Internet DRAFT - draft-allan-nadeau-mpls-oam-frmwk
draft-allan-nadeau-mpls-oam-frmwk
Internet Draft David Allan, Editor
Thomas D. Nadeau, Editor
Document: draft-allan-nadeau-mpls-oam-frmwk-00.txt
Category: Informational
Expires: March 2005 September 2004
A Framework for MPLS Operations
and Management (OAM)
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright(C) The Internet Society (2001). All Rights Reserved.
Abstract
This document is a framework for how data plane OAM functions can be
applied to operations and maintenance procedures. The document is
structured to outline how OAM functionality can be used to assist in
fault management, configuration, accounting, performance management
and security, commonly known by the acronym FCAPS.
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Table of Contents
1. Introduction and Scope ........................................2
2. Terminology....................................................2
3. Fault Management...............................................2
3.1 Fault detection...............................................2
3.1.1 Enumeration and detection of types of data plane faults.....3
3.1.2 Timeliness..................................................5
3.2 Diagnosis.....................................................5
3.2.1 Characterization............................................5
3.2.2 Isolation...................................................5
3.3 Availability..................................................5
4. Configuration Management.......................................5
5. Administration.................................................6
6. Performance measurement........................................6
7. Security.......................................................6
8. Full Copyright Statement.......................................7
9. Intellectual Property Rights Notices...........................7
10. References.....................................................7
11. Editors Address................................................8
1. Introduction and Scope
This memo outlines in broader terms how data plane OAM functionality
can assist in meeting the operations and management (OAM)
requirements outlined in [REQ] and can apply to the operational
functions of fault, configuration, accounting, performance and
security (commonly known as FCAPS). The approach of the document is
to outline the requisite functionality, the potential mechanisms to
provide the function and the applicability of data plane OAM
functions.
2. Terminology
OAM Operations and Management
FCAPS Fault, Administration, Configuration,
Provisioning, and Security
ILM Incoming Label Map
NHLFE Next Hop Label Forwarding Entry
MIB Management Information Base
LSR Label Switching Router
RTT Round Trip Time
3. Fault Management
3.1 Fault detection
Fault detection encompasses identifying all causes of failure to
transfer information between the ingress and egress of an LSP
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ingress. This section will enumerate common failure scenarios and
explain how one might (or might not) detect the situation.
3.1.1 Enumeration and detection of types of data plane faults
Physical layer faults:
Lower layer faults are those that impact the physical layer or
link layer that transports MPLS between adjacent LSRs. Some
physical links (such as SONET/SDH) may have link layer OAM
functionality and detect and notify the LSR of link layer
faults directly. Some physical links (such as Ethernet) may not
have this capability and require MPLS or IP layer heartbeats to
detect failures. However, once detected, reaction to these
fault notifications is often the same as those described in the
first case.
Node failures:
Node failures are those that impact the forwarding capability
of an entire node, including its entire set of links. This can
be due to component failure, power outage, or reset of control
processor in an LSR employing a distributed architecture, etc.
MPLS LSP misbranching:
Misbranching occurs when there is a loss of synchronization
between the data and the control planes. This can occur due to
hardware failure, software failure or configuration problems.
It will manifest itself in one of two forms:
- packets belonging to a particular LSP are cross connected
into a an NHLFE for which there is no corresponding ILM at
the next downstream LSR. This can occur in cases where the
NHLFE entry is corrupted. Therefore the packet arrives at
the next LSR with a top label value for which the LSR has no
corresponding forwarding information, and is typically
dropped. This is a No Incoming Label Map (ILM) condition and
can be detected directly by the downstream LSR which
receives the incorrectly labeled packet.
- packets belonging to a particular LSP are cross connected
into an incorrect NHLFE entry for which there is a
corresponding ILM at the next downstream LSR, but which was
is associated with a different LSP. This may be detected by
a number of means:
o some or all of the misdirected traffic is not routable
at the egress node.
o Or OAM probing is able to detect the fault by detecting
the inconsistency between the path and the control
plane.
