Network Working Group
KireetiK. Kompella (Juniper) Internet Draft PingP. Pan (Juniper) Expiration Date: September 2002 Nischal(Ciena) draft-ietf-mpls-lsp-ping-01.txt N. Sheth (Juniper) Network Working Group DaveCategory: Standards Track D. Cooper (Global Crossing) GeorgeExpires: April 2003 G. Swallow (Cisco) SanjayS. Wadhwa (Unisphere) Ron(Juniper) R. Bonica (Worldcom)(WorldCom) October 2002 Detecting MPLS Data Plane Liveliness in MPLS draft-ietf-mpls-lsp-ping-00.txtLiveness *** DRAFT *** Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.Internet- Drafts. 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. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document describes a simple and efficient mechanism that can be used to detect data plane failures in MPLS LSPs.Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs). There are two parts to this document: information carried in an MPLS "echo request" and "echo reply" for the purposes of fault detection and isolation; and mechanisms for transportingreliably sending the echo reply. Sub-IP ID Summary (This section to be removed before publication.) (See Abstract above.) RELATED DOCUMENTS May be found in the "references" section. WHERE DOES IT FIT IN THE PICTURE OF THE SUB-IP WORK Fits in the MPLS box. WHY IS IT TARGETED AT THIS WG MPLS WG is currently looking at MPLS-specific error detection and recovery mechanisms. The mechanisms proposed here are for packet-basedpacket- based MPLS LSPs, which is why the MPLS WG is targeted. JUSTIFICATION The WG should consider this document, as it allows network operators to detect MPLS LSP data plane failures in the network. This type of failures have occurred, and are a source of concern to operators implementing MPLS networks. 1. Introduction This document describes a simple and efficient mechanism that can be used to detect data plane failures in MPLS LSPs. There are two parts to this document: information carried in an MPLS "echo request" and "echo reply"; and mechanisms for transporting the echo reply. The first part aims at providing enough information to check correct operation of the data plane, as well as a mechanism to verify the data plane against the control plane, and thereby localize faults. The second part suggests two methods of reliable reply channels for the echo request message, for more robust fault isolation. An important consideration in this design is that MPLS echo requests follow the same data path that normal MPLS packets would traverse. MPLS echo requests are meant primarily to validate the data plane, and secondarily to verify the data plane against the control plane. Mechanisms to check the control plane are valuable, but are not covered in this document. To avoid potential Denial of Service attacks, it is recommended to regulate the MPLS ping traffic going to the control plane. A rate limiter should be applied to the well-known UDP port defined below. 1.1. Conventions 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 [KEYWORDS]. 1.2. Changes since last revision (This section to be removed before publication.) - Packet format changed; Version Number field added - Reply modes: "don't reply" added - Reply flags removed - Return codes extended - RSVP session formats modified - VPN IPv4/v6 formats defined - L2 VPN endpoint and L2 circuits defined - Downstream mapping format changed - Pad and Error Code TLVs introduced - Aspects dealing with CR-LDP moved to non-normative appendix - IPR notices and Full Copyright Statement (per 2026) added - other nits to better conform to 2223bis 2. Motivation When an LSP fails to deliver user traffic, the failure cannot always be detected by the MPLS control plane. There is a need to provide a tool that would enable users to detect such traffic "black holes" or misrouting within a reasonable period of time; and a mechanism to isolate faults. In this document, we describe a mechanism, termed "MPLS ping",mechanism that accomplishes these goals. This mechanism is modeled after the ICMPping/traceroute philosophy: ping (ICMP echo request/reply,request [ICMP]) is used by pingfor connectivity checks, and traceroute to detect and localize faults in IP networks.is used for hop-by-hop fault localization as well as path tracing. This document also offers some alternative methodsspecifies a "ping mode" and a "traceroute" mode for replying totesting MPLS echo requests.LSPs. The