Internet DRAFT - draft-salam-l2vpn-evpn-oam-req-frmwk
draft-salam-l2vpn-evpn-oam-req-frmwk
INTERNET-DRAFT Samer Salam
Intended Status: Informational Ali Sajassi
Cisco
Sam Aldrin
Huawei
John E. Drake
Juniper Networks
Expires: July 27, 2014 January 23, 2014
E-VPN Operations, Administration and Maintenance
Requirements and Framework
draft-salam-l2vpn-evpn-oam-req-frmwk-02
Abstract
This document specifies the requirements and reference framework for
Ethernet VPN (E-VPN) Operations, Administration and Maintenance
(OAM). The requirements cover the OAM aspects of E-VPN, PBB-EVPN and
TRILL-EVPN. The framework defines the layered OAM model encompassing
the E-VPN service layer, network layer and underlying Packet Switched
Network (PSN) transport layer.
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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Copyright and License Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Relationship to Other OAM Work . . . . . . . . . . . . . . . 4
1.2 Specification of Requirements . . . . . . . . . . . . . . . 5
1.3 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
2 E-VPN OAM Framework . . . . . . . . . . . . . . . . . . . . . . 5
2.1 OAM Layering . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 E-VPN Service OAM . . . . . . . . . . . . . . . . . . . . . 7
2.3 E-VPN Network OAM . . . . . . . . . . . . . . . . . . . . . 7
2.4 Transport OAM for E-VPN . . . . . . . . . . . . . . . . . . 9
2.5 Link OAM . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.6 OAM Inter-working . . . . . . . . . . . . . . . . . . . . . 9
3 E-VPN OAM Requirements . . . . . . . . . . . . . . . . . . . . . 10
3.1 Fault Management Requirements . . . . . . . . . . . . . . . 10
3.1.1 Proactive Fault Management Functions . . . . . . . . . . 10
3.1.1.1 Fault Detection (Continuity Check) . . . . . . . . . 10
3.1.1.2 Defect Indication . . . . . . . . . . . . . . . . . 11
3.1.2 On-Demand Fault Management Functions . . . . . . . . . . 12
3.1.2.1 Connectivity Verification . . . . . . . . . . . . . 12
3.1.2.2 Fault Isolation . . . . . . . . . . . . . . . . . . 13
3.2 Performance Management . . . . . . . . . . . . . . . . . . . 13
3.2.1 Packet Loss . . . . . . . . . . . . . . . . . . . . . . 13
3.2.2 Packet Delay . . . . . . . . . . . . . . . . . . . . . . 14
4. Security Considerations . . . . . . . . . . . . . . . . . . . 14
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1 Normative References . . . . . . . . . . . . . . . . . . . 14
7.2 Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1 Introduction
This document specifies the requirements and defines a reference
framework for Ethernet VPN (E-VPN) Operations, Administration and
Maintenance (OAM, [RFC6291]). In this context, we use the term E-VPN
OAM to loosely refer to the OAM functions required for and/or
applicable to [E-VPN], [PBB-EVPN] as well as [TRILL-EVPN].
E-VPN introduces an L2VPN solution for multipoint Ethernet services,
with advanced multi-homing capabilities, using BGP for distributing
customer/client MAC address reach-ability information over the core
MPLS/IP network.
PBB-EVPN combines Provider Backbone Bridging (PBB) [802.1ah] with E-
VPN in order to reduce the number of BGP MAC advertisement routes,
provide client MAC address mobility using C-MAC aggregation and B-MAC
sub-netting, confine the scope of C-MAC learning to only active
flows, offer per site policies and avoid C-MAC address flushing on
topology changes.
TRILL-EVPN provides a solution for interconnecting TRILL [TRILL]
networks over an MPLS/IP network using E-VPN, with two key
characteristics: C-MAC address transparency on the hand-off point and
control-plane isolation among the interconnected TRILL networks.
This document focuses on the fault management and performance
management aspects of E-VPN OAM.
