draft-ietf-mpls-lsp-ping-01.txt		draft-ietf-mpls-lsp-ping-02.txt
	Network Working Group K. Kompella (Juniper)		Network Working Group K. Kompella (Juniper)
	Internet Draft P. Pan (Ciena)		Internet Draft P. Pan (Ciena)
	draft-ietf-mpls-lsp-ping-01.txt N. Sheth (Juniper)		draft-ietf-mpls-lsp-ping-02.txt N. Sheth (Juniper)
	Category: Standards Track D. Cooper (Global Crossing)		Category: Standards Track D. Cooper (Global Crossing)
	Expires: April 2003 G. Swallow (Cisco)		Expires: September 2003 G. Swallow (Cisco)
	S. Wadhwa (Juniper)		S. Wadhwa (Juniper)
	R. Bonica (WorldCom)		R. Bonica (WorldCom)
	October 2002		March 2003
	Detecting MPLS Data Plane Liveness		Detecting MPLS Data Plane Liveness
	*** DRAFT ***		*** DRAFT ***
	Status of this Memo		Status of this Memo
	This document is an Internet-Draft and is in full conformance with		This document is an Internet-Draft and is in full conformance with
	all provisions of Section 10 of RFC2026.		all provisions of Section 10 of RFC2026.
	skipping to change at page 1, line 39		skipping to change at page 1, line 39
	material or to cite them other than as ``work in progress.''		material or to cite them other than as ``work in progress.''
	The list of current Internet-Drafts can be accessed at		The list of current Internet-Drafts can be accessed at
	http://www.ietf.org/ietf/1id-abstracts.txt		http://www.ietf.org/ietf/1id-abstracts.txt
	The list of Internet-Draft Shadow Directories can be accessed at		The list of Internet-Draft Shadow Directories can be accessed at
	http://www.ietf.org/shadow.html.		http://www.ietf.org/shadow.html.
	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society (2002). All Rights Reserved.		Copyright (C) The Internet Society (2003). All Rights Reserved.
	Abstract		Abstract
	This document describes a simple and efficient mechanism that can be		This document describes a simple and efficient mechanism that can be
	used to detect data plane failures in Multi-Protocol Label Switching		used to detect data plane failures in Multi-Protocol Label Switching
	(MPLS) Label Switched Paths (LSPs). There are two parts to this		(MPLS) Label Switched Paths (LSPs). There are two parts to this
	document: information carried in an MPLS "echo request" and "echo		document: information carried in an MPLS "echo request" and "echo
	reply" for the purposes of fault detection and isolation; and		reply" for the purposes of fault detection and isolation; and
	mechanisms for reliably sending the echo reply.		mechanisms for reliably sending the echo reply.
	skipping to change at page 3, line 34		skipping to change at page 3, line 34
	To avoid potential Denial of Service attacks, it is recommended to		To avoid potential Denial of Service attacks, it is recommended to
	regulate the MPLS ping traffic going to the control plane. A rate		regulate the MPLS ping traffic going to the control plane. A rate
	limiter should be applied to the well-known UDP port defined below.		limiter should be applied to the well-known UDP port defined below.
	1.1. Conventions		1.1. Conventions
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in RFC 2119 [KEYWORDS].		document are to be interpreted as described in RFC 2119 [KEYWORDS].
	1.2. Changes since last revision		1.2. Structure of this document
			The body of this memo contains four main parts: motivation, MPLS echo
			request/reply packet format, MPLS ping operation, and a reliable
			return path. It is suggested that first-time readers skip the actual
			packet formats and read the Theory of Operation first; the document
			is structured the way it is to avoid forward references.
			The last section (reliable return path for RSVP LSPs) may be removed
			in a future revision.
			1.3. Changes since last revision
	(This section to be removed before publication.)		(This section to be removed before publication.)
	- Packet format changed; Version Number field added		- Clarified definition of downstream router/interface.