basic idea is to test that packets that belong to a particular Forwarding Equivalence Class (FEC) actually end their MPLS path on an LSR that is an egress for that FEC. Therefore,This document proposes that this test be carried out by sending a packet (called an "MPLS echo request") along the same data path as other packets belonging to this FEC. An MPLS echo request also carries information about the FEC whose MPLS path is being verified. This echo request is forwarded just like any other packet belonging to that FEC. In "ping" mode (basic connectivity check), the packet should reach the end of the path, at which point it is sent to the control plane of the egress LSR, which then verifies that it is indeed an egress for the FEC. In "traceroute" mode (fault isolation), the packet is sent to the control plane of each transit LSR, which performs various checks that it is indeed a transit LSR for this path; this LSR also returns further information that helps check the control plane against the data plane, i.e., that forwarding matches what the routing protocols determined as the path. One way these tools can be used is to periodically ping a FEC to ensure connectivity. If the ping fails, one can then initiate a traceroute to determine where the fault lies. One can also periodically traceroute FECs to verify that forwarding matches the control plane; however, this places a greater burden on transit LSRs and thus should be used with caution. 3. Packet Format An MPLS ping packetecho request is a (possibly labelled) UDP packet; the contents of the UDP packet withhave the following payloadformat: 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 Number | Must Be Zero | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message Type | Reply mode | Return Code | Return Subcode| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender's Handle | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TimeStamp Sent (seconds) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TimeStamp Sent (microseconds) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reply mode | Reply flagsTimeStamp Received (seconds) | Return Code+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Must be zeroTimeStamp Received (microseconds) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TLVs ... | . . . . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The SequenceVersion Number is assigned by the sender ofcurrently 1. (Note: the MPLS echo request, and can be used to detect missed replies (for example). The TimeStampVersion Number is setto be incremented whenever a change is made that affects the timeability of day (in seconds and microseconds) when thean implementation to correctly parse or process an MPLS echo requestrequest/reply. These changes include any syntactic or reply is sent, and may be usedsemantic changes made to compute delay or round trip time (for example). The Reply Mode can take oneany of the following values: Value Meaning ----- ------- 1 Reply viafixed fields, or to any TLV or sub-TLV assignment or format that is defined at a certain version number. The Version Number may not need to be changed if a TLV or sub-TLV is added.) The Message Type is one of the following: Value Meaning ----- ------- 1 MPLS Echo Request 2 MPLS Echo Reply The Reply Mode can take one of the following values: Value Meaning ----- ------- 1 Do not reply 2 Reply via an IPv4 UDP packet 23 Reply via an IPv4 UDP packet with Router Alert 34 Reply via the control plane Reply Flags are a bit vectorAn MPLS echo request with bit 0x1 being"Do not reply" may be used for one-way connectivity tests; the Least Significant Bit and bit 0x80 beingreceiving router may log gaps in the Most Significant Bit;sequence numbers and/or maintain delay/jitter statistics. An MPLS echo request would normally have "Reply via an IPv4 UDP packet"; if the following bits are defined: Bit Meaning when set --- ---------------- 0x1 Downstream Mappings desired 0x2 Upstream direction pinged Bit 0x2normal IPv4 return path is set whendeemed unreliable, one may use "Reply via an IPv4 UDP packet with Router Alert" (note that this requires that all intermediate routers understand and know how to forward MPLS echo replies) or "Reply via the reverse (upstream) direction of a bidirection LSPcontrol plane" (this is being tested. The details of the procedures in this case will be given in a later version.currently only defined for control plane that uses RSVP). The rest ofReturn Code is set to zero by the bits are reserved and must be zero.sender. The Return codereceiver can takeset it to one of the following values: Value Meaning ----- ------- 0 The error code is contained in the Error Code TLV 1 Malformed echo request received 2 One or more of the TLVs was not understood 3 Replying router is an egress for the FEC 24 Replying router has no mapping for the FEC 35 Replying router is not one of the "Downstream Routers". 