MPLS Working Group Dave Allan, Ed.
Internet Draft Ericsson
Intended status: Standards Track
Expires: February 2012 George Swallow Ed.
Cisco Systems, Inc
John Drake Ed.
Juniper
August 2011
Proactive Connectivity Verification, Continuity Check and Remote
Defect indication for MPLS Transport Profile
draft-ietf-mpls-tp-cc-cv-rdi-06
Abstract
Continuity Check, Proactive Connectivity Verification and Remote
Defect Indication functionalities are required for MPLS-TP OAM.
Continuity Check monitors a label switched path for any loss-of-
continuity defect. Connectivity Verification augments Continuity
Check in order to provide confirmation that the desired source is
connected to the desired sink. Remote defect indication enables an
End Point to report, to its associated End Point, a fault or defect
condition that it detects on a pseudo wire, label switched path or
Section.
This document specifies specific extensions to BFD and methods for
proactive Continuity Check, Continuity Verification, and Remote
Defect Indication for MPLS-TP label switched paths, pseudo wires and
Sections using Bidirectional Forwarding Detection as extended by
this memo.
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 RFC2119 [1].
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance
with the provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction...................................................3
2. Conventions used in this document..............................4
2.1. Terminology..................................................4
3. MPLS-TP CC, proactive CV and RDI Mechanism using BFD...........5
3.1. Existing Capabilities........................................5
3.2. CC, CV, and RDI Overview.....................................6
3.3. ACH code points for CC and proactive CV......................7
3.4. MPLS-TP BFD CC Message format................................7
3.5. MPLS-TP BFD proactive CV Message format......................8
3.5.1. Section MEP-ID.............................................9
3.5.2. LSP MEP-ID................................................10
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3.5.3. PW Endpoint MEP-ID........................................10
3.6. BFD Session in MPLS-TP terminology..........................11
3.7. BFD Profile for MPLS-TP.....................................12
3.7.1. Session initiation and Modification.......................13
3.7.2. Defect entry criteria.....................................13
3.7.3. Defect entry consequent action............................15
3.7.4. Defect exit criteria......................................15
3.7.5. State machines............................................15
3.7.6. Configuration of MPLS-TP BFD sessions.....................18
3.7.7. Discriminator values......................................18
4. Configuration Considerations..................................18
5. Acknowledgments...............................................19
6. IANA Considerations...........................................19
7. Security Considerations.......................................20
8. References....................................................20
8.1. Normative References........................................20
8.2. Informative References......................................21
1. Introduction
In traditional transport networks, circuits are provisioned on two or
more switches. Service Providers (SP) need Operations, Administration
and Maintenance (OAM) tools to detect mis-connectivity and loss-of-
continuity of transport circuits. Both pseudo wires (PWs) and MPLS-TP
label switched paths (LSPs) [12] emulating traditional transport
circuits need to provide the same Continuity Check (CC), proactive
Continuity Verification (CV), and Remote Defect Indication (RDI)
capabilities as required in RFC 5860[3]. This document describes the
use of Bidirectional Forwarding Detection (BFD)[4] for CC, proactive
CV, and RDI of a PW, LSP or sub-path maintenance entity (SPME)
between two Maintenance Entity Group End Points (MEPs).
As described in [13], CC and CV functions are used to detect loss-of-
continuity (LOC), and unintended connectivity between two MEPs (e.g.
mis-merging or mis-connectivity or unexpected MEP).
RDI is an indicator that is transmitted by a MEP to communicate to
its peer MEP that a signal fail condition exists. RDI is only used
for bidirectional LSPs and is associated with proactive CC & CV BFD
control packet generation.
This document specifies the BFD extension and behavior to satisfy the
CC, proactive CV monitoring and the RDI functional requirements for
both co-routed and associated bi-directional LSPs. Supported
encapsulations include generic alert label (GAL)/generic associated
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channel (G-ACh), virtual circuit connectivity verification (VCCV) and
UDP/IP. Procedures for uni-directional point-to-point (p2p) and
point-to-multipoint (p2mp) LSPs are for further study.
