSPF uses a fixed packet format, therefore it is not easy to introduce any backward compatible extensions. However, the OSPF specification [OSPF] introduced TOS metric in an earlier specification [RFC1583] in order to announce a different link cost based on TOS. TOS based routing as described in [RFC1583] was never deployed and was subsequently deprecated. We propose to reuse the TOS based metric fields. They have been redefined as MT-ID and MT-ID Metric and are used to advertise different topologies by advertising separate metrics for each of them. 2. Terminology We define the following terminology in this document: Non-MT router : Routers that do not have the MT capability MT router : Routers that have MT capability as described in this document MT-ID : Renamed TOS field in LSAs to represent multi topology ID. Default topology : Topology that is built using the TOS 0 metric (default metric) MT topology : Topology that is built using the corresponding MT-ID metric MT : Shorthand notation for MT topology MT#0 topology : Representation of TOS 0 metric in MT-ID format Non-MT-Area : An area that contains only non-MT routers MT-Area : An area that contains both non-MT routers and MT routers or only MT routers 3. MT area boundary Each OSPF interface belongs to a single area and all MTs sharing that link need to belong to the same area. Therefore the area boundaries for all MTs are the same but each MT's attachment to the area is independent. Psenak et al. [Page 2]
Internet Draft MT-OSPF September 2005 4. Adjacency for MTs Each interface can be configured to belong to a set of topologies. A single adjacency will be formed with neighbors on the interface even if the interface is configured to participate in multiple topologies. Furthermore, adjacency formation will be independent of the topologies configured for the interface or neighbors on that interface. 5. Sending OSPF control packets OSPF control packets MUST be sent over the default topology. OSPF control packets sent to the remote end-point of a virtual link may need to traverse multiple hops. These control packets MUST be correctly classified by the virtual link end-point routers as packets belonging to the default topology. Even though the VL may belong to one or more non-default topologies, OSPF control packets sent to the remote end of a virtual link MUST be forwarded using the default topology. 6. Advertising MT adjacencies and corresponding IP prefixes We will reuse the TOS metric field in order to advertise a topology and prefixes belonging to that topology. The TOS field is redefined as MT-ID in the payload of Router-LSAs, Summary-LSAs, NSSA-LSAs, and AS-External-LSAs (see Appendix A). MT-ID metrics in LSAs SHOULD be in ascending order of MT-ID. If an MT-ID exists in an LSA or router link multiple times, the metric in the first MT-ID instance MUST be used. 6.1 Intra-area routing When a router establishes a FULL adjacency over a link that belongs to a set of MTs, it will advertise the corresponding cost for each MT-ID. By default, all links are included in default topology and all advertised prefixes belonging to the default topology will use the TOS0 metric the same as in standard OSPF [OSPF]. Each MT has its own MT-ID metric field. When a link is not part of a given MT, the corresponding MT-ID metric is excluded from the LSA. The Network-LSA does not contain any MT information since the DR is shared by all MTs. Hence, there is no change to the Network-LSA. Psenak et al. [Page 3]
Internet Draft MT-OSPF September 2005 6.2 Inter-area and External Routing In Summary-LSAs, NSSA-LSAs, and AS-External-LSAs, the TOS metric fields are defined as MT-ID metric fields and are used in order to advertise prefix and router reachability in the corresponding topology. When a router originates a Summary-LSA, NSSA-LSA, or AS-External-LSA that belongs to a set of MTs, it will include the corresponding cost for each MT-ID. By default, the router participates in the default topology and uses the TOS0 metric for the default topology the same as in standard OSPF [OSPF]. Setting the P-bit in NSSA-LSAs is topology independent and pertains to all MT-ID advertised in the body of the LSA. 7. Flushing MT information When a certain link or prefix that existed or was reachable in a certain topology is no longer part of that topology or is unreachable in that topology, a new version of the LSA must be originated excluding metric information representing the link or prefix in that topology. The MT metric in the Router-LSA can also be set to the maximum possible metric to enable the router to become a stub in a certain topology [STUB]. 8. MT SPF Computation By considering MT-ID metrics in the LSAs, OSPF will be able to compute multiple topologies and find paths to IP prefixes for each MT independently. A separate SPF will be computed for each MT-ID to find independent paths to IP prefixes. Each nexthop computed during the MT SPF MUST belong to the same MT. Network-LSAs are used by all topologies during the SPF computation. During the SPF for a given MT-ID, only the links and metrics for that MT-ID will be considered. Entries in the Router Routing table will be MT-ID specific. During the SPF computation for the default topology only the TOS0 metric is considered during the SPF computation. Psenak et al. [Page 4]