4Routers" 6 Replying router is one of the "Downstream Routers", and its mapping for this FEC on the received interface is the given label 57 Replying router is one of the "Downstream Routers", but its mapping for this FEC is not the given label TLVs (Type-Length-Value tuples) haveThe Return Subcode is unused at present and SHOULD be set to zero. The Sender's Handle is filled in by the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0sender, and returned unchanged by the receiver in the echo reply (if any). There are no semantics associated with this handle, although a sender may find this useful for matching up requests with replies. The Sequence Number is assigned by the sender of the MPLS echo request, and can be (for example) used to detect missed replies. The TimeStamp Sent is the time-of-day (in seconds and microseconds, wrt the sender's clock) when the MPLS echo request is sent. The TimeStamp Received in an echo reply is the time-of-day (wrt the receiver's clock) that the corresponding echo request was received. TLVs (Type-Length-Value tuples) have the following 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Value | . . . . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Types are defined below; Length is the length of the Value field in octets. The Value field depends on the Type; it is zero padded to align to a four-octet boundary. Type # Value Field ------ ----------- 1 Target FEC Stack 2 Downstream Mapping 3 Pad 4 Error Code 3.1. Target FEC Stack A Target FEC Stack is a list of sub-TLVs. The number of elements is determined by the looking at the sub-TLV length fields. TypeSub-Type # Length Value Field ---------------- ------ ----------- 1 5 LDP IPv4 prefix 2 17 LDP IPv6 prefix 3 1620 RSVP IPv4 Session Query 4 5256 RSVP IPv6 Session Query 5 6 CR-LDP LSP IDReserved; see Appendix 6 13 VPN IPv4 prefix 7 25 VPN IPv4IPv6 prefix 8 ??14 L2 VPN "prefix"endpoint 9 10 L2 circuit ID Other FEC StackTypes will be defined as needed. Note that this TLV defines a stack of FECs, the first FEC element corresponding to the top of the label stack, etc. However, we will assume for nowAn MPLS echo request MUST have a Target FEC Stack that describes the FEC stack consists of just one element. Also, only the formatsbeing tested. For example, if an LSR X has an LDP mapping for FEC Types 1-5 will be described in this version. 3.1.1. IPv4 Prefix The value consists of four octets of192.168.1.1 (say label 1001), then to verify that label 1001 does indeed reach an IPv4egress LSR that announced this prefix followed byvia LDP, X can send an MPLS echo request with a FEC Stack TLV with one octet of prefix lengthFEC in bits. Theit, namely of type LDP IPv4 prefix, with prefix is in network byte order. 3.1.2. IPv6 Prefix The value consists192.168.1.1/32, and send the echo request with a label of sixteen octets1001. If LSR X wanted to verify that a label stack of <1001, 23456> is the right label stack to use to reach an IPv6IP VPN prefix followed by one octetof prefix length10/8 in bits.VPN foo on an egress LSR with loopback address 192.168.1.1 (learned via LDP), X has two choices. X can send an MPLS echo request with a FEC Stack TLV with a single FEC of type VPN IPv4 prefix with a prefix of 10/8 with the Route Distinguisher for VPN foo. Alternatively, X can send a FEC Stack TLV with two FECs, the first of type LDP IPv4 with a prefix of 192.168.1.1/32 and the second of type of IP VPN with a prefix 10/8 in VPN foo. In either case, the MPLS echo request would have a label stack of <1001, 23456>. (Note: in this example, 1001 is the "outer" label and 23456 is the "inner" label.) 3.1.1. IPv4 Prefix The value consists of four octets of an IPv4 prefix followed by one octet of prefix length in bits. The IPv4 prefix is in network byte order. See [LDP] for an example of a Mapping for an IPv4 FEC. 3.1.2. IPv6 Prefix The value consists of sixteen octets of an IPv6 prefix followed by one octet of prefix length in bits. The IPv6 prefix is in network byte order. 