1.1 Relationship to Other OAM Work
This document leverages concepts and draws upon elements defined
and/or used in the following documents:
[RFC6136] specifies the requirements and a reference model for OAM as
it relates to L2VPN services, pseudowires and associated Packet
Switched Network tunnels. This document focuses on VPLS and VPWS
solutions and services.
[RFC4379] defines mechanisms for detecting data plane failures in
MPLS LSPs, including procedures to check the correct operation of the
data plane, as well as mechanisms to verify the data plane against
the control plane.
[802.1Q] specifies the Ethernet Connectivity Fault Management (CFM)
protocol, which defines the concepts of Maintenance Domains,
Maintenance Associations, Maintenance End Points, and Maintenance
Intermediate Points.
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[Y.1731] extends Connectivity Fault Management in the following
areas: it defines fault notification and alarm suppression functions
for Ethernet. It also specifies mechanisms for Ethernet performance
management, including loss, delay, jitter, and throughput
measurement.
1.2 Specification of Requirements
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].
1.3 Terminology
This document uses the following terminology defined in [RFC6136]:
MA Maintenance Association is a set of MEPs belonging to the
same Maintenance Domain, established to verify the
integrity of a single service instance.
MEP Maintenance End Point is responsible for origination and
termination of OAM frames for a given MA.
MIP Maintenance Intermediate Point is located between peer
MEPs and can process and respond to certain OAM frames
but does not initiate them.
MD Maintenance Domain, an OAM Domain that represents a
region over which OAM frames can operate unobstructed.
2 E-VPN OAM Framework
2.1 OAM Layering
Multiple layers come into play for implementing an L2VPN service
using the E-VPN family of solutions:
- The Service Layer runs end to end between the sites, or Ethernet
Segments, that are being interconnected by the E-VPN solution. It can
be either Ethernet (as in [E-VPN], [PBB-EVPN] and [SPB-EVPN]) or
TRILL (as in [TRILL-EVPN]).
- The Network Layer extends in between the E-VPN PE nodes and is
mostly transparent to the core nodes (except where Flow Entropy comes
into play). It leverages MPLS for service (i.e. EVI) multiplexing and
Split-Horizon functions.
- The Transport Layer is dictated by the networking technology of the
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PSN. It may be either based on MPLS LSPs or IP.
- The Link Layer is dependent upon the physical technology used.
Ethernet is a popular choice for this layer, but other alternatives
are deployed (e.g. POS, DWDM etc...).
This layering extends to the set of OAM protocols that are involved
in the ongoing maintenance and diagnostics of E-VPN networks. The
figure below depicts the OAM layering, and shows which devices have
visibility into what OAM layer(s).
+---+ +---+
+--+ | | +---+ +---+ +---+ | | +--+
|CE|----|PE1|----| P |----| P |----| P |----|PE2|----|CE|
+--+ | | +---+ +---+ +---+ | | +--+
+---+ +---+
o--------o--------- Service OAM -------------o--------o
o----------- Network OAM -----------o
o-------o--------o---------o-------o Transport OAM
o-----o o-----o o-----o o-----o o-----o o-----o Link OAM
Figure 1: E-VPN OAM Layering
Figure 2 below shows an example network where native Ethernet domains
are interconnected via E-VPN, and the OAM mechanisms applicable at
each layer. The details of the layers are described in the sections
that follow.
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+---+ +---+
+--+ | | +---+ +---+ +---+ | | +--+
|CE|----|PE1|----| P |----| P |----| P |----|PE2|----|CE|
+--+ | | +---+ +---+ +---+ | | +--+
+---+ +---+
o--------o--------- Ethernet CFM ------------o--------o
o-------- E-VPN Network OAM --------o
o-------o--------o---------o-------o MPLS OAM
o-----o o-----o o-----o o-----o o-----o o-----o 802.3 OAM
Figure 2: E-VPN OAM Example
2.2 E-VPN Service OAM
The E-VPN Service OAM protocol depends on what service layer
technology is being interconnected by the E-VPN solution. In case of
[E-VPN] and [PBB-EVPN], the service layer is Ethernet; hence, the
corresponding service OAM protocol is Ethernet Connectivity Fault
Management (CFM) [802.1Q]. Whereas, in the case of [TRILL-EVPN], the
service layer is TRILL and the associated service OAM protocol is
TRILL OAM [TRILL-OAM].
