wdiff draft-akiya-mpls-entropy-lsp-ping-00.txt draft-akiya-mpls-entropy-lsp-ping-01.txt

Internet Engineering Task Force N. Akiya
Internet-Draft G. Swallow
Updates: 4379,6790 (if approved) C. Pignataro
Intended status: Standards Track Cisco Systems
Expires: April 24, June 18, 2014 October 21, December 15, 2013

Label Switched Path (LSP) Ping/Trace over MPLS Network
using Entropy Labels (EL)
draft-akiya-mpls-entropy-lsp-ping-00
draft-akiya-mpls-entropy-lsp-ping-01

Abstract

The Multiprotocol Label Switching (MPLS) Label Switched Path (LSP)
Ping and Traceroute are used to exercise specific paths of Equal Cost
Multipath (ECMP). This When LSP is signaled to use Entropy Label (EL)
described in RFC6790, the ability for LSP Ping and Traceroute
operation to discover and exercise ECMP paths has been lost on some in
scenarios which
makes use of [RFC6790]: Entropy Labels (EL). LSRs apply deviating load balance techniques. One
such scenario is when some LSRs apply EL based load balancing while
other LSRs apply non-EL based load balancing (ex: IP). Another
scenario is when EL based LSP is stitched with another LSP which can
be EL based or non-EL based.

This document extends the MPLS LSP Ping and Traceroute mechanisms to
restore the ability of exercising specific paths of ECMP over LSP
which make use of Entropy Label. This document updates [RFC4379] RFC4379 and
[RFC6790].
RFC6790.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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
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This Internet-Draft will expire on April 24, June 18, 2014.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Multipath Type 9 . . . . . . . . . . . . . . . . . . . . . . 5
4. Initiating LSR Procedures . . . . . . . . . . . . . . . . . . 6
5. Responder LSR Procedures . . . . . . . . . . . . . . . . . . 7
5.1. IP Based Load Balancer & Not Imposing Pushing ELI/EL . . . . . . 7 . 8
5.2. IP Based Load Balancer & Imposing Pushes ELI/EL . . . . . . . . . 8
5.3. Label Based Load Balancer & Not Imposing Pushing ELI/EL . . . . . 8 9
5.4. Label Based Load Balancer & Imposing Pushes ELI/EL . . . . . . . . 9
5.5. FAT MS-PW Stitching LSR . . . . . . . . . . . . . . . . . 9 10
6. Entropy Label FEC . . . . . . . . . . . . . . . . . . . . . . 10
7. DS Flags: L and E . . . . . . . . . . . . . . . . . . . . . . 10 11
8. New Multipath Information Type: 10 . . . . . . . . . . . . . 11 12
9. Unsupported Cases . . . . . . . . . . . . . . . . . . . . . . 13
10. Security Considerations . . . . . . . . . . . . . . . . . . . 13 14
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 14
11.1. New Sub-Registries . . . . . . . . . . . . . . . . . . . 14
11.1.1. DS Flags . . . . . . . . . . . . . . . . . . . . . . 14
11.1.2. Multipath Type . . 13
11.2. Multipath Information Types . . . . . . . . . . . . . . 13
11.3. . . . 15
11.2. Entropy Label FEC . . . . . . . . . . . . . . . . . . . 13 15
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 15
13. Contributing Authors . . . . . . . . . . . . . . . . . . . . 14 15
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 16
14.1. Normative References . . . . . . . . . . . . . . . . . . 14 16
14.2. Informative References . . . . . . . . . . . . . . . . . 14 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 16

1. Introduction

Section 3.3.1 of [RFC4379] specifies multipath information encoding
which can be used by LSP Ping initiator to trace and validate all
ECMP paths between ingress and egress. These encodings are
sufficient when all the LSRs along the path(s), between ingress and
egress, consider same set of "keys" as input for load balancing
algorithm: all IP based or all label based.