3.1.3. RSVP IPv4 Session The value has the format below. The value fields are taken from [RFC3209, sections 220.127.116.11 and 18.104.22.168]22.214.171.124]. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 tunnel end point address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LSP IDMust Be Zero | Tunnel ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extended Tunnel ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 tunnel sender address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Must Be Zero | LSP ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3.1.4. RSVP IPv6 Session The value has the format below. The value fields are taken from [RFC3209, sections 126.96.36.199 and 188.8.131.52]184.108.40.206]. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 tunnel end point address | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LSP IDMust Be Zero | Tunnel ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extended Tunnel ID | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 tunnel sender address | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3.1.5. CR-LDP| Must Be Zero | LSP ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3.1.5. VPN IPv4 Prefix The value field consists of the LSPID of the LSP being pinged. An LSPID is a four octet IPv4 address (a local address on the head end LSR) plusa two octet identifier that is unique for each LSP that starts on an LSR. 3.2. Downstream Mapping The Downstream Mapping is an optional TLV inRoute Distinguisher, an echo request. The Length is 4 + 4*N, where N is the number of Downstream Labels. The Value ofIPv4 prefix and a Downstream Mapping has the following format:prefix length, 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Downstream IPv4 RouterRoute Distinguisher | | (8 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Length | Must Be Zero | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3.1.6. VPN IPv6 Prefix The value field consists of a Route Distinguisher, an IPv6 prefix and a prefix length, 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Route Distinguisher | | (8 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 prefix | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Length | Must Be Zero | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3.1.7. L2 VPN Endpoint The value field consists of a Route Distinguisher (8 octets), the sender (of the ping)'s CE ID (2 octets), the receiver's CE ID (2 octets), and an encapsulation type (2 octets), formatted 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Route Distinguisher | | (8 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender's CE ID | Receiver's CE ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Encapsulation Type | Must Be Zero | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3.1.8. L2 Circuit ID The value field consists of a remote PE address (the address of the targetted LDP session), a VC ID and an encapsulation type, 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote PE Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VC ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Encapsulation Type | Must Be Zero | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3.2. Downstream Mapping The Downstream Mapping is an optional TLV in an echo request. The Length is 12 + 4*N octets, where N is the number of Downstream Labels. The Value of a Downstream Mapping has the following 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Downstream IPv4 Router ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MTU | Address Type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Downstream Label | Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Downstream Label | Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The MTU is the largest MPLS frame (including label stack) that fits on the interface to the Downstream LSR. The Address Type is one of: Type # Address Type ------ ------------ 1 IPv4 2 Unnumbered 'Protocol' is taken from the following table: Protocol # Signaling Protocol ---------- ------------------ 0 Unknown 1 Static 2 BGP 3 LDP 4 RSVP-TE 5 CR-LDPReserved; see Appendix The notion of "downstream router" should be explained. Consider an LSR X. If a packet with outermost label L and TTL n>1 arrived at X on interface I, X must be able to compute which LSRs could receive the packet with TTL=n,TTL=n+1, and what label they would see. (It is outside the scope of this document to specify how this computation may be done.) The set of these LSRs are the downstream routers (and their corresponding labels) for X with respect to L. The case where X is the LSR originating the echo request is a special case. X needs to figure out what LSRs would receive a labelled packet with TTL=1 when X tries to send a packet to the FEC Stack that is being pinged. 