Internet Draft MT-OSPF September 2005 9. MT ID Values Since AS-External-LSAs use the high order bit in the MT-ID field (E bit) for the external metric-type, only MT-IDs in the range [0-127] are valid. The following MT-ID values are reserved: 0 - Reserved for routers in MTRoutingExclusionCapability mode to advertise the metric associated with the default topology (see section 11.2). 1 - Reserved for the default multicast topology. Unknown MT-IDs SHOULD be ignored. 10. Forwarding in MT Forwarding assures that only routes belonging to a single topology are used to forward a packet along its way from source to destination. Therefore, user configuration MUST be consistently applied throughout the network so that an incoming packet is associated with the same topology through each hop end to end. It is outside of the scope of this document to consider different methods of associating an incoming packet to a corresponding topology. Psenak et al. [Page 5]
Internet Draft MT-OSPF September 2005 11. Exclusion of links in the default topology The multi-topologies imply that all the routers participate in the default topology. However, it can be useful to exclude some links from the default topology and reserve them for some specific classes of traffic. The multi-topologies extension for default topology link or prefix exclusion is described in the following subsections. 11.1 MT-bit in Hello packet OSPF does not have the notion of an unreachable link. All links can have a maximum metric of 0xFFFF advertised in the Router-LSA. The link exclusion capability requires routers to ignore TOS0 metrics in Router-LSAs in the default topology and to alternately use the MT-ID#0 metric to advertise the metric associated with the default topology. Hence, all routers within an area MUST agree on how the metric for default topology will be advertised. The unused T-bit is defined as the MT-bit in the option field in order to assure that a multi-topology link-excluding capable router will only form an adjacency with another similarly configured router. +---+---+---+---+---+---+---+---+ |DN |O |DC |EA |NP |MC |E |MT | +---+---+---+---+---+---+---+---+ MT-bit: This bit MUST be set in the Hello packet only if MTRoutingExclusionCapability is enabled (see section 11.2). 11.2 New parameter in the Area Data Structure We define a new parameter in the Area Data Structure: MTRoutingExclusionCapability This is a configurable parameter that will be used to facilitate the introduction of MT routers in an area and ensure backward compatibility. Psenak et al. [Page 6]
Internet Draft MT-OSPF September 2005 By default, when an area data structure is created the MTRoutingExclusionCapability is disabled. If MTRoutingExclusionCapability is disabled: o The MT-bit MUST be cleared in Hello packets. o If a link participates in a non-default topology, it is automatically included in the default topology to support backward compatibility between MT and non-MT routers. This is accomplished through advertisement via the TOS0 metric field the same as in standard OSPF [OSPF]. If MTRoutingExclusionCapability is enabled: o The MT-bit MUST be set in Hello packets o The router will only accept a Hello if the MT-bit is set (see section 11.3) When MTRoutingExclusionCapability is set to enabled a router is said to be operating in MTRoutingExclusionCapability mode. 11.3 Adjacency Formation with Link Exclusion Capability In order to have a smooth transition from a non-MT area to an MT-area, an MT router with MTRoutingExclusionCapability disabled will form adjacencies with non-MT routers and will include all links as part of default topology. A link may cease participating in default topology if MTRoutingExclusionCapability is set to enabled. In this state, a router will only form adjacency with routers that set the MT-bit in their Hello packets. This will ensure that all routers have MTRoutingExclusionCapability enabled before the default topology can be disabled on a link. Receiving OSPF Hello packets as defined in section 10.5 of [OSPF] is modified as follows: o If the MTRoutingExclusionCapability of the Area Data structure is set to enabled, the Hello packets are discarded if the the received Hello packet does not have the MT-bit in the hello options set. 11.4 OSPF Control Packets Transmission Over Excluded Links If MTRoutingExclusionCapability is enabled and the default topology is not configured on an interface, connected routes MUST still exist for the default topology and should enable OSPF control packets to be sent and received over that interface. Psenak et al. [Page 7]
