Internet Draft Network Working Group Kireeti Kompella Internet Draft Juniper Networks Expiration Date: March 2001 Yakov Rekhter Cisco Systems Lou Berger LabN Consulting, LLC Link Bundling in MPLS Traffic Engineering draft-kompella-mpls-bundle-03.txt 1. Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. 2. Abstract In some cases a pair of Label Switching Routers (LSRs) may be connected by several (parallel) links. From the MPLS Traffic Engineering point of view for reasons of scalability it may be desirable to advertise all these links as a single link into OSPF and/or IS-IS. This document describes how to accomplish this. This document also defines corresponding signaling (RSVP-TE) support. Kompella, K., Rekhter, Y., Berger, L. [Page 1] Internet Draft draft-kompella-mpls-bundle-03.txt September 2000 3. Link Bundling When a pair of LSRs are connected by multiple links, then for the purpose of MPLS Traffic Engineering it is possible to advertise several (or all) of these links as a single link into OSPF and/or IS-IS. We refer to this process as "link bundling", or just "bundling". We refer to the link that is advertised into OSPF/IS-IS as a "bundled link". We refer to the links associated with that bundled link as "component links". The purpose of link bundling is to improve routing scalability by reducing the amount of information that has to be handled by OSPF and/or IS-IS. This reduction is accomplished by performing information aggregation/abstraction. As with any other information aggregation/abstraction, this results in losing some of the information. To limit the amount of losses one need to restrict the type of the information that can be aggregated/abstracted. 3.1. Restrictions on Bundling All component links in a bundle must have the same Link Type (if any), the same Traffic Engineering metric, the same set of resource classes, and the same Link Multiplex Capability (see [LSP-HIER]). If the component links are all multi-access links, the set of IS-IS or OSPF routers connected to each component link must be the same, and the Designated Router for each component link must be the same. If these conditions cannot be enforced, multi-access links must not be bundled. 3.2. Numbering Considerations Component links may be either numbered or unnumbered. If all the component links within a bundled link are unnumbered, then the bundled link is unnumbered by default. In all cases, the bundled link's addresses may be overridden by configuration with IP addresses assigned to some "virtual" interfaces on an LSR (it is assumed that an LSR may have multiple virtual interfaces). If a component link is numbered, this document assumes that the link has a dedicated control channel (which may be the link itself) that could be used to send RSVP/CR-LDP messages. If a component link is unnumbered, then the link may, but doesn't have to have a dedicated control channel. In this case, the bundled link must have a control channel that is shared by all component links that do not have Kompella, K., Rekhter, Y., Berger, L. [Page 2] Internet Draft draft-kompella-mpls-bundle-03.txt September 2000 dedicated control channels. If a bundled link is unnumbered, then it has to have its own interface identifier, just like any other unnumbered link [UNNUM]. This document assumes that each unnumbered component link on a Label Switching Router (LSR) is given a 16-bit identifier by this LSR. We refer to this identifier as the component interface identifier. The scope of this identifier is the bundled link that contains the component link. Thus multiple component links on an LSR may share the same component interface identifier, as long as these component links belong to different bundled links. The component interface identifiers are not visible to the IS-IS and/or OSPF, but are visible to RSVP and/or CR-LDP. 3.3. Other Considerations If several component links are bundled, IS-IS/OSPF flooding can be restricted to just one of the component links [ZININ]. Similarly, IS-IS/OSPF hellos can be restricted to just one component link; however, it may be useful to send hellos on all links that do not have a link layer mechanism (e.g., keep-alive) to ensure that a failure of the link is detected. In the future, as new Traffic Engineering parameters are added to IS-IS and OSPF, they should be accompanied by descriptions as to how they can be bundled, and possible restrictions on bundling. 4. Traffic Engineering Parameters for Bundled Links In this section, we define the Traffic Engineering parameters to be advertised for a bundled link, based on the configuration of the component links and of the bundled link. The definition of these parameters for component links was undertaken in [ISIS] and [OSPF]; we use the terminology from [OSPF]. 4.1. Link Type The Link Type of a bundled link is the (unique) Link Type of the component links. (Note: this parameter is not present in IS-IS.) Kompella, K., Rekhter, Y., Berger, L. [Page 3] Internet Draft draft-kompella-mpls-bundle-03.txt September 2000 4.2. Link ID For point-to-point links, the Link ID of a bundled link is the (unique) Router ID of the neighbor. For multi-access links, this is the interface address of the (unique) Designated Router. (Note: this parameter is not present in IS-IS.) 4.3. Local and Remote Interface IP Address (Note: in IS-IS, these are known as IPv4 Interface Address and IPv4 Neighbor Address, respectively.) If the bundled link is numbered (see section 3.1), the Local Interface IP Address is the local address of the bundled link; similarly, the Remote Interface IP Address is the remote address of the bundled link. If the bundled link is unnumbered, the local interface IP address (OSPF) or IPv4 interface address (ISIS) is set to the Router ID of advertising LSR. The first two octets of the remote interface IP address (OSPF) or IPv4 neighbor address (ISIS) are set to zero; the remaining two octets are set to the interface identifier assigned to the bundled link. 4.4. Traffic Engineering Metric The Traffic Engineering Metric for a bundled link is that of the component links. 