3.3. Pad TLV The value part of the Pad TLV contains a variable number (>= 1) of octets. The first octet takes values from the following table; all the other octets (if any) are ignored. The receiver SHOULD verify that the TLV is received in its entirety, but otherwise ignores the contents of this TLV, apart from the first octet. Value Meaning ----- ------- 1 Drop Pad TLV from reply 2 Copy Pad TLV to reply 3-255 Reserved for future use 3.4. Error Code The Error Code TLV is currently not defined; its purpose is to provide a mechanism for a more elaborate error reporting structure, should the reason arise. 4. Theory of Operation 4.1. Sending an MPLS Echo Request An MPLS echo request is a labeled(possibly) labelled UDP packet sentpacket. The IP header is set as follows: the source IP address is a routable address of the sender; the destination IP address is a (randomly chosen) address from 127/8; the IP TTL is set to 1. The source UDP port is chosen by the well-knownsender; the destination UDP port is set to 3503 (assigned by IANA for MPLS ping [UDP port # 3503 assignedecho requests). If the echo request is labelled, the MPLS TTL on all the labels except the outermost should be set to 1. In "ping" mode (end-to-end connectivity check), the TTL in the outermost label is set to 255. In "traceroute" mode (fault isolation mode), the TTL is set successively to 1, 2, .... The sender chooses a Sender's Handle, and a Sequence Number. When sending subsequent MPLS echo requests, the sender SHOULD increment the sequence number by IANA],1. However, a sender MAY choose to send a group of echo requests with destination IP address setthe same sequence number to improve the ALL-ROUTERS multicast address (220.127.116.11).chance of arrival of at least one packet with that sequence number. The source IP addressTimeStamp Sent is set to a routable address ofthe sender; the source port identifiestime-of-day (in seconds and microseconds) that the sending process.echo request is sent. The IP TTL in the UDP packetTimeStamp Received is set to 1.zero. An MPLS echo request MUST have a FEC Stack TLV. Also, the Reply Mode must be set to the desired reply mode; the Return Code is set to zeroand ignored on receipt. In "ping" mode (end-to-end connectivity check), the TTL in the outermost label is set to 255. In "traceroute" mode (fault isolation mode), the TTL isSubcode are set successivelyto 1, 2, ....zero. In the "traceroute" mode, the echo request SHOULD contain one or more Downstream Mapping TLVs. For TTL=1, all the downstream routers (and corresponding labels) for the sender with respect to the FEC Stack being pinged SHOULD be sent in the echo request. For n>1, the Downstream Mapping TLVs from the echo reply for TTL=(n-1) are copiedreply for TTL=(n-1) are copied to the echo request with TTL=n. 4.2. Receiving an MPLS Echo Request An LSR L that receives an MPLS echo request first parses the packet to ensure that it is a well-formed packet, and that the TLVs are understood. If not, L SHOULD send an MPLS echo reply with the Return Code set to "Malformed echo request received" or "TLV not understood" (as appropriate), and the Subcode set to the appropriate value. If the echo request is good, L then checks whether it is a valid transit or egress LSR for the FEC in the echo request. If not, L MAY log this fact. If the echo request contains a Downstream Mapping TLV, L MUST further check whether its Router ID matches one of the Downstream IPv4 Router IDs; and if so, whether the given Downstream Label is in fact the label that L sent as its mapping for the FEC. For an RSVP FEC, the downstream label is the label that L sent in its Resv message. The result of the checks in the previous and this paragraph are captured in the Return Code/Subcode. If the echo request has a Reply Mode that wants a reply, L uses the procedure in the next subsection to send the echo request with TTL=n. 4.2.reply. 