This document utilizes identifiers for MPLS-TP systems as defined in
[9]. Work is on-going in the ITU-T to define a globally-unique
semantic for ITU Carrier Codes (ICCs), and future work may extend
this document to utilize ICCs as identifiers for MPLS-TP systems.
The mechanisms specified in this document are restricted to BFD
asynchronous mode.
2. Conventions used in this document
2.1. Terminology
ACH: Associated Channel Header
BFD: Bidirectional Forwarding Detection
CC: Continuity Check
CV: Connectivity Verification
GAL: G-ACh Label
G-ACh: Generic Associated Channel
LDI: Link Down Indication
LKI: Lock Instruct
LKR: Lock Report
LSP: Label Switched Path
LSR: Label Switching Router
ME: Maintenance Entity
MEG: Maintenance Entity Group
MEP: Maintenance Entity Group End Point
MIP: Maintenance Entity Group Intermediate Point
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MPLS: Multi-Protocol Label Switching
MPLS-OAM: MPLS Operations, Administration and Maintenance
MPLS-TP: MPLS Transport Profile
MPLS-TP LSP: Uni-directional or Bidirectional Label Switched Path
representing a circuit
MS-PW: Multi-Segment PseudoWire
NMS: Network Management System
OAM: Operations, Administration, and Maintenance [14]
PW: Pseudo Wire
PDU: Protocol Data Unit
P/F: Poll-Final
RDI: Remote Defect Indication
SPME: Sub-Path Maintenance Entity
TTL: Time To Live
TLV: Type Length Value
VCCV: Virtual Circuit Connectivity Verification
3. MPLS-TP CC, proactive CV and RDI Mechanism using BFD
This document describes procedures for achieve combined CC, CV and
RDI functionality within a single MPLS-TP MEG using BFD. This
augments the capabilities that can be provided for MPLS-TP LSPs using
existing specified tools and procedures.
3.1. Existing Capabilities
A CC-only mode may be provided via protocols and procedures described
in RFC 5885[7] with ACH channel 7. These procedures may be applied to
bi-directional LSPs (via the use of the GAL), as well as PWs.
Implementations may also interoperate with legacy equipment by
implementing RFC 5884[8] for LSPs and RFC 5085[10] for PWs, in
addition to the procedures documented in this memo. In accordance
with RFC 5586[2], when BFD control packets are encapsulated in an IP
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header, the fields in the IP header are set as defined in RFC
5884[8]. When IP encapsulation is used CV mis-connectivity defect
detection can be performed by inferring a globally unique source on
the basis of the combination of the source IP address and My
Discriminator" fields.
3.2. CC, CV, and RDI Overview
The combined CC, CV, and RDI functionality for MPLS-TP is achieved by
multiplexing CC and CV PDUs within a single BFD session. The CV PDUs
are augmented with a source MEP ID TLV to permit mis-connectivity
detection to be performed by sink MEPs.
The interleaving of PDUs is achieved via the use of distinct
encapsulations and code points for generic associated channel (G-ACh)
encapsulated BFD depending on whether the PDU format is CC or CV:
o CC format: defines a new code point in the Associated Channel
Header (ACH) described in RFC 5586[2].This format supports
Continuity Check and RDI functionalities.
o CV format: defines a new code point in the Associated Channel
Header (ACH) described in RFC 5586[2]. The ACH with "MPLS-TP
Proactive CV" code point indicates that the message is an MPLS-TP
BFD proactive CV message, and information for CV processing is
appended in the form of the source MEP ID TLV.
RDI is communicated via the BFD diagnostic field in BFD CC messages,
and the diagnostic code field in CV messages MUST be ignored. It is
not a distinct PDU. As per [4], a sink MEP SHOULD encode a diagnostic
code of "1 - Control detection time expired" when the interval times
detect multiplier have been exceeded. A sink MEP SHOULD encode a
diagnostic code of "5 - Path Down" as a consequence of the sink MEP
receiving LDI. A sink MEP MUST encode a diagnostic code of "XX -
-
Misconnectivity defect" (to be assigned by IANA) when CV PDU
processing indicates a misconnectivity defect. A sink MEP that has
started sending diagnostic code 5 SHOULD NOT change it to 1 when the
detection timer expires.
