Network Working Group Thomas D. Nadeau
Internet Draft Monique Morrow
Expires: October 2003 George Swallow
Cisco Systems, Inc.
April 2003
Pseudo Wire (PW) Virtual Circuit Connection Verification
(VCCV)
draft-nadeau-pwe3-vccv-00.txt
Status of this Memo
This document is an Internet-Draft and is in full
conformance with all provisions of Section 10 of RFC 2026
[RFC2026].
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Abstract
This document describes the Virtual Circuit Connection
Verification Protocol (VCCV). VCCV supports connection
verification applications for pseudowire VCs regardless of
the underlying MPLS or IP tunnel technology. A network
operator may use the VCCV protocol to test the network's
forwarding plane liveliness.
1. Specification of Requirements 2
2. Acronyms 2
3. Introduction 2
4. Scope 4
5. L2TPv3/IP as PSN 4
6. MPLS as PSN 4
7. OAM Capability Negotiation 6
8. Security Considerations 7
9. Acknowledgments 7
10. References 8
11. Authors' Addresses 9
12. Intellectual Property Rights Notices 9
13. Full Copyright Statement 10
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1. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",
and "OPTIONAL" in this document are to be interpreted
as described in RFC 2119.
2. Acronyms
CE Customer Edge
CV Connection Verification
FEC Forward Equivalency Class
PE Provider Edge
PSN Packet Service Network
TLV Type Length Value
VC Virtual Circuit
VCCV Virtual Circuit Connection Verification
3. Introduction
As network operators deploy pseudowire services, fault
detection and diagnostic mechanisms particularly for the PSN
portion of the network are pivotal. Specifically, the ability
to provide end-to-end fault detection and diagnostics for an
emulated pseudowire service is critical for the network
operator. Operators have indicated in [MPLSOAMREQS] that such
a tool is required for pseudowire deployments. This document
describes a protocol for PSN-agnostic fault detection and
diagnostics called virtual circuit connection verification
(VCCV).
|<------- pseudowire ------>|
| |<-- PSN Tunnel -->| |
PW V V V V PW
End Service +----+ +----+ End Service
+-----+ | | PE1|==================| PE2| | +-----+
| |----------|............PW1.............|------------| |
| CE1 | | | | | | | | CE2 |
| |----------|............PW2.............|------------| |
+-----+ | | |==================| | | +-----+
Customer | +----+ +----+ | Customer
Edge 1 | Provider Edge 1 Provider Edge 2 | Edge 2
|<----------- Emulated Service ---------->|
|<---------- VCCV ---------->|
Figure 1: PWE3 VCCV Operation Reference Model
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Figure 1 depicts the basic functionality of VCCV. The protocol
runs between PEs that attaches the VC under test. The protocol
encapsulates packets using the same encapsulation as is used
for data.
+-------------+ +-------------+
| Layer2 | | Layer2 |
| Emulated | | Emulated |
| Services | Emulated Service | Services |
| |<==============================>| |
+-------------+ VCCV/pseudowire +-------------+
|Demultiplexer|<==============================>|Demultiplexor|
+-------------+ +-------------+
| PSN | PSN Tunnel | PSN |
| MPLS |<==============================>| MPLS |
+-------------+ +-------------+
| Physical | | Physical |
+-----+-------+ +-----+-------+
| |
| ____ ___ ____ |
| _/ \___/ \ _/ \__ |
| / \__/ \_ |
| / \ |
+========/ MPLS or IP Network |===+
\ /
\ ___ ___ __ _/
\_/ \____/ \___/ \____/
Figure 2: PWE3 Protocol Stack Reference Model
including VCCV.
Figure 2 depicts how VCCV is run over the pseudowire to
verify specific VCs. VCCV messages are encapsulated using the
PWE3 encapsulation as described below in sections 5 and 6.
These messages are exchanged only after the desire to exchange
such traffic has been negotiated between the PEs (see section
8). The figure also illustrates how VCCV traffic should be
routed and handled using the same data plane path as normal
data traffic until it reaches the PE de-multiplextor point.
When VCCV messages are intercepted at the de-multiplextor
point, they are processed specially. Normal data traffic would
be de-capsulated and forwarded to the emulated service at this
point. This provides a true test of the data plane integrity
of the pseudowire data traffic.
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4. Scope
VCCV is intended to provide connectivity verification of a
psuedowire. As shown in figure 1, a pseudowire rides over a
PSN and is used to provide an Emulated Serivce. Verification
of the underlying PSN is specific to the PSN technology
employed, and is therefore beyond the scope of this document.
In all cases, connection verification of the Emulated Service
between two CEs should be performed using the CV mechanism(s)
provided by the emulated services running between the CEs.
It may be necessary to inject indications of errors discovered
by VCCV into the attachment circuits that are affected by
those errors. In these cases an OAM message mapping mechanism
is required. OAM mapping is beyond the scope of this document;
it is discussed in [OAMMsgMap].
5. L2TPv3/IP as PSN
When IP is used as the underlying PSN, T.B.D. is used to
perform connectivity verification and tracing functions
between PEs.