With introduction of [RFC6790], it is quite normal to see set of LSRs
performing load balancing based on EL/ELI while others still follow
the traditional way (IP based). This results in LSP Ping initiator
not be able to trace and validate all ECMP paths in following
scenarios:

o One or more transit LSRs along ELI/EL imposed LSP with ELI/EL in label stack do
not perform ECMP load balancing based on EL (hashes based on
"keys" including IP destination address). This scenario is not
only possible but quite common due transit LSRs not implementing
[RFC6790] or transit LSRs implementing [RFC6790] but not
implementing suggested transit LSR behavior in Section 4.3 of
[RFC6790].

o Two or more LSPs stitched together with at least one of these LSP being ELI
/EL imposing LSP.
pushing ELI/EL in label stack. Such scenarios are described in
[I-D.ravisingh-mpls-el-for-seamless-mpls].

These scenarios will be quite common because every deployment of
[RFC6790] will invariably end up with nodes that support ELI/EL and
nodes that do not. There will typically be areas that support ELI/EL
and areas that do not.

As pointed out in [RFC6790] the procedures of [RFC4379] with respect
to multipath information type {9} are incomplete. However [RFC6790]
does not actually update [RFC4379]. Further the specific EL location
is not clearly defined, particularly in the case of FAT Flow-Aware
Transport Pseudowires [RFC6391]. Herein is defined This document defines a new FEC
Stack sub-TLV for the Entropy Label. Section 3 of this document
updates the procedures for multipath information type {9}. {9} described
in [RFC4379] Rest of this document describes extensions required to
restore ECMP discovery and tracing capabilities for scenarios
described.

2. Overview

[RFC4379] describes LSP traceroute as an operation performed through where the
initiating LSR sending LSP Ping send a series of MPLS echo requests towards the same
destination. The first packet (LSP in the series have the TTL set to 1.
When the echo request) with
incrementing TTL, starting reply is received from the LSR one hop away the second
echo request in the series is sent with the TTL of one. set to 2, for each
echo request the TLL is incremented by one until a response is
received from the intended destination. Initiating LSR discovers and
exercises ECMP by obtaining multipath information from each transit
LSR and using specific destination IP address or specific entropy
label.

LSP Ping initiating LSR sends LSP MPLS echo request with multipath
information. This multipath information is described in DSMAP/DDMAP
TLV of echo request, and can contain set of IP addresses or set of
labels today. Multipath information types {2, 4, 8} carry set of IP
addresses and multipath information type {9} carries set of labels.
Responder LSR (receiver of LSP MPLS echo request) is to determine subset
of initiator specified multipath information which load balances to
each downstream (outgoing interface). Responder LSR sends LSP MPLS echo
reply with resulting multipath information per downstream (outgoing
interface) back to the initiating LSR. Initiating LSR is then able
to use specific IP destination address or specific label to exercise
specific ECMP path on the responder LSR.

Current behavior is problematic in following scenarios:

o Initiating LSR sends IP multipath information, but responder LSR
load balances on labels.

o Initiating LSR sends label multipath information, but responder
LSR load balances on IP addresses.

o Initiating LSR sends any one of existing multipath information to ELI/
EL imposing LSR, LSR
which pushes ELI/EL in label stack, but initiating LSR can only
continue to discover and exercise specific path of ECMP if ELI/EL imposing LSR
which pushes ELI/EL responds with both IP addresses and associated
EL corresponding to each IP address. This is because:

* ELI/EL imposing pushing LSR that is a stitching point will load balance
based on IP address.

* Downstream LSR(s) of ELI/EL imposing pushing LSR may load balance based
on ELs.

o Initiating LSR sends any one of existing multipath information to ELI/
EL imposing pushing LSR, but initiating LSR can only continue to discover
and exercise specific path of ECMP if ELI/EL imposing pushing LSR responds
with both labels and associated EL corresponding to label. This
is because:

* ELI/EL imposing pushing LSR that is a stitching point will load balance
based on EL from previous LSP and imposes pushes new EL.

* Downstream LSR(s) of ELI/EL imposing pushing LSR may load balance based
on new ELs.

The above scenarios point to how the existing multipath information
is insufficient when LSP traceroute is operated on an LSP with
Entropy Labels described by [RFC6790]. Therefore, this document
defines a multipath information type to be used in the DSMAP/DDMAP of
LSP
MPLS echo request/reply packets in Section 8.