E-VPN service OAM is visible to the CEs and E-VPN PEs, but not to the
core (P) nodes. This is because the PEs operate at the Ethernet MAC
layer in [E-VPN][PBB-EVPN], or the TRILL RBridge layer in [TRILL-
EVPN], whereas the P nodes do not.
The E-VPN PE MUST support MIP functions in the applicable service OAM
protocol (Ethernet CFM or TRILL OAM).
The E-VPN PE SHOULD support MEP functions in the applicable service
OAM protocol. This includes both Up and Down MEP functions.
2.3 E-VPN Network OAM
E-VPN Network OAM is visible to the PE nodes only. This OAM layer is
analogous to VCCV [RFC5085] in the case of VPLS/VPWS. It provides
mechanisms to check the correct operation of the data plane, as well
as a mechanism to verify the data plane against the control plane.
This includes the ability to perform fault detection and diagnostics
on:
- the MP2P tunnels used for the transport of unicast traffic between
PEs. E-VPN allows for three different models of unicast label
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assignment: label per EVI, label per <ESI, Ethernet Tag> and label
per MAC address. In all three models, the label is bound to an E-VPN
Unicast FEC.
E-VPN Network OAM MUST provide mechanisms to check the operation of
the data plane and verify that operation against the control plane
view for the E-VPN Unicast FEC.
- the MP2P tunnels used for aliasing unicast traffic destined to a
multi-homed Ethernet Segment. The three label assignment models,
discussed above, apply here as well. In all three models, the label
is bound to an E-VPN Aliasing FEC. E-VPN Network OAM MUST provide
mechanisms to check the operation of the data plane and verify that
operation against the control plane view for the E-VPN Aliasing FEC.
- the multicast tunnels (either MP2P or P2MP) used for the transport
of broadcast, unknown unicast and multicast traffic between PEs. In
the case of ingress replication, a label is allocated per EVI or per
<EVI, Ethernet Tag> and is bound to an E-VPN Multicast FEC. In the
case of LSM, and more specifically aggregate inclusive trees, again a
label may be allocated per EVI or per <EVI, Ethernet Tag> and is
bound to an E-VPN Multicast FEC.
E-VPN Network OAM MUST provide mechanisms to check the operation of
the data plane and verify that operation against the control plane
view for the E-VPN Multicast FEC.
- the correct operation of the ESI split-horizon filtering function.
In E-VPN, a label is allocated per multi-homed Ethernet Segment for
the purpose of performing the access split-horizon enforcement. The
label is bound to an E-VPN Ethernet Segment FEC.
E-VPN Network OAM MUST provide mechanisms to check the operation of
the data plane and verify that operation against the control plane
view for the E-VPN Ethernet Segment FEC.
- the correct operation of the DF filtering function.
E-VPN Network OAM MUST provide provide mechanisms to check the
operation of the data plane and verify that operation against the
control plane view for the DF filtering function.
E-VPN network OAM mechanisms MUST provide in-band management
capabilities. As such, OAM messages MUST be encoded so that they
exhibit identical entropy characteristics to data traffic.
E-VPN network OAM SHOULD provide both proactive and on-demand
mechanisms of monitoring the data plane operation and data plane
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conformance to the state of the control plane.
2.4 Transport OAM for E-VPN
The transport OAM protocol depends on the nature of the underlying
transport technology in the PSN. MPLS OAM mechanisms
[RFC4379][RFC6425] as well as ICMP [RFC792] are applicable, depending
on whether the PSN employs MPLS or IP transport, respectively.
Furthermore, BFD mechanisms per [RFC5880], [RFC5881], [RFC5883] and
[RFC5884] apply. Also, the BFD mechanisms pertaining to MPLS-TP LSPs
per [RFC6428] are applicable.
