MPLS, Internet Traffic Engineering Sudheer Dharanikota Internet Draft Senthil K. Venkatachalam Category: Standards Track Alcatel USA September 2000 OSPF, IS-IS, RSVP, CR-LDP Extensions to Support Inter-Area Traffic Engineering Using MPLS TE Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [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. 1. Abstract In this draft, we propose the extensions required to the routing protocols, signaling protocols, and the MIB to support the idea of inter-area LSPs. A companion document [INTER_AREA_FWK] provides the architectural requirements for such a concept. This document also provides the signaling extensions to support the crankback as defined in the architecture document [INTER_AREA_FWK]. S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 1] Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000 2. Notations and conventions used in this document ABR Area Border Router ASBR Autonomous System Border Router CR-LDP Constraint Based Routing LDP CSPF Constraint-based Shortest Path First ER Explicit Route ERO Explicit Route Object IACO Inter Area Criteria Object IACUO Inter Area Criteria Used Object IGP Interior Gateway Protocol ISIS Intermediate System to Intermediate System ISP Internet Service Provider LDP Label Distribution Protocol LER Label Edge Router LSA Link State Attribute LSR Label Switch Router LSP Label Switched Path MIB Management Information Base MPLS Multi Protocol Label Switching OSPF Open Shortest Path First PDU Protocol Data Unit PLRO Primary LSP Route Object PRO Path Route Object PV Path Vector RSVP Resource Reservation Protocol TBD To Be Defined TE Traffic Engineering TLV Type Length Value The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119 [RFC2119]. 3. Introduction Current work in the MPLS traffic engineering group (such as [TE_FRAMEWORK], [QOS_CONST]) focuses only on the intra-area LSP setup issues. In this work we propose an architecture to extend the traffic engineering capability across IGP areas and recommend relevant modifications to the routing protocols, the signaling protocols and the MIBs. S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 2] Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000 The ISP's networks are divided into Autonomous Systems (ASs), where each AS is divided into IGP areas to allow the hiding and aggregating of routing information. Although this concept of hierarchical routing by an IGP makes sense from the routing perspective, it is a bottleneck for traffic engineering as it hides the path taken by a packet to destinations in the other routing areas. Hence, from the TE perspective, requirements such as path selection and crankback need different architectural additions to the existing IGPs and signaling protocols for inter-area LSP setup. Traffic engineering practice currently involves the setup and use of Label Switched Paths (LSPs) as dedicated bandwidth pipes between two end points. LSPs can be setup across several routers, either through the use of manually specified routes, or routes that are computed. The routes can be computed offline through the use of a dedicated tool, or through the use of online constraint based routing using an IGP [IGP_REQ, RSVP_EXT]. The offline tool will be centralized, and has the advantage of being able to consider the traffic pattern history over a large period of time, and hence will be efficient in optimizing the resources over time, not just the particular instant when the request is received. The offline traffic engineering tool, if also used for LSP setup in addition to routing, may be able to optimize the resources across LSPs. This would include mechanisms to tear down LSP segments and reroute them when better resources become available or new requests arrive. The online constraint based routing model [IGP_REQ] requires (1) a constraint based routing process implemented on certain LSRs that serve as LERs to the LSPs, and (2) a set of mechanisms to flood out and maintain the TE characteristics of the topology. >From [TOOL_VS_RP] discussion, it is clear that traffic engineering can be implemented with the help of tools and routing protocol extensions, as initiated by [IGP_REQ]. Although there has been some work in the area of realizing some of the issues such as TE crankback [CRANKBACK] and DiffServ realizations [QOS_CONST], [QOS_TE_EXT], no work has been performed that directly related to the inter-area extensions and a framework for such in the TE working group. In our solution, we propose to send across IGP areas, the summary routes containing criteria-based route attributes, which will be used at the ASBRs in their TE path computation. Since an off-line TE tool cannot compute the