	- Reply modes: "don't reply" added		- Added text for multipath (mostly just taken from Curtis)
	- Reply flags removed		- Mandated the use of Router Alert for sending echo requests
	- Return codes extended		- If reply mode says IPv4 with router alert, and the reply is
	- RSVP session formats modified		labeled, the top label MUST be the router alert label
	- VPN IPv4/v6 formats defined		- Expanded the Theory of Operation, and added a section on ECMP
	- L2 VPN endpoint and L2 circuits defined		- Expanded checks on receipt of echo requests, per email on list
	- Downstream mapping format changed
	- Pad and Error Code TLVs introduced		1.4. Issues remaining
	- Aspects dealing with CR-LDP moved to non-normative appendix
	- IPR notices and Full Copyright Statement (per 2026) added		(This section to be removed before publication.)
	- other nits to better conform to 2223bis
			- Monitoring mode
			- Finalize ECMP format and semantics
			- Keep or remove replies via control plane?
			- Normalize error codes
	2. Motivation		2. Motivation
	When an LSP fails to deliver user traffic, the failure cannot always		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		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		tool that would enable users to detect such traffic "black holes" or
	misrouting within a reasonable period of time; and a mechanism to		misrouting within a reasonable period of time; and a mechanism to
	isolate faults.		isolate faults.
	In this document, we describe a mechanism that accomplishes these		In this document, we describe a mechanism that accomplishes these
	goals. This mechanism is modeled after the ping/traceroute		goals. This mechanism is modeled after the ping/traceroute paradigm:
	philosophy: ping (ICMP echo request [ICMP]) is used for connectivity		ping (ICMP echo request [ICMP]) is used for connectivity checks, and
	checks, and traceroute is used for hop-by-hop fault localization as		traceroute is used for hop-by-hop fault localization as well as path
	well as path tracing. This document specifies a "ping mode" and a		tracing. This document specifies a "ping mode" and a "traceroute"
	"traceroute" mode for testing MPLS LSPs.		mode for testing MPLS LSPs.
	The basic idea is to test that packets that belong to a particular		The basic idea is to test that packets that belong to a particular
	Forwarding Equivalence Class (FEC) actually end their MPLS path on an		Forwarding Equivalence Class (FEC) actually end their MPLS path on an
	LSR that is an egress for that FEC. This document proposes that this		LSR that is an egress for that FEC. This document proposes that this
	test be carried out by sending a packet (called an "MPLS echo		test be carried out by sending a packet (called an "MPLS echo
	request") along the same data path as other packets belonging to this		request") along the same data path as other packets belonging to this
	FEC. An MPLS echo request also carries information about the FEC		FEC. An MPLS echo request also carries information about the FEC
	whose MPLS path is being verified. This echo request is forwarded		whose MPLS path is being verified. This echo request is forwarded
	just like any other packet belonging to that FEC. In "ping" mode		just like any other packet belonging to that FEC. In "ping" mode
	(basic connectivity check), the packet should reach the end of the		(basic connectivity check), the packet should reach the end of the
	skipping to change at page 5, line 42		skipping to change at page 5, line 47
	. .		. .
	| |		| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The Version Number is currently 1. (Note: the Version Number is to		The Version Number is currently 1. (Note: the Version Number is to
	be incremented whenever a change is made that affects the ability of		be incremented whenever a change is made that affects the ability of
	an implementation to correctly parse or process an MPLS echo		an implementation to correctly parse or process an MPLS echo
	request/reply. These changes include any syntactic or semantic		request/reply. These changes include any syntactic or semantic
	changes made to any of the fixed fields, or to any TLV or sub-TLV		changes made to any of the fixed fields, or to any TLV or sub-TLV
	assignment or format that is defined at a certain version number.		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		The Version Number may not need to be changed if an optional TLV or
	added.)		sub-TLV is added.)
	The Message Type is one of the following:		The Message Type is one of the following:
	Value Meaning		Value Meaning
	----- -------		----- -------
	1 MPLS Echo Request		1 MPLS Echo Request
	2 MPLS Echo Reply		2 MPLS Echo Reply
	The Reply Mode can take one of the following values:		The Reply Mode can take one of the following values:
	skipping to change at page 8, line 23		skipping to change at page 8, line 31
	on an egress LSR with loopback address 192.168.1.1 (learned via LDP),		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		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		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		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		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 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		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		have a label stack of <1001, 23456>. (Note: in this example, 1001 is
	the "outer" label and 23456 is the "inner" label.)		the "outer" label and 23456 is the "inner" label.)
