Internet Draft Eric Gray <draft-gray-mpls-generic-ldp-spec-00.txt> Zheng Wang Grenville Armitage Lucent Technologies, Inc. Expires May 1998 Generic Label Distribution Protocol Specification Status of this Memo This document is an Internet-Draft. 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." To learn the current status of any Internet-Draft, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Abstract This document describes the specification of generic Label Distribution Protocol (LDP) for Multi-Protocol Label Switching (MPLS). Its purpose is to define those parts of LDP that are media/technology independent. Other documents, both existing works in progress and yet to come, will describe specifics of MPLS protocol behavior that apply to a particular media or technology. Acknowledgements While not otherwise specifically referred to in this document, the authors would like to acknowledge the influence, ideas, examples and - in some cases - text from a number of sources ([1], [2], [3], [7], [8], [9], [10] and [11]). Gray, et al Expires in six months [Page 1]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 Table of Contents Status of this Memo ...................................... 1 Abstract ................................................. 1 Acknowledgements ......................................... 1 Table of Contents ........................................ 2 1 Protocol Overview ........................................ 2 2 LDP Messages ............................................. 5 2.1 Common Message Header .................................... 6 2.2 LDP Message Extension Elements ........................... 7 2.2.1 Null MEE ............................................... 9 2.2.2 Forwarding Equivalency MEE ............................. 9 2.2.3 Explicit Route MEE ..................................... 11 2.2.4 Traversal List MEE ..................................... 12 2.2.5 Authentication MEE ..................................... 14 2.2.6 Vendor Specific MEE .................................... 15 2.3 LDP Neighbor Notification ................................ 15 2.4 LDP Bind Request ......................................... 17 2.5 LDP Label Bind ........................................... 19 2.6 LDP Teardown and Acknowledge ............................. 21 2.7 LDP Bind Reject .......................................... 24 3 LDP State Transitions .................................... 25 4 LDP Interaction With Routing ............................. 26 5 LDP Multicast ............................................ 27 6 Security Considerations .................................. 28 7 References ............................................... 28 8 Author Information ....................................... 29 1. Protocol Overview A Multi-Protocol Label Switch (MPLS) architecture is proposed in [6]. As suggested in that document, a mechanism is needed for distribution of labels with semantic significance to adjacent Label Switch Routers (LSRs). This section provides an overview of the necessary protocol interactions required of a generic Label Distribution Protocol (LDP). MPLS Neighbor Discovery MPLS is intended to be a simple extension to L3 technologies, such as IP, to allow for simplified forwarding syntax. Instead of making a forwarding decision with each L3 datagram - based on the entire contents of the L3 header - a forwarding equivalency is determined for classes of L3 datagrams and a fixed-length label is negotiated between neighboring LSRs along Label Switch Paths (LSPs) from ingress to egress. Thus forwarding for a class of L3 datagrams is determined at each LSR during LSP setup and the per-datagram forwarding process is reduced to label-lookup, label swap and forwarding port selection. Gray, et al Expires in six months [Page 2]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 To do this, routers with label switching capabilities must be able to determine which of their neighboring peers are similarly capable and - in order to ensure reliable continued operation - the state of each neighbor's label-switch engine. This protocol assumes that the state of the label-switch and route engines is not necessarily identical - i.e. - continued peer-level communication with adjacent routers known earlier to be LSR-enabled is not sufficient evidence of the continued operation of LSR function in the adjacent router. The local LSR sends notification messages periodically (once in a notification period) to each routing neighbor until it has both sent and received such a notification for that neighbor. This message may be sent periodically thereafter in order to maintain the neighbor relationship. The maximum time between such messages is referred to as notification time (NT). Once neighbor relation- ship is established, normal LDP control traffic received from a neighbor within the notification period is sufficient to maintain the relationship. After three notification periods have elapsed with out receiving any LDP protocol messages from a neighboring LSR, the neighbor relationship is considered to have ended and any LDP label bindings acquired from that neighbor are removed. It may be necessary to unsplice and remove bindings for other neighbors as a result of ending a neighbor relationship. LSP Setup An LSR needs to establish and maintain label-associations with the routing neighbors which it knows are LSR capable at any given time in order to provide MPLS functionality across negotiated LSPs. The local LSR may request label bindings (associations of a label with a forwarding equivalency) from downstream neighbors (i.e. - those neighbors advertising reachability for L3 datagrams in that forwarding equivalency), it may create label bindings for its up- stream neighbors (possibly as a result of a bind request) and it may remove bindings (teardown an LSP) associated with specific forwarding equivalencies with any of its neighbors. The local LSR may request a label bind from downstream neighbors corresponding to forwarding equivalencies for which it received bind requests from upstream neighbors, for which it will ingress matching L3 datagrams or in anticipation of LDP bind