4.3. Sending an MPLS Echo Reply An MPLS echo reply is a UDP packet. It MUST ONLY be sent in response to an MPLS echo request. The source IP address is the Router IDa routable address of the replier; the source port is the well-known UDP port for MPLS ping. The destination IP address and UDP port are copied from the source IP address and UDP port of the echo request. The IP TTL is set to 255. If the Reply Mode in the echo request is "Reply via an IPv4 UDP packet with Router Alert", then the IP header MUST contain the Router Alert IP option. The format of the echo reply is the same as the echo request. The Sender's Handle, the Sequence Number isand TimeStamp Sent are copied from the echo request; the TimeStamp Received is set to the time-of-daytime-of- day that the echo request is received (note that this information is most useful if the time-of-day clocks on the requestor and the replier are synchronized). The FEC Stack TLV from the echo request isMAY be copied to the reply. The replier MUST fill in the Return Code. This is set based on whetherCode and Subcode, as determined in the replier has a mapping forprevious subsection. If the FEC, and whether it is an egress for that FEC. Note that 'havingecho request contains a mapping' for an RSVP FEC means thatPad TLV, the replier is a transit LSR for the RSVP LSP defined byMUST interpret the FEC.first octet for instructions regarding how to reply. If the echo request contains a Downstream Mapping TLV, the replier MUST further check whetherSHOULD compute its Router ID matches one of the Downstream IPv4 Router IDs;downstream routers and if so, whethercorresponding labels for the givenincoming label, and add Downstream Label is in fact the label that the replier sent as its mappingMapping TLVs for each one to the FEC. Forecho reply it sends back. 4.4. Receiving an RSVP FEC,MPLS Echo Reply An LSR X should only receive an MPLS Echo Reply in response to an MPLS Echo Request that it sent. Thus, on receipt of an MPLS Echo Reply, X should parse the downstream labelpacket to assure that it is well-formed, then attempt to match up the labelEcho Reply with an Echo Request that it had previously sent, using the replier sent in its Resv message. The result of these checks are captured indestination UDP port and the Return Code.Sender's Handle. If the flag requesting Downstream Mapping TLVsno match is set infound, then X jettisons the Reply Flags,Echo Reply; otherwise, it checks the replier SHOULD compute its downstream routersSequence Number to see if it matches. Gaps in the Sequence Number MAY be logged and corresponding labelsSHOULD be counted. Once an Echo Reply is received for a given Sequence Number (for a given UDP port and Handle), the incoming label,Sequence Number for subsequent Echo Requests for that UDP port and addHandle SHOULD be incremented. If the Echo Reply contains Downstream Mapping TLVs for each oneMappings, and X wishes to the echo replytraceroute further, it sends back. 4.3.SHOULD copy the Downstream Mappings into its next Echo Request (with TTL incremented by one). 4.5. Non-compliant Routers If the egress for the FEC Stack being pinged does not support MPLS ping, then no reply will be sent, resulting in possible "false negatives". If in "traceroute" mode, a transit LSR does not support MPLS ping, then no reply will be forthcoming from that LSR for some TTL, say n. The LSR originating the echo request SHOULD try sending the echo request with TTL=n+1, n+2, ..., n+k in the hope that some transit LSR further downstream may support MPLS echo requests and reply. In such a case, the echo request for TTL>n MUST NOT have Downstream Mapping TLVs, until a reply is received with a Downstream Mapping. 5. Reliable Reply Path One of the issues that are faced with MPLS ping is to distinguish between a failure in the forward path (the MPLS path being 'pinged') and a failure in the return path. Note that this problem exists with vanilla IP ping as well. In the case of MPLS ping, it is assumed that the IP control and data planes are reliable. However, it could be that the forwarding in the return path is via an MPLS LSP. In this specification, we give two solutions for this problem. One is to set the Router Alert option in the MPLS echo reply. When a router sees this option, it MUST forward the packet as an IP packet. Note that this may not work if some transit LSR does not support MPLS ping. Another option is to send the echo reply via the control plane. At present, this is defined only for RSVP-TE LSPs, and described below. These options are controlled by the ingress LSR, using the Reply Mode in the MPLS echo request packet. 