	3.1.1. IPv4 Prefix		3.1.1. LDP IPv4 Prefix
	The value consists of four octets of an IPv4 prefix followed by one		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		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.		order. See [LDP] for an example of a Mapping for an IPv4 FEC.
	3.1.2. IPv6 Prefix		3.1.2. LDP IPv6 Prefix
	The value consists of sixteen octets of an IPv6 prefix followed by		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		one octet of prefix length in bits. The IPv6 prefix is in network
	byte order.		byte order. See [LDP] for an example of a Mapping for an IPv6 FEC.
	3.1.3. RSVP IPv4 Session		3.1.3. RSVP IPv4 Session
	The value has the format below. The value fields are taken from		The value has the format below. The value fields are taken from
	[RFC3209, sections 4.6.1.1 and 4.6.2.1].		[RFC3209, sections 4.6.1.1 and 4.6.2.1].
	0 1 2 3		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 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 |		| IPv4 tunnel end point address |
	skipping to change at page 11, line 19		skipping to change at page 11, line 26
	The Downstream Mapping is an optional TLV in an echo request. The		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		Length is 12 + 4*N octets, where N is the number of Downstream
	Labels. The Value of a Downstream Mapping has the following format:		Labels. The Value of a Downstream Mapping has the following format:
	0 1 2 3		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 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 |		| Downstream IPv4 Router ID |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| MTU | Address Type | Reserved |		| MTU | Address Type | DS Index |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Interface Address |		| Downstream Interface Address |
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			| Hash Key Type | Depth Limit | Multipath Length |
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			| IP Address or Next Label |
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			. .
			. (more IP Addresses or Next Labels) .
			. .
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Downstream Label | Protocol |		| Downstream Label | Protocol |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	. .		. .
	. .		. .
	. .		. .
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Downstream Label | Protocol |		| Downstream Label | Protocol |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The MTU is the largest MPLS frame (including label stack) that fits		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:		on the interface to the Downstream LSR. The Downstream Interface
			Address Type is one of:
	Type # Address Type		Type # Address Type
	------ ------------		------ ------------
	1 IPv4		1 IPv4
	2 Unnumbered		2 Unnumbered
	'Protocol' is taken from the following table:		'Protocol' is taken from the following table:
	Protocol # Signaling Protocol		Protocol # Signaling Protocol
	---------- ------------------		---------- ------------------
	0 Unknown		0 Unknown
	1 Static		1 Static
	2 BGP		2 BGP
	3 LDP		3 LDP
	4 RSVP-TE		4 RSVP-TE
	5 Reserved; see Appendix		5 Reserved; see Appendix
	The notion of "downstream router" should be explained. Consider an		The notion of "downstream router" and "downstream interface" should
	LSR X. If a packet with outermost label L and TTL n>1 arrived at X		be explained. Consider an LSR X. If a packet that was originated
	on interface I, X must be able to compute which LSRs could receive		with TTL n>1 arrived with outermost label L at LSR X, X must be able
	the packet with TTL=n+1, and what label they would see. (It is		to compute which LSRs could receive the packet if it was originated
	outside the scope of this document to specify how this computation		with TTL=n+1, over which interface the request would arrive and what
	may be done.) The set of these LSRs are the downstream routers (and		label stack those LSRs would see. (It is outside the scope of this
	their corresponding labels) for X with respect to L.		document to specify how this computation is done.) The set of these
			LSRs/interfaces are the downstream routers/interfaces (and their
			corresponding labels) for X with respect to L. Each pair of
			downstream router and interface requires a separate Downstream
			Mapping to be added to the reply, and is given a unique DS Index.
			(Note that there are multiple Downstream Label fields in each TLV as
			the incoming label L may be swapped with a label stack.)
	The case where X is the LSR originating the echo request is a special		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		case. X needs to figure out what LSRs would receive the MPLS echo
	packet with TTL=1 when X tries to send a packet to the FEC Stack that		request for a given FEC Stack that X originates with TTL=1.
	is being pinged.