requests from upstream neighbors. Until receiving a corresponding label bind, the local LSR forwards datagrams using routing (egressing corresponding LSPs if necessary). Gray, et al Expires in six months [Page 3]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 On receiving a bind request, an LSR may respond with a label bind immediately or it may wait for corresponding label binds from its downstream neighbors. The local LSR may provide a label bind immediately if it 1) has corresponding downstream labels or 2) it will act as egress for the corresponding LSP. If the LSR does not provide an immediate bind, it may continue to receive unlabeled L3 datagrams from the requesting neighbor until such time as it does provide the requested bind. If the LSR has elected to wait for corresponding downstream label binds, it may create a label bind for upstream neighbors at a later time (when it has obtained these binds and spliced them with the labels it will use in binds to upstream neighbors). On receiving a label bind from a downstream neighbor, an LSR may immediately splice this label to labels it has provided, or will provide, to its upstream neighbors. Any LSR receiving unlabeled L3 datagrams either acts as ingress to a corresponding LSP (classifying the L3 datagram, assigning and attaching an appropriate label and forwarding the labeled L3 datagram) or it forwards the datagram using routing. An LSR must handle unlabeled L3 datagrams received from routing neighbors until successful in negotiating labels with those neighbors; thus a downstream neighbor is encouraged to provide label binds to its upstream neighbors. Any LSR receiving labeled datagrams for which it has an unspliced label binding (port-label match but the Label Information Base - LIB - entry is incomplete) must act as egress for these datagrams. LSP Teardown If, for some reason (such as a routing change), labels associated with a forwarding equivalence are not valid for - or will not be supported by - the local LSR, the local LSR must invalidate the previous label bind by sending a label teardown message to its corresponding upstream neighbors. If the local LSR will no longer be using a label it has received from a downstream neighbor, it must send a teardown message to that neighbor. This might happen, for example in the case where the local LSR asked for the label in a bind request, received it in a label bind and no longer requires this label. This is required in order to eliminate associated unused labels. Teardown messages are sent in a reliable way in order to ensure that associated label bindings are released. When an LSR receives an explicit teardown, it must acknowledge the message using a teardown acknowledge. This ensures that the local LSR is able to free-up corresponding resources and - in the upstream case - does not continue to receive L3 datagrams that are incorrectly labeled. Gray, et al Expires in six months [Page 4]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 Implicit teardown occurs when the local LSR receives a bind request (label bind) from a neighboring LSR containing the same label as was used in a previous binding with the same neighbor. Implicit teardown may occur as a result of duplicate bind request (label bind) messages. In general, use of implicit teardown is undesirable behavior. On receiving a label bind with a label already assigned by the downstream neighbor, the local LSR performs a level of checking to determine if the label identifies the same binding. If it does not, an appropriate reject is returned. If the label bind contains a hop-count that differs from that used in an earlier label bind but otherwise identifies the same binding, the local LSR removes the previous LIB entry and processes the label bind. On receiving a bind request specifying a label already in use for the upstream neighbor, the local LSR performs a level of checking to determine if it identifies the same binding. If it does not, a label bind with an appropriate status is returned. Otherwise, the local LSR removes the corresponding LIB entry and processes the bind request. Other An LSR receiving labeled datagrams for which it has no label binding may look beyond the label to determine if this label is the bottom of the stack and act as egress for those datagrams for which this is the case but must otherwise discard these datagrams. In this case, a teardown must be sent to the upstream neighbor for the unknown label. Except for teardown messages, reliable delivery of LDP messages is not required by the protocol. Thus, explicit acknowledgement is defined for teardown messages only and then only in implementations not using reliable transport. Bindings may, as a local matter, be aged out using a very long time period. If this is done - in order to ensure that labels are eventually removed when all other efforts to remove them have somehow failed - labels should be associated with individual expiry times (perhaps using randomization) in order to reduce clumping of protocol activity. 2. LDP Messages LDP Messages are defined below in a media-independent format. The intent is that several messages may be combined in a single datagram Gray, et al Expires in six months [Page 5]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 to minimize the CPU processing overhead associated with input/output. Media-specific companion documents will specify how to encapsulate LDP messages into actual datagrams, etc. and these specifications shall support the carriage of multiple LDP messages in any datagram where possible. To simplify implementation, media-specific companion documents should specify use of reliable transport (e.g. - TCP). The following sections describe details of the six messages making up the generic MPLS protocol, consisting of a neighbor notification message (used to drive neighbor discovery and adjacency state) and and five messages associated with label setup and teardown (label distribution and teardown). The specific messages are: LDP Neighbor Notification (section 2.3). LDP Bind Request (section 2.4). LDP Label Bind (section 2.5). LDP Teardown and Acknowledge (section 2.6). LDP Bind Reject (section 2.7). Section 2.1 describes the details of the message header common to all MPLS messages, section 2.2 describes the format of Message Extension Elements and sections 2.3 through 2.7 describe format and handling of the specific messages. 