In addition, responder LSR can reply with empty multipath information
if no IP address set or label set from received multipath information
matched load balancing to a downstream. Empty return is also
possible if initiating LSR sends multipath information of one type,
IP address or label, but responder LSR load balances on the other
type. To disambiguate between the two results, this document
introduces new flags in the DSMAP/DDMAP TLV to allow responder LSR to
describe the load balance technique being used.

It is required that all LSRs along the LSP understand new flags as
well as new multipath information type. It is also required that
initiating LSR can select both IP destination address and label to
use on transmitting LSP MPLS echo request packets. Two additional DS
Flags are defined for the DSMAP and DDMAP TLVs in Section 7.

3. Multipath Type 9

[RFC4379] defined multipath type {9} for tracing of LSPs where label
based load-balancing is used. However, as pointed out in [RFC6790],
the procedures for using this type are incomplete. First, the
specific location of the label was not defined. What was assumed,
but not spelled out, was that the presence of multipath type {9}
meant the responder should act as if the payload of the received
packet were non-IP and that the bottom-of-stack label should be
replaced by the values indicated by multipath type {9} to determine
their respective out-going interfaces.

Further, with the introduction of [RFC6790], entropy labels may now
appear anywhere in a label stack.

This section defines to which labels multipath type {9} can apply.
Additionally it defines procedures for tracing pseudowires and flow-
aware pseudowires. These procedures pertain to the use of multipath
information type {9} as well as type {10}.

Section 6 defines a new FEC-Stack sub-TLV to indicate and entropy
label. Multipath type {9} applies exclusively to this sub-TLV. Any
LSP Ping message containing a DD-MAP or DS-MAP with multipath type
{9} MUST include an EL_FEC at the bottom of the FEC-Stack.

When an MPLS echo request message is received containing a FEC-Stack
with an EL-FEC at the bottom of the FEC stack and is not preceded by
an entropy label, the responder must behave (for load balancing
purposes) as if the first word of the message were a Pseudowire
Control Word.

In order to trace a non-FAT pseudowire, instead of including the
appropriate PW-FEC in the FEC-Stack, an EL-FEC is included. Tracing
in this way will cause compliant routers to return the proper
outgoing interface. Note that this procedure only traces to the end
of the MPLS transport LSP at transport layer (e.g. LDP and/or RSVP). To
actually verify the PW-FEC or in the case of a MS-PW, to determine
the next pseudowire label value, the initiator MUST repeat that step
of the trace, (i.e., repeating the TTL value used) but with the FEC-Stack FEC-
Stack modified to contain the appropriate PW-FEC.

In order to trace a FAT pseudowire, Flow-Aware Transport Pseudowire, the initiator
includes an EL-FEC at the bottom of the FEC-Stack and pushes the
appropriate PW-FEC onto the FEC-Stack.

4. Initiating LSR Procedures

In order to facilitate the flow of the following text we speak in
terms of a boolean called EL_LSP maintained by the initiating LSR.
This value controls the multipath information type to be used in
transmitted echo request packets. When the initiating LSR is
transmitting an echo request packet with DSMAP/DDMAP with a non-zero
multipath information type, then EL_LSP boolean MUST be consulted to
determine the multipath information type to use.

In addition to procedures described in [RFC4379] as updated by
Section 3 and [RFC6424], initiating LSR MUST operate with following
procedures.

o When initiating LSR is IP based load balancer (not imposing pushing ELI/
EL), initialize EL_LSP=False.

o When initiating LSR imposes pushes ELI/EL, initialize EL_LSP=True.

o When initiating LSR is transmitting non-zero multipath information
type:

* If (EL_LSP) initiating LSR MUST use multipath information type
{10}.

* Else initiating LSR MUST use multipath information type {2, 4,
8, 9}.

o When initiating LSR is transmitting multipath information type
{10}, both "IP Multipath Information" and "Label Multipath
Information" MUST be included, and "IP Associated Label Multipath
Information" MUST be omitted (NULL).

o When initiating LSR receives echo reply with {L=0, E=1} in DS
flags with valid contents, set EL_LSP=True.

