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3.5.2. PWE3 OAM using G-ACh
As mentioned above, VCCV enables OAM for PWs by
using a control
channel for OAM packets. When PWs are used in
MPLS-TP networks,
rather than the control channels defined in VCCV,
the G-ACh can be
used as an alternative control channel. The usage of
the G-ACh for
PWs is defined in [PW-G-ACh].
3.6. OWAMP and TWAMP
3.6.1. Overview
The IPPM working group in the IETF defines common
criteria and
metrics for measuring performance of IP traffic
([IPPM-FW]). Some of
the key RFCs published by this working group have
defined metrics for
measuring connectivity [IPPM-Con], delay
([IPPM-1DM], [IPPM-2DM]),
and packet loss [IPPM-1LM].
Alternative protocols for performance measurement
are defined, for
example, in MPLS-TP OAM ([MPLS-LM-DM], [TP-LM-DM]),
and in Ethernet
OAM [ITU-T-Y1731].
The IPPM working group has defined not only metrics
for performance
measurement, but also protocols that define how the
measurement is
carried out. The One-way Active Measurement Protocol
[OWAMP] and the
Two-Way Active Measurement Protocol [TWAMP] define a
method and
protocol for measuring delay and packet loss in IP
networks.
OWAMP [OWAMP] enables measurement of one-way
characteristics of IP
networks, such as one-way packet loss and one-way
delay. For its
proper operation OWAMP requires accurate time of day
setting at its
end points.
TWAMP [TWAMP] is a similar protocol that enables
measurement of two-
way (round trip) characteristics. TWAMP does not
require accurate
time of day, and, furthermore, allows the use of a
simple session
reflector, making it an attractive alternative to
OWAMP.
OWAMP and TWAMP use two separate protocols: a
Control plane protocol,
and a Test plane protocol.
3.6.2. Control and Test Protocols
OWAMP and TWAMP control protocols run over TCP,
while the test
protocols run over UDP. The purpose of the control
protocols is to
initiate, start, and stop test sessions, and for
OWAMP to fetch
results. The test protocols introduce test packets
(which contain
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sequence numbers and timestamps) along the IP path
under test
according to a schedule, and record statistics of
packet arrival.
Multiple sessions may be simultaneously defined,
each with a session
identifier, and defining the number of packets to be
sent, the amount
of padding to be added (and thus the packet size),
the start time,
and the send schedule (which can be either a
constant time between
test packets or exponentially distributed
pseudo-random). Statistics
recorded conform to the relevant IPPM RFCs.
OWAMP and TWAMP test traffic is designed with
security in mind. Test
packets are hard to detect because they are simply
UDP streams
between negotiated port numbers, with potentially
nothing static in
the packets. OWAMP and TWAMP also include optional
authentication
and encryption for both control and test packets.
3.6.3. OWAMP
OWAMP defines the following logical roles:
Session-Sender, Session-
Receiver, Server, Control-Client, and Fetch-Client.
The Session-
Sender originates test traffic that is received by
the Session-
Receiver. The Server configures and manages the
session, as well as
returning the results. The Control-Client initiates
requests for
test sessions, triggers their start, and may trigger
their
termination. The Fetch-Client requests the results
of a completed
session. Multiple roles may be combined in a single
host - for
example, one host may play the roles of
Control-Client, Fetch-Client,
and Session-Sender, and a second playing the roles
of Server and
Session-Receiver.
In a typical OWAMP session the Control-Client
establishes a TCP
connection to port 861 of the Server, which responds
with a server
greeting message indicating supported
security/integrity modes. The
Control-Client responds with the chosen
communications mode and the
Server accepts the modes. The Control-Client then
requests and fully
describes a test session to which the Server
responds with its
acceptance and supporting information. More than
one test session
may be requested with additional messages. The
Control-Client then
starts a test session and the Server acknowledges.
The Session-
Sender then sends test packets with pseudorandom
padding to the
Session-Receiver until the session is complete or
until the Control-
client stops the session. Once finished, the
Fetch-Client sends a
fetch request to the server, which responds with an
acknowledgement
and immediately thereafter the result data.
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3.6.4. TWAMP
TWAMP defines the following logical roles:
session-sender, session-
reflector, server, and control-client. These are
similar to the
OWAMP roles, except that the Session-Reflector does
not collect any
packet information, and there is no need for a
Fetch-Client.
In a typical TWAMP session the Control-Client
establishes a TCP
connection to port 862 of the Server, and mode is
negotiated as in
OWAMP. The Control-Client then requests sessions
and starts them.