6. MPLS as PSN
In order to apply IP monitoring tools to PWE3 circuits, VCCV
creates a control channel between PWE3 PEs[]. Packets sent
across this channel are IP packets, allowing maximum
flexibility.
Ideally such a control channel would be completely in band.
When a control word is present on virtual circuit, it is
possible to indicate the control channel by setting a bit in
the control header. This method is described in section 6.1
and is referred to as inband MPLS VCCV.
However in order to address the case when the control header
is not in use as well as to deal with a number of existent
hardware devices, use of the MPLS Router Alert Label to indicate
the IP control channel is also proposed. This is described in
section 6.2.
The actual channel type is agreed through signaling as
described in section 8.
6.1. Inband MPLS VCCV
The PWE control word [PWE-ENCAP] is defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Rsvd | Flags |Res| Length | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
We propose that bit 7 of the control word (low order bit in
the Flagsfield) of each PWE3 header type be allocated for the
purpose of indicating control channel messages.
6.2. Router Alert Label Approach
When the control word is not used, or the receiving hardware
cannot divert control traffic, an IP control channel can be
created by including the MPLS router alert label immediately
above the VC label. If the control word is in use on this VC
it is also included in the IP control flow.
0x1 OAM Flag in PWE header
0x2 Include the control channel label in stack above VC
label
7. IP Probe Traffic
For connectivity verification, both ICMP Ping and LSP-Ping
packets may be used on the control channel. The type of
packets used is agreed in signaling as described in section 8.
7.1. ICMP Ping
When ICMP packets are used, the source address should be set
to the source address of the LDP session and the destination
address to the destination of the LDP session. The Identifier
and Sequence Number fields of the ICMP Echo Request / Echo
Reply messages are used to track what VCs are being tested.
These fields are only interpreted by the sending PE. Specific
use of these fields is an implementation matter.
7.2. MPLS Ping Packet
The LSP Ping header must be used as described [LSP-PING] and
must also contain the sub-TLV of 8 for PW circuits. This sub-
TLV must be sent containing the circuit to be verified as the
"VC ID" field:
7.2.1 L2 Circuit ID TLV for MPLS LSP Ping
The value field consists of a remote PE address (the address
of the targeted LDP session), the source address of the PE
that originated this request, a VC ID and an encapsulation
type, as follows.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote PE Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source PE Address|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PWID Type |PWID Length | PWID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameters |
| " |
| " |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Two PWID types are defined:
1. A FEC 128 VCID as defined in [MARTINISIG].
2. A FEC 129 Attachment Identifier, as defined [L2SIG].
The PWID length field contains the length of the
PWID field in bytes. Zero to three bytes of padding will follow
the PWID field, so that the parameters field starts on a 64-bit
boundary.
Parameters are:
- Interface parameters, as defined in [MARTINISIG].
***Note that we propose that this field be removed from the
LSP Ping draft [LSPPING] and defined here instead.
8. LDP OAM Capability Negotiation
To permit negotiation of the use and type of OAM for
Connectivity Verification, a VCCV parameter is defined below.
When a PE signals a PWE VC and desires OAM, it must indicate
this during VC establishment. Specifically for LDP it MUST
include the VCCV parameter in the VC setup message.
The requesting PE indicates its desire for the remote PE to
support OAM capability by including the VCCV parameter with
appropriate options set to indicate which methods of OAM are
desired. The remote PE indicates it will support returning
the VCCV parameter. The requesting PE MAY indicate multiple
IP control channel options. The remote PE MUST respond with a
single IP control channel selected. If it does not wish to
support OAM functions, it MUST zero all bits of the control
channel type field. The absence of the VCCV FEC TLV also
indicates that no OAM functions are supported or desired by
the requesting PE. This last method MUST be supported by all
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PEs in order to handle backward-compatibility with older PEs.
The requesting PE MAY indicate multiple IP control channel
probe packets. The remote PE MAY respond with any or all of
IP control channel probe packets selected.
8.1. Optional VCCV Parameter
[PWE3CONTROL] defines a VC FEC TLV for LDP. Parameters can be
carried within that TLV to signal different capabilities for
specific PWs. We propose an optional parameter to be used to
indicate the desire to use a control channel for VCCV as
follows. As the overall method of PWE3 signaling is
downstream, unsolicited, this leaves the decision of the type
of IP control channel completely to the receiving control
entity. OAM capability MUST be signaled BEFORE a PE may send
OAM messages. If a PE receives OAM messages prior to reception
of a VCCV parameter, it MUST discard these messages. In this
case, the LSR SHOULD increment an error counter and optionally
issues a system and/or SNMP notification to indicate to the
system administrator that a mis-configuration exists.
When included, this optional parameter MUST be used to
validate that the LSRs, and the ingress and egress ports at
the edges of the circuit, have the necessary capabilities to
support VCCV.