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3.3. ACH code points for CC and proactive CV
Figure 1 illustrates the G-ACh encoding for BFD CC-CV-RDI
functionality.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Flags | BFD CC/CV Code Point |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: ACH Indication of MPLS-TP CC/CV/RDI
The first nibble (0001b) indicates the G-ACh as per RFC 5586[2].
The version and the flags are set to 0 as specified in [2].
The code point is either
- BFD CC code point = XX1. [XX1 to be assigned by IANA from the PW
Associated Channel Type registry.] or,
- BFD proactive CV code point = XX2. [XX2 to be assigned by IANA from
the PW Associated Channel Type registry.]
CC and CV PDUs apply to all pertinent MPLS-TP structures, including
PWs, MPLS LSPs (including SPMEs), and Sections.
CC and CV operation is simultaneously employed on a maintenance
entity (ME) within a single BFD session. The expected usage is that
normal operation is to send CC BFD protocol data units (PDUs)
interleaved with a CV BFD PDU (augmented with a source MEP-ID and
identified as requiring additional processing by the different ACh
channel type). The insertion interval for CV PDUs is one per second.
Detection of a loss-of-continuity defect is the detect multiplier
(fixed at 3 for the CC code point) times the session periodicity.
Mis-connectivity defects are detected in a maximum of one second.
3.4. MPLS-TP BFD CC Message format
The format of an MPLS-TP CC Message is shown below.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Flags | BFD CC Code point |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ BFD Control Packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MPLS-TP CC Message
As shown in figure 2, the MPLS-TP CC message consists of the BFD
control packet as defined in [4] pre-pended by the G-ACh.
3.5. MPLS-TP BFD proactive CV Message format
The format of an MPLS-TP CV Message is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Flags | BFD CV Code Point |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ BFD Control Packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ MEP Source ID TLV ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: MPLS-TP CV Message
As shown in figure 3, the MPLS-TP CV message consists of the BFD
control packet as defined in [4] pre-pended by the ACH, and appended
by a MEP source ID TLV.
A MEP Source ID TLV is encoded as a 2 octet field that specifies a
Type, followed by a 2 octet Length Field, followed by a variable
length Value field. A BFD session will only use one encoding of the
Source ID TLV.
The length in the BFD control packet is as per [4]; the length of the
MEP Source ID TLV is not included. There are 3 possible Source MEP
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TLVs (corresponding to the MEP-IDs defined in [9]) [type fields to be
assigned by IANA]. The type fields are:
X1 - Section MEP-ID
X2 - LSP MEP-ID
X3 - PW MEP-ID
When GAL label is used, the time to live (TTL) field of the GAL MUST
be set to at least 1, and the GAL MUST be the end of stack label
(S=1) as per [2].
A node MUST NOT change the value in the MEP Source ID TLV.
When digest based authentication is used, the Source ID TLV MUST NOT
be included in the digest
3.5.1. Section MEP-ID
The IP compatible MEP-IDs for MPLS-TP sections is the interface ID.
The format of the Section MEP-ID TLV is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-TP Global_ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-TP Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-TP Interface Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Section MEP-ID TLV format
Where the type is of value 'X1' (to be assigned by IANA). The length
is the length of the value fields. The MPLS-TP Global ID, Node
Identifier and Interface Numbers are as per [9].
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3.5.2. LSP MEP-ID
The fields for the LSP MEP-ID is as defined in [9]. This is
applicable to both LSPs and SPMEs. This consists of 32-bit MPLS-TP
Global ID, the 32-bit Node Identifier, followed by the 16-bit
Tunnel_Num (that MUST be unique within the context of the Node
Identifier), and the 16-bit LSP_NUM (that MUST be unique with the
context of the Tunnel Num). The format of the TLV is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-TP Global_ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-TP Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tunnel_Num | LSP_Num |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: LSP MEP-ID TLV format
Where the type is of value 'X2' (to be assigned by IANA). The length
is the length of the value fields. The MPLS-TP Global ID, Node
Identifier, Tunnel Num and LSP_Num are as per [9].
3.5.3. PW Endpoint MEP-ID
The fields for the MPLS-TP PW Endpoint MEP-ID is as defined in [9].