5.1. RSVP-TE Extension To test an LSP's liveliness, an ingress LSR sends MPLS echo requests over the LSP being tested. When an egress LSR receives the message, it needs to acknowledge the ingress LSR by sending an LSP_ECHO object in a RSVP Resv message. The object has the following format: Class = LSP_ECHO (use form 11bbbbbb for compatibility) C-Type = 1 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TimeStamp (seconds) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TimeStamp (microseconds) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | UDP Source Port | Return Code | Must be zero |Return Subcode| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Sequence Number is copied from the Sequence Number of the echo request. The TimeStamp is set to the time the echo request is received. The UDP Source Port is copied from the UDP source port of the MPLS echo request. The FEC is implied by the Session and the Sender Template Objects. 5.2. Operation For the sake of brevity in the context of this document by "the control plane" we mean "the RSVP-TE component of the control plane". Consider an LSP between an ingress LSR and an egress LSR spanning multiple LSR hops. 5.3. Procedures at the ingress LSR One must ensure before setting the Reply Mode to "reply via the control plane" that the egress LSR supports this feature. The ingress LSR, say X, selects a unique UDP source port for itsbuilds an MPLS ping. X also sets theecho request as in section "Sending an MPLS Echo Request". The FEC Stack TLVType to RSVP IPv4 (IPv6), and copies the SESSION and SENDER_TEMPLATE into the appropriate fields of the value field. Finally,must be an RVSP Session Query. X also sets the Reply Mode to "reply via the control plane". If X does not receive an Resv message from the egress LSR that contains an LSP_ECHO object within some period of time, it declares the LSP as "down". At this point, the ingress LSR may apply the necessary procedures to fix the LSP. These may include generating a message to network management, tearing-down and re-building the LSP, and/or rerouting user traffic to a backup LSP. To test an LSP that carries non-IP traffic, before injecting ICMP and MPLS ping messages into the LSP, the IPv4 Explicit NULL label should be prepended to such messages. The ingress and egress LSR's must follow the procedures defined in [LABEL-STACKING]. 5.4. Procedures at the egress LSR When the egress LSR receives an MPLS ping message, it follows the procedures given above. If the Reply Mode is set to "Reply via the control plane", the LSR can, based on the RSVP SESSION and SENDER_TEMPLATE objects carried in the MPLS ping message, find the corresponding LSP in its RSVP-TE database. The LSR then checks to see if the Resv message for this LSP contains an LSP_ECHO object with the same source UDP port value. If not, the LSR adds or updates the LSP_ECHO object and refreshes the Resv message. 5.5. Procedures for the intermediate LSR's At intermediate LSRs, normal RSVP processing procedures will cause the LSP_ECHO object to be forwarded as RSVP messages are refreshed. At the LSR's that support MPLS ping the Resv messages that carry the LSP_ECHO object MUST be delivered upstream immediately. Note that an intermediate LSR using RSVP refresh reduction [RSVP- REFRESH], the new or changed LSP_ECHO object will cause the LSR to classify the RSVP message as a trigger message. 6. Security Considerations The security considerations pertainingNormative References [KEYWORDS] Bradner, S., "Key words for use in RFCs to the original RSVPIndicate Requirement Levels", BCP 14, RFC 2119, March 1997. [LABEL-STACKING] Rosen, E., et al, "MPLS Label Stack Encoding", RFC 3032, January 2001. [RSVP] Braden, R. (Editor), et al, "Resource ReSerVation protocol remain relevant.(RSVP) -- Version 1 Functional Specification," RFC 2205, September 1997. [RSVP-REFRESH] Berger, L., et al, "RSVP Refresh Overhead Reduction Extensions", RFC 2961, April 2001. [RSVP-TE] Awduche, D., et al, "RSVP-TE: Extensions to RSVP for LSP tunnels", RFC 3209, December 2001. 