			The set of downstream routers at X may be alternative paths (see the
			discussion below on ECMP) or simultaneous paths (e.g., for MPLS
			multicast). In the former case, the Multipath sub-field is used as a
			hint to the sender as to how it may influence the choice of these
			alternatives. The Multipath Length is the total length of the
			Multipath field (i.e., 4 + 4*M, where M is the number of IP
			Address/Next Label fields). The Hash Key Type is taken from the
			following table:
			Hash Key Type IP Address or Next Label
			-------------------- ------------------------
			0 no multipath (nothing; M = 0)
			1 label M labels
			2 IP address M IP addresses
			3 label range M/2 low/high label pairs
			4 IP address range M/2 low/high address pairs
			5 no more labels (nothing; M = 0)
			6 All IP addresses (nothing; M = 0)
			7 no match (nothing; M = 0)
			The Depth Limit is applicable only to a label stack, and is the
			maximum number of labels considered in the hash; this SHOULD be set
			to zero if unspecified or unlimited.
			IP Address or Next Label is an IP address from the range 127/8 or an
			next label which will exercise this particular path.
			The semantics of the Hash Key Type and IP Address/Next Label are as
			follows:
			type 1 - a list of single labels is provided, any one of which
			will
			cause the hash to match this MP path.
			type 2 - a list of single IP addresses is provided, any one of
			which will cause the hash to match this MP path.
			type 3 - a list of label ranges is provided, any one of which will
			cause the hash to match this MP path.
			type 4 - a list of IP address ranges is provided, any one of which
			will cause the hash to match this MP path.
			type 5 - if no more labels are provided on the stack, this MP path
			will apply (can only appear once).
			type 6 - Any IP addresses matches. Undertlying labels may go
			elsewhere, but all IP takes only one MP path (can only
			appear once).
			type 7 - no matches are possible given the set of "Multipath
			Exercise TLV" provided by prior hops.
			If prior hops provide a "Downstream Multipath Mapping TLV" the labels
			and IP addresses should be picked from the set provided in prior
			"Multipath Exercise TLV" or "Hash Key Type" of 7 used.
	3.3. Pad TLV		3.3. Pad TLV
	The value part of the Pad TLV contains a variable number (>= 1) of		The value part of the Pad TLV contains a variable number (>= 1) of
	octets. The first octet takes values from the following table; all		octets. The first octet takes values from the following table; all
	the other octets (if any) are ignored. The receiver SHOULD verify		the other octets (if any) are ignored. The receiver SHOULD verify
	that the TLV is received in its entirety, but otherwise ignores the		that the TLV is received in its entirety, but otherwise ignores the
	contents of this TLV, apart from the first octet.		contents of this TLV, apart from the first octet.
	Value Meaning		Value Meaning
	skipping to change at page 12, line 38		skipping to change at page 14, line 13
	3-255 Reserved for future use		3-255 Reserved for future use
	3.4. Error Code		3.4. Error Code
	The Error Code TLV is currently not defined; its purpose is to		The Error Code TLV is currently not defined; its purpose is to
	provide a mechanism for a more elaborate error reporting structure,		provide a mechanism for a more elaborate error reporting structure,
	should the reason arise.		should the reason arise.
	4. Theory of Operation		4. Theory of Operation
	4.1. Sending an MPLS Echo Request		An MPLS echo request is used to test a particular LSP. The LSP to be
			tested is identified by the "FEC Stack"; for example, if the LSP was
			set up via LDP, and is to an egress IP address of 10.1.1.1, the FEC
			stack contains a single element, namely, an LDP IPv4 prefix sub-TLV
			with value 10.1.1.1/32. If the LSP being tested is an RSVP LSP, the
			FEC stack consists of a single element that captures the RSVP Session
			and Sender Template which uniquely identifies the LSP.
			FEC stacks can be more complex. For example, one may wish to test a
			VPN IPv4 prefix of 10.1/8 that is tunneled over an LDP LSP with
			egress 10.10.1.1. The FEC stack would then contain two sub-TLVs, the
			first being a VPN IPv4 prefix, and the second being an LDP IPv4
			prefix. If the underlying (LDP) tunnel were not known, or was
			considered irrelevant, the FEC stack could be a single element with
			just the VPN IPv4 sub-TLV.
			When an MPLS echo request is received, the receiver is expected to do
			a number of tests that verify that the control plane and data plane
			are both healthy (for the FEC stack being pinged), and that the two
			planes are in sync.