The format of the TLV is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-TP Global_ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-TP Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC_ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AGI Type | AGI Length | AGI Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AGI Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: PW Endpoint MEP-ID TLV format
Where the type is value 'X3' (to be assigned by IANA). The length is
the length of the following data. The Global ID, Node Identifier and
Attachment Circuit (AC)_ID are as per [9]. The Attachment Group
Identifier (AGI) Type is as per [6], and the AGI length is the length
of the AGI value field.
3.6. BFD Session in MPLS-TP terminology
A BFD session corresponds to a CC and proactive CV OAM instance in
MPLS-TP terminology. A BFD session is enabled when the CC and
proactive CV functionality is enabled on a configured Maintenance
Entity (ME).
When the CC and proactive CV functionality is disabled on an ME, the
BFD session transitions to the ADMIN DOWN State and the BFD session
ends.
A new BFD session is initiated when the operator enables or re-
enables the CC and CV functionality.
All BFD state changes and P/F exchanges MUST be done using CC
packets. P/F and session state information in CV packets MUST be
ignored.
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3.7. BFD Profile for MPLS-TP
BFD operates in asynchronous mode utilizing the encapsulation defined
in section 3 for all sessions in a given MEG. For LSPs, SPMEs and
sections this is GAL/G-ACh encapsulated BFD using the code points
specified in section 3.3. For PWs, this is G-ACh or GAL/G-ACh
encapsulated BFD using the code points specified in section 3.3. In
this mode, the BFD Control packets are periodically sent at
configurable time rate. This rate is a fixed value common for both
directions of MEG for the lifetime of the MEG.
This document specifies bi-directional BFD for p2p transport LSPs;
hence all BFD packets MUST be sent with the M bit clear.
There are two modes of operation for bi-directional LSPs. One in
which the session state of both directions of the LSP is coordinated
and one constructed from BFD sessions in such a way that the two
directions operate independently but are still part of the same MEG.
A single bi-directional BFD session is used for coordinated
operation. Two independent BFD sessions are used for independent
operation. It should be noted that independent operation treats
session state and defect state as independent entities. For example
an independent session can be in the UP state while receiving RDI
indication. For a coordinated session, the session state will track
the defect state.
In coordinated mode, an implementation SHOULD NOT reset
bfd.RemoteDiscr until it is exiting the DOWN state.
In independent mode, an implementation MUST NOT reset bfd.RemoteDiscr
upon transitioning to the DOWN state.
Overall operation is as specified in [4] and augmented for MPLS in
[8]. Coordinated operation is as described in [4]. Independent
operation requires clarification of two aspects of [4]. Independent
operation is characterized by the setting of bfd.MinRxInterval to
zero by the MEP that is typically the session originator (referred to
as the source MEP), and there will be a session originator at either
end of the bi-directional LSP. Each source MEP will have a
corresponding sink MEP that has been configured to a Tx interval of
zero.
This memo specifies a preferred interpretation of the base spec on
how a MEP with a BFD transmit rate set to zero behaves. One
interpretation is that no periodic messages on the reverse component
of the bi-directional LSP originate with that MEP, it will only
originate messages on a state change.
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The first clarification is that when a state change occurs a MEP set
to a transmit rate of zero sends BFD control messages with a one
second period on the reverse component until such time that the state
change is confirmed by the session peer. At this point the MEP set to
a transmit rate of zero can resume quiescent behavior. This adds
robustness to all state transitions in the RxInterval=0 case.
The second is that the originating MEP (the one with a non-zero
bfd.TxInterval) will ignore a DOWN state received from a zero
interval peer. This means that the zero interval peer will continue
to send DOWN state messages that include the RDI diagnostic code as
the state change is never confirmed. This adds robustness to the
exchange of RDI indication on a uni-directional failure (for both
session types DOWN with a diagnostic of either control detection
period expired or neighbor signaled session down offering RDI
functionality).
A further extension to the base specification is that there are
additional OAM protocol exchanges that act as inputs to the BFD state
machine; these are the Link Down Indication [5] and the Lock
Instruct/Lock Report transactions; Lock Report interaction being
optional.