2.5 Link OAM
Link OAM depends on the data link technology being used between the
PE and P nodes. For e.g., if Ethernet links are employed, then
Ethernet Link OAM [802.3] Clause 57 may be used.
2.6 OAM Inter-working
When inter-working two networking domains, such as native Ethernet
and E-VPN to provide an end-to-end emulated service, there is a need
to identify the failure domain and location, even when a PE supports
both the Service OAM mechanisms and the E-VPN Network OAM mechanisms.
In addition, scalability constraints may not allow running proactive
monitoring, such as Ethernet Continuity Check Messages (CCMs), at a
PE to detect the failure of an EVI across the E-VPN domain. Thus, the
mapping of alarms generated upon failure detection in one domain
(e.g. native Ethernet or E-VPN network domain) to the other domain is
needed. There are also cases where a PE may not be able to process
Service OAM messages received from a remote PE over the PSN even when
such messages are defined, as in the Ethernet case, thereby
necessitating support for fault notification message mapping between
the E-VPN Network domain and the Service domain.
OAM inter-working is not limited though to scenarios involving
disparate network domains. It is possible to perform OAM inter-
working across different layers in the same network domain. In
general, alarms generated within an OAM layer, as a result of
proactive fault detection mechanisms, may be injected into its client
layer OAM mechanisms. This allows the client layer OAM to trigger
event-driven (i.e. asynchronous) fault notifications. For example,
alarms generated by the Link OAM mechanisms may be injected into the
Transport OAM layer, and alarms generated by the Transport OAM
mechanism may be injected into the Network OAM mechanism, and so on.
E-VPN OAM MUST support inter-working between the Network OAM and
Service OAM mechanisms. E-VPN OAM MAY support inter-working among
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other OAM layers.
3 E-VPN OAM Requirements
This section discusses the E-VPN OAM requirements pertaining to Fault
Management and Performance Management.
3.1 Fault Management Requirements
3.1.1 Proactive Fault Management Functions
Proactive fault management functions are configured by the network
operator to run periodically without a time bound. Certain actions,
e.g. protection switchover or alarm indication signaling, can be
associated with specific events, such as entering or clearing fault
states.
3.1.1.1 Fault Detection (Continuity Check)
Proactive fault detection is performed by periodically monitoring the
reachability between service endpoints, i.e. MEPs in a given MA,
through the exchange of Continuity Check messages. The reachability
between any two arbitrary MEPs may be monitored for:
- in-band per-flow monitoring. This enables per flow monitoring
between MEPs. E-VPN Network OAM MUST support fault detection with per
user flow granularity. E-VPN Service OAM MAY support fault detection
with per user flow granularity.
- a representative path. This enables liveness check of the nodes
hosting the MEPs assuming that the loss of continuity to the MEP is
interpreted as a failure of the hosting node. This, however, does not
conclusively indicate liveness of the path(s) taken by user data
traffic. This enables node failure detection but not path failure
detection, through the use of a test flow. E-VPN Network OAM and
Service OAM MUST support fault detection using test flows.
- all paths. For MPLS/IP networks with ECMP, monitoring of all
unicast paths between MEPs (on non-adjacent nodes) may not be
possible, since the per-hop ECMP hashing behavior may yield
situations where it is impossible for a MEP to pick flow entropy
characteristics that result in exercising the exhaustive set of ECMP
paths. Monitoring of all ECMP paths between MEPs (on non-adjacent
nodes) is not a requirement for E-VPN OAM.
The fact that MPLS/IP networks do not enforce congruency between
unicast and multicast paths means that the proactive fault detection
mechanisms for E-VPN network OAM MUST provide procedures to monitor
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the unicast paths independently of the multicast paths. This applies
to E-VPN Service OAM and Network OAM.
3.1.1.2 Defect Indication
E-VPN Service OAM MUST support event-driven defect indication upon
the detection of a connectivity defect. Defect indications can be
categorized into two types: forward and reverse defect indications.