In following conditions, initiating LSR may have lost the ability to
exercise specific ECMP paths. Initiating LSR MAY continue with "best
effort".

o Received echo reply contains empty multipath information.

o Received echo reply contains {L=0, E=<any>} DS flags, but does not
contain IP multipath information.

o Received echo reply contains {L=1, E=<any>} DS flags, but does not
contain label multipath information.

o Received echo reply contains {L=<any>, E=1} DS flags, but does not
contain associated label multipath information.

o IP multipath information types {2, 4, 8} sent, and received echo
reply with {L=1, E=0} in DS flags.

o Multipath information type {10} sent, and received echo reply with
multipath information type other than {10}.

5. Responder LSR Procedures

Common Procedures: Responder LSR receiving LSP MPLS echo request packet
with multipath information type {10} MUST validate following
contents. Any deviation MUST result in responder LSR to consider the
packet as malformed and return code 1 (Malformed echo request
received) in LSP MPLS echo reply packet.

o IP multipath information MUST be included.

o Label multipath information MUST be included.

o IP associated label multipath information MUST be omitted (NULL).

Following subsections describe expected responder LSR procedures when
echo reply is to include DSMAP/DDMAP TLVs, based on local load
balance technique being employed. In case responder LSR performs
deviating load balance techniques per downstream basis, appropriate
procedures matching to each downstream load balance technique MUST be
operated.

5.1. IP Based Load Balancer & Not Imposing Pushing ELI/EL

o Responder MUST set {L=0, E=0} in DS flags.

o If multipath information type {2, 4, 8} is received, responder
MUST comply with [RFC4379]/[RFC6424].

o If multipath information type {9} is received, responder MUST
reply with multipath type {0}.

o If multipath information type {10} is received, responder MUST
reply with multipath information type {10}. "Label Multipath
Information" and "Associated Label Multipath Information" sections
MUST be omitted (NULL). If no matching IP address is found, then
"IPMultipathType" field MUST be set to multipath information type
{0} and "IP Multipath Information" section MUST also be omitted
(NULL). If at least one matching IP address is found, then
"IPMultipathType" field MUST be set to appropriate multipath
information type {2, 4, 8} and "IP Multipath Information" section
MUST be included.

5.2. IP Based Load Balancer & Imposing Pushes ELI/EL

o Responder MUST set {L=0, E=1} in DS flags.

o If multipath information type {9} is received, responder MUST
reply with multipath type {0}.

o If multipath type {2, 4, 8, 10} is received, responder MUST
respond with multipath type {10}. See Section 8 for details of
multipath type {10}. "Label Multipath Information" section MUST be
omitted (NULL). (i.e. is it not there). IP address set specified in
received IP multipath information MUST be used to determine the
returning IP/Label pairs. If received multipath information type
was {10}, received "Label Multipath Information" sections MUST NOT
be used to determine the associated label portion of returning IP/
Label pairs. If no matching IP address is found, then
"IPMultipathType" field MUST be set to multipath information type
{0} and "IP Multipath Information" section MUST be omitted (NULL). omitted. In
addition, "Assoc Label Multipath Length" MUST be set to 0, and
"Associated Label Multipath Information" section MUST also be
omitted (NULL).
omitted. If at least one matching IP address is found, then
"IPMultipathType" field MUST be set to appropriate multipath
information type {2, 4, 8} and "IP Multipath Information" section
MUST be included. In addition, "Associated Label Multipath
Information" section MUST be populated with list of labels
corresponding to each IP address specified in "IP Multipath
Information" section. "Assoc Label Multipath Length" MUST be set
to appropriate value. a value representing length in octets of "Associated Label
Multipath Information" field.

5.3. Label Based Load Balancer & Not Imposing Pushing ELI/EL

o Responder MUST set {L=1, E=0} in DS flags.

o If multipath information type {2, 4, 8} is received, responder
MUST reply with multipath type {0}.

o If multipath information type {9} is received, responder MUST
comply with [RFC4379] /[RFC6424] as updated by Section 3.

o If multipath information type {10} is received, responder MUST
reply with multipath information type {10}. "IP Multipath
Information" and "Associated Label Multipath Information" sections
MUST be omitted (NULL). If no matching label is found, then
"LbMultipathType" field MUST be set to multipath information type
{0} and "Label Multipath Information" section MUST also be omitted
(NULL). If at least one matching label is found, then
"LbMultipathType" field MUST be set to appropriate multipath
information type {9} and "Label Multipath Information" section
MUST be included.