4.5. Maximum Link Bandwidth This TLV is not used. The maximum LSP Bandwidth (as described below) replaces the maximum link bandwidth for bundled links. For backward compatibility, one MAY advertise the Maximum LSP Bandwidth at priority 7 of the bundle as the Maximum Link Bandwidth. 4.6. Maximum Reservable Bandwidth We assume that for a given bundled link either each of its component links is configured with the maximum reservable bandwidth, or the bundled link is configured with the maximum reservable bandwidth. In the former case, the Maximum Reservable Bandwidth of the bundled link is set to the sum of the maximum reservable bandwidths of all component links associated with the bundled link. Kompella, K., Rekhter, Y., Berger, L. [Page 4] Internet Draft draft-kompella-mpls-bundle-03.txt September 2000 4.7. Unreserved Bandwidth The unreserved bandwidth of a bundled link at priority p is the sum of the unreserved bandwidths at priority p of all the component links associated with the bundled link. 4.8. Resource Classes (Administrative Groups) The Resource Classes for a bundled link are the same as those of the component links. 4.9. Maximum LSP Bandwidth The Maximum LSP Bandwidth takes the place of the Maximum Link Bandwidth. However, while Maximum Link Bandwidth is a single fixed value (usually simply the link capacity), Maximum LSP Bandwidth is carried per priority, and may vary as LSPs are set up and torn down. The Maximum LSP Bandwidth of a bundled link at priority p is defined to be the maximum of the Maximum LSP Bandwidth at priority p of each component link. If a component link is a simple (unbundled) link, define its Maximum LSP Bandwidth at priority p to be the smaller of its unreserved bandwidth at priority p and its maximum link bandwidth. Since bundling may be applied recursively, a component link may itself be a bundled link. In this case, its Maximum LSP Bandwidth as a component link is the same as its Maximum LSP Bandwidth as a bundled link. In IS-IS, the Maximum LSP Bandwidth TLV is a sub-TLV of the Extended IS Reachability TLV with type 21. In OSPF, this TLV is a sub-TLV of the Link TLV within the Traffic Engineering LSA, with type 11. The length of the Maximum LSP Bandwidth TLV is 32 octets. The value is a list of eight 4 octet fields in IEEE floating point format of the Maximum LSP Bandwidth of the bundle, from priority 0 to priority 7. Kompella, K., Rekhter, Y., Berger, L. [Page 5] Internet Draft draft-kompella-mpls-bundle-03.txt September 2000 5. Procedures 5.1. Bandwidth Accounting The RSVP Traffic Control module, or its equivalent, on an LSR with bundled links must apply admission control on a per-component link basis. An LSP with a bandwidth requirement b and setup priority p fits in a bundled link if at least one component link has maximum LSP bandwidth >= b at priority p. If there are several such links, the choice of which link is used for the LSP is up to the implementation. In order to know the maximum LSP bandwidth (per priority) of each component link, the Traffic Control module must track the unreserved bandwidth (per priority) for each component link. This is done as follows. If an LSP with bandwidth b and holding priority p is set up through a component link, that component link's unreserved bandwidth at priority p and lower is reduced by b. If an LSP with bandwidth b and holding priority p that is currently set up through a component link is torn down, the unreserved bandwidth at priority p and lower for that component link is increased by b. A change in the unreserved bandwidth of a component link results in a change in the unreserved bandwidth of the bundled link. It also potentially results in a change in the maximum LSP bandwidth of the bundle; thus, the maximum LSP bandwidth should be recomputed. If one of the component links goes down, the associated bundled link remains up and continues to be advertised, provided that at least one component link associated with the bundled link is up. The unreserved bandwidth of the component link that is down is set to zero, and the unreserved bandwidth and maximum LSP bandwidth of the bundle must be recomputed. If all the component links associated with a given bundled link are down, the bundled link MUST not be advertised into OSPF/IS-IS. 5.2. Signaling Signaling must identify both the component link to use and the label to use. For unidirectional LSPs the sender of the Resv message chooses the label (as before). The sender of the Path message selects the component link to be used for the LSP and communicates the choice downstream. For bidirectional LSPs [GMPLS-SIG], in addition to the above, the sender of the Path message selects the (upstream) label, and the component link to be used with the (upstream) label, and communicates the choice downstream. Kompella, K., Rekhter, Y., Berger, L. [Page 6] Internet Draft draft-kompella-mpls-bundle-03.txt September 2000 There are two methods for communicating