			4.1. Dealing with Equal-Cost Multi-Path (ECMP)
			LSPs need not be simple point-to-point tunnels. Frequently, a single
			LSP may originate at several ingresses, and terminate at several
			egresses; this is very common with LDP LSPs. LSPs for a given FEC
			may also have multiple "next hops" at transit LSRs. At an ingress,
			there may also be several different LSPs to choose from to get to the
			desired endpoint. Finally, LSPs may have backup paths, detour paths
			and other alternative paths to take should the primary LSP go down.
			To deal with the last two first: it is assumed that the LSR sourcing
			MPLS echo requests can force the echo request into any desired LSP,
			so choosing among multiple LSPs at the ingress is not an issue. The
			problem of probing the various flavors of backup paths that will
			typically not be used for forwarding data unless the primary LSP is
			down will not be addressed here.
			Since the actual LSP and path that a given packet may take may not be
			known a priori, it is useful if MPLS echo requests can exercise all
			possible paths. This, while desirable, may not be practical, because
			the algorithms that a given LSR uses to distribute packets over
			alternative paths may be proprietary.
			To achieve some degree of coverage of alternate paths, there is a
			certain lattitude in choosing the destination IP address and source
			UDP port for an MPLS echo request. This is clearly not sufficient;
			in the case of traceroute, more lattitude is offered by means of the
			"Multipath Exercise" sub-TLV of the Downstream Mapping TLV. This is
			used as follows. An ingress LSR periodically sends an MPLS
			traceroute message to determine whether there are multipaths for a
			given LSP. If so, each hop will provide some information how each of
			its downstreams can be exercised. The ingress can then send MPLS
			echo requests that exercise these paths. If several transit LSRs
			have ECMP, the ingress may attempt to compose these to exercise all
			possible paths. However, full coverage may not be possible.
			4.2. Sending an MPLS Echo Request
	An MPLS echo request is a (possibly) labelled UDP packet. The IP		An MPLS echo request is a (possibly) labelled UDP packet. The IP
	header is set as follows: the source IP address is a routable address		header is set as follows: the source IP address is a routable address
	of the sender; the destination IP address is a (randomly chosen)		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		address from 127/8; the IP TTL is set to 1. The source UDP port is
	chosen by the sender; the destination UDP port is set to 3503		chosen by the sender; the destination UDP port is set to 3503
	(assigned by IANA for MPLS echo requests). If the echo request is		(assigned by IANA for MPLS echo requests). The Router Alert option
	labelled, the MPLS TTL on all the labels except the outermost should		is set in the IP header. If the echo request is labelled, the MPLS
	be set to 1.		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		In "ping" mode (end-to-end connectivity check), the TTL in the
	outermost label is set to 255. In "traceroute" mode (fault isolation		outermost label is set to 255. In "traceroute" mode (fault isolation
	mode), the TTL is set successively to 1, 2, ....		mode), the TTL is set successively to 1, 2, ....
	The sender chooses a Sender's Handle, and a Sequence Number. When		The sender chooses a Sender's Handle, and a Sequence Number. When
	sending subsequent MPLS echo requests, the sender SHOULD increment		sending subsequent MPLS echo requests, the sender SHOULD increment
	the sequence number by 1. However, a sender MAY choose to send a		the sequence number by 1. However, a sender MAY choose to send a
	group of echo requests with the same sequence number to improve the		group of echo requests with the same sequence number to improve the
	chance of arrival of at least one packet with that sequence number.		chance of arrival of at least one packet with that sequence number.
	skipping to change at page 13, line 25		skipping to change at page 16, line 8
	An MPLS echo request MUST have a FEC Stack TLV. Also, the Reply Mode		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 and Subcode		must be set to the desired reply mode; the Return Code and Subcode
	are set to zero.		are set to zero.
	In the "traceroute" mode, the echo request SHOULD contain one or more		In the "traceroute" mode, the echo request SHOULD contain one or more
	Downstream Mapping TLVs. For TTL=1, all the downstream routers (and		Downstream Mapping TLVs. For TTL=1, all the downstream routers (and
	corresponding labels) for the sender with respect to the FEC Stack		corresponding labels) for the sender with respect to the FEC Stack
	being pinged SHOULD be sent in the echo request. For n>1, the		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 copied		Downstream Mapping TLVs from the echo reply for TTL=(n-1) are copied
	to the echo request with TTL=n.		to the echo request with TTL=n; the sender MAY choose to reduce the
			size of a "Downstream Multipath Mapping TLV" when copying into the
			next echo request as long as the Hash Key Type matching the label or
			IP address used to exercise the current MP is still present.