The Session-Sender sends test packets with
pseudorandom padding to
the Session-Reflector which returns them with
insertion of
timestamps.
3.7. Summary of OAM Functions
Table 3 summarizes the OAM functions that are
supported in each of
the categories that were analyzed in this section.
+-----------+-------+--------+--------+-----------+-------+--------+
| Standard |Continu|Connecti|Path |Defect
|Perform|Other |
| |ity |vity
|Discover|Indications|ance |Function|
| |Check |Verifica|y |
|Monitor|s |
| | |tion | |
|ing | |
+-----------+-------+--------+--------+-----------+-------+--------+
|IP Ping | |Echo | | |
| |
+ --------- + ----- + ------ + ------ + --------- +
----- + ------ +
|IP | | |Tracerou| |
| |
|Traceroute | | |te | |
| |
+ --------- + ----- + ------ + ------ + --------- +
----- + ------ +
|BFD |BFD |BFD | | |
| |
| |Control|Echo | | |
| |
+ --------- + ----- + ------ + ------ + --------- +
----- + ------ +
|MPLS OAM | |"Ping" |"Tracero| |
| |
|(LSP Ping) | |mode |ute" | |
| |
| | | |mode | |
| |
+ --------- + ----- + ------ + ------ + --------- +
----- + ------ +
|MPLS-TP |CC |CV/pro- |Route |-Alarm
|-LM |-Diagnos|
|OAM | |active |Tracing | Reporting
|-DM | tic Tes|
| | |or on- | |-Client |
| t |
| | |demand | | Failure |
|-Lock |
| | | | | Indication|
| |
| | | | |-Remote |
| |
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| | | | | Defect |
| |
| | | | | Indication|
| |
+ --------- + ----- + ------ + ------ + --------- +
----- + ------ +
|PWE3 OAM |BFD |-BFD |LSP-Ping| |
| |
| | |-ICMP | | |
| |
| | | Ping | | |
| |
| | |-LSP- | | |
| |
| | | Ping | | |
| |
+ --------- + ----- + ------ + ------ + --------- +
----- + ------ +
|OWAMP and | | | |
|-Delay | |
|TWAMP | | | | |
measur| |
| | | | | |
ement | |
| | | | |
|-Packet| |
| | | | | |
loss | |
| | | | | |
measur| |
| | | | | |
ement | |
+-----------+-------+--------+--------+-----------+-------+--------+
Table 3 Summary of OAM Functions
4. Security Considerations
This memo presents an overview of existing OAM
mechanisms, and
proposes no new OAM mechanisms. Therefore, this
document introduces
no security considerations. However, the OAM
mechanism reviewed in
this document can and do present security issues.
The reader is
encouraged to review the Security Considerations
section of each
document reference by this memo.
5. IANA Considerations
There are no new IANA considerations implied by this
document.
6. Acknowledgments
The authors gratefully acknowledge Sasha Vainshtein,
Carlos
Pignataro, David Harrington, Dan Romascanu, Ron
Bonica and other
members of the OPSAWG mailing list for their helpful
comments.
This document was prepared using
2-Word-v2.0.template.dot.
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7. References
7.1. Normative References
[LSP-Ping] Kompella, K., Swallow, G., "Detecting
Multi-Protocol
Label Switched (MPLS) Data Plane
Failures", RFC 4379,
February 2006.
[MPLS-OAM] Nadeau, T., Morrow, M., Swallow, G.,
Allan, D.,
Matsushima, S., "Operations and
Management (OAM)
Requirements for Multi-Protocol Label
Switched (MPLS)
Networks", RFC 4377, February 2006.
[MPLS-OAM-FW] Allan, D., Nadeau, T., "A Framework
for Multi-Protocol
Label Switching (MPLS) Operations and
Management
(OAM)", RFC 4378, February 2006.
[OAM-Label] Ohta, H., "Assignment of the 'OAM
Alert Label' for
Multiprotocol Label Switching
Architecture (MPLS)
Operation and Maintenance (OAM)
Functions", RFC 3429,
November 2002.
[MPLS-TP-OAM] Vigoureux, M., Ward, D., Betts, M.,
"Requirements for
OAM in MPLS Transport Networks", RFC
5860, May 2010.
[G-ACh] Bocci, M., Vigoureux, M., Bryant, S.,
"MPLS Generic
Associated Channel", RFC 5586, June
2009.
[VCCV] Nadeau, T., Pignataro, C., "Pseudowire
Virtual Circuit
Connectivity Verification (VCCV): A
Control Channel
for Pseudowires", RFC 5085, December
2007.
[PW-ACH] Bryant, S., Swallow, G., Martini, L.,
McPherson, D.,
"Pseudowire Emulation Edge-to-Edge
(PWE3) Control Word
for Use over an MPLS PSN", RFC 4385,
February 2006.
[ICMPv4] Postel, J., "Internet Control Message
Protocol", STD 5,
RFC 792, September 1981.
[ICMPv6] Conta, A., Deering, S., and M. Gupta,
"Internet Control
Message Protocol (ICMPv6) for the
Internet Protocol
Version 6 (IPv6) Specification", RFC
4443, March 2006.
[MPLS-P2MP] Yasukawa, S., Farrel, A., King, D.,
Nadeau, T.,
"Operations and Management (OAM)
Requirements for
Point-to-Multipoint MPLS Networks",
RFC 4687,
September 2006.
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[ICMP-Ext] Bonica, R., Gan, D., Tappan, D.,
Pignataro, C., "ICMP
Extensions for Multiprotocol Label
Switching", RFC
4950, August 2007.
[ICMP-MP] Bonica, R., Gan, D., Tappan, D.,
Pignataro, C.,
"Extended ICMP to Support Multi-Part
Messages", RFC
4884, April 2007.
[ICMP-Int] Atlas, A., Bonica, R., Pignataro, C.,
Shen, N., Rivers,
JR., "Extending ICMP for Interface and
Next-Hop
Identification", RFC 5837, April 2010.
[TCPIP-Tools] Kessler, G., Shepard, S., "A Primer On
Internet and
TCP/IP Tools and Utilities", RFC 2151,
June 1997.
[NetTools] Stine, R., "FYI on a Network
Management Tool Catalog:
Tools for Monitoring and Debugging
TCP/IP Internets
and Interconnected Devices", RFC 1147,
April 1990.
[IPPM-FW] Paxson, V., Almes, G., Mahdavi, J.,
and Mathis, M.,
"Framework for IP Performance
Metrics", RFC 2330, May
1998.
[IPPM-Con] Mahdavi, J., Paxson, V., "IPPM Metrics
for Measuring
Connectivity", RFC 2678, September
1999.
[IPPM-1DM] Almes, G., Kalidindi, S., Zekauskas,
M., "A One-way
Delay Metric for IPPM", RFC 2679,
September 1999.
[IPPM-1LM] Almes, G., Kalidindi, S., Zekauskas,
M., "A One-way
Packet Loss Metric for IPPM", RFC
2680, September
1999.
[IPPM-2DM] Almes, G., Kalidindi, S., Zekauskas,
M., "A Round-trip
Delay Metric for IPPM", RFC 2681,
September 1999.
[OWAMP] Shalunov, S., Teitelbaum, B., Karp,
A., Boote, J., and
Zekauskas, M., "A One-way Active
Measurement Protocol
(OWAMP)", RFC 4656, September 2006.
[TWAMP] Hedayat, K., Krzanowski, R., Morton,
A., Yum, K., and
Babiarz, J., "A Two-Way Active
Measurement Protocol
(TWAMP)", RFC 5357, October 2008.
[BFD] Katz, D., Ward, D., "Bidirectional
Forwarding Detection
(BFD)", RFC 5880, June 2010.
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[BFD-IP] Katz, D., Ward, D., "Bidirectional
Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)",
RFC 5881, June
2010.
[BFD-Gen] Katz, D., Ward, D., "Generic
Application of
Bidirectional Forwarding Detection
(BFD)", RFC 5882,
June 2010.
[BFD-Multi] Katz, D., Ward, D., "Bidirectional
Forwarding Detection
(BFD) for Multihop Paths", RFC 5883,
June 2010.
[BFD-LSP] Aggarwal, R., Kompella, K., Nadeau,
T., and Swallow,
G., "Bidirectional Forwarding
Detection (BFD) for MPLS
Label Switched Paths (LSPs)", RFC
5884, June 2010.
[BFD-VCCV] Nadeau, T., Pignataro, C.,
"Bidirectional Forwarding
Detection (BFD) for the Pseudowire
Virtual Circuit
Connectivity Verification (VCCV)", RFC
5885, June
2010.
[TP-OAM-FW] Busi, I., Allan, D., "Operations,
Administration and
Maintenance Framework for MPLS-based
Transport
Networks ", RFC 6371, September 2011.
[TP-CC-CV] Allan, D., Swallow, G., Drake, J.,
"Proactive
Connectivity Verification, Continuity
Check and Remote
Defect indication for MPLS Transport
Profile", RFC
6428, November 2011.
[OnDemand-CV] Gray, E., Bahadur, N., Boutros, S.,
Aggarwal, R. "MPLS
On-Demand Connectivity Verification
and Route
Tracing", RFC 6426, November 2011.
[MPLS-LM-DM] Frost, D., Bryant, S., "Packet Loss
and Delay
Measurement for MPLS Networks", RFC
6374, September
2011.
[TP-LM-DM] Frost, D., Bryant, S., "A Packet Loss
and Delay
Measurement Profile for MPLS-Based
Transport
Networks", RFC 6375, September 2011.
[TP-Fault] Swallow, G., Fulignoli, A., Vigoureux,
M., Boutros, S.,
"MPLS Fault Management Operations,
Administration, and
Maintenance (OAM)", RFC 6427, November
2011.
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[Lock-Loop] Boutros, S., Sivabalan, S., Aggarwal,
R., Vigoureux,
M., Dai, X., "MPLS Transport Profile
Lock Instruct and
Loopback Functions", RFC 6435,
November 2011.
[ITU-T-CT] Betts, M., "Allocation of a Generic
Associated Channel
Type for ITU-T MPLS Transport Profile
Operation,
Maintenance, and Administration
(MPLS-TP OAM)", RFC
6671, November 2012.
[PW-Map] M. Aissaoui, P. Busschbach, L.
Martini, M. Morrow, T.
Nadeau, "Pseudowire (PW) Operations,
Administration,
and Maintenance (OAM) Message
Mapping", RFC 6310, July
2011.
[PW-G-ACh] Li, H., Martini, L., He, J., Huang,
F., "Using the
Generic Associated Channel Label for
Pseudowire in the
MPLS Transport Profile (MPLS-TP)", RFC
6423, November
2011.
7.2. Informative References
[OAM-Def] Andersson, L., Van Helvoort, H.,
Bonica, R., Romascanu,
D., Mansfield, S., "Guidelines for the
use of the OAM
acronym in the IETF ", RFC 6291, June
2011.
[OAM-Analys] Sprecher, N., Fang, L., "An Overview
of the OAM Tool
Set for MPLS based Transport
Networks", RFC 6669,
July 2012.
[TP-Term] Van Helvoort, H., Andersson, L.,
Sprecher, N., "A
Thesaurus for the Terminology used in
Multiprotocol
Label Switching Transport Profile
(MPLS-TP)
drafts/RFCs and ITU-T's Transport
Network
Recommendations", work-in-progress,
draft-ietf-mpls-
tp-rosetta-stone, July 2012.
[IEEE802.1ag] IEEE 802.1Q, "IEEE Standard for Local
and metropolitan
area networks - Media Access Control
(MAC) Bridges and
Virtual Bridged Local Area Networks",
October 2012.
[ITU-T-Y1731] ITU-T Recommendation G.8013/Y.1731,
"OAM Functions and
Mechanisms for Ethernet-based
Networks", July 2011.
[ITU-T-Y1711] ITU-T Recommendation Y.1711,
"Operation & Maintenance
mechanism for MPLS networks", February
2004.
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[IEEE802.3ah] IEEE 802.3, "IEEE Standard for
Information technology -
Local and metropolitan area networks -
Carrier sense
multiple access with collision
detection (CSMA/CD)
access method and physical layer
specifications",
clause 57, December 2008.
[ITU-T-G.806] ITU-T Recommendation G.806,
"Characteristics of
transport equipment - Description
methodology and
generic functionality", January 2009.
[ITU-G8113.2] ITU-T Recommendation
G.8113.2/Y.1372.2, "Operations,
administration and maintenance
mechanisms for MPLS-TP
networks using the tools defined for
MPLS", November
2012.
[ITU-G8113.1] ITU-T Recommendation
G.8113.1/Y.1372.1, "Operations,
Administration and Maintenance
mechanism for MPLS-TP
in Packet Transport Network (PTN)",
November 2012.
Authors' Addresses
Tal Mizrahi
Marvell
6 Hamada St.
Yokneam, 20692
Israel
Nurit Sprecher
Nokia Siemens Networks
3 Hanagar St. Neve Ne'eman B
Hod Hasharon, 45241
Israel
Elisa Bellagamba
Ericsson
6 Farogatan St.
Stockholm, 164 40
Sweden
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Phone: +46 761440785
Yaacov Weingarten
34 Hagefen St.
Karnei Shomron, 4485500
Israel