complete explicit path from ASBR to ASBR unless it knows the complete routing table of the AS, we expect to have loose path specification, which can be translated into explicit path in-steps at the intermediate ABRs. The solutions we are providing in this draft are applicable to the destination networks inside the AS or outside the AS. For the sake of simplicity we consider the customer networks inside an autonomous system. S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 3] Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000 The requirements of criteria-based inter-area routing are separated into routing protocol requirements, signaling protocol requirements and configuration requirements. In section 4, we present the OSPF and IS-IS extensions. The signaling extensions for RSVP and CR-LDP are presented in section 5. The configuration requirements for such architectural changes are presented in section 6. Security considerations, references and acknowledgements follow in sections 7, 8, and 9. 4. Routing protocol extensions 4.1 Intra-area requirements OSPF or ISIS implementation SHOULD support the [OSPF_INTRA_TE], [ISIS_INTRA_TE] extensions to advertise and distribute the TE information of the interfaces of the area. In addition, [QOS_TE_EXT] may be supported to flood the bandwidth per class type of each interface. [OSPF_INTRA_TE], [ISIS_INTRA_TE] defines the following TE attributes: - Traffic engineering metric - Maximum bandwidth - Maximum reservable bandwidth - Unreserved bandwidth - Resource class/color [QOS_TE_EXT] defines the unreserved bandwidth for different class types. Not all of the TE attributes specified in [OSPF_INTRA_TE], [ISIS_INTRA_TE] and [QOS_TE_EXT] need to be supported - in fact a subset may be chosen that reflects the traffic engineering condition of the network and does not impose a burden on the storage and flooding of the TE information. Specific to OSPF: When a request for the setup of a constraint based LSP within the area is received, a CSPF computation will be performed on the TE resources of the area (as specified by the intra-area TE-LSAs) to determine the best path that satisfies the constraints. The constraints on the LSP can be one or more of the TE attributes flooded by OSPF in the intra-area TE LSA. Specific to ISIS: When a request for the setup of a constraint based LSP within the area is received, a CSPF computation will be performed on the TE resources of the area (as specified by the intra-area TE-LSAs) to determine the best path that satisfies the constraints of the LSP. The constraints on the LSP can be one or more of the TE attributes flooded by ISIS in the L1 extended IS reachability TE sub-TLVs. S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 4] Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000 4.2 Inter-area requirements The route computation process uses the inter-area TE summary information: - to determine if a path to the inter-area destination that satisfies the constraints does exist, and - to determine the ABR to reach the next area. TE attribute summarization is similar to the route summarization that is already a part of OSPF or ISIS. The TE attributes can be summarized through the use of a dijkstra based algorithm as described in section 4.3. The value of the TE summary attribute to a destination advertised by an ABR represents the TE resources of the best path available from the ABR to that destination based on that TE attribute alone. A separate route calculation is necessary to determine the summary value for each TE attribute that needs to be summarized. Since these route calculations are based on the intra-area TE attribute values, the set of TE attributes to be summarized should be a subset of the set of TE attributes supported inside the areas. In the general case of TE attribute summarization, any number of TE attributes such as bandwidth, delay to a destination can be summarized. However, since a large number of TE attributes to be summarized will result in an increase in processing required, the number of TE attributes to be summarized should be kept small. 4.2.1 Requirements for OSPF The summarized TE attributes will be distributed inside the areas by the use of a new link state message (called TE summary LSA) as defined in [OSPF_INTER_TE]. The definitions for the various TE attributes in the TE summary LSA are also described in [OSPF_INTER_TE]. In addition to those TE attributes, the following three TLVs are proposed to be added in the TE summary LSA. 4.2.1.1 Unreserved Bandwidth for CT1 to CT3 The unreserved bandwidth for class-types 1, 2 and 3 [QOS_CONST] to the destination are each individually described in a TLV. The units are bytes/second and the representation is IEEE floating point. The TLV types are 7, 8, and 9, respectively and the length is 32 octets each. S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 5] Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000 4.2.2 Requirements for ISIS The summarized TE attributes will be distributed inside the areas by extending the IP reachability TLV in the L1 and L2 link state PDU [ISIS_ISO], [ISIS_IETF] to include TE sub-TLVs as described below. 