3.7.1. Session initiation and Modification
Session initiation occurs starting from MinRx = 1 second, MinTx >= 1
second and the detect multiplier = 3.
Once in the UP state, poll/final discipline is used to modify the
periodicity of control message exchange from their default rates to
the desired rates and set the detect multiplier to 3.
Once the desired rate has been reached using the poll/final
mechanism, implementations SHOULD NOT attempt further rate
modification.
In the rare circumstance where an operator has a reason to further
change session parameters, beyond the initial migration from default
values; poll/final discipline can be used with the caveat that a peer
implementation may consider a session change unacceptable and/or
bring the BFD session down via the use of the ADMIN DOWN state.
3.7.2. Defect entry criteria
There are further defect criteria beyond those that are defined in
[4] to consider given the possibility of mis-connectivity defects.
The result is the criteria for a LSP direction to transition from the
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defect free state to a defect state is a superset of that in the BFD
base specification [4].
The following conditions cause a MEP to enter the defect state for CC
PDUs (in no particular order):
1. BFD session times out (loss-of-continuity defect).
2. Receipt of a link down indication or lock report.
And the following will cause the MEP to enter the mis-connectivity
defect state for CV operation (again not in any particular order):
1. BFD control packets are received with an unexpected
encapsulation (mis-connectivity defect), these include:
- receiving an IP encoded CC or CV BFD control packet on a
LSP configured to use GAL/G-ACh, or vice versa
(note there are other possibilities that can also alias as an
OAM packet)
2. Receipt of an unexpected globally unique Source MEP identifier
(Mis-connectivity defect). Note that as each encoding of the
Source MEP ID TLV contains unique information (there is no
mechanical translation possible between MEP ID formats), receipt
of an unexpected source MEP ID type is the same as receiving an
unexpected value.
3. Receipt of a session discriminator that is not in the local BFD
database in the Your Discriminator field (mis-connectivity
defect).
4. Receipt of a session discriminator that is in the local database
but does not have the expected label (mis-connectivity defect).
5. IF BFD authentication is used, receipt of a message with
incorrect authentication information (password, MD5 digest, or
SHA1 hash).
The effective defect hierarchy (order of checking) is
1. Receiving nothing.
2. Receiving link down indication. E.g. a local link failure, an
MPLS-TP LDI indication, or Lock Report.
3. Receiving from an incorrect source (determined by whatever
means).
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4. Receiving from a correct source (as near as can be determined),
but with incorrect session information).
5. Receiving BFD control packets in all discernable ways correct.
3.7.3. Defect entry consequent action
Upon defect entry a sink MEP will assert signal fail into any client
(sub-)layers. It will also communicate session DOWN to its session
peer using CC messages.
The blocking of traffic as a consequent action MUST be driven only by
a defect's consequent action as specified in [13] section 5.1.1.2.
When the defect is mis-connectivity, the section, LSP or PW
termination will silently discard all non-OAM traffic received. The
sink MEP will also send a defect indication back to the source MEP
via the use of a diagnostic code of mis-connectivity defect to be
assigned by IANA.
3.7.4. Defect exit criteria
3.7.4.1. Exit from a loss-of-continuity defect
For a coordinated session, exit from a loss-of-connectivity defect is
as described in figure 7 which updates [4].
For an independent session, exit from a loss-of-connectivity defect
occurs upon receipt of a well formed BFD control packet from the peer
MEP as described in figures 8 and 9.
3.7.4.2. Exit from a mis-connectivity defect
Exit from a mis-connectivity defect state occurs when no CV messages
with mis-connectivity defects have been received for a period of 3.5
seconds.
3.7.5. State machines
The following state machines update [4]. They have been modified to
include LDI and LKR as specified in [5] as inputs to the state
machine and to clarify the behavior for independent mode. LKR is an
optional input.
The coordinated session state machine has been augmented to indicate
LDI and optionally LKR as inputs to the state machine. For a session
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that is in the UP state, receipt of LDI or optionally LKR will
transition the session into the DOWN state.