2.1 Common Message Header Common Message Header 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version | Msg Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum | Address Family | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Transaction ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Version: LDP Version - set to 0x01. Gray, et al Expires in six months [Page 6]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 Msg Type: Set to the type of this message. Types are as follows: Msg Type Message ======== ===================================== 0x01 LDP Neighbor Notification 0x02 LDP Bind Request 0x03 LDP Label Bind 0x04 LDP Teardown 0x05 LDP Teardown Acknowledge 0xFF LDP Bind Reject Length: Length of this message, in octets, minus the 12 octets in this header. Checksum: A checksum as defined in [5], except computed for the entire message, including header. The Checksum field is not needed when the implementation uses an encasulation that provides for detection of corrupted data in messages; when not needed for a specific implementation, the contents of this field are ignored by the message recipient. Address Family: This 16 bit integer contains a value from ADDRESS FAMILY NUMBERS in Assigned Numbers [4] that encodes the address family that the network layer addresses in this message are from. This provides support for multiple network protocols and corresponding address families. Transaction ID: Used to consistently identify pending transactions. This ID is intended to be unique across all transactions currently pending at the local LSR but may not be unique to pairs of LSRs in a neighbor relationship. 2.2 LDP Message Extension Elements. LDP MEEs consist of data structured in four fields. In order the fields are X, Type, Length and Value. Gray, et al Expires in six months [Page 7]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 LDP MEE format is as shown: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | X | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Value... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / --- / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ...Value | Pad (0's) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ X: determines how a recipient should behave when it doesn't recognize the MEE Type field. Required behaviors are: X = 0 Skip the MEE, continue processing the list. X = 1 Stop processing, silently drop the LDP message. X = 2 Stop processing, drop message, give error indication. X = 3 Reserved (currently treat as x = 0). Unless otherwise specified for MEEs in LDP messages below, the value of X is determined by the originating LSR as follows: - zero if it is sufficient for ANY dowstream (Bind Request), or upstream (Label Bind) LSR to be able to interpret the MEE; - one if it is sufficient that failure to interpret this MEE results in no further processing of the message that includes it; - two if it is necessary to receive an error indication from the first LSR that is unable to process this MEE. Type: A 14 bit integer value encoding how Value is to be interpreted. Behavior of an LSR on processing an MEE with an unknown type is defined by X above. Type space is subdivided to encourage use outside the IETF as follows: 0 Null MEE. 0x0001 - 0x0FFF Reserved for the IETF. 0x1000 - 0x11FF Allocated to the ATM Forum. 0x1200 - 0x37FF Reserved for the IETF. 0x3800 - 0x3FFE Experimental use. Gray, et al Expires in six months [Page 8]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 Length: The length in octets of the value (not including X, Type and Length fields; a null extension will have only an extension header and a length of zero). Length is always a multiple of four. Value: An octet string containing information in a format defined for Type and having a length in octets of Length. Value is zero padded to the nearest 32-bit boundary. The extensions list is terminated by the Null MEE, having Type = 0 and Length = 0. 2.2.1 Null MEE 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 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0|0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2.2.2 Forwarding Equivalency MEE Example Forwarding Equivalency Extensions for destination, multicast group address, source and multicast group address and source-desti- nation based forwarding equivalencies. Destination Forwarding Equivalency (DFE) MEE 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | X | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Len| Destination Prefix (variable length) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix (cont.) | Pad (0's) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: Type is set to 0x0001 Gray, et al Expires in six months [Page 9]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 Multicast Forwarding Equivalency (MFE) MEE 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | X | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Multicast Group Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: Type is set to 0x0002 Source-qualified Multicast Forwarding Equivalency (SMFE) MEE 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | X | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Len| Source Prefix (variable length) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix (cont.) | Pad (0's) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Multicast Group Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: Type is set to 0x0003 Source-destination Forwarding Equivalency (SFE) MEE 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | X | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Len| Destination Prefix (variable length) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix (cont.) | Pad (0's) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Len| Source Prefix (variable length) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix (cont.) | Pad (0's) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Gray, et