the selected component link. The first method communicates the selected component link via the COMPONENT_INTERFACE_ID object class defined below. Doing this assumes that an LSR connected to a component link knows the component interface identifier assigned to that link by the LSR at the other end of the link. Exchanging the identity of a component link between the LSRs connected by that link is accomplished either by configuration or by means of a protocol such as [LMP], or in the case where a component link is a Forwarding Adjacency by RSVP/CR-LDP [LSP-HIER]. The second method is for the upstream node to indicate the selected link by sending the Path message over the control channel corresponding to the selected component link. This method may only be used when LMP is not used or there are no configured component link values, and when there is a one-to-one correspondence between component links and control channels. When this method is used on bidirectional LSPs, both upstream and downstream labels MUST be assigned on the same component link. When a component link is numbered, the first method is non- applicable, and only the second method is used. 5.2.1. COMPONENT_INTERFACE_ID Object Class A new object class, the COMPONENT_INTERFACE_ID object class, is defined. The Length field is set to 8. The Class Num is TBD of form 0bbbbbbb. The DOWNSTREAM_COMPONENT_INTERFACE_ID object, which has a C_Type of 1, is used to indicate the component interface to be used for traffic flowing in the downstream direction. The UPSTREAM_COMPONENT_INTERFACE_ID object, which has a C_Type of 2, is used to indicate the component interface to be used for traffic flowing in the upstream direction. Both objects have the same format and carry a 16-bit Component Interface Identifier. The format of the objects are: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length |Class Num (TBD)| C_Type (1|2) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Component Interface Identifier| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ We introduce a new error value for the error code "Routing problem", namely "Unknown Component Interface ID" with error value 11. Kompella, K., Rekhter, Y., Berger, L. [Page 7] Internet Draft draft-kompella-mpls-bundle-03.txt September 2000 If the receiver doesn't recognize the COMPONENT_INTERFACE_ID object class, per [RSVP], it SHOULD send an error message with an "Unknown Object Class". If the class is recognize but the C-Type is not, per [RSVP], the receiver SHOULD send an "Unknown Object C-Type" error. A node that recognizes either COMPONENT_INTERFACE_ID objects, but that is unable to support it (possibly because of a failure to allocate labels) SHOULD send an error message with the error code "Routing problem" and the error value "MPLS label allocation failure." If LMP or some other link identification protocol is not running, or there is no component link with the Component Interface Identifier in either object, the receiver SHOULD send an error message with the error code "Routing problem" and the error value "Unknown Component Interface ID". 5.2.2. COMPONENT_INTERFACE_ID Object Class Usage The COMPONENT_INTERFACE_ID objects are carried in RSVP messages as part of the sender descriptor. They are optional with respect to the protocol, and are only used when component links are being identified using the COMPONENT_INTERFACE_ID objects. There are two formats for the sender descriptor, one for traditional LSPs and one for bidirectional LSPs. The format of the sender descriptor for unidirectional LSPs is:::= [ ] [ ] [ ] The format of the sender descriptor for bidirectional LSPs is: ::= [ ] [ ] [ ] Kompella, K., Rekhter, Y., Berger, L. [Page 8] Internet Draft draft-kompella-mpls-bundle-03.txt September 2000 6. Security Considerations This document raises no new security issues for IS-IS, OSPF or RSVP. 7. References [GMPLS-SIG] Ashwood, P., et al., "Generalized MPLS - Signalling Functional Description", draft-ashood-generalized-mpls-signalling- 00.txt [ISIS] Smit, H., Li, T., "IS-IS extensions for Traffic Engineering", draft-ietf-isis-traffic-01.txt (work in progress) [LMP] Lang, J., Mitra, K., et al., "Link Management Protocol (LMP)", draft-lang-mpls-lmp-00.txt (work in progress) [OSPF] Katz, D., Yeung, D., "Traffic Engineering Extensions to OSPF", draft-katz-yeung-ospf-traffic-01.txt (work in progress) [RSVP] Braden, Ed., et. al., "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", RFC2205, September 1997. [RSVP-TE] Awduche, D., Berger, L., Gan, D., et al, "Extensions to RSVP for LSP Tunnels", draft-ietf-mpls-rsvp-lsp-tunnel-05.txt (work in progress) [LSP-HIER] Kompella, K., Rekhter, Y., "LSP Hierarchy with MPLS TE", draft-ietf-mpls-lsp-hierarchy-01.txt (work in progress) [UNNUM] Kompella, K., Rekhter, Y., "Traffic Engineering with Unnumbered Links", draft-kompella-mpls-unnum-01.txt (work in progress) [ZININ] Zinin, A., Shand, M., "Flooding optimizations in link-state routing protocols", draft-zinin-flood-opt-00.txt (work in progress) Kompella, K., Rekhter, Y., Berger, L. [Page 9] Internet Draft draft-kompella-mpls-bundle-03.txt September 2000 8. Author Information Kireeti Kompella Juniper Networks, Inc. 1194 N. Mathilda Ave. Sunnyvale, CA 94089 Email: kireeti@juniper.net Yakov Rekhter Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 Email: yakov@cisco.com Lou Berger LabN Consulting, LLC Voice: +1 301 468 9228 Email: lberger@labn.net Kompella, K., Rekhter, Y., Berger, L. 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