3.1.1.2.1 Forward Defect Indication
This is used to signal a failure that is detected by a lower layer
OAM mechanism. Forward Defect indication is transmitted by a server
MEP (i.e. an actual or virtual MEP) in a direction that is away from
the direction of the failure (refer to Figure 2 below).
Failure
|
+-----+ +-----+ V +-----+ +-----+
| A |------| B |--XXX--| C |------| D |
+-----+ +-----+ +-----+ +-----+
<===========| |============>
Forward Forward
Defect Defect
Indication Indication
Figure 3: Forward Defect Indication
Forward defect indication may be used for alarm suppression and/or
for purpose of inter-working with other layer OAM protocols. Alarm
suppression is useful when a transport/network level fault translates
to multiple service or flow level faults. In such a scenario, it is
enough to alert a network management station (NMS) of the single
transport/network level fault in lieu of flooding that NMS with a
multitude of Service or Flow granularity alarms. E-VPN PEs SHOULD
support Forward Defect Indication in the Service OAM mechanisms.
3.1.1.2.2 Reverse Defect Indication (RDI)
RDI is used to signal that the advertising MEP has detected a loss of
continuity (LoC) defect. RDI is transmitted in the direction of the
failure (refer to Figure 3).
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Failure
|
+-----+ +-----+ V +-----+ +-----+
| A |------| B |--XXX--| C |------| D |
+-----+ +-----+ +-----+ +-----+
|===========> <============|
Reverse Reverse
Defect Defect
Indication Indication
Figure 3: Reverse Defect Indication
RDI allows single-sided management, where the network operator can
examine the state of a single MEP and deduce the overall health of a
monitored service. E-VPN PEs SHOULD support Reverse Defect Indication
in the Service OAM mechanisms. This includes both the ability to
signal LoC defect to a remote MEP, as well as the ability to
recognize RDI from a remote MEP. It is worth noting that, in a
multipoint MA, RDI is not a useful indicator of unidirectional fault.
This is because RDI carries no indication of the affected MEP(s) with
which the sender had detected a LoC defect.
3.1.2 On-Demand Fault Management Functions
On-demand fault management functions are initiated manually by the
network operator and continue for a time bound period. These
functions enable the operator to run diagnostics to investigate a
defect condition.
3.1.2.1 Connectivity Verification
E-VPN Network OAM MUST support on-demand connectivity verification
mechanisms for unicast and multicast destinations. The connectivity
verification mechanisms SHOULD provide a means for specifying and
carrying in the messages:
- variable length payload/padding to test MTU related connectivity
problems.
- test frame formats as defined in Appendix C of [RFC2544] to detect
potential packet corruption.
E-VPN Network OAM MUST support connectivity verification at per flow
granularity. This includes both user flows (to test a specific path
between PEs) as well as test flows (to rest a representative path
between PEs).
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E-VPN Service OAM MUST support connectivity verification on test
flows and MAY support connectivity verification on user flows.
For multicast connectivity verification, E-VPN Network OAM MUST
support reporting on:
- the DF filtering status of specific port(s) or all the ports in a
given bridge-domain.
- the Split Horizon filtering status of specific port(s) or all the
ports in a given bridge-domain.
3.1.2.2 Fault Isolation
E-VPN OAM MUST support an on-demand fault localization function. This
involves the capability to narrow down the locality of a fault to a
particular port, link or node. The characteristic of forward/reverse
path asymmetry, in MPLS/IP, renders fault isolation into a direction-
sensitive operation. That is, given two PEs A and B, localization of
continuity failures between them requires running fault isolation
procedures from PE A to PE B as well as from PE B to PE A.
E-VPN Service OAM mechanisms only have visibility to the PEs but not
the MPLS/IP P nodes. As such, they can be used to deduce whether the
fault is in the customer's own network, the local CE-PE segment or
remote CE-PE segment(s). E-VPN Network and Transport OAM mechanisms
can be used for fault isolation between the PEs and P nodes.
3.2 Performance Management
Performance Management functions can be performed both proactively
and on-demand. Proactive management involves a recurring function,
where the performance management probes are run continuously without
a trigger. We cover both proactive and on-demand functions in this
section.
