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IETF RFC 6414
Last modified on Tuesday, November 22nd, 2011
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Internet Engineering Task Force (IETF) S. Poretsky
Request for Comments: 6414 Allot Communications
Category: Informational R. Papneja
ISSN: 2070-1721 Huawei
J. Karthik
S. Vapiwala
Cisco Systems
November 2011
Benchmarking Terminology for Protection Performance
 Abstract
This document provides common terminology and metrics for
benchmarking the performance of sub-IP layer protection mechanisms.
The performance benchmarks are measured at the IP layer; protection
may be provided at the sub-IP layer. The benchmarks and terminology
can be applied in methodology documents for different sub-IP layer
protection mechanisms such as Automatic Protection Switching (APS),
Virtual Router Redundancy Protocol (VRRP), Stateful High Availability
(HA), and Multiprotocol Label Switching Fast Reroute (MPLS-FRR).
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 6414.
Poretsky, et al. Informational PAGE 1 
RFC 6414 Benchmarking Terms for Protection November 2011
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction ....................................................4
1.1. Scope ......................................................4
1.2. General Model ..............................................5
2. Existing Definitions ............................................8
3. Test Considerations .............................................9
3.1. Paths ......................................................9
3.1.1. Path ................................................9
3.1.2. Working Path .......................................10
3.1.3. Primary Path .......................................10
3.1.4. Protected Primary Path .............................11
3.1.5. Backup Path ........................................11
3.1.6. Standby Backup Path ................................12
3.1.7. Dynamic Backup Path ................................12
3.1.8. Disjoint Paths .....................................13
3.1.9. Point of Local Repair (PLR) ........................13
3.1.10. Shared Risk Link Group (SRLG) .....................14
3.2. Protection ................................................14
3.2.1. Link Protection ....................................14
3.2.2. Node Protection ....................................15
Poretsky, et al. Informational PAGE 2
RFC 6414 Benchmarking Terms for Protection November 2011
3.2.3. Path Protection ....................................15
3.2.4. Backup Span ........................................16
3.2.5. Local Link Protection ..............................16
3.2.6. Redundant Node Protection ..........................17
3.2.7. State Control Interface ............................17
3.2.8. Protected Interface ................................18
3.3. Protection Switching ......................................18
3.3.1. Protection-Switching System ........................18
3.3.2. Failover Event .....................................19
3.3.3. Failure Detection ..................................19
3.3.4. Failover ...........................................20
3.3.5. Restoration ........................................20
3.3.6. Reversion ..........................................21
3.4. Nodes .....................................................22
3.4.1. Protection-Switching Node ..........................22
3.4.2. Non-Protection-Switching Node ......................22
3.4.3. Headend Node .......................................23
3.4.4. Backup Node ........................................23
3.4.5. Merge Node .........................................24
3.4.6. Primary Node .......................................24
3.4.7. Standby Node .......................................25
3.5. Benchmarks ................................................26
3.5.1. Failover Packet Loss ...............................26
3.5.2. Reversion Packet Loss ..............................26
3.5.3. Failover Time ......................................27
3.5.4. Reversion Time .....................................27
3.5.5. Additive Backup Delay ..............................28
3.6. Failover Time Calculation Methods .........................28
3.6.1. Time-Based Loss Method (TBLM) ......................29
3.6.2. Packet-Loss-Based Method (PLBM) ....................29
3.6.3. Timestamp-Based Method (TBM) .......................30
4. Security Considerations ........................................31
5. References .....................................................32
5.1. Normative References ......................................32
5.2. Informative References ....................................32
6. Acknowledgments ................................................32
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RFC 6414 Benchmarking Terms for Protection November 2011
1. Introduction
The IP network layer provides route convergence to protect data
traffic against planned and unplanned failures in the Internet. Fast
convergence times are critical to maintain reliable network
connectivity and performance. Convergence Events [6] are recognized
at the IP Layer so that Route Convergence [6] occurs. Technologies
that function at sub-IP layers can be enabled to provide further
protection of IP traffic by providing the failure recovery at the
sub-IP layers so that the outage is not observed at the IP layer.
Such sub-IP protection technologies include, but are not limited to,
High Availability (HA) stateful failover, Virtual Router Redundancy
Protocol (VRRP) [8], Automatic Link Protection (APS) for SONET/SDH,
Resilient Packet Ring (RPR) for Ethernet, and Fast Reroute for
Multiprotocol Label Switching (MPLS-FRR) [9].