	4.2. Receiving an MPLS Echo Request		4.3. Receiving an MPLS Echo Request
	An LSR L that receives an MPLS echo request first parses the packet		An LSR X that receives an MPLS echo request first parses the packet
	to ensure that it is a well-formed packet, and that the TLVs are		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		understood. If not, X SHOULD send an MPLS echo reply with the Return
	Return Code set to "Malformed echo request received" or "TLV not		Code set to "Malformed echo request received" or "TLV not understood"
	understood" (as appropriate), and the Subcode set to the appropriate		(as appropriate), and the Subcode set to the appropriate value.
	value.
	If the echo request is good, L then checks whether it is a valid		If the echo request is good, X then checks whether it is a valid
	transit or egress LSR for the FEC in the echo request. If not, L MAY		transit or egress LSR for the FEC in the echo request. If not, X MAY
	log this fact.		log this fact. If it is, X notes that interface I over which the
			echo was received, and the label L with which it came. X checks
			whether it actually advertised L over interface I for the FEC in the
			echo request.
	If the echo request contains a Downstream Mapping TLV, L MUST further		If the echo request contains a Downstream Mapping TLV, X MUST further
	check whether its Router ID matches one of the Downstream IPv4 Router		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		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		label that X sent as its mapping for the FEC over the downstream
	downstream label is the label that L sent in its Resv message. The		interface. The result of the checks in the previous and this
	result of the checks in the previous and this paragraph are captured		paragraph are captured in the Return Code/Subcode.
	in the Return Code/Subcode.
	If the echo request has a Reply Mode that wants a reply, L uses the		If the echo request has a Reply Mode that wants a reply, X uses the
	procedure in the next subsection to send the echo reply.		procedure in the next subsection to send the echo reply.
	4.3. Sending an MPLS Echo Reply		4.4. Sending an MPLS Echo Reply
	An MPLS echo reply is a UDP packet. It MUST ONLY be sent in response		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 a routable address		to an MPLS echo request. The source IP address is a routable address
	of the replier; the source port is the well-known UDP port for MPLS		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		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		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		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		IPv4 UDP packet with Router Alert", then the IP header MUST contain
	the Router Alert IP option.		the Router Alert IP option. If the reply is sent over an LSP, the
			topmost label MUST in this case be the Router Alert label (1) (see
			[LABEL-STACK]).
	The format of the echo reply is the same as the echo request. The		The format of the echo reply is the same as the echo request. The
	Sender's Handle, the Sequence Number and TimeStamp Sent are copied		Sender's Handle, the Sequence Number and TimeStamp Sent are copied
	from the echo request; the TimeStamp Received is set to the time-of-		from the echo request; the TimeStamp Received is set to the time-of-
	day that the echo request is received (note that this information is		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		most useful if the time-of-day clocks on the requestor and the
	replier are synchronized). The FEC Stack TLV from the echo request		replier are synchronized). The FEC Stack TLV from the echo request
	MAY be copied to the reply.		MAY be copied to the reply.
	The replier MUST fill in the Return Code and Subcode, as determined		The replier MUST fill in the Return Code and Subcode, as determined
	in the previous subsection.		in the previous subsection.
	If the echo request contains a Pad TLV, the replier MUST interpret		If the echo request contains a Pad TLV, the replier MUST interpret
	the first octet for instructions regarding how to reply.		the first octet for instructions regarding how to reply.
	If the echo request contains a Downstream Mapping TLV, the replier		If the echo request contains a Downstream Mapping TLV, the replier
	SHOULD compute its downstream routers and corresponding labels for		SHOULD compute its downstream routers and corresponding labels for
	the incoming label, and add Downstream Mapping TLVs for each one to		the incoming label, and add Downstream Mapping TLVs for each one to
	the echo reply it sends back.		the echo reply it sends back.