Discontinuities in the MPLS Encapsulation
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The forwarding path of the FEC carried by an LSP may transit
nodes for which MPLS is not configured. This may result in a
number of behaviors (most undesirable). When there was only one
label in the stack and the payload was IP, IP forwarding will
direct the packet to the correct interface. This would be the
same if PHP is employed. Packets with a label stack will be
discarded (Tom: can you confirm this for your end).
MTU problems
MTU problems occur when client traffic cannot be fragmented by
intermediate LSRs, and is dropped somewhere along the path of
the LSP. MTU problems should appear as a discrepancy in the
traffic count between the set of ingresses and the egresses for
a FEC and will appear in the corresponding MIB performance
tables in the transit LSRs as discarded packets.
TTL Mishandling
Some Penultimate hop LSRs may consistently process TTL expiry
and propagation at penultimate hop LSRs. In these cases, it is
possible for tools that rely on consistent processing to fail.
Congestion
Congestion occurs when the offered load on any interface
exceeds the link capacity for sufficient time that the
interface buffering is exhausted. Congestion problems will
appear as a discrepancy in the traffic count between the set of
ingresses and the egresses for a FEC and will appear in the MIB
performance tables in the transit LSRs as discarded packets.
Misordering
Misordering of LSP traffic occurs when incorrect or
inappropriate load sharing is implemented within an MPLS
network. Load sharing typically takes place when equal cost
paths exist between the ingress and egress of an LSP. In these
cases, traffic is split among these equal cost paths using a
variety of algorithms. One such algorithm relies on splitting
traffic between each path on a per-packet basis. When this is
done, it is possible for some packets along the path to be
delayed due to congestion or slower links, which may result in
packets being received out of order at the egress. Detection
and remedy of this situation may be left up to client
applications that use the LSPs. For instance, TCP is capable of
re-ordering packets belonging to a specific flow. Detection of
mis-ordering can also be determined by sending probe traffic
along the path and verifying that all probe traffic is indeed
received in the order it was transmitted.
LSRs do not normally implement mechanisms to detect misordering
of flows.
Payload Corruption
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Payload corruption may occur and be undetectable by LSRs. Such
errors are typically detected by client payload integrity
mechanisms.
3.1.2 Timeliness
(for a future version)
3.2 Diagnosis
3.2.1 Characterization
Characterization is defined as determining the forwarding path of a
packet (which may not be necessarily known). Characterization may be
performed on a working path through the network. This is done for
example, to determine ECMP paths, the MTU of a path, or simply to
know the path occupied by a specific FEC. Characterization will be
able to leverage mechanisms used for isolation.
3.2.2 Isolation
Isolation of a fault can occur in two forms. In the first case, the
local failure is detected, and the node where the failure occurred
is capable of issuing an alarm for such an event. The node should
attempt to withdraw the defective resources and/or rectify the
situation prior to raising an alarm. Active data plane OAM
mechanisms may also detect the failure conditions remotely and issue
their own alarms if the situation is not rectified quickly enough.
In the second case, the fault has not been detected locally. In this
case, the local node cannot raise an alarm, nor can it be expected
to rectify the situation. In this case, the failure may be detected
remotely via data plane OAM. This mechanism should also be able to
determine the location of the fault, perhaps on the basis of limited
information such as a customer complaint. This mechanism may also be
able to automatically remove the defective resources from and the
network and restore service, but should at least provide a network
operator with enough information by which they can perform this
operation. Given that detection of faults is desired to happen as
quickly as possible, tools which posses the ability to incrementally
test LSP health should be used to uncover faults.
3.3 Availability
Availability is the measure of the percentage of time that a service
is operating within specification.
MPLS has several forwarding modes (depending on the control plane
used). As such more than one availability models may be defined.