1.1. Scope
Benchmarking terminology was defined for IP-layer convergence in [6].
Different terminology and methodologies specific to benchmarking sub-
IP layer protection mechanisms are required. The metrics for
benchmarking the performance of sub-IP protection mechanisms are
measured at the IP layer, so that the results are always measured in
reference to IP and independent of the specific protection mechanism
being used. The purpose of this document is to provide a single
terminology for benchmarking sub-IP protection mechanisms.
A common terminology for sub-IP layer protection mechanism
benchmarking enables different implementations of a protection
mechanism to be benchmarked and evaluated. In addition,
implementations of different protection mechanisms can be benchmarked
and evaluated. It is intended that there can exist unique
methodology documents for each sub-IP protection mechanism based upon
this common terminology document. The terminology can be applied to
methodologies that benchmark sub-IP protection mechanism performance
with a single stream of traffic or multiple streams of traffic. The
traffic flow may be unidirectional or bidirectional as to be
indicated in the methodology.
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RFC 6414 Benchmarking Terms for Protection November 2011
1.2. General Model
The sequence of events to benchmark the performance of sub-IP
protection mechanisms is as follows:
1. Failover Event - Primary Path fails
2. Failure Detection - Failover Event is detected
3. Failover - Backup Path becomes the Working Path due to Failover
Event
4. Restoration - Primary Path recovers from a Failover Event
5. Reversion (optional) - Primary Path becomes the Working Path
These terms are further defined in this document.
Figures 1 through 5 show models that MAY be used when benchmarking
sub-IP protection mechanisms, which MUST use a Protection-Switching
System that consists of a minimum of two Protection-Switching Nodes,
an Ingress Node known as the Headend Node and an Egress Node known as
the Merge Node. The Protection-Switching System MUST include either
a Primary Path and Backup Path, as shown in Figures 1 through 4, or a
Primary Node and Standby Node, as shown in Figure 5. A Protection-
Switching System may provide link protection, node protection, path
protection, local link protection, and high availability, as shown in
Figures 1 through 5, respectively. A Failover Event occurs along the
Primary Path or at the Primary Node. The Working Path is the Primary
Path prior to the Failover Event and the Backup Path after the
Failover Event. A Tester is set outside the two paths or nodes as it
sends and receives IP traffic along the Working Path. The tester
MUST record the IP packet sequence numbers, departure time, and
arrival time so that the metrics of Failover Time, Additive Latency,
Packet Reordering, Duplicate Packets, and Reversion Time can be
measured. The Tester may be a single device or a test system. If
Reversion is supported, then the Working Path is the Primary Path
after Restoration (Failure Recovery) of the Primary Path.
Link Protection, as shown in Figure 1, provides protection when a
Failover Event occurs on the link between two nodes along the Primary
Path. Node Protection, as shown in Figure 2, provides protection
when a Failover Event occurs at a Node along the Primary Path. Path
Protection, as shown in Figure 3, provides protection for link or
node failures for multiple hops along the Primary Path. Local Link
Protection, as shown in Figure 4, provides sub-IP protection of a
link between two nodes, without a Backup Node. An example of such a
sub-IP protection mechanism is SONET APS. High Availability
Protection, as shown in Figure 5, provides protection of a Primary
Node with a redundant Standby Node. State Control is provided
between the Primary and Standby Nodes. Failure of the Primary Node
Poretsky, et al. Informational PAGE 5
RFC 6414 Benchmarking Terms for Protection November 2011
is detected at the sub-IP layer to force traffic to switch to the
Standby Node, which has state maintained for zero or minimal packet
loss.