al Expires in six months [Page 10]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 Type: Type is set to 0x0004 2.2.3 Explicit Route MEE 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | X | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Length (Bits) | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address 1 (cont) | Address 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address N (cont) | Pad (0's) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ X: X is set to either one or two, in LDP messages, as processing of this MEE is significant to message semantics. Whether or not an error is to be reported on failure to interpret this MEE is local to the originating LSR, if the MEE is included in a Bind Request. In a Label Bind, however, X must be set to two in this MEE such that bindings may be released if one of the listed LSRs is unable to interpret this MEE. Type: Type is set to 0x0005 Address Length: Length in bits of each address in the list. All addresses in the list must be of the same length. Gray, et al Expires in six months [Page 11]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 Address 1 - N: Addresses of the LSRs which this LSP is to traverse. On Receipt, the first address should be an address of the local LSR. On transmittal, the first address should be an address of the next neighboring LSR in the intended LSP. This MEE may be included in Bind Request and Label Bind messages. Each LSR processing a message containing this MEE must: verify that the first address in the list corresponds to a local address associated with this LSR; construct a new MEE omitting the first address; include this new MEE in Bind Request (downstream) or Label Bind (upstream), with additional values and MEEs as required and send this message to the next addressed LSR in the explicit path. Bind Requests with an Explicit Route MEE containing at least two addresses on receipt result in Bind Requests with one less address sent to the next downstream LSR neighbor. In the same way, Label Bind messages result in Label Binds to the next upstream neighbor. If the only address present in the MEE is that of the local LSR, no further processing (beyond that of creating the binding) is required. 2.2.4 Traversal List MEE This MEE may be included in in Bind Requests in order to prevent rippling LDP messages in a loop (useful - for instance - in Multi- cast LSPs setup using upstream allocation). Gray, et al Expires in six months [Page 12]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | X | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Length (Bits) | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address 1 (cont) | Address 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address N (cont) | Pad (0's) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ X: X is set to one, in LDP messages, as processing of this MEE is significant to message semantics yet an error due to not being able to interpret this MEE should not result in a Bind Reject message. Type: Type is set to 0x0006 Address Length: Length in bits of each address in the list. All addresses in the list must be of the same length. Address 1 - N: Addresses of the LSRs which this LSP has traversed. On Receipt, this list must not contain the address of this LSR (as defined for the address family in the Common Message Header. In the event that it does, the message containing this MEE is silently dropped. Gray, et al Expires in six months [Page 13]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 2.2.5 Authentication MEE 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | X | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Authentication Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+ Authentication Data... -+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ X: X is set to two, in LDP messages, as processing of this MEE is significant to message semantics and an error should be reported as a result of authentication failure. Type: Type is set to 0x0007 Authentication Type: Identifies the authentication method in use. Current allowed values are: 1 - Cleartext Password 2 - Keyed MD5 3+ - Reserved Authentication Data: Contains the type-specific authentication information. For Cleartext Password Authentication, this field consists of a variable length password. For Keyed MD5 Authentication, the Authentication Data contains the 16 byte MD5 digest of the entire datagram, including the encapsulating protocol's header, with the authentication key appended to the end of the packet. The authentication key is not transmitted with the packet. The MD5 digest covers only the the Common Message Header. Gray, et al Expires in six months [Page 14]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 2.2.6 Vendor Specific MEE 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | X | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor ID | Data.... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / Data (continued) / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: Type is set to 0x3FFF Vendor ID: 802 Vendor ID as assigned by the IEEE [4] Data: The remaining octets after the Vendor ID in the payload are vendor-dependent data. 2.3 LDP Neighbor Notification Neighbor Notification messages are similar to those defined in [12] - that is, each notification contains addresses of those neighbors heard from. The addresses are contained in a Neighbor List MEE as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | X | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Length (Bits) | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address 1 (cont) | Address 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address N (cont) | Pad (0's) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Gray, et al Expires in six months [Page 15]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 X: X is set to 2. Type: Type is set to 0x0008 Address Length: Length in bits of each address in the list. All addresses in the list must be of the same length. Address 1 - N: Addresses of the LSRs which this LSR has heard from. Provided that the cannonical address of the route engine is the same