The TLV field structure is defined in [PWE3CONTROL] as
follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter ID | Length | Variable Length Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable Length Value |
| " |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The VCCV parameter ID is defined as follows:
Parameter ID Length Description
0x06 4 VCCV
The format of the VCCV parameter TLV is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x06 | 0x04 | CC Type | CV Types |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The CC type field defines the type of IP control channel.
The defined values are:
0x1 OAM Flag set in PWE header
0x2 MPLS Router Alert Label
The CV Types field defines the types of IP control packets
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that may be sent on the control channel. The defined values
are:
0x1 ICMP Ping
0x2 LSP Ping
9. Security Considerations
TBD
10. Acknowledgments
The authors would like to thank Hari Rakotoranto, Michel
Khouderchah, Bertrand Duvivier, Vanson Lim, Chris Metz, W.
Mark Townsley, Eric Rosen, Dan Tappan, Rahul Aggarwal, and
Danny McPherson for their valuable comments and suggestions.
11. References
[PWREQ] Xiao, X., McPherson, D., Pate, P., Gill, V.,
Kompella, K., Nadeau, T., White, C., "Requirements
for Pseudo Wire Emulation Edge-to-Edge (PWE3)",
<draft-ietf-pwe3-requirements-02.txt>, November 2001.
[PWE3FW] Prayson Pate, et al., Internet draft, Framework for
Pseudo Wire Emulation Edge-to-Edge (PWE3), draft-
ietf-pwe3-framework-01.txt, work in progress.
[PWEARCH] Bryant, S., Pate, P., Johnson, T., Kompella, K.,
Malis, A., McPherson, D., Nadeau, T., So, T., Townsley,
W., Systems, White., C., Wood, L., Xiao, X., Internet
draft, Framework for Pseudo Wire Emulation Edge-to-Edge
(PWE3), draft-ietf-pwe3-framework-01.txt, work in
progress.
[L2SIG] Rosen, E., LDP-based Signaling for L2VPNs,
Internet Draft <draft-rosen-ppvpn-l2-signaling-02.txt>,
September 2002.
[LSPPING] Kompella, K., Pan, P., Sheth, N., Cooper, D.,
Swallow, G., Wadhwa, S., Bonica, R., " Detecting
Data Plane Liveliness in MPLS", Internet Draft
<draft-ietf-mpls-lsp-ping-01.txt>, April 2003.
[MARTINISIG] "Transport of Layer 2 Frames Over MPLS", Martini et.
al., draft-martini-l2circuit-trans-mpls-10.txt,
August 2002
[GTTP] Bonica, R., Kompella, K., Meyer, D., "Generic
Tunnel Tracing Protocol (GTTP) Specification", Internet
Draft <draft-bonica-tunproto-01.txt>, April, 2003
[FRF 8.1] Frame Relay Forum, Frame Relay / ATM PVC Service
Interworking Implementation Agreement, February 2000
[ITU-T] "Draft Recommendation Y.17fw" (MPLS Management
Framework), July 2002.
[ITU-T] "Frame Relay Bearer Service Interworking," I.555,
September 2997.
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[ITU-T], "Frame Relay Operations Principles and Functions",
I.620, October, 1996.
[ITU-T] Q.933, ISDN Digital Subscriber Signalling System
No. 1 (DSS 1) - Signalling specification for frame
mode basic call control, November 1995.
[ICMP] Postel, J. "Internet Control Message Protocol, "
RFC 792
[PWEATM] Martini, L., et al., "Encapsulation Methods for
Transport of ATM Cells/Frame Over IP and MPLS
Networks", Internet Draft <draft-ietf-pwe3-atm-
encap-00.txt>, October 2002
[MPLSOAMREQS] Nadeau, T., et al,"OAM Requirements for MPLS
Networks, Internet Draft <draft-nadeau-ietf-oam-
requirements-00.txt>, January 2003.
[OAMMsgMap] Nadeau, T., et al, " Pseudo Wire (PW) OAM Message
Mapping, Internet Draft < draft-nadeau-pwe3-OAMMap.txt>,
December, 2002.
[PWE3CONTROL] L.Martini et al., "Transport of Layer 2 Frames
over MPLS, Internet Draft, <draft-ietf-pwe3-control-
protocol-01.txt>, May 2003
[PPVPNFW] Callon, R., Suzuki, M., Gleeson, B., Malis, A.,
Muthukrishnan, K., Rosen, E., Sargor, C., and J. Yu,
"A Framework for Provider Provisioned Virtual
Private Networks", Internet Draft <draft-ietf-
ppvpn-framework-01.txt>, July 2001.
[SAJASSI] A.Sajassi et al., "L2VPN Interworking," Internet
Draft <draft-sajassi-l2vpn-interworking-00.txt>,
November 2002.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon,
"Multiprotocol Label Switching Architecture", RFC
3031, January 2001.
12. Authors' Addresses
Thomas D. Nadeau
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA 01824
Email: tnadeau@cisco.com
George Swallow
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA 01824
Email: swallow@cisco.com
Monique Morrow
Cisco Systems, Inc.
Glatt-com
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CH-8301 Glattzentrum
Switzerland
Email: mmorrow@cisco.com
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14. Full Copyright Statement
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