5.4. Label Based Load Balancer & Imposing Pushes ELI/EL

o Responder MUST set {L=1, E=1} in DS flags.

o If multipath information type {2, 4, 8} is received, responder
MUST reply with multipath type {0}.

o If multipath type {9, 10} is received, responder MUST respond with
multipath type {10}. "IP Multipath Information" section MUST be
omitted (NULL).
omitted. Label set specified in received label multipath
information MUST be used to determine the returning Label/Label
pairs. If received multipath information type was {10}, received
"Label Multipath Information" sections MUST NOT be used to
determine the associated label portion of returning Label/Label
pairs. If no matching label is found, then "LbMultipathType"
field MUST be set to multipath information type {0} and "Label
Multipath Information" section MUST be omitted (NULL). omitted. In addition,
"Assoc Label Multipath Length" MUST be set to 0, and "Associated
Label Multipath Information" section MUST also be
omitted (NULL). omitted. If at
least one matching label is found, then "LbMultipathType" field
MUST be set to appropriate multipath information type {9} and
"Label Multipath Information" section MUST be included. In
addition, "Associated Label Multipath Information" section MUST be
populated with list of labels corresponding to each label
specified in "Label Multipath Information" section. "Assoc Label
Multipath Length" MUST be set to appropriate value. a value representing length in
octets of "Associated Label Multipath Information" field.

5.5. FAT MS-PW Stitching LSR

MS-PW stitching

Stitching LSR that xconnects flow-aware pseudowires behaves Flow-Aware Transport Pseudowires behave
in one of two ways:

o Load balances on previous flow label, and carries over same flow
label. For this case, stitching LSR is to behave as procedures
described in Section 5.3.

o Load balances on previous flow label, and replaces flow label with
newly computed. For this case, stitching LSR is to behave as
procedures described in Section 5.4.

6. Entropy Label FEC

Entropy Label Indicator (ELI) is a reserved label that has no
explicit FEC associated, and has label value 7 assigned from the
reserved range. Use Nil FEC as Target FEC Stack sub-TLV to account
for ELI in a Target FEC Stack TLV.

Entropy Label (EL) is a special purpose label with label value being
discretionary (i.e. label value may not be from the reserved range).
For LSP verification mechanics to perform its purpose, it is
necessary for a Target FEC Stack sub-TLV to clearly describe EL,
particularly in the scenario where label stack does not carry ELI
(ex: FAT-PW [RFC6391]). Therefore, this document defines a EL FEC to
allow a Target FEC Stack sub-TLV to be added to the Target FEC Stack
to account for EL.

The Length is 4. Labels are 20-bit values treated as numbers.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Label is the actual label value inserted in the label stack; the MBZ
fields MUST be zero when sent and ignored on receipt.

7. DS Flags: L and E

Two flags, L and E, are added in DS Flags field of the DSMAP/DDMAP
TLVs. Both flags MUST NOT be set in echo request packets when
sending, and ignored when received. Zero, one or both new flags MUST
be set in echo reply packets.

DS Flags
--------

0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |L|E|I|N|
+-+-+-+-+-+-+-+-+

Flag Name and Meaning
---- ----------------
L Label based load balance indicator
This flag MUST be set to zero in the echo request. LSR
which performs load balancing on a label MUST set this
flag in the echo reply. LSR which performs load
balancing on IP MUST NOT set this flag in the echo
reply.

E ELI/EL imposer push indicator
This flag MUST be set to zero in the echo request. LSR
which imposes pushes ELI/EL MUST set this flag in the echo
reply. LSR which does not impose push ELI/EL MUST NOT set
this flag in the echo reply.

Two flags result in four load balancing techniques which echo reply
generating LSR can indicate:

o {L=0, E=0} LSR load balances based on IP and does not impose ELI/
EL. push ELI/EL.

o {L=0, E=1} LSR load balances based on IP and imposes pushes ELI/EL.

o {L=1, E=0} LSR load balances based on label and does not impose
ELI/EL. push ELI/
EL.

o {L=1, E=1} LSR load balances based on label and imposes pushes ELI/EL.