	4.4. Receiving an MPLS Echo Reply		4.5. Receiving an MPLS Echo Reply
	An LSR X should only receive an MPLS Echo Reply in response to an		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		MPLS Echo Request that it sent. Thus, on receipt of an MPLS Echo
	Reply, X should parse the packet to assure that it is well-formed,		Reply, X should parse the packet to assure that it is well-formed,
	then attempt to match up the Echo Reply with an Echo Request that it		then attempt to match up the Echo Reply with an Echo Request that it
	had previously sent, using the destination UDP port and the Sender's		had previously sent, using the destination UDP port and the Sender's
	Handle. If no match is found, then X jettisons the Echo Reply;		Handle. If no match is found, then X jettisons the Echo Reply;
	otherwise, it checks the Sequence Number to see if it matches. Gaps		otherwise, it checks the Sequence Number to see if it matches. Gaps
	in the Sequence Number MAY be logged and SHOULD be counted. Once an		in the Sequence Number MAY be logged and SHOULD be counted. Once an
	Echo Reply is received for a given Sequence Number (for a given UDP		Echo Reply is received for a given Sequence Number (for a given UDP
	port and Handle), the Sequence Number for subsequent Echo Requests		port and Handle), the Sequence Number for subsequent Echo Requests
	for that UDP port and Handle SHOULD be incremented.		for that UDP port and Handle SHOULD be incremented.
	If the Echo Reply contains Downstream Mappings, and X wishes to		If the Echo Reply contains Downstream Mappings, and X wishes to
	traceroute further, it SHOULD copy the Downstream Mappings into its		traceroute further, it SHOULD copy the Downstream Mappings into its
	next Echo Request (with TTL incremented by one).		next Echo Request (with TTL incremented by one).
	4.5. Non-compliant Routers		4.6. Non-compliant Routers
	If the egress for the FEC Stack being pinged does not support MPLS		If the egress for the FEC Stack being pinged does not support MPLS
	ping, then no reply will be sent, resulting in possible "false		ping, then no reply will be sent, resulting in possible "false
	negatives". If in "traceroute" mode, a transit LSR does not support		negatives". If in "traceroute" mode, a transit LSR does not support
	MPLS ping, then no reply will be forthcoming from that LSR for some		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		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		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		transit LSR further downstream may support MPLS echo requests and
	reply. In such a case, the echo request for TTL>n MUST NOT have		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		Downstream Mapping TLVs, until a reply is received with a Downstream
	skipping to change at page 16, line 47		skipping to change at page 19, line 33
	If X does not receive an Resv message from the egress LSR that		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		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		the LSP as "down". At this point, the ingress LSR may apply the
	necessary procedures to fix the LSP. These may include generating a		necessary procedures to fix the LSP. These may include generating a
	message to network management, tearing-down and re-building the LSP,		message to network management, tearing-down and re-building the LSP,
	and/or rerouting user traffic to a backup LSP.		and/or rerouting user traffic to a backup LSP.
	To test an LSP that carries non-IP traffic, before injecting ICMP and		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		MPLS ping messages into the LSP, the IPv4 Explicit NULL label should
	be prepended to such messages. The ingress and egress LSR's must		be prepended to such messages. The ingress and egress LSR's must
	follow the procedures defined in [LABEL-STACKING].		follow the procedures defined in [LABEL-STACK].
	5.4. Procedures at the egress LSR		5.4. Procedures at the egress LSR
	When the egress LSR receives an MPLS ping message, it follows the		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		procedures given above. If the Reply Mode is set to "Reply via the
	control plane", the LSR can, based on the RSVP SESSION and		control plane", the LSR can, based on the RSVP SESSION and
	SENDER_TEMPLATE objects carried in the MPLS ping message, find the		SENDER_TEMPLATE objects carried in the MPLS ping message, find the
	corresponding LSP in its RSVP-TE database. The LSR then checks to		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		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		the same source UDP port value. If not, the LSR adds or updates the
	skipping to change at page 17, line 33		skipping to change at page 20, line 15
	Note that an intermediate LSR using RSVP refresh reduction [RSVP-		Note that an intermediate LSR using RSVP refresh reduction [RSVP-
	REFRESH], the new or changed LSP_ECHO object will cause the LSR to		REFRESH], the new or changed LSP_ECHO object will cause the LSR to
	classify the RSVP message as a trigger message.		classify the RSVP message as a trigger message.