length as the network local address, that address would be used. Other- wise the network local address associated with the local route engine is used. LDP Neighbor Notification format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / Common Header / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / Neighbor List MEE / / (Variable Length) / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / Additional Message Extension Elements / / (if any) / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Common Header: In the common header, Type is set to 0x01. Transaction ID is set to zero. Neighbor List Message Extension Element: Formatted as described above. Neighbor List contains addresses of neighboring LSRs heard from. The local LSR - if originating the message - attaches a Neighbor List MEE containing its address. On receiving a Neighbor Notification message not containing its address, the local LSR appends its address to the list and sends a new Neighbor Notification message. Gray, et al Expires in six months [Page 16]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 Additional Message Extension Elements: The Neighbor Notification may contain additional MEE information. This information can have no bearing on processing the preceding portions of the message. Any interpretable MEEs may be included in Neighbor Notifications occurring as a result of processing this message. Non-interpretable MEEs must be so included. After all such additional MEEs (if any), a Null MEE must be appended. Neighbor Notification processing is further described in the state transition table in section 3 (LDP neighbor state transitions). 2.4 LDP Bind Request 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / Common Header / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label Bits | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / Forwarding Equivalency MEE Information / / (Variable Length) / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / Additional Message Extension Elements / / (if any) / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Common Header: In the common header, Type is set to 0x02 and Transaction ID is a locally unique (non-zero) identifier which the local LSR may use to pair this request to a corresponding subsequent Label Bind. Label Bits: This field contains an integer in which binary 1 positions indicate the bits available for assignment in a label by the downstream neighboring LSR. The responding LSR should not assign labeling significance to any bit positions not set in this field. If this field is set to all ones, the downstream LSR is free to allocate any label for this request. Gray, et al Expires in six months [Page 17]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 Label: A Label requested by the upstream (requesting) LSR. In the case where the Label Bits field is not all ones, this field defines values for bit positions not available for assignment by the downstream LSR. For example, a Label Bits field of all zeros indicates an upstream label allocation with the label requested exactly as defined by this field. This field is set equal to zero to indicate that downstream allocation of all available bit positions is desired. Forwarding Equivalency MEE Information: This variable length field contains FEC-related information - for example - in a format defined in section 2.2.2 above, associated with this request. Only one Forwarding Equivalency MEE may be included in each Bind Request. Additional Message Extension Elements: The Bind Request message may contain additional MEE information intended to further qualify the semantics associated with this label negotiation. An example is inclusion of an Explicit Route MEE. After all such additional MEEs (if any), a Null MEE must be appended. Bind Request messages may be satisfied by the local LSR if a label matching the the restrictions (if any) of the Bind Request can be allocated and any of the following conditions are met: the local LSR is able to interpret all MEEs included in the Bind Request message and has a LIB entry with an exactly matching qualified forwarding equivalency; the local LSR is able to interpret all MEEs included in the Bind Request message and will act as egress for L3 datagrams arriving labeled for this qualified forwarding equivalency; the local LSR is able to find a bit-wise match in an associated cache for all uninterpretable MEEs in a single LIB entry which otherwise matches interpretable portions of the Bind Request. If the Bind Request can be satisfied by the local LSR, the LSR creates a binding, splices it in the LIB, builds a Label Bind message as described in section 2.5 below and sends it to the requesting neighbor. If the Bind Request cannot be satisfied for reasons of labeling restrictions, a Label Bind is constructed as described below, with Status 0x0002 and labeling problem information (set bits in the Label field). Gray, et al Expires in six months [Page 18]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 If the Bind Request cannot be satisfied because one or more MEEs cannot be interpreted by the local LSR and at least one of these has an "X" value of 2 OR the local LSR has no downstream neighbors (as potentially qualified by interpretable MEEs), a Label Bind is constructed with a Status of 0x0005, including all non-interprable MEEs. Otherwise, the local LSR sends a corresponding Bind Request to downstream neighbors (possibly restricted by qualifications in the pending Bind Request - e.g. Explicit Route MEE) including at least all semantically significant and uninterpretable MEEs. The local LSR preserves state information relating pending upstream (received) Bind Requests to pending downstream (sent) Bind Requests including a mapping of corresponding Transaction IDs. 2.5 LDP Label Bind 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / Common Header / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Bind Status | Hop Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / Forwarding Equivalency MEE Information / / (Variable Length) / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / Additional Message Extension Elements / / (if any) / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Common Header: In the common header, Type is set to 0x03. Transaction ID is set equal to the transaction ID in the corresponding Bind Request, if any, otherwise, it is set equal to zero. Bind Status: This 16 bit integer contains the status of the binding. A non-zero value here indicates that the LDP Bind Request associated with the included Request ID was unsuccessful for reasons indicated by the status value. This field is not significant and must be set to zero if this message is not the result of a LDP Bind Request message (Transaction ID equal zero). Gray, et al Expires in six months [Page 19]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 Status values are: 0x0001 - Insufficient Resources 0x0002 - Invalid Labeling Restrictions 0x0003 - No suitable egress found 0x0004 - Label in use or may not be assigned 0x0005 - Unable to interpret MEE Hop Count: This is set to indicate the Hop Count reported to this LSR by its downstream neighbors (relative to this LSP) plus the number that this LSR would decrement TTL by for L3 datagrams on this LSP if these datagrams were being forwarded using L3 routing. The LSR assumes a downstream Hop Count of zero if it is the egress for this LSP. Label: The Label associated with this message. If this field is non-zero in an unsuccessful binding, non-zero bit positions indicate invalid bit-values or assignment in the corresponding LDP Bind Request. Forwarding Equivalency MEE Information: This variable length field contains FEC-related information - for example - in a format defined in section 2.2.2 above, associated with this request. Only one Forwarding Equivalency MEE may be included in each Label Bind. Additional Message Extension Elements: The Label Bind message may contain additional MEE information intended to further qualify the semantics associated with this label negotiation. After all such additional MEEs (if any), a Null MEE must be appended. Label Binds may be sent to upstream LSR neighbors for a number of reasons. The local LSR may have information required to create a LIB entry and provide a Label Bind in response to a pending Bind Request, the local LSR may have detected a routing change and be in the process of setting up topology based labeling, the local LSR may have received an unlabelled datagram or the local LSR may need to negotiate labels with upstream neighbors in order to meet the requirements of a Label Bind received from a downstream LSR. Gray, et al Expires in six months [Page 20]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 On receipt of a Label Bind with a zero Transaction ID, the local LSR may create a LIB entry binding the downstream label to a forwarding equivalency (with possible MEE qualification) and construct corresponding Label Bind messages and forward them to its upstream neighbors (potentially restricted by qualifications in the Label Bind - e.g. Explicit Route MEE) including at least semantically significant and all uninterpretable MEEs. The local LSR may act as ingress to the corresponding LSP if it is able to interpret all MEEs included in the Label Bind message. If the received Label Bind has a non-zero Transaction ID, the local LSR finds the corresponding Bind Request information. If the status code in the Label Bind is success, the local LSR may insert the new label in a LIB entry from Label Bind and, if the Transaction ID corresponds to a Bind Request from one or more upstream neighbors, create appropriate label(s) for inclusion in Label Bind Message(s) to upstream neighbor(s). If the Status is non-zero, processing is as follows: if there are no corresponding pending Bind Requests from upstream neighbors, the local LSR makes a local determination as to whether or not to repeat the Bind Request - based on the specific Status given, if there are corresponding pending Bind Requests from upstream meighbors, the action is determined using this table - Status Action ========== =============================================== 0x0001|3 Accumulate Status from pending downstream Bind Requests associated with upstream Bind Requests and, if no further pending Bind Requests exist, return a Label Bind with a Status code of 0x0003. 0x0002|4 Make a local determination on whether or not to repeat the Bind Request using different values. In the event that Bind Request is not retried, return a Label Bind to upstream neighbors with with associated pending Bind Requests using a Status code of 0x0003. Other Return a Label Bind for associated pending Bind Requests with this Status code to corresponding upstream neighbors. Gray, et al Expires in six months [Page 21]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 As described in section 2.4 above, an LSR may make a local determination to satisfy Bind Requests of upstream neighbors in certain conditions. In the event that the local LSR is able to act as egress, it may do so rather than returning a Label Bind with a Status code of either 0x0003 or 0x0005. Receipt of a Label Bind is not a commitment to use it, hence no acknowledgement is required. However, if the local LSR is unable to use a label included in a Label Bind, it should respond with an appropriate LDP Bind Reject. Examples of why this might occur are: the current LSR has no upstream neighbors and is itself unable to act as ingress for the qualified forwarding equivalency (e.g. - it is unable to interpret one or more MEEs); the label provided is not consistent with the hardware used by the downstream interface; the label provided is already bound to a different qualified forwarding equivalency for this interface; the locally configured maximum hop-count is exceeded (indicating a possible labeling loop). Returning a Bind Reject message when appropriate allows the down- stream neighbor to release invalid bindings and, potentially try again. An LSR should report a Bind Reject downstream if, processing of the Label Bind message results in a excessive hop-count - either as reported by an upstream LSR or as determined by the local LSR. Excessive hop-count results when the incremented value of the hop-count field in the Label Bind exceeds a locally configured maximum. The default value for this maximum is 32. 