8. New Multipath Information Type: 10

One new multipath information type is added to be used in DSMAP/DDMAP
TLVs. New multipath type has value of 10.

Key Type Multipath Information
--- ---------------- ---------------------
10 IP and label set IP addresses and label prefixes

Multipath type 10 is comprised of three sections. One section to
describe IP address set. One section to describe label set. One
section to describe another label set which associates to either IP
address set or label set specified in the other section.

Multipath information type 10 has 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|IPMultipathType| Reserved(MBZ) | IP Multipath Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| (IP Multipath Information) |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|LbMultipathType| Reserved(MBZ) | Label Multipath Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| (Label Multipath Information) |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved(MBZ) | Assoc Label Multipath Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| (Associated Label Multipath Information) |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

o IPMultipathType

* 0 when "IP Multipath Information" is omitted. Otherwise one of
IP multipath information values: {2, 4, 8}.

o IP Multipath Information
* This section is omitted when "IPMultipathType" is 0. Otherwise
this section reuses IP multipath information from [RFC4379].
Specifically, multipath information for values {0, 2, {2, 4, 8} can be
used.

o LbMultipathType

* 0 when "Label Multipath Information" is omitted. Otherwise
label multipath information value {9}.

o Label Multipath Information

* This section is omitted when "LbMultipathType" is 0. Otherwise
this section reuses label multipath information from [RFC4379].
Specifically, values {0, 9} multipath information for value {9} can be used.

o Associated Label Multipath Information

* "Assoc Label Multipath Length" is a 16 bit field of multipath
information which indicates length in octets of the associated
label multipath information.

* "Associated Label Multipath Information" is a list of labels
with each label described in 24 bits. This section MUST be
omitted (NULL) in an MPLS Echo Request echo request message. A midpoint which imposes
pushes ELI/EL labels SHOULD include "Assoc Label Multipath
Information" in its MPLS Echo Reply echo reply message, along with either
"IP Multipath Information" or "Label Multipath Information".
Each specified associated label described in this section maps
to specific IP address OR label described in the "IP Multipath
Information" section or "Label Multipath Information" section.
For example, if 3 IP addresses are specified in the "IP
Multipath Information" section, then there MUST be 3 labels
described in this section. First label maps to the lowest IP
address specified, second label maps to the second lowest IP
address specified and third label maps to the third lowest IP
address specified.

9. Unsupported Cases

There are couple of scenarios where LSP path tracing mechanics are
not supported in this draft revision.

o When one or more LSP transit node(s) performs label based load
balancing on a label that is not bottom-of-stack label when
Entropy Label Indicator is not included.

o When one or more LSP transit node(s) performs label based load
balancing on a label other than Entropy Label when Entropy Label
Indicator and Entropy Label pair is included.

10. Security Considerations

Beyond those specified in [RFC4379], [RFC6424]

This document extends LSP Traceroute mechanism to discover and [RFC6790], there
exercise ECMP paths when LSP uses ELI/EL in label stack. Additional
processings are no further required for responder and initiator nodes.
Responder node that pushes ELI/EL will need to compute and return
multipath data including associated EL. Initiator node will need to
store and handle both IP multipath and label multipath information,
and include destination IP addresses and/or ELs in MPLS echo request
packet as well as in carried multipath information to downstream
nodes. Due to additional processing, it is critical that proper
security measured required. measures described in [RFC4379] and [RFC6424] are followed.

11. IANA Considerations

11.1. DS Flags

DS flags ... New Sub-Registries

[RFC4379] defines the Downstream Mapping TLV, which has the Type 2
assigned from the "Multi-Protocol Label Switching (MPLS) Label
Switched Paths (LSPs) Ping Parameters - TLVs" registry. [RFC6424]
defines the Downstream Detailed Mapping TLV, which has the Type 20
assigned from the "Multi-Protocol Label Switching (MPLS) Label
Switched Paths (LSPs) Ping Parameters - TLVs" registry. Both TLVs
shares two fields: "DS Flags" and "Multipath Type". This document
requires allocation of new values in both the "DS Flags" and
"Multipath Type" fields, which are not maintained by IANA. Should it be?