+-----------+
+--------------| Tester |<-----------------------+
| +-----------+ |
| IP Traffic | Failover IP Traffic |
| | Event |
| ------------ | ---------- |
+--->| Ingress/ | V | Egress/ |---+
|Headend Node|------------------|Merge Node| Primary
------------ ---------- Path
| ^
| --------- | Backup
+--------| Backup |-------------+ Path
| Node |
---------
Figure 1. System Under Test (SUT) for Sub-IP Link Protection
+-----------+
+--------------------| Tester |<-----------------+
| +-----------+ |
| IP Traffic | Failover IP Traffic |
| | Event |
| V |
| ------------ -------- ---------- |
+--->| Ingress/ | |Midpoint| | Egress/ |---+
|Headend Node|----| Node |----|Merge Node| Primary
------------ -------- ---------- Path
| ^
| --------- | Backup
+--------| Backup |-------------+ Path
| Node |
---------
Figure 2. System Under Test (SUT) for Sub-IP Node Protection
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RFC 6414 Benchmarking Terms for Protection November 2011
+-----------+
+---------------------------| Tester |<----------------------+
| +-----------+ |
| IP Traffic | Failover IP Traffic |
| | Event |
| Primary Path | |
| ------------ -------- | -------- ---------- |
+--->| Ingress/ | |Midpoint| V |Midpoint| | Egress/ |---+
|Headend Node|----| Node |---| Node |---|Merge Node|
------------ -------- -------- ----------
| ^
| --------- -------- | Backup
+--------| Backup |----| Backup |--------+ Path
| Node | | Node |
--------- --------
Figure 3. System Under Test (SUT) for Sub-IP Path Protection
+-----------+
+--------------------| Tester |<-------------------+
| +-----------+ |
| IP Traffic | Failover IP Traffic |
| | Event |
| Primary | |
| +--------+ Path v +--------+ |
| | |------------------------>| | |
+--->| Ingress| | Egress |----+
| Node |- - - - - - - - - - - - >| Node |
+--------+ Backup Path +--------+
| |
| IP-Layer Forwarding |
+<----------------------------------------->+
Figure 4. System Under Test (SUT) for Sub-IP Local Link Protection
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RFC 6414 Benchmarking Terms for Protection November 2011
+-----------+
+-----------------| Tester |<--------------------+
| +-----------+ |
| IP Traffic | Failover IP Traffic |
| | Event |
| V |
| --------- -------- ---------- |
+--->| Ingress | |Primary | | Egress/ |------+
| Node |----| Node |----|Merge Node| Primary
--------- -------- ---------- Path
| State |Control ^
| Interface |(Optional) |
| --------- |
+---------| Standby |---------+
| Node |
---------
Figure 5. System Under Test (SUT)
for Sub-IP Redundant Node Protection
Some protection-switching technologies may use a series of steps that
differ from the general model. The specific differences SHOULD be
highlighted in each technology-specific methodology. Note that some
protection-switching technologies are endowed with the ability to re-
optimize the working path after a node or link failure.
2. Existing Definitions
This document uses existing terminology defined in other BMWG work.
Examples include, but are not limited to:
Latency [2], Section 3.8
Frame Loss Rate [2], Section 3.6
Throughput [2], Section 3.17
Device Under Test (DUT) [3], Section 3.1.1
System Under Test (SUT) [3], Section 3.1.2
Offered Load [3], Section 3.5.2
Out-of-order Packet [4], Section 3.3.4
Duplicate Packet [4], Section 3.3.5
Forwarding Delay [4], Section 3.2.4
Jitter [4], Section 3.2.5
Packet Loss [6], Section 3.5
Packet Reordering [7], Section 3.3
This document has the following frequently used acronyms:
DUT Device Under Test
SUT System Under Test
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This document adopts the definition format in Section 2 of RFC 1242
[2]. Terms defined in this document are capitalized when used within
this document.
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119 [5].
RFC 2119 defines the use of these keywords to help make the intent of
Standards Track documents as clear as possible. While this document
uses these keywords, this document is not a Standards Track document.
3. Test Considerations
3.1. Paths
3.1.1. Path
Definition:
A unidirectional sequence of nodes <R1, ..., Rn> and links
<L12,... L(n-1)n> with the following properties:
a. R1 is the ingress node and forwards IP packets, which input
into DUT/SUT, to R2 as sub-IP frames over link L12.
b. Ri is a node which forwards data frames to R(i+1) over Link
Li(i+1) for all i, 1<i<n-1, based on information in the sub-IP
layer.
c. Rn is the egress node, and it outputs sub-IP frames from
DUT/SUT as IP packets. L(n-1)n is the link between the R(n-1)
and Rn.
Discussion:
The path is defined in the sub-IP layer in this document, unlike
an IP path in RFC 2026 [1]. One path may be regarded as being
equivalent to one IP link between two IP nodes, i.e., R1 and Rn.