2.6 LDP Teardown and Acknowledge LDP Teardown format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / Common Header / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / Additional Message Extension Elements / / (if any) / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Gray, et al Expires in six months [Page 22]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 Common Header: In the common header, Type is set to 0x04 and Transaction ID is a locally unique (non-zero) identifier which the local LSR may use to pair this message to a corresponding Teardown Acknowledge. Label: The Label associated with this message. The value in this field is intended to reflect an existing label bound to the remaining contents of this message. Additional Message Extension Elements: The Teardown message may contain additional MEE information. This information can have no bearing on processing the preceding portions of the message. For example, inclusion of a Forwarding Equivalency MEE does not scope this message. Any interpretable MEEs may be included in Teardown messages which occur as a result of processing this message. Non-interpretable MEEs must be so included. After all such additional MEEs (if any), a Null MEE must be appended. LDP Teardown Acknowledge format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / Common Header / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Common Header: In the common header, Type is set to 0x05. Transaction ID is set equal to the Transaction ID in the corresponding Teardown message. When the local LSR determines that a label or its corresponding LSP is no longer valid, it must send a Teardown message using reliable protocol. This is necessary because the local LSR only invalidates LIB entries on loss of neighbor, Bind Reject, timeout (locally con- figurable parameter with a default on the order of hours) and Tear- down. Consequently, for implementations using unreliable transport, Teardown messages must be acknowledged with a Teardown Acknowledge; un-acknowledged Teardown messages must be periodically repeated until they are acknowledged. Repeat Teardown messages must use the same Transaction ID as was used in the original Teardown message. For reliable transport, Teardown messages may be considered to have been acknowledged on successful transmission; in such implementations, the Transaction ID is without meaning and may be ignored by the receiver. Gray, et al Expires in six months [Page 23]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 2.7 LDP Bind Reject 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / Common Header / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reject Status | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / Message Extension Elements / / (if any) / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Common Header: In the common header, Type is set to 0xFF. Transaction ID is copied from the Transaction ID in the Label Bind triggering the Bind Reject. Reject Status: Valid Status numbers are: 0x0001 - Unusable label (label is incompatible with interface) 0x0002 - Label in use 0x0003 - No suitable ingress found 0x0004 - locally configured maximum hop-count exceeded 0x0005 - Unable to interpret MEE Label: When non-zero, used to indicate the label in a corresponding Label Bind or Teardown. This field is needed in order to allow for the correction of invalid Label Binds in a state-less Label Bind protocol. This label is used to find a LIB entry and remove the corresponding label - after which, the local LSR may make a local determination to retry. Message Extension Elements: Bind Rejects resulting from inability to process MEEs must include offending MEEs. With Status "Unable to interpret MEE" (0x0005), the MEE may be truncated after the MEE header (Length set to 0). After all included MEEs (if any), a Null MEE must be appended. Gray, et al Expires in six months [Page 24]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 On receiving a Bind Reject message with a zero Transaction ID, the local LSR removes the (non-zero) label associated with the interface on which the reject was received and makes a local determination - based on Status code - as to whether or not to retry. In the event that the label removed was part of otherwise complete LIB entries, the local LSR is unable to act as ingress for the corresponding LSP and will not retry, the local LSR must generate corresponding Bind Reject messages using downstream labels to appropriate downstream neighbors. 3. LDP State Transitions LDP neighbor state transitions (ND-FSM neighbors on one interface) State Event Action New State ============ ================ ================ ============ Down NT Expires Notify, Reset NT Self Up Down Get Notify(+) Notify, Reset NT LDP Up Self Up NT Expires Notify, Reset NT Self Up Self Up Get Notify(+) Notify, Reset NT Self Up Self Up Get Notify(*) Reset NT LDP Up Self Up Get LDP Message Notify, Reset NT Self Up LDP Up NT Expires Reset NT Expired 1 Expired 1 NT Expires Notify, Reset NT Expired 2 Expired 2 NT Expires Notify, Reset NT Self Up LDP Up Get Notify(+) Notify, Reset NT LDP Up LDP Up Get LDP Message Reset NT LDP Up Expired 1 Get LDP Message Reset NT LDP Up Expired 2 Get LDP Message Reset NT LDP Up * - Neighbor Notify containing the ID of the local LSR. + - Neighbor Notify not containing the ID of the local LSR. NT - Neighbor Notification Timer Down: Starting state for LDP neighbor discovery. Self Up: Sending Notify to a neighbor which has not yet sent Notify. LDP Up: Neighbors in full LDP communication. Expired 1: One Notification Time (NT) has expired without receiving a Notify from this neighbor. Gray, et al Expires in six months [Page 25]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 Expired 2: Two Notification Times have elapsed without receiving a Notify from this neighbor. LDP state transitions (for each routing neighbor) State Event New State ================= ===================== ================= Routing Only Reach LDP Up (ND-FSM) Topology Labeling Topology Labeling complete labeling LDP Idle LDP Idle get unlabeled datagram Flow Labeling LDP