4.2.2.1 Traffic Engineering Extensions to the IP Reachability TLV This draft extends the IP Reachability TLV in the L1 and L2 link state PDUs to allow the representation of TE information in the form of TE sub-TLVs. Each TE sub-TLV in the IP Reachability TLV carries the type and value of a traffic engineering attribute to the remote destination. An L2 link state PDU containing the IP reachability TLV with the TE extensions will be originated by an L1/L2 router and flooded throughout the L2 domain. This PDU will contain IP reachability TLV with the TE sub-TLVs for each reachable address in the connected areas. The value for each TE attribute will have been computed through the use of a dijkstra based algorithm as detailed in the next section. (This is the 'up' part of the redistribution as detailed in [ISIS_INTRA_TE]). An L1 link state PDU containing the IP reachability TLV with the TE extensions will be originated by an L1/L2 router and flooded throughout its connected areas. This PDU will contain IP reachability TLV with the TE sub-TLVs for each reachable address in a remote area. (This is the 'down' part of the redistribution as detailed in [ISIS_INTRA_TE]). 4.2.2.2 Format of the IP reachability TLV with TE Sub-TLVs The extended IP reachability TLV as described in [ISIS_INTRA_TE] with TYPE = 135 is further extended with the addition of the TE sub-TLVs describing the traffic engineering attributes to the destination network. Hence the IP reachability TLV has a structure as described in [ISIS_INTRA_TE], followed by zero or more TE sub-TLVs, each of which is of the form: No. of Octets +---------------------------+ | CODE | 1 +---------------------------+ | LENGTH | 1 +---------------------------+ | VALUE | LENGTH +---------------------------+ S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 6] Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000 4.2.2.3 The Traffic Engineering Sub-TLVs The following traffic engineering attributes are defined: Sub-TLV type Length (octets) Name 3 4 Resource Class/Color 9 4 Maximum Bandwidth 10 4 Reservable Bandwidth 11 32 Unreserved Bandwidth 18 3 TE Default Metric TBD 4 Delay TBD 32 Unreserved Bandwidth for CT1 TBD 32 Unreserved Bandwidth for CT2 TBD 32 Unreserved Bandwidth for CT3 Most of these traffic engineering attributes have sizes and types the same as in [ISIS_INTRA_TE]. Note that new traffic engineering attributes and sub-TLVs to represent them may be defined in the future. The TE attributes are described below. 4.2.2.3.1 Resource Class/Color The resource class or color of the destination network is a combination of the colors for the various paths to the network. The sub-TLV type of the resource class/color attribute is 3, and the length is 4 octets. 4.2.2.3.2 Maximum Bandwidth The maximum bandwidth to the destination is described in bytes/second as an IEEE floating point number. The sub-TLV type is 9, and the length is 4 octets. 4.2.2.3.3 Reservable Bandwidth The reservable bandwidth to the destination is described in bytes/second as an IEEE floating point number. The sub-TLV type is 10, and the length is 4 octets. 4.2.2.3.4 Unreserved Bandwidth The unreserved bandwidth to the destination is described in bytes/second as an IEEE floating point number. The sub-TLV type is 11, and the length is 4 octets. S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 7] Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000 4.2.2.3.5 Traffic Engineering Metric The traffic engineering metric represents the traffic engineering cost of reaching the destination network from the advertising L2 router. The sub-TLV type is 18, and the length of this attribute is 3 octets. 4.2.2.3.6 Delay The delay attribute is the delay cost to reach the destination network in milliseconds, represented as an unsigned (4-byte) long integer. The TLV-type is TBD, and the length is 4 octets. 4.2.2.3.7 Unreserved Bandwidth for CT1 to CT3 The unreserved bandwidth for class-types 1, 2 and 3 [QOS_CONST] to the destination are each individually described in a sub-TLV. The units is bytes/second and the representation is IEEE floating point. The sub-TLV types are TBD, and the length is 4 octets. 4.3 Inter-Area Summarization of Traffic Engineering Attributes The traffic engineering metric is an additive metric similar to the OSPF/ISIS metrics, but need not be the same. The traffic engineering metric advertised by the router for the given summary destination will have been computed in a manner similar to the dijkstra computation for the OSPF/ISIS metric. The delay is an additive metric. The value of the delay attribute for a summary destination will have been determined through a dijkstra computation based on the delay. The maximum bandwidth to the summary destination is the largest of all path-capacities, each associated with a possible path to the destination. The path-capacity is the smallest link capacity of all the links in the path. Hence, the maximum bandwidth is the maximum amount of traffic that can be sent to that destination, when there is no other traffic on the links. The unreserved bandwidth to the summary destination is the largest of all path-unreserved bandwidths, each associated with a possible path to the destination. The path-unreserved bandwidth is the smallest unreserved bandwidth of all the links in the path. Hence, the unreserved bandwidth is the maximum amount of traffic that can currently be sent to that destination, the other traffic on the links being steady. The unreserved bandwidth for Class-Types 1, 2, and 3 [QOS_CONST] will be computed similarly. The value of the color attribute to the summary destination is some combination of the path-colors, each associated with a possible path to the destination. The path-color is a combination of the colors of the links in the path. This combination can be a "logical and" of the colors, or a concatenation. S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 8] Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000 5. Signaling requirements The signaling protocol requirements for the setup of the inter-area LSP are (as mentioned in [INTE_AREA_REQ]): 1. Signaling SHOULD be extended to carry the criteria based elements, such as: Primary criteria (Attribute 1, .., Attribute N); Secondary criteria (Attribute 1, ..., Attribute N). 2. Signaling SHOULD trigger IGP computation for the explicit route in an area at the transit ABRs. If the path, which satisfies the primary criteria, is not available then it should trigger for the IGP computation of the path for the secondary criteria. 3. It MAY inform the initiating node about the change the criteria for the path set up in the intermediate path. This deliberate notification can also be derived when the actual setup is completed. 4. The intermediate ABRs SHOULD know the difference between the primary and the backup LSPs. This enables the signaling component to distinguish between the paths taken by the primary LSP during the computation of the backup LSP. 5. The same mechanisms used for the primary LSP setup SHOULD be used for the backup LSP setup also. 6. Crankback in an area SHOULD always be performed from the starting ABR of that LSP section. If the path is not available send the information one area back and try to perform the computation. 5.1 RSVP extensions In this section we describe extensions to RSVP for the support of Inter-Area LSP setup as described in [INTER_AREA_FWK]. These extensions are in addition to the extensions to RSVP as defined in [RSVP_EXT] and includes attributes from [QOS_TE_EXT] [TE_FRAMEWORK] as sub-objects. Three new objects are introduced as follows: - object (from now on is also abbreviated as IACO) introduced to carry the primary and the secondary criteria in the PATH message. - object (from now on is also abbreviated as IACUO) is introduced in the RESV message to capture the route taken by the primary or the secondary PATH message. - object (from now on abbreviated as PLRO) to carry the path followed by the primary LSP in the PATH message. S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 9] Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000 In the following sections we also demonstrate different uses of ERO (EXPLICIT ROUTE OBJECT) and RRO (RECORD ROUTE OBJECT) from the [RSVP_EXT] draft. Note that constraint-related objects such as as mentioned in [QOS_TE_EXT] can be sub-objects in the IACO. The following table illustrates the objects discussed that are relevant for this draft. Object type Message Importance -------------------------------------------------------------------- Path Mandatory Resv Mandatory Path Mandatory Path Optional Path Optional Path Optional Path, Resv Optional but Recommended 5.1.1 PATH and RESV message format changes The format of the Path message is changed as follows: ::= [] [] [] [] (For Primary Criteria) [][] [] [] (For Secondary Criteria) [][] [] [] [ ... ] [] ::= [] [] [] The format of the Resv message is changed as follows: ::= [ ] [] [] [...]