+--+
| | UP, ADMIN DOWN, TIMER, LDI, LKR
| V
DOWN +------+ INIT
+------------| |------------+
| | DOWN | |
| +-------->| |<--------+ |
| | +------+ | |
| | MISCONNECTIVITY,| |
| | ADMIN DOWN,| |
| |ADMIN DOWN, DOWN,| |
| |TIMER TIMER,| |
V |LDI,LKR LDI,LKR | V
+------+ +------+
+----| | | |----+
DOWN| | INIT |--------------------->| UP | |INIT, UP
+--->| | INIT, UP | |<---+
+------+ +------+
Figure 7: MPLS CC state machine for coordinated session operation
For independent mode, there are two state machines. One for the
source MEP (which requested bfd.MinRxInterval=0) and the sink MEP
(which agreed to bfd.MinRxInterval=0).
The source MEP will not transition out of the UP state once
initialized except in the case of a forced ADMIN DOWN. Hence LDI and
optionally LKR do not enter into the state machine transition from
the UP state, but do enter into the INIT and DOWN states.
+--+
| | UP, ADMIN DOWN, TIMER, LDI, LKR
| V
DOWN +------+ INIT
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+------------| |------------+
| | DOWN | |
| +-------->| |<--------+ |
| | +------+ | |
| | | |
| |ADMIN DOWN ADMIN DOWN | |
| |TIMER, | |
| |LDI, | |
V |LKR | V
+------+ +------+
+----| | | |----+
DOWN| | INIT |--------------------->| UP | | INIT, UP, DOWN,
+--->| | INIT, UP | |<---+ LDI, LKR
+------+ +------+
Figure 8: MPLS CC State machine for source MEP for independent
session operation
The sink MEP state machine (for which the transmit interval has been
set to zero) is modified to:
1) Permit direct transition from DOWN to UP once the session has been
initialized. With the exception of via the ADMIN DOWN state, the
source MEP will never transition from the UP state, hence in normal
unidirectional fault scenarios will never transition to the INIT
state.
+--+
| | ADMIN DOWN, TIMER, LDI, LKR
| V
DOWN +------+ INIT, UP
+------------| |------------+
| | DOWN | |
| +-------->| |<--------+ |
| | +------+ | |
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| | MISCONNECTIVITY,| |
| | ADMIN DOWN,| |
| |ADMIN DOWN, TIMER, | |
| |TIMER, DOWN, | |
| |LDI, LDI, | V
V |LKR LKR | |
+------+ +------+
+----| | | |----+
DOWN| | INIT |--------------------->| UP | |INIT, UP
+--->| | INIT, UP | |<---+
+------+ +------+
Figure 9: MPLS CC State machine for the sink MEP for independent
session operation
3.7.6. Configuration of MPLS-TP BFD sessions
Configuration of MPLS-TP BFD session parameters and coordination of
same between the source and sink MEPs is out of scope of this memo.
3.7.7. Discriminator values
In the BFD control packet the discriminator values have either local
to the sink MEP or no significance (when not known).
My Discriminator field MUST be set to a nonzero value (it can be a
fixed value), the transmitted Your Discriminator value MUST reflect
back the received value of My Discriminator field or be set to 0 if
that value is not known.
Per RFC5884 Section 7 [8], a node MUST NOT change the value of the My
Discriminator" field for an established BFD session.
4. Configuration Considerations
The following is an example set of configuration parameters for a BFD
session:
Mode and Encapsulation
RFC 5884 - BFD CC in UDP/IP/LSP
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RFC 5885 - BFD CC in G-ACh
RFC 5085 - UDP/IP in G-ACh
MPLS-TP - CC/CV in GAL/G-ACh or G-ACh
For MPLS-TP, the following additional parameters need to be
configured:
1) Session mode, coordinated or independent
2) CC periodicity
3) The MEP ID for the MEPs at either end of the LSP
4) Whether authentication is enabled (and if so, the associated
parameters)
And the the discriminators used by each MEP, both bfd.LocalDiscr and
bfd.RemoteDiscr can optionally be configured or locally assigned.
Finally a detect multiplier of 3 is directly inferred from the code
points.
5. Acknowledgments
Nitin Bahadur, Rahul Aggarwal, Tom Nadeau, Nurit Sprecher and Yaacov
Weingarten also contributed to this document.
6. IANA Considerations
This draft requires the allocation of two channel types from the IANA
"PW Associated Channel Type" registry in RFC4446 [6].
XX1 MPLS-TP CC message
XX2 MPLS-TP CV message
This draft requires the creations of a source MEP-ID TLV
registry. The parent registry will be the "PW Associated Channel
Type" registry of RFC4446 [6]. All code points within this
registry shall be allocated according to the "Standards Action"
procedures as specified in [11].
The initial values are:
X1 - Section MEP-ID
X2 - LSP MEP-ID
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X3 - PW MEP-ID
The items tracked in the registry will be the type, and the
associated name and reference. The source MEP-ID TLV will require
standards action registration procedures for additional values.
This memo requests a code point from the registry for BFD
diagnostic codes [4]:
XX -
- mis-connectivity defect
7. Security Considerations
The use of CV improves network integrity by ensuring traffic is
not "leaking" between LSPs.
Base BFD foresees an optional authentication section (see [4]
section 6.7); that can be applied to this application. Although
the source MEP-ID TLV is not included in the BFD authentication
digest, there is a chain of trust such that the discriminator
associated with the digest is also associated with the expected
MEP-ID which will prevent impersonation of CV messages in this
application.
This memo specifies the use of globally unique identifiers for
MEP IDs. This provides absolutely authoritative detection of
persistent leaking of traffic between LSPs. Non-uniqueness can
result in undetected leaking in the scenario where two LSPs with
common MEP IDs are misconnected. This would be considered to be
undesirable but rare, it would also be difficult to exploit for
malicious purposes as at a minimum, both a network end point,
and a node that was a transit point for the target MEG would
need to be compromised.
8. References
8.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[2] Bocci, M. et al., "MPLS Generic Associated Channel ", RFC
5586 , June 2009
[3] Vigoureux, M., Betts, M. and D. Ward, "Requirements for
Operations Administration and Maintenance in MPLS
Transport Networks", RFC5860, May 2010
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[4] Katz, D. and D. Ward, "Bidirectional Forwarding
Detection", RFC 5880, June 2010
[5] Swallow, G. et al., "MPLS Fault Management OAM", draft-
ietf-mpls-tp-fault-04 (work in progress), April 2011
[6] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
Emulation (PWE3)", RFC 4446, April 2006
[7] Nadeau, T. et al. "Bidirectional Forwarding Detection
(BFD) for the Pseudowire Virtual Circuit Connectivity
Verification (VCCV) ", IETF RFC 5885, June 2010
[8] Aggarwal, R. et.al., "Bidirectional Forwarding Detection
(BFD) for MPLS Label Switched Paths (LSPs)", RFC 5884,
June 2010
[9] Bocci, M. and G. Swallow, "MPLS-TP Identifiers", draft-
ietf-mpls-tp-identifiers-06 (work in progress), June 2011
[10] Nadeau, T, et al., "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007
[11] Narten, T., Alvestrand, H., "Guidelines for Writing an
IANA Considerations Section in RFCs", IETF RFC 5226, May
2008
8.2. Informative References
[12] Bocci, M., et al., "A Framework for MPLS in Transport
Networks", RFC5921, July 2010
[13] Allan, D., and Busi, I. "MPLS-TP OAM Framework", draft-
ietf-mpls-tp-oam-framework-11 (work in progress), February
2011
[14] Andersson et. al., "OAM Terminology", IETF RFC 6291, June
2011
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Authors' Addresses
Dave Allan
Ericsson
Email: david.i.allan@ericsson.com
John Drake
Juniper
Email: jdrake@juniper.net
George Swallow
Cisco Systems, Inc.
Email: swallow@cisco.com
Annamaria Fulignoli
Ericsson
Email: annamaria.fulignoli@ericsson.com
Sami Boutros
Cisco Systems, Inc.
Email: sboutros@cisco.com
Martin Vigoureux
Alcatel-Lucent
Email: martin.vigoureux@alcatel-lucent.com
Siva Sivabalan
Cisco Systems, Inc.
Email: msiva@cisco.com
David Ward
Juniper
Email: dward@juniper.net
Robert Rennison
ECI Telecom
Email: robert.rennison@ecitele.com
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