11.2. IANA today.
Therefore, this document requests IANA to create new registries
within [IANA-MPLS-LSP-PING] protocol to maintain "DS Flags" and
"Multipath Type" fields. Name of registries and initial values are
described in immediate sub-sections to follow.

11.1.1. DS Flags

Bit number Name Reference
---------- ---------------------------------------- ---------
7 N: Treat as a Non-IP Packet RFC4379
6 I: Interface and Label Stack Object Request RFC4379
5 E: ELI/EL push indicator this document
4 L: Label based load balance indicator this document
3-0 Unassigned

Assignments of DS Flags are via Standards Action [RFC5226] or IESG
Approval [RFC5226].

Note that "DS Flags" is a field included in two TLVs defined in
"Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
Ping Parameters - TLVs" registry: Downstream Mapping TLV (value 2)
and Downstream Detailed Mapping TLV (value 20). Modification to "DS
Flags" registry will affect both TLVs.

11.1.2. Multipath Information Types Type

Value Meaning Reference
---------- ---------------------------------------- ---------
0 no multipath RFC4379
1 Unassigned
2 IP address RFC4379
3 Unassigned
4 IP address range RFC4379
5-7 Unassigned
8 Bit-masked IP address set RFC4379
9 Bit-masked label set RFC4379
10 IP and label set this document
11-255 Unassigned

Assignments of Multipath information types ... not maintained by IANA. Should it
be?

11.3. Type are via IETF Review [RFC5226] or IESG
Approval [RFC5226].

Note that "Multipath Type" is a field included in two TLVs defined in
"Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
Ping Parameters - TLVs" registry: Downstream Mapping TLV (value 2)
and Downstream Detailed Mapping TLV (value 20). Modification to
"Multipath Type" registry will affect both TLVs.

11.2. Entropy Label FEC

IANA is requested to assign a new sub-TLV from the "Sub-TLVs for TLV
Types 1 and 16" section from "TLVs" sub-registry within the "Multi-
Protocol "Multi-Protocol Label Switching (MPLS)
Label Switched Paths (LSPs) Ping
Parameters" Parameters - TLVs" registry.

Following value appears to be next available sub-TLV value.
Requesting IANA to allow specified value as early allocation.

Value Meaning

Sub-Type Sub-TLV Name Reference
----- -------
-------- ------------ ---------
26
TBD1 Entropy Label FEC this document

12. Acknowledgements

TBD

Authors would like to thank Loa Andersson for performing thorough
review and providing valuable comments.

13. Contributing Authors

Nagendra Kumar
Cisco Systems
Email: naikumar@cisco.com

14. References

14.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.

[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, November 2012.

14.2. Informative References

[I-D.ravisingh-mpls-el-for-seamless-mpls]
Singh, R., Shen, Y., and J. Drake, "Entropy label for
seamless MPLS", draft-ravisingh-mpls-el-for-seamless-
mpls-00
mpls-01 (work in progress), February October 2013.

[IANA-MPLS-LSP-PING]
IANA, "Multi-Protocol Label Switching (MPLS) Label
Switched Paths (LSPs) Ping Parameters",
<http://www.iana.org/assignments/mpls-lsp-ping-parameters/
mpls-lsp-ping-parameters.xhtml>.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.

[RFC6391] Bryant, S., Filsfils, C., Drafz, U., Kompella, V., Regan,
J., and S. Amante, "Flow-Aware Transport of Pseudowires
over an MPLS Packet Switched Network", RFC 6391, November
2011.

[RFC6424] Bahadur, N., Kompella, K., and G. Swallow, "Mechanism for
Performing Label Switched Path Ping (LSP Ping) over MPLS
Tunnels", RFC 6424, November 2011.

Authors' Addresses
Nobo Akiya
Cisco Systems

Email: nobo@cisco.com

George Swallow
Cisco Systems

Email: swallow@cisco.com

Carlos Pignataro
Cisco Systems

Email: cpignata@cisco.com