The two IP nodes may have multiple paths for protection. A packet
will travel on only one path between the nodes. Packets belonging
to a microflow [10] will traverse one or more paths. The path is
unidirectional. For example, the link between R1 and R2 in the
direction from R1 to R2 is L12. For traffic flowing in the
reverse direction from R2 to R1, the link is L21. Example paths
are the SONET/SDH path and the label switched path for MPLS.
Measurement Units:
n/a
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RFC 6414 Benchmarking Terms for Protection November 2011
Issues:
"A bidirectional path", which transmits traffic in both directions
along the same nodes, consists of two unidirectional paths.
Therefore, the two unidirectional paths belonging to "one
bidirectional path" will be treated independently when
benchmarking for "a bidirectional path".
See Also:
Working Path
Primary Path
Backup Path
3.1.2. Working Path
Definition:
The path that the DUT/SUT is currently using to forward packets.
Discussion:
A Primary Path is the Working Path before occurrence of a Failover
Event. A Backup Path shall become the Working Path after a
Failover Event.
Measurement Units:
n/a
Issues:
None.
See Also:
Path
Primary Path
Backup Path
3.1.3. Primary Path
Definition:
The preferred point-to-point path for forwarding traffic between
two or more nodes.
Discussion:
The Primary Path is the Path that traffic traverses prior to a
Failover Event.
Measurement Units:
n/a
Issues:
None.
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RFC 6414 Benchmarking Terms for Protection November 2011
See Also:
Path
Failover Event
3.1.4. Protected Primary Path
Definition:
A Primary Path that is protected with a Backup Path.
Discussion:
A Protected Primary Path must include at least one Protection-
Switching Node.
Measurement Units:
n/a
Issues:
None.
See Also:
Path
Primary Path
3.1.5. Backup Path
Definition:
A path that exists to carry data traffic only if a Failover Event
occurs on a Primary Path.
Discussion:
The Backup Path shall become the Working Path upon a Failover
Event. A Path may have one or more Backup Paths. A Backup Path
may protect one or more Primary Paths. There are various types of
Backup Paths:
a. dedicated recovery Backup Path (1+1) or (1:1), which has 100%
redundancy for a specific ordinary path
b. shared Backup Path (1:N), which is dedicated to the protection
for more than one specific Primary Path
c. associated shared Backup Path (M:N) for which a specific set of
Backup Paths protects a specific set of more than one Primary
Path
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A Backup Path may be signaled or unsignaled. The Backup Path must
be created prior to the Failover Event. The Backup Path generally
originates at the point of local repair (PLR) and terminates at a
node along a primary path.
Measurement Units:
n/a
Issues:
None.
See Also:
Path
Working Path
Primary Path
3.1.6. Standby Backup Path
Definition:
A Backup Path that is established prior to a Failover Event to
protect a Primary Path.
Discussion:
The Standby Backup Path and Dynamic Backup Path provide
protection, but are established at different times.
Measurement Units:
n/a
Issues:
None.
See Also:
Backup Path
Primary Path
Failover Event
3.1.7. Dynamic Backup Path
Definition:
A Backup Path that is established upon occurrence of a Failover
Event.
Discussion:
The Standby Backup Path and Dynamic Backup Path provide
protection, but are established at different times.
Poretsky, et al. Informational PAGE 12
RFC 6414 Benchmarking Terms for Protection November 2011
Measurement Units:
n/a
Issues:
None.
See Also:
Backup Path
Standby Backup Path
Failover Event
3.1.8. Disjoint Paths
Definition:
A pair of paths that do not share a common link or nodes.
Discussion:
Two paths are disjoint if they do not share a common node or link
other than the ingress and egress.
Measurement Units:
n/a
Issues:
None.
See Also:
Path
Primary Path
SRLG
3.1.9. Point of Local Repair (PLR)
Definition:
A node capable of Failover along the Primary Path that is also the
ingress node for the Backup Path to protect another node or link.
Discussion:
Any node along the Primary Path from the ingress node to the
penultimate node may be a PLR. The PLR may use a single Backup
Path for protecting one or more Primary Paths. There can be
multiple PLRs along a Primary Path. The PLR must be an ingress to
a Backup Path. The PLR can be any node along the Primary Path
except the egress node of the Primary Path. The PLR may
simultaneously be a Headend Node when it is serving the role as
ingress to the Primary Path and the Backup Path. If the PLR is
also the Headend Node, then the Backup Path is a Disjoint Path
from the ingress to the Merge Node.