	6. Normative References		6. Normative References
	[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate		[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[LABEL-STACKING] Rosen, E., et al, "MPLS Label Stack Encoding", RFC		[LABEL-STACK] Rosen, E., et al, "MPLS Label Stack Encoding", RFC
	3032, January 2001.		3032, January 2001.
	[RSVP] Braden, R. (Editor), et al, "Resource ReSerVation protocol		[RSVP] Braden, R. (Editor), et al, "Resource ReSerVation protocol
	(RSVP) -- Version 1 Functional Specification," RFC 2205,		(RSVP) -- Version 1 Functional Specification," RFC 2205,
	September 1997.		September 1997.
	[RSVP-REFRESH] Berger, L., et al, "RSVP Refresh Overhead Reduction		[RSVP-REFRESH] Berger, L., et al, "RSVP Refresh Overhead Reduction
	Extensions", RFC 2961, April 2001.		Extensions", RFC 2961, April 2001.
	[RSVP-TE] Awduche, D., et al, "RSVP-TE: Extensions to RSVP for LSP		[RSVP-TE] Awduche, D., et al, "RSVP-TE: Extensions to RSVP for LSP
	skipping to change at page 19, line 11		skipping to change at page 21, line 24
	9. IANA Considerations		9. IANA Considerations
	(To be filled in a later revision)		(To be filled in a later revision)
	10. Acknowledgments		10. Acknowledgments
	This document is the outcome of many discussions among many people,		This document is the outcome of many discussions among many people,
	that include Manoj Leelanivas, Paul Traina, Yakov Rekhter, Der-Hwa		that include Manoj Leelanivas, Paul Traina, Yakov Rekhter, Der-Hwa
	Gan, Brook Bailey, Eric Rosen and Ina Minei.		Gan, Brook Bailey, Eric Rosen and Ina Minei.
			The Multipath Exercise sub-field of the Downstream Mapping TLV was
			adapted from text suggested by Curtis Villamizar.
	11. Appendix		11. Appendix
	This appendix specifies non-normative aspects of detecting MPLS data		This appendix specifies non-normative aspects of detecting MPLS data
	plane liveness.		plane liveness.
	11.1. CR-LDP FEC		11.1. CR-LDP FEC
	This section describes how a CR-LDP FEC can be included in an Echo		This section describes how a CR-LDP FEC can be included in an Echo
	Request using the following FEC subtype:		Request using the following FEC subtype:
	skipping to change at page 21, line 29		skipping to change at page 24, line 7
	be obtained from the IETF Secretariat.		be obtained from the IETF Secretariat.
	The IETF invites any interested party to bring to its attention any		The IETF invites any interested party to bring to its attention any
	copyrights, patents or patent applications, or other proprietary		copyrights, patents or patent applications, or other proprietary
	rights which may cover technology that may be required to practice		rights which may cover technology that may be required to practice
	this standard. Please address the information to the IETF Executive		this standard. Please address the information to the IETF Executive
	Director.		Director.
	Full Copyright Statement		Full Copyright Statement
	Copyright (C) The Internet Society (2002). All Rights Reserved.		Copyright (C) The Internet Society (2003). All Rights Reserved.
	This document and translations of it may be copied and furnished to		This document and translations of it may be copied and furnished to
	others, and derivative works that comment on or otherwise explain it		others, and derivative works that comment on or otherwise explain it
	or assist in its implmentation may be prepared, copied, published and		or assist in its implmentation may be prepared, copied, published and
	distributed, in whole or in part, without restriction of any kind,		distributed, in whole or in part, without restriction of any kind,
	provided that the above copyright notice and this paragraph are		provided that the above copyright notice and this paragraph are
	included on all such copies and derivative works. However, this		included on all such copies and derivative works. However, this
	document itself may not be modified in any way, such as by removing		document itself may not be modified in any way, such as by removing
	the copyright notice or references to the Internet Society or other		the copyright notice or references to the Internet Society or other
	Internet organizations, except as needed for the purpose of		Internet organizations, except as needed for the purpose of
End of changes.
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