Internet Draft Network Working Group Kireeti Kompella Internet Draft Juniper Networks Expiration Date: January 2001 Yakov Rekhter Cisco Systems Lou Berger LabN Consulting, LLC Link Bundling in MPLS Traffic Engineering draft-kompella-mpls-bundle-02.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. Kompella, K., Rekhter, Y., Berger, L. [Page 1] Internet Draft draft-kompella-mpls-bundle-02.txt July 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 interfaces 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". 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 [RTG]). 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. Component links may be unnumbered, or the various component links may be numbered differently, or all components links may be numbered identically. In the first two cases, the bundled link is unnumbered by default; in the last case, the bundled link is numbered the same as the component links 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). 3.2. Other Considerations If several component links are bundled, IS-IS/OSPF flooding can be restricted to just one of the component links. 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 keep-alive mechanism to ensure that a failure of the link is detected. If the component links are not Packet Switch Capable, LSP setup signalling needs to identify the component link to use. This protocol is outside the scope of this document; however, see [LMP]. If a bundled link consists of "working" and "protect" component links, then for the purposes of bandwidth computation, only the Kompella, K., Rekhter, Y., Berger, L. [Page 2] Internet Draft draft-kompella-mpls-bundle-02.txt July 2000 working links should be taken into account. 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.) 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 Address is the Router ID of the advertising LSR, and the Remote Address is the Router ID of the neighboring LSR. Kompella, K., Rekhter, Y., Berger, L. [Page 3] Internet Draft draft-kompella-mpls-bundle-02.txt July 2000 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. 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. 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. Kompella, K., Rekhter, Y., Berger, L. [Page 4] Internet Draft draft-kompella-mpls-bundle-02.txt July 2000 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. 5. Procedures 5.1. Bandwidth Accounting The RSVP Traffic Control module 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 RSVP 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 Kompella, K., Rekhter, Y., Berger, L. [Page 5] Internet Draft draft-kompella-mpls-bundle-02.txt July 2000 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. The sender of the Path message identifies the component link to be used for the LSP. The sender of the Resv message chooses the label (as before). If the bundled link is composed of packet-switch capable links and there is no designated control channel, then the component link to be used is the link over which the Path message is sent. If, however, there is a protocol such as LMP that uniquely identifies each component link and allocates a designated control channel, then the sender of the Path message MUST send the Path message over the control channel. In this case, the LINK_ID object is used to identify the component link to use. This method of choosing the link is required if the component links are not packet-switch capable. 5.2.1. LINK_ID object A new object, the LINK_ID object, is defined. The Length field is set to 8. The Class Num and C_Type of the LINK_ID object are to be obtained from IANA. The format is given below; it consists simply of a 32-bit Link Identifier that identifies the link to be used for the LSP being set up. 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 (TBD) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ This object is an optional subobject of the Path and Resv messages. We introduce a new error value for the error code "Routing problem", namely "Unknown Link ID" with error value 11. If the receiver doesn't recognize the LINK_ID object, it SHOULD send an error message with an "Unknown Object Class" or an "Unknown Object C-Type" error. A node that recognizes the LINK_ID object, but that Kompella, K., Rekhter, Y., Berger, L. [Page 6] Internet Draft draft-kompella-mpls-bundle-02.txt July 2000 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 Link Identifier in the LINK_ID object, the receiver SHOULD send an error message with the error code "Routing problem" and the error value "Unknown Link ID". 6. Security Considerations This document raises no new security issues for IS-IS, OSPF or RSVP. 7. References [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-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) [RTG] Kompella, K., Rekhter, Y., et al, "Extensions to IS-IS/OSPF and RSVP in support of MPL(ambda)S", draft-kompella-mpls-optical.txt (work in progress) (new version forthcoming) 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 Kompella, K., Rekhter, Y., Berger, L. [Page 7] Internet Draft draft-kompella-mpls-bundle-02.txt July 2000 Lou Berger LabN Consulting, LLC Voice: +1 301 468 9228 Email: lberger@labn.net Kompella, K., Rekhter, Y., Berger, L. [Page 8]