3.2.1 Packet Loss
E-VPN Network OAM SHOULD provide mechanisms for measuring packet loss
for a given service.
Given that E-VPN provides inherent support for multipoint-to-
multipoint connectivity, then packet loss cannot be accurately
measured by means of counting user data packets. This is because user
packets can be delivered to more PEs or more ports than are necessary
(e.g. due to broadcast, un-pruned multicast or unknown unicast
flooding). As such, a statistical means of approximating packet loss
rate is required. This can be achieved by sending "synthetic" OAM
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packets that are counted only by those ports (MEPs) that are required
to receive them. This provides a statistical approximation of the
number of data frames lost, even with multipoint-to-multipoint
connectivity.
3.2.2 Packet Delay
E-VPN Service OAM SHOULD support measurement of one-way and two-way
packet delay and delay variation (jitter) across the E-VPN network.
Measurement of one-way delay requires clock synchronization between
the probe source and target devices. Mechanisms for clock
synchronization are outside the scope of this document. Note that
Service OAM performance management mechanisms defined in [Y.1731] and
[TRILL-LOSS-DELAY] can be used.
E-VPN Network OAM MAY support measurement of one-way and two-way
packet delay and delay variation (jitter) across the E-VPN network.
4. Security Considerations
E-VPN OAM must provide mechanisms for:
- Preventing denial of service attacks caused by exploitation of the
OAM message channel.
- Optionally authenticate communicating endpoints (MEPs and MIPs)
- Preventing OAM packets from leaking outside of the E-VPN network or
outside their corresponding Maintenance Domain. This can be done by
having MEPs implement a filtering function based on the Maintenance
Level associated with received OAM packets.
5. Acknowledgements
The authors would like to thank Gregory Mirsky for his thorough
review of this work and invaluable comments.
6. IANA Considerations
None.
7. References
7.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC6291] Andersson et al., BCP 161 "Guidelines for the Use of the
"OAM" Acronym in the IETF", June 2011.
[E-VPN] Sajassi et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
l2vpn-evpn-01.txt, work in progress, July 2012.
[PBB-EVPN] Sajassi et al., "PBB-EVPN", draft-ietf-l2vpn-pbb-evpn-
03.txt, work in progress, June 2012.
[TRILL-EVPN] Sajassi et al., "TRILL-EVPN", draft-ietf-l2vpn-trill-
evpn-00.txt, work in progress, June 2012.
7.2 Informative References
[802.1Q] "IEEE Standard for Local and metropolitan area networks -
Media Access Control (MAC) Bridges and Virtual Bridge Local Area
Networks", 31 August 2011.
[Y.1731] "ITU-T Recommendation Y.1731 (02/08) - OAM functions and
mechanisms for Ethernet based networks", February 2008.
[TRILL-OAM] Senevirathne et al., "Requirements for Operations,
Administration and Maintenance (OAM) in TRILL", draft-ietf-trill-oam-
req-01.txt, work in progress, August 2012.
[RFC5085] Nadeau et al., "Pseudowire Virtual Circuit Connectivity
Verification (VCCV): A Control Channel for Pseudowires", December
2007.
[TRILL-LOSS-DELAY] Mizrahi et al., "Loss and Delay Measurement in
TRILL", draft-mizrahi-trill-loss-delay, work in progress, February
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Authors' Addresses
Samer Salam
Cisco
595 Burrard Street, Suite 2123
Vancouver, BC V7X 1J1, Canada
Email: ssalam@cisco.com
Ali Sajassi
Cisco
170 West Tasman Drive
San Jose, CA 95134, USA
Email: sajassi@cisco.com
Salam et al. Expires July 27, 2014 [Page 15]
INTERNET DRAFT E-VPN OAM Requirements and Framework January 23, 2014
Sam Aldrin
Huawei Technologies
2330 Central Express Way
Santa Clara, CA 95951, USA
Email: aldrin.ietf@gmail.com
John E. Drake
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089, USA
Email: jdrake@juniper.net
Salam et al. Expires July 27, 2014 [Page 16]