Idle management directive Flow Labeling Flow Labeling complete labeling LDP Idle LDP Idle routing change Topology Labeling Any state Self Up (ND-FSM) Routing Only Routing Only: In the routing only state, the local LSR can have no valid LIB entries for this neighbor. Topology Labeling: Normal active label distribution mode. Primarily used to setup topology based best effort label switched paths. LDP Idle: LDP essentially innactive. Randomized aging of labels, Neighbor Notifications being sent (to neighbors). Flow Labeling: Triggered by receipt of an unlabelled datagram or management or other directive. The local LSR seeks to negotiate labels with neighbors to establish an LSP. 4. LDP Interaction With Routing Routing protocols drive LDP. Changes in how datagrams classified in a forwarding equivalency would be forwarded must result in new LDP associated with the new LSP to be established. Routing protocols may produce temporary routing loops - loops which are potentially more severe given improved forwarding as a result of MPLS. Gray, et al Expires in six months [Page 26]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 In this document, discussion of how any particular routing change results in setup of a new LSP is out-of-scope. We assert that implementers are responsible for ensuring that this occurs. However, there are a few things that may be observed about this protocol as currently defined. a) given that routing protocols are used to drive LDP in any particular LSR, this protocol converges as corresponding routing protocols converge; b) routing changes driven by reachability advertisement tend to result in new Label Bind driving further Label Binds, thus increasing the likelihood that temporary loops in LDP will be detected via the hop-count mechanism; c) the local focus with end-to-end effect in this specification tends to break LSPs in highly dynamic route-change scenarios (rather then twisting them together) - forcing traffic to be routed conventionally under these conditions and reducing the likelihood of looping LSPs; d) the most likely scenarios in this specification for producing a loop are when performing upstream label allocation (as may be used for explicit route or multicast LSPs); e) looping in an explicit route is impossible and this document includes recommended mechanisms for preventing other types of looping LSP formation. 5. LDP Multicast Setting up Multicast LSPs using upstream allocation can be done using Bind Request messages including the appropriate Multicast FEC MEE. The Traversal List MEE should be included in these Bind Request messages. Determination of the paths to be used in any Multicast tree is accomplished locally by the individual Multicast capable LSRs. Where it might be impossible for the local LSR to determine which of its neighbors need to be included, that neighbor will know whether it needs to be in the specified Multicast tree and may reject Bind Requests using Label Bind messages with a Status code of 0x0003. Hence, if any LSR (Multicast capable or not) is unable to determine which of its neighbors need to be part of a Multicast LSP, that LSR forwards appropriate Bind Requests to all of its neighbors, except the one from which it received the original one, and only returns a successful Label Bind when it receives a successful Label Bind from at least one downstream neighbor. Gray, et al Expires in six months [Page 27]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 6. Security Considerations When and where required, one or more Authentication MEEs may be included in the first LDP message in a transmission datagram. Successful authentication of the first message in a datagram is sufficient for all messages in the same transmission. The entire transmission datagram is silently discarded on failure to authenticate. Media-specific companion documents may provide for security by inclusion of authentication in datagram encasulation, or by some other means. Distribution of authentication keys used in comparison with the content of the Authentication MEE is outside the scope of this document. 7. References [1] "Tag Switching Architecture - Overview", Rekhter, Davie, Katz, Rosen, Swallow, Farinacci, work in progress, Internet Draft <draft-rekhter-tagswitch-arch-01.txt> [2] "NBMA Next Hop Resolution Protocol (NHRP)", J. Luciani et al., work in progress, draft-ietf-rolc-nhrp-11.txt, March 1997. [3] "Cisco System's Tag Switching Overview", IETF RFC 2105, Y.Rekhter, B.Davie, D.Katz, E.Rosen, G.Swallow, February, 1997. [4] Reynolds J, Postel J. "Assigned numbers" RFC 1700, October 1994 [5] Postel, J. "INTERNET PROTOCOL" RFC 791, September 1981. [6] "A Proposed Architecture for MPLS", E. Rosen, A. Viswanathan, R. Callon, work in progress, draft-rosen-architecture-00.txt, July 1997. [7] "Tag distribution Protocol", Doolan, Davie, Katz, Rekhter, Rosen, work in progress, internet draft <draft-doolan-tdp-spec-01.txt> [8] "Label Switching: Label Stack Encodings", Rosen, Rekhter, Tappan, Farinacci, Fedorkow, Li, work in progress, internet draft <draft-rosen-tag-stack-02.txt> [9] "A Framework for Multiprotocol Label Switching", 5/12/97, draft- ietf-mpls-framework-01.txt, Callon, Doolan, Feldman, Fredette, Swallow, Visanathawan Gray, et al Expires in six months [Page 28]
Internet Draft draft-gray-mpls-generic-ldp-spec-00 November 1997 [10] "ARIS: Aggregate Route-Based IP Switching", A. Viswanathan, N. Feldman, R. Boivie, R. Woundy, work in progress, Internet Draft <draft-viswanathan-aris-overview-00.txt>, March 1997. [11] "ARIS Specification", N. Feldman, A. Viswanathan, work in progress, Internet Draft <draft-feldman-aris-spec-00.txt>, March 1997. [12] "Server Cache Synchronization Protocol", J. Luciani, et al, work in progress, Internet Draft <draft-ietf-ion-scsp-01.txt>, March, 1997. 8. Author Information Eric Gray Lucent Technologies, Inc. 1600 Osgood Street North Andover, MA 01845 ewgray@lucent.com Zheng Wang Lucent Technologies, Inc. 101 Crawfords Corner Road Holmdel, NJ 07733 zhwang@lucent.com Grenville Armitage Lucent Technologies, Inc. 101 Crawfords Corner Road Holmdel, NJ 07733 gja@lucent.com Gray, et al Expires in six months [Page 29]