Internet Draft MT-OSPF September 2005 11.5 OSPF LSA Advertisement and SPF Computation for Excluded Links When MTRoutingExclusionCapability is enabled and the link does not participate in the default topology, the MT-ID#0 metric is not advertised. The TOS0 metric is set to infinity (0xFFFF) but is ignored during the default topology SPF computation. When MTRoutingExclusionCapability is enabled and a link participates in the default topology, MT-ID#0 metric is used to advertise the metric associated with the default topology. The TOS0 metric is set to the same value as the MT-ID#0 metric but is ignored during the default topology SPF computation. Independent of the MTRoutingExclusionCapability setting, the TOS0 metric is used for Summary-LSAs, NSSA-LSAs, and AS-External-LSAs. o If the prefix or router does not exist in the default topology, the TOS0 metric is set to infinity (0xFFFFFF). o If the prefix or router exists in default the topology, the TOS0 metric is used to advertise the metric in the default topology. During the summary and external prefix calculation for the default topology the TOS0 metric is used for Summary-LSAs, NSSA-LSAs, and AS-External-LSAs. 12. Interoperability between MT capable and non-MT capable routers The default metric field is mandatory in all LSAs (even when metric value is 0). Even when a link or prefix does not exist in the default topology, a non-MT router can consider the zero value in the metric field as a valid metric and consider the link or prefix as part of the default topology. In order to prevent the above problem, an MT capable router will include all links as part of the default topology. If links need to be removed from the default topology, an MT capable router MUST be configured in MTRoutingExclusionCapability mode. In this mode, routers will assure that all other routers in the area are in the MTRoutingExclusionCapability mode before considering the MT-ID#0 metric in the SPF calculation. Only then can the TOS0 metric field in Router LSAs be safely ignored during the default topology SPF computation. Psenak et al. [Page 8]
Internet Draft MT-OSPF September 2005 Note that for any prefix or router to become reachable in a certain topology, a contiguous path inside that topology must exist between the calculating router and the destination prefix or router. 13. Migration from non-MT-Area to MT-area Introducing MT-OSPF into a network can be done gradually to allow MT routers and non-MT routers to participate in the default topology while MT routers participate in other topologies. If there is a requirement to exclude some links from the default topology in an area, all routers in the area MUST be in MTRoutingExclusionCapability mode. In this section we describe the migration steps to consider while transitioning from a non-MT network to an MT network. Consider a network with a backbone area and a set of non-backbone areas functioning in standard OSPF mode. We would like to migrate to an MT network either partially or completely. 1) As required, part of an area is upgrade to be MT capable. The MT routers will interact with non-MT routers in the default topology and participate in other topologies as required. 2) If a new non-backbone area is created for MT routers, it may be configured in MTRoutingExclusionCapability mode since there is no interaction required with non-MT routers. In this mode, the default topology can be excluded on links as required. 3) If there is more than one non-backbone areas where MT is being used, it is desirable that the backbone area first be upgraded to be MT capable so that inter-area routing is assured for MT destinations in different areas. 4) Gradually the whole network can be made MT capable. Note that inter-area routing for the MT-area still depends on the backbone area. Therefore, if different areas configured for a given topology need to communicate, the backbone area also needs to be configured for this topology. Psenak et al. [Page 9]
Internet Draft MT-OSPF September 2005 14. Acknowledgments The authors would like to thank Scott Sturgess and Alvaro Retana for their comments on the document. Thanks to Acee Lindem for review and extensive editing. 15. Security Consideration The described protocol extension does not introduce any new security issues into the OSPF protocol. 16. IANA Considerations The T-bit as defined in [RFC1583] for a router's TOS capability is redefined as the MT-bit in this document. Similarly, the TOS field for Router-LSAs, Summary-LSAs, NSSA-LSAs, and AS-External LSAs as defined in [OSPF] is redefined as MT-ID in this document. 17. Normative References [OSPF] Moy, J., "OSPF Version 2", RFC 2328, April 1998. [RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994. [NSSA] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option", RFC 3101, January 2003. [RFC2119] Bradner, S., "Key words for use in RFC's to Indicate Requirement Levels", RFC 2119, March 1997. 18. Informative References [M-ISIS] Przygienda, T., Shen, N., Sheth, N., "M-ISIS: Multi Topology (MT) Routing in IS-IS", draft-ietf-isis-wg-multi-topology-07.txt, Work in progress. [STUB] Retana, A., Nguyen, L., White, R., Zinin, A. and D. McPherson, "OSPF Stub Router Advertisement", RFC 3137, June 2001. Psenak et al. [Page 10]
Internet Draft MT-OSPF September 2005 Appendix A. LSA content defined in [OSPF] is modified to introduce the MT-ID. A.1 Router-LSAs Router-LSAs are the Type 1 LSAs. Each router in an area originates a router-LSA. The LSA describes the state and cost of the router's links (i.e., interfaces) to the area. All of the router's links to the area must be described in a single router-LSA. For details concerning the construction of router-LSAs, see Section 12.4.1 [OSPF]. 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 | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link State ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |*|*|*|N|W|V|E|B| 0 | # links | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | # MT-ID | metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID | 0 | MT-ID metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID | 0 | MT-ID metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | Psenak et al. [Page 11]