Poretsky, et al. Informational PAGE 13
RFC 6414 Benchmarking Terms for Protection November 2011
Measurement Units:
n/a
Issues:
None.
See Also:
Primary Path
Backup Path
Failover
3.1.10. Shared Risk Link Group (SRLG)
Definition:
SRLG is a set of links that share the same risk (physical or
logical) within a network.
Discussion:
SRLG is considered the set of links to be avoided when the primary
and secondary paths are considered disjoint. The SRLG will fail
as a group if the shared resource (physical or anything abstract
such as software version) fails.
Measurement Units:
n/a
Issues:
None.
See Also:
Path Primary Path
3.2. Protection
3.2.1. Link Protection
Definition:
A Backup Path that is signaled to at least one Backup Node to
protect for failure of interfaces and links along a Primary Path.
Discussion:
Link Protection may or may not protect the entire Primary Path.
Link Protection is shown in Figure 1.
Measurement Units:
n/a
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RFC 6414 Benchmarking Terms for Protection November 2011
Issues:
None.
See Also:
Primary Path Backup Path
3.2.2. Node Protection
Definition:
A Backup Path that is signaled to at least one Backup Node to
protect for failure of interfaces, links, and nodes along a
Primary Path.
Discussion:
Node Protection may or may not protect the entire Primary Path.
Node Protection also provides Link Protection. Node Protection is
shown in Figure 2.
Measurement Units:
n/a
Issues:
None.
See Also:
Link Protection
3.2.3. Path Protection
Definition:
A Backup Path that is signaled to at least one Backup Node to
provide protection along the entire Primary Path.
Discussion:
Path Protection provides Node Protection and Link Protection for
every node and link along the Primary Path. A Backup Path
providing Path Protection may have the same ingress node as the
Primary Path. Path Protection is shown in Figure 3.
Measurement Units:
n/a
Issues:
None.
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See Also:
Primary Path
Backup Path
Node Protection
Link Protection
3.2.4. Backup Span
Definition:
The number of hops used by a Backup Path.
Discussion:
The Backup Span is an integer obtained by counting the number of
nodes along the Backup Path.
Measurement Units:
number of nodes
Issues:
None.
See Also:
Primary Path
Backup Path
3.2.5. Local Link Protection
Definition:
A Backup Path that is a redundant path between two nodes and does
not use a Backup Node.
Discussion:
Local Link Protection must be provided as a Backup Path between
two nodes along the Primary Path without the use of a Backup Node.
Local Link Protection is provided by Protection-Switching Systems
such as SONET APS. Local Link Protection is shown in Figure 4.
Measurement Units:
n/a
Issues:
None.
See Also:
Backup Path
Backup Node
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3.2.6. Redundant Node Protection
Definition:
A Protection-Switching System with a Primary Node protected by a
Standby Node along the Primary Path.
Discussion:
Redundant Node Protection is provided by Protection-Switching
Systems such as VRRP and HA. The protection mechanisms occur at
sub-IP layers to switch traffic from a Primary Node to Backup Node
upon a Failover Event at the Primary Node. Traffic continues to
traverse the Primary Path through the Standby Node. The failover
may be stateful, in which the state information may be exchanged
in-band or over an out-of-band State Control Interface. The
Standby Node may be active or passive. Redundant Node Protection
is shown in Figure 5.
Measurement Units:
n/a
Issues:
None.
See Also:
Primary Path
Primary Node
Standby Node
3.2.7. State Control Interface
Definition:
An out-of-band control interface used to exchange state
information between the Primary Node and Standby Node.
Discussion:
The State Control Interface may be used for Redundant Node
Protection. The State Control Interface should be out-of-band.
It is possible to have Redundant Node Protection in which there is
no state control or state control is provided in-band. The State
Control Interface between the Primary and Standby Node may be one
or more hops.
Measurement Units:
n/a
Issues:
None.
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RFC 6414 Benchmarking Terms for Protection November 2011
See Also:
Primary Node
Standby Node
3.2.8. Protected Interface
Definition:
An interface along the Primary Path that is protected by a Backup
Path.
Discussion:
A Protected Interface is an interface protected by a Protection-
Switching System that provides Link Protection, Node Protection,
Path Protection, Local Link Protection, and Redundant Node
Protection.
Measurement Units:
n/a
Issues:
None.
See Also:
Primary Path
Backup Path
3.3. Protection Switching
3.3.1. Protection-Switching System
Definition:
A DUT/SