Internet Engineering Task Force Q. Zhao Internet-Draft Huawei Technology Intended status: Standards Track L. Fang Expires: May 3, 2012 C. Zhou Cisco Systems L. Li China Mobile N. So Verizon Business R. Torvi Juniper Networks October 31, 2011 LDP Extensions for Multi Topology Routing draft-ietf-mpls-ldp-multi-topology-01.txt Abstract Multi-Topology (MT) routing is supported in IP through extension of IGP protocols, such as OSPF and IS-IS. It would be advantageous to extend Multiprotocol Label Switching (MPLS), using Label Distribution Protocol (LDP), to support multiple topologies. These LDP extensions, known as Multiple Topology Label Distribution Protocol (MT LDP), would allow the configuration of multiple topologies within an MPLS LDP enabled network. This document describes the protocol extensions required to extend the existing MPLS LDP signalling protocol for creating and maintaining LSPs in an MT environment. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any Zhao, et al. Expires May 3, 2012 [Page 1] Internet-Draft LDP Multi Topology Extension October 2011 time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on May 3, 2012. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Zhao, et al. Expires May 3, 2012 [Page 2] Internet-Draft LDP Multi Topology Extension October 2011 Table of Contents 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Application Scenarios . . . . . . . . . . . . . . . . . . 6 3.1.1. Simplified Data-plane . . . . . . . . . . . . . . . . 6 3.1.2. Using MT for p2p Protection . . . . . . . . . . . . . 6 3.1.3. Using MT for mLDP Protection . . . . . . . . . . . . . 7 3.1.4. Service Separation . . . . . . . . . . . . . . . . . . 7 3.1.5. An Alternative inter-AS VPN Solution . . . . . . . . . 7 3.2. Associating a FEC or group of FECs with MT-ID . . . . . . 8 3.2.1. MT-ID TLV . . . . . . . . . . . . . . . . . . . . . . 8 3.2.2. FEC TLV with MT-ID Extension . . . . . . . . . . . . . 9 3.3. LDP MT Capability Advertisement . . . . . . . . . . . . . 9 3.3.1. Session Initialization . . . . . . . . . . . . . . . . 10 3.3.2. Post Session Setup . . . . . . . . . . . . . . . . . . 11 3.4. LDP Sessions . . . . . . . . . . . . . . . . . . . . . . . 12 3.5. Reserved MT ID Values . . . . . . . . . . . . . . . . . . 12 3.6. LDP Messages with FEC TLV and MT-ID TLV . . . . . . . . . 12 3.6.1. Label Mapping Message . . . . . . . . . . . . . . . . 13 3.6.2. Label Request Message . . . . . . . . . . . . . . . . 14 3.6.3. Label Abort Request Message . . . . . . . . . . . . . 14 3.6.4. Label Withdraw Message . . . . . . . . . . . . . . . . 15 3.6.5. Label Release Message . . . . . . . . . . . . . . . . 16 3.7. Session Initialization Message with MT Capability . . . . 16 3.8. MT Applicability on FEC-based features . . . . . . . . . . 17 3.8.1. Typed Wildcard Prefix FEC Element . . . . . . . . . . 17 3.8.2. End-of-LIB . . . . . . . . . . . . . . . . . . . . . . 17 3.9. MPLS Forwarding in MT . . . . . . . . . . . . . . . . . . 18 3.10. Security Consideration . . . . . . . . . . . . . . . . . . 18 3.11. IANA Considerations . . . . . . . . . . . . . . . . . . . 18 3.12. Acknowledgement . . . . . . . . . . . . . . . . . . . . . 18 4. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.1. Normative References . . . . . . . . . . . . . . . . . . . 18 4.2. Informative References . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 Zhao, et al. Expires May 3, 2012 [Page 3] Internet-Draft LDP Multi Topology Extension October 2011 1. Terminology Terminology used in this document MT-ID: A 12 bit value to represent Multi-Topology ID. Default Topology: A topology that is built using the MT-ID value 0. MT topology: A topology that is built using the corresponding MT-ID. 1.1. Requirements Language 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 RFC 2119 [RFC2119]. 2. Introduction There are increasing requirements to support multi-topology in MPLS network. For example, service providers may want to assign different level of service(s) to different topologies so that the service separation can be achieved. It is also possible to have an in-band management network on top of the original MPLS topology, or maintain separate routing and MPLS domains for isolated multicast or IPv6 islands within the backbone, or force a subset of an address space to follow a different MPLS topology for the purpose of security, QoS or simplified management and/or operations. OSPF and IS-IS use MT-ID (Multi-Topology Identification) to identify different topologies. For each topology identified by a MT-ID, IGP computes a separate SPF tree independently to find the best paths to the IP prefixes associated with this topology. For FECs that are associated with a specific topology, this solution utilises the same MT-ID of this topology in LDP. Thus LSP for a certain FEC may be created and maintained along the IGP path in this topology. Maintaining multiple MTs for MPLS network in a backwards-compatible manner requires several extensions to the label signaling encoding and processing procedures. When label is associated with a FEC, the FEC includes both IP address and topology it belongs to. There are a few possible ways to apply the MT-ID of a topology in LDP. One way is to have a new TLV for MT-ID and insert the TLV into Zhao, et al. Expires May 3, 2012 [Page 4] Internet-Draft LDP Multi Topology Extension October 2011 messages describing a FEC that needs Multi-Topology information. Another approach is to expand the FEC TLV to contain MT-ID if the FEC needs Multi-Topology information. MT based MPLS in general can be used for a variety of purposes such as service separation by assigning each service or a group of services to a topology, where the managment, QoS and security of the service or the group of the services can be simplified and guaranteed, in-band management network "on top" of the original MPLS topology, maintain separate routing and MPLS forwrding domains for isolated multicast or IPv6 islands within the backbone, or force a subset of an address space to follow a different MPLS topology for the purpose of security, QoS or simplified management and/or operations. One of the use of the MT based MPLS is where one class of data requires low latency links, for example Voice over Internet Protocol (VoIP) data. As a result such data may be sent preferably via physical landlines rather than, for example, high latency links such as satellite links. As a result an additional tolology is defined as all low latency links on the network and VoIP data packets are assinged to the additional topology. Another example is security- critical traffic which may be assigned to an additional topology for non-radiative links. Further possible examples are file transfer prtocol (FTP) or SMTP (simple mail transfer protocol) traffic which can be assigned to additional topology comprising high latency links, Internet Protocol version 4 (IPv4) versus Internet Protocol version 6 (IPv6) traffic which may be assigned to different topology or data to be distingushed by the quality of service (QoS) assinged to it. This document describes the protocol extensions required to extend the existing MPLS LDP signalling protocol for creating and maintaining LSPs in an MT environment. 3. Requirements MPLS-MT may be used for a variety of purposes such as service separation by assigning each service or a group of services to a topology, where the management, QoS and security of the service or the group of the services can be simplified and guaranteed, in-band management network "on top" of the original MPLS topology, maintain separate routing and MPLS forwarding domains for isolated multicast or IPv6 islands within the backbone, or force a subset of an address space to follow a different MPLS topology for the purpose of security, QoS or simplified management and/or operations. The following specific requirements and objectives have been defined Zhao, et al. Expires May 3, 2012 [Page 5] Internet-Draft LDP Multi Topology Extension October 2011 in order to provide the functionality described above, and facilitate service provider configuration and operation. o Deployment of MPLS-MT within existing MPLS networks should be possible, with MPLS-MT non-capable nodes existing with MPLS-MT capable nodes. o Minimise configuration and operation complexity of MPLS-MT across the network. o The MPLS-MT solution SHOULD NOT require data-plane modification. o The MPLS-MT solution MUST support multiple topologies. Allowing a an MPLS LSP to be established across a specific, or set of, multiple topologies. o Control and filtering of LSPs using explicitly including or excluding multiple topologies MUST be supported. o The MPLS-MT solution MUST be capable of supporting QoS mechanisms. [Editors Note - We expect these base MPLS-MT protocol requirements to be evolved over the next few versions of this document. Note that all Editors notes will be deleted before publication of the document] 3.1. Application Scenarios 3.1.1. Simplified Data-plane IGP-MT requires additional data-plane resources maintain multiple forwarding for each configured MT. On the other hand, MPLS-MT does not change the data-plane system architecture, if an IGP-MT is mapped to an MPLS-MT. In case MPLS-MT, incoming label value itself can determine an MT, and hence it requires a single NHLFE space. MPLS-MT requires only MT-RIBs in the control-plane, no need to have MT-FIBs. Forwarding IP packets over a particular MT requires either configuration or some external means at every node, to maps an attribute of incoming IP packet header to IGP-MT, which is additional overhead for network management. Whereas, MPLS-MT mapping is required only at the ingress-PE of an MPLS-MT LSP, because of each node identifies MPLS-MT LSP switching based on incoming label, hence no additional configuration is required at every node. 3.1.2. Using MT for p2p Protection We know that [IP-FRR-MT] can be used for configuring alternate path via backup-mt, such that if primary link fails, then backup-MT can be used for forwarding. However, such techniques require special Zhao, et al. Expires May 3, 2012 [Page 6] Internet-Draft LDP Multi Topology Extension October 2011 marking of IP packets that needs to be forwarded using backup-MT. MPLS-LDP-MT procedures simplify the forwarding of the MPLS packets over backup-MT, as MPLS-LDP-MT procedure distribute separate labels for each MT. How backup paths are computed depends on the implementation, and the algorithm. The MPLS-LDP-MT in conjunction with IGP-MT could be used to separate the primary traffic and backup traffic. For example, service providers can create a backup MT that consists of links that are meant only for backup traffic. Service providers can then establish bypass LSPs, standby LSPs, using backup MT, thus keeping undeterministic backup traffic away from the primary traffic. 3.1.3. Using MT for mLDP Protection Fro the P2mP or MP2MP LSPs setup by using mLDP protocol, there is a need to setup a backup LSP to have an end to end protection for the priamry LSP in the appplicaitons such IPTV, where the end to end protection is a must. Since the mLDP lSp is setup following the IGP routes, the second LSP setup by following the IGP routes can not be guranteed to have the link and node diversity from the primary LSP. By using MPLS-LDP-MT, two topology can be configured with complete link and node diversity, where the primary and secondary LSP can be set up independantly within each topology. The two LSPs setup by this mechanism can protect each other end-to-end. 3.1.4. Service Separation MPLS-MT procedures allow establishing two distinct LSPs for the same FEC, by advertising separate label mapping for each configured topology. Service providers can implement CoS using MPLS-MT procedures without requiring to create separate FEC address for each class. MPLS-MT can also be used separate multicast and unicast traffic. 3.1.5. An Alternative inter-AS VPN Solution When the lsp is crossing multiple domains for the inter-as VPN scenarios, the LSP setup process can be done by configuring a set of routers which are in different domains into a new single domain with a new topology ID using the LDP multiple topology. All the routers belong this new topology will be used to carry the traffic across multiple domains and since they are in a single domain with the new topology ID, so the LDP lsp set up can be done without propagating VPN routes across AS boundaries. Zhao, et al. Expires May 3, 2012 [Page 7] Internet-Draft LDP Multi Topology Extension October 2011 3.2. Associating a FEC or group of FECs with MT-ID This section describes multiple approaches to associate a FEC or a group of FECs to a MT-ID in LDP. One way is to have a new TLV for MT-ID and insert the MT-ID TLV into messages describing a FEC that needs Multi-Topology information. Another approach is to extend FEC TLV to contain the MT-ID if the FEC needs Multi-Topology information. There are also other choices such as defining new address family or associate the MPLS MT-ID with each FEC element in the FEC TLV. In this version, we discuss the first two choices, and in the future versions, we will add the discussions for other choices into the draft. 3.2.1. MT-ID TLV The new TLV for MT-ID is defined as below: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |U|F| TLV Code Point(TBD) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | reserved | MT-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: U and F bits: As specified in [RFC5036]. TLV Code Point: The TLV type which identifies a specific capability. MT-ID is a 12-bit field containing the ID of the topology corresponding to the MT-ID used in IGP and LDP. Lack of MT-ID TLV in messages MUST be interpreted as FECs are used in default MT-ID (0) only. A MT-ID TLV can be inserted into the following LDP messages as an optional parameter. Label Mapping "Label Mapping Message" Label Request "Label Request Message" Label Abort Request "Label Abort Request Message" Label Withdraw "Label Withdraw Message" Label Release "Label Release Message" The message with inserted MT-ID TLV associates a FEC in same message to the topology identified by MT-ID. Figure 1: MT-ID TLV Format Zhao, et al. Expires May 3, 2012 [Page 8] Internet-Draft LDP Multi Topology Extension October 2011 3.2.2. FEC TLV with MT-ID Extension The new TLV for MT-ID is defined as below: The extended FEC TLV has the format below. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |U|F| FEC (TBD) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | reserved | MT-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FEC Element 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FEC Element n | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ This new FEC TLV may contain a number of FEC elements and a MT-ID. It associates these FEC elements with the topology identified by the MT-ID. Each FEC TLV can contain only one MT-ID. Figure 2: Extended FEC with MT-ID 3.3. LDP MT Capability Advertisement The LDP MT capability can be advertised either during the LDP session initializatin or after the LDP session is setup. The capability for supporting multi-topology in LDP can be advertised during LDP session initialization stage by including the LDP MT capability TLV in LDP Initialization message. After LDP session is established, the MT capability can also be advertised or changed using Capability message. If an LSR has not advertised MT capability, its peer must not send messages that include MT identifier to this LSR. If an LSR receives a Label Mapping message with MT parameter from downstream LSR-D and its upstream LSR-U has not advertised MT Zhao, et al. Expires May 3, 2012 [Page 9] Internet-Draft LDP Multi Topology Extension October 2011 capability, an LSP for the MT will not be established. If an LSR is changed from non-MT capable to MT capable, it sets the S bit in MT capability TLV and advertises via the Capability message. The existing LSP is treated as LSP for default MT (ID 0). If an LSR is changed from MT capable to non-MT capable, it may initiate withdraw of all label mapping for existing LSPs of all non- default MTs. Alternatively, it may wait until the routing update to withdraw FEC and release the label mapping for existing LSPs of specific MT. There will be case where IGP is MT capable but MPLS is not and the handling procedure for this case is TBD. 3.3.1. Session Initialization In an LDP session initialization, the MT capability may be advertised through an extended session initialization message. This extended message has the same format as the original session initialization message but contains the LDP MT capability TLV as an optional parameter. The format of the TLV for LDP MT is specified in the [RFC5036] as below: Zhao, et al. Expires May 3, 2012 [Page 10] Internet-Draft LDP Multi Topology Extension October 2011 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |U|F| TLV Code Point(TBD) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |S| Reserved | | +-+-+-+-+-+-+-+-+ Capability Data | | +-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: U and F bits: As specified in [RFC5036]. TLV Code Point: The TLV type which identifies a specific capability. The "IANA Considerations" section of [RFC5036] specifies the assignment of code points for LDP TLVs. S-bit: The State Bit indicates whether the sender is advertising or withdrawing the capability corresponding to the TLV Code Point. The State bit is used as follows: 1 - The TLV is advertising the capability specified by the TLV Code Point. 0 - The TLV is withdrawing the capability specified by the TLV Code Point. Capability Data: Information, if any, about the capability in addition to the TLV Code Point required to fully specify the capability. Figure 3: LDP MT CAP TLV 3.3.2. Post Session Setup During the normal operating stage of LDP sessions, the capability message defined in the [RFC5036] will be used with an LDP MT capability TLV. The format of the Capability message is as follows: Zhao, et al. Expires May 3, 2012 [Page 11] Internet-Draft LDP Multi Topology Extension October 2011 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| Capability (IANA) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TLV_1 (LDP-MT Capability TLV) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TLV_N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: LDP CAP Format where TLV_1 (LDP-MT Capability TLV) specifies that the LDP MT capability is enabled or disabled by setting the S bit of the TLV to 1 or 0. 3.4. LDP Sessions Depending on the number of label spaces supported, if a single global label space is supported, there will be one session supported for each pair of peer, even there are multiple topologies supported between these two peers. If there are different label spaces supported for different topologies, which means that label spaces overlap with each other for different MTs, then it is suggested to establish multiple sessions for multiple topologies between these two peers. In this case, multiple LSR-IDs need to be allocated beforehand so that each multiple topology can have its own label space ID. [Editors Note - This section requires further discussion] 3.5. Reserved MT ID Values Certain MT topologies are assigned to serve pre-determined purposes: [Editors Note - This section requires further discussion] 3.6. LDP Messages with FEC TLV and MT-ID TLV Zhao, et al. Expires May 3, 2012 [Page 12] Internet-Draft LDP Multi Topology Extension October 2011 3.6.1. Label Mapping Message An LSR sends a Label Mapping message to an LDP peer to advertise FEC- label bindings. In the Optional Parameters' field, the MT-ID TLV will be inserted. The encoding for the Label Mapping message is: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| Label Mapping (0x0400) | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FEC TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Other Optional Parameters | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Optional Parameters This variable length field contains 0 or more parameters, each encoded as a TLV. The optional parameters are: Optional Parameter Length Value Label Request 4 See below Message ID TLV Hop Count TLV 1 See below Path Vector TLV variable See below MT TLV variable See below MT TLV see the definition section for this new TLV. Figure 5: Label Mapping Message Zhao, et al. Expires May 3, 2012 [Page 13] Internet-Draft LDP Multi Topology Extension October 2011 3.6.2. Label Request Message An LSR sends the Label Request message to an LDP peer to request a binding (mapping) for a FEC. The MT TLV will be inserted into the Optional parameters' field. The encoding for the Label Request message is: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| Label Request (0x0401) | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FEC TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Optional Parameters | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: Label Request Message In the DU mode, when a label mapping is received by a LSR which has a downstream with MT capability advertised and an upstream without the MT capability advertised, it will not send label mapping to its upstream. in the DoD mode, the label request is sent down to the downstream LSR until it finds the downstream LSR which doesn't support the MT, then the current LSPR will send a notification to its upstream LSR. In this case, no LSP is setup. We propose to add a new notification event to signal the upstream that the downstream is not capable. 3.6.3. Label Abort Request Message The Label Abort Request message may be used to abort an outstanding Label Request message. The MT TLV may be inserted into the optional parameters' field. The encoding for the Label Abort Request message is: Zhao, et al. Expires May 3, 2012 [Page 14] Internet-Draft LDP Multi Topology Extension October 2011 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| Label Abort Req (0x0404) | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FEC TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label Request Message ID TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID TLV (optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Optional Parameters | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 7: Label Abort Request Message 3.6.4. Label Withdraw Message An LSR sends a Label Withdraw Message to an LDP peer to signal the peer that the peer may not continue to use specific FEC-label mappings the LSR had previously advertised. This breaks the mapping between the FECs and the labels. The MT TLV will be added into the optional paramters field. The encoding for the Label Withdraw Message is: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| Label Withdraw (0x0402) | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FEC TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label TLV (optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Optional Parameters | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 8: Label Withdraw Message Zhao, et al. Expires May 3, 2012 [Page 15] Internet-Draft LDP Multi Topology Extension October 2011 3.6.5. Label Release Message An LSR sends a Label Release message to an LDP peer to signal the peer that the LSR no longer needs specific FEC-label mappings previously requested of and/or advertised by the peer. The MT TLV will be added into the optional paramers field. The encoding for the Label Release Message is: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| Label Release (0x0403) | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FEC TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label TLV (optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Optional Parameters | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 9: Label Release Message 3.7. Session Initialization Message with MT Capability The session initializtion message is extended to contain the LDP MT capability as an optional parameter. The extended session initialization message has the format below. Zhao, et al. Expires May 3, 2012 [Page 16] Internet-Draft LDP Multi Topology Extension October 2011 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| Initialization (0x0200) | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Common Session Parameters TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LDP MT Capability TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Optional Parameters | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 10: Session Initialization Message with MT Capability 3.8. MT Applicability on FEC-based features 3.8.1. Typed Wildcard Prefix FEC Element RFC-5918 extends base LDP and defines Typed Wildcard FEC Element framework [RFC5918]. Typed Wildcard FEC element can be used in any LDP message to specify a wildcard operation/action for given type of FEC. The impact of the MT extensions proposed in document on the procedures for Typed Wildcard Prefix FEC element depends on the MPLS MT-ID representation mechanism we chose at the end. For example, if the MPLS-MT ID TLV option is the final choice, then the procedures defined in [RFC5918] apply as-is to Prefix FEC element or the Prefix FEC element along with the MPLS MT-ID TLV. For instance, upon local un-configuration of topology "x", an LSR may send wildcard label withdraw with MT-ID TLV "x" to withdraw all its labels from peer that were advertised under the scope of topology "x". 3.8.2. End-of-LIB [RFC5919] specifies extensions and procedures for an LDP speaker to signal its convergence for given FEC type towards a peer. The impact of the MT extensions proposed in document on the procedures for End-of-LIB depends on the MPLS MT-ID representation mechanism we chose at the end. For example, if the MPLS-MT ID TLV option is the final choice, the Zhao, et al. Expires May 3, 2012 [Page 17] Internet-Draft LDP Multi Topology Extension October 2011 procedures defined in [RFC5919] apply as-is to Prefix FEC element or the Prefix FEC element along with the MPLS MT-ID TLV. This means that an LDP speaker MAY signal its IP convergence using Typed Wildcard Prefix FEC element, and its MT IP convergence per topology using the Typed Wildcard Prefix FEC element along with the MPLS MT-ID TLV. 3.9. MPLS Forwarding in MT Although forwarding is out of the scope of this draft, we include some forwarding consideration for informational purpose here. The specified signaling mechanisms allow all the topologies to share the platform-specific label space; this is the feature that allows the existing data plane techniques to be used; and the specified signaling mechanisms do not provide any way for the data plane to associate a given packet with a context-specific label space. 3.10. Security Consideration MPLS security applies to the work presented. No specific security issues with the proposed solutions are known. The authentication procedure for RSVP signalling is the same regardless of MT information inside the RSVP messages. 3.11. IANA Considerations [Editors Note - This section requires further discussion] 3.12. Acknowledgement The authors would like to thank Dan Tappan, Nabil Bitar, Huang Xin, Daniel King and Eric Rosen for their valuable comments on this draft. 4. References 4.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers Considered Useful", BCP 82, RFC 3692, January 2004. [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, February 2008. Zhao, et al. Expires May 3, 2012 [Page 18] Internet-Draft LDP Multi Topology Extension October 2011 4.2. Informative References Authors' Addresses Quintin Zhao Huawei Technology 125 Nagog Technology Park Acton, MA 01719 US Email: quintin.zhao@huawei.com Huaimo Chen Huawei Technology 125 Nagog Technology Park Acton, MA 01719 US Email: huaimochen@huawei.com Emily Chen Huawei Technology No. 5 Street, Shangdi Information, Haidian Beijing China Email: chenying220@huawei.com Lianyuan Li China Mobile 53A, Xibianmennei Ave. Xunwu District, Beijing 01719 China Email: lilianyuan@chinamobile.com Zhao, et al. Expires May 3, 2012 [Page 19] Internet-Draft LDP Multi Topology Extension October 2011 Chen Li China Mobile 53A, Xibianmennei Ave. Xunwu District, Beijing 01719 China Email: lichenyj@chinamobile.com Lu Huang China Mobile 53A, Xibianmennei Ave. Xunwu District, Beijing 01719 China Email: huanglu@chinamobile.com Luyuang Fang Cisco Systems 300 Beaver Brook Road Boxborough, MA 01719 US Email: lufang@cisco.com Chao Zhou Cisco Systems 300 Beaver Brook Road Boxborough, MA 01719 US Email: czhou@cisco.com Kamran Raza Cisco Systems 2000 Innovation Drive Kanata, ON K2K-3E8, MA Canada Email: E-mail: skraza@cisco.com Zhao, et al. Expires May 3, 2012 [Page 20] Internet-Draft LDP Multi Topology Extension October 2011 Ning So Verizon Business 2400 North Glenville Drive Richardson, TX 75082 USA Email: Ning.So@verizonbusiness.com Raveendra Torvi Juniper Networks 10, Technoogy Park Drive Westford, MA 01886-3140 US Email: rtorvi@juniper.net Zhao, et al. Expires May 3, 2012 [Page 21]