4. Configuration Management
Data plane OAM can assist in configuration management by providing
the ability to verify configuration of an LSP or of applications
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that may utilize that LSP. This would be an ad-hoc data plane probe
that should both verify path integrity (a complete path exists) as
well as verifying that the path function is synchronized with the
control plane. The probe would carry as part of the payload relevant
control plane information that the receiver would be able to compare
with the local control plane configuration.
5. Accounting
Ed Note: (for a future version)
6. Performance measurement
Performance measurement permits the information transfer
characteristics of LSPs to be measured. This falls into two
categories, latency and information loss.
Latency can be measured in two ways: one is to have precisely
synchronized clocks at the ingress and egress such that timestamps
in PDUs flowing from the ingress to the egress can be compared. The
other is to use an exchange of PING type PDUs that gives a round
trip time (RTT) measurement, and an estimate of the one way latency
can be inferred with some loss of precision. Use of load spreading
techniques such as ECMP mean that any individual RTT measurement is
only representative of the typical RTT for a FEC.
To measure information loss, a common practice is to periodically
read ingress and egress counters (i.e.: MIB module counters). This
information may also be used for offline correlation. Another common
practice is to send explicit probe traffic. This probe traffic can
also be used to measure jitter and delay.
7. Security
Support for intra-provider data plane OAM messaging does not
introduce any new security concerns to the MPLS architecture.
Though it does actually address some that already exist, i.e.
through rigorous defect handling operator's can offer their
customers a greater degree of integrity protection that their
traffic will not be misdelivered (for example by being able to
detect leaking LSP traffic from a VPN).
Support for inter-provider data plane OAM messaging introduces a
number of security concerns as by definition, portions of LSPs will
not be in trusted space, the provider has no control over who may
inject traffic into the LSP. This creates opportunity for malicious
or poorly behaved users to disrupt network operations. Attempts to
introduce filtering on target LSP OAM flows may be problematic if
flows are not visible to intermediate LSRs. However it may be
possible to interdict flows on the return path between providers (as
faithfulness to the forwarding path is not a return path
requirement) to mitigate aspects of this vulnerability.
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OAM tools may permit unauthorized or malicious users to extract
significant amounts of information about network configuration. This
would be especially true of IP based tools as in many network
configurations, MPLS does not typically extend to untrusted hosts,
but IP does. For example, TTL hiding at ingress and egress LSRs will
prevent external users from using TTL-based mechanisms to probe an
operator's network. This suggests that tools used for problem
diagnosis or which by design are capable of extracting significant
amounts of information will require authentication and authorization
of the originator. This may impact the scalability of such tools
when employed for monitoring instead of diagnosis.
8. Full Copyright Statement
Copyright (C) The Internet Society (year). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
9. Intellectual Property Rights Notices.
By submitting this Internet-Draft, the authors certify that any
applicable patent or other IPR claims of which they are aware have
been disclosed, or will be disclosed, and any of which they become
aware will be disclosed, in accordance with RFC 3668.
10. References
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon,
"Multiprotocol Label Switching Architecture", RFC
3031, January 2001.
[ALLAN] Allan, D., "Guidelines for MPLS Load Balancing", draft-
allan-mpls-loadbal-05.txt, IETF work in progress, October 2003
[MPLSREQS] Nadeau et.al., "OAM Requirements for MPLS Networks",
draft-ietf-mpls-oam-requirements-01.txt, June 2003
[Y1710] ITU-T Recommendation Y.1710(2002), "Requirements for OAM
Functionality for MPLS Networks"
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11. Editors Address
David Allan
Nortel Networks Phone: +1-613-763-6362
3500 Carling Ave. Email: dallan@nortelnetworks.com
Ottawa, Ontario, CANADA
Thomas D. Nadeau
Cisco Systems Phone: +1-978-936-1470
300 Beaver Brook Drive Email: tnadeau@cisco.com
Boxborough, MA 01824