7. Intellectual PropertyInformative References [ICMP] Postel, J., "Internet Control Message Protocol", RFC 792. [LDP] Andersson, L., et al, "LDP Specification", RFC 3036, January 2001. 8. Security Considerations Juniper Networks, Inc. is seeking patent protection on technology described in this Internet-Draft. If technology in this Internet- DraftThere are at least two approaches to attacking LSRs using the mechanisms defined here. One is adopted asa standard, Juniper Networks agreesDenial of Service attack, by sending MPLS echo requests/replies to LSRs and thereby increasing their workload. The other is obfuscating the state of the MPLS data plane liveness by spoofing, hijacking, replaying or otherwise tampering with MPLS echo requests and replies. Authentication will help reduce the number of seemingly valid MPLS echo requests, and thus cut down the Denial of Service attacks; beyond that, each LSR must protect itself. Authentication sufficiently addresses spoofing, replay and most tampering attacks; one hopes to use some mechanism devised or suggested by the RPSec WG. It is not clear how to license, on reasonable and non-discriminatory terms, any patent rightsprevent hijacking (non-delivery) of echo requests or replies; however, if these messages are indeed hijacked, MPLS ping will report that the data plane isn't working as it obtains covering such technologyshould. It doesn't seem vital (at this point) to secure the extent necessary to comply withdata carried in MPLS echo requests and replies, although knowledge of the standard. 8.state of the MPLS data plane may be considered confidential by some. 9. IANA Considerations (To be filled in a later revision) 10. Acknowledgments This document is the outcome of many discussions among many people, that alsoinclude Manoj Leelanivas, Paul Traina, Yakov Rekhter, Der-Hwa Gan, Brook Bailey andBailey, Eric Rosen. 9. References [ICMP] J. Postel, "Internet Control Message Protocol", RFC792. [RSVP] R. Braden, Ed., et al, "Resource ReSerVation protocol (RSVP) -- version 1 functional specification," RFC2205. [RSVP-TE] D. Awduche, et al, "RSVP-TE: Extensions to RSVPRosen and Ina Minei. 11. Appendix This appendix specifies non-normative aspects of detecting MPLS data plane liveness. 11.1. CR-LDP FEC This section describes how a CR-LDP FEC can be included in an Echo Request using the following FEC subtype: Sub-Type # Length Value Field ---------- ------ ----------- 5 6 CR-LDP LSP ID The value consists of the LSPID of the LSP being pinged. An LSPID is a four octet IPv4 address (a local address on the ingress LSR, for example, the Router ID) plus a two octet identifier that is unique per LSP tunnels" Internet Draft. [LABEL-STACKING] E. Rosen, et al, "MPLS Label Stack Encoding", RFC3032. [RSVP-REFRESH] L. Berger, et al, "RSVP Refresh Overhead Reduction Extensions", RFC2961. [RFC-IANA] T. Narten and H. Alvestrand, "Guidelineson a given ingress LSR. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ingress LSR Router ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Must Be Zero | LSP ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 11.2. Downstream Mapping for Writing an IANA Considerations SectionCR-LDP If a label in RFCs", RFC 2434. 10. Author Informationa Downstream Mapping was learned via CR-LDP, the Protocol field in the Mapping TLV can use the following entry: Protocol # Signaling Protocol ---------- ------------------ 5 CR-LDP 12. Authors' Addresses Kireeti Kompella Ping PanNischal Sheth Juniper Networks 1194 N.Mathilda Ave Sunnyvale, CA 94089 e-mail: firstname.lastname@example.org e-mail: email@example.com e-mail:firstname.lastname@example.org Ping Pan Ciena 10480 Ridgeview Court Cupertino, CA 95014 e-mail: email@example.com phone: 408.745.2000+1 408.366.4700 Dave Cooper Global Crossing 960 Hamlin Court Sunnyvale, CA 94089 email: firstname.lastname@example.org phone: +1 916.415.0437 George Swallow Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA 01824 e-mail: email@example.com phone: 978.244.8143+1 978.497.8143 Sanjay Wadhwa Unisphere Networks, Inc.Juniper Networks 10 Technology Park Drive Westford, MA 01886-3146 email: firstname.lastname@example.org phone: +1 978.589.0697 Ronald P. Bonica WorldCom 22001 Loudoun County Pkwy Ashburn, Virginia, 20147 email: email@example.com phone: +1 703.886.1681 13. 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