Internet Draft MT-OSPF September 2005 A.2 Network-LSAs Network-LSAs are the Type 2 LSAs. A network-LSA is originated for each broadcast and NBMA network in the area which supports two or more routers. The network-LSA is originated by the network's Designated Router. The LSA describes all routers attached to the network, including the Designated Router itself. The LSA's Link State ID field lists the IP interface address of the Designated Router. The distance from the network to all attached routers is zero. This is why metric fields need not be specified in the network-LSA. For details concerning the construction of network-LSAs, see Section 12.4.2 [OSPF]. 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 | 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link State ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Network Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Attached Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | Note that network LSA does not contain any MT-ID fields as the cost of the network to the attached routers is 0 and DR is shared by all topologies. Psenak et al. [Page 12]
Internet Draft MT-OSPF September 2005 A.3 Summary-LSAs Summary-LSAs are the Type 3 and 4 LSAs. These LSAs are originated by area border routers. Summary-LSAs describe inter-area destinations. For details concerning the construction of summary- LSAs, see Section 12.4.3 [OSPF]. Type 3 summary-LSAs are used when the destination is an IP network. In this case the LSA's Link State ID field is an IP network number (if necessary, the Link State ID can also have one or more of the network's "host" bits set; see Appendix E [OSPF] for details). When the destination is an AS boundary router, a Type 4 summary-LSA is used, and the Link State ID field is the AS boundary router's OSPF Router ID. (To see why it is necessary to advertise the location of each ASBR, consult Section 16.4 of [OSPF]). Other than the difference in the Link State ID field, the format of Type 3 and 4 summary-LSAs is identical. 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 | 3 or 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link State ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Network Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0 | metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID | MT-ID metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID | MT-ID metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Psenak et al. [Page 13]
Internet Draft MT-OSPF September 2005 A.4.5 AS-external-LSAs AS-external-LSAs are the Type 5 LSAs. These LSAs are originated by AS boundary routers, and describe destinations external to the AS. For details concerning the construction of AS-external-LSAs, see Section 12.4.3 [OSPF]. AS-external-LSAs usually describe a particular external destination. For these LSAs the Link State ID field specifies an IP network number (if necessary, the Link State ID can also have one or more of the network's "host" bits set; see Appendix E [OSPF] for details). AS-external-LSAs are also used to describe a default route. Default routes are used when no specific route exists to the destination. When describing a default route, the Link State ID is always set to DefaultDestination (0.0.0.0) and the Network Mask is set to 0.0.0.0. 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 | 5 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link State ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Network Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |E| 0 | metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Forwarding address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | External Route Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |E| MT-ID | MT-ID metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Forwarding address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | External Route Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |E| MT-ID | MT-ID metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Forwarding address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | External Route Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Psenak et al. [Page 14]
Internet Draft MT-OSPF September 2005 A.4.6 NSSA-LSAs NSSA-LSAs are the Type 7 LSAs. These LSAs are originated by AS boundary routers local to an NSSA, and describe destinations external to the AS. The changes to NSSA-LSAs are identical to those for External-LSAs (Appendix A.4.5). For details concerning the construction of NSSA-LSAs see Section 2.4 [NSSA]. Authors' address Peter Psenak Abhay Roy Cisco Systems Cisco systems Parc Pegasus, 170 W. Tasman Dr. De Kleetlaan 6A San Jose, CA 95134 1831 Diegem, Belgium USA E-mail: ppsenak@cisco.com E-mail: akr@cisco.com Sina Mirtorabi Liem Nguyen Cisco Systems Cisco Systems 225 West Tasman drive 7025 Kit Creek Rd. San Jose, CA 95134 Research Triangle Park, NC 27709 USA USA E-mail: sina@cisco.com E-mail: lhnguyen@cisco.com Padma Pillay-Esnault Cisco Systems 3750 Cisco Way San Jose, CA 95134 USA E-mail: ppe@cisco.com Full Copyright Statement Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Psenak et al. [Page 15]
Internet Draft MT-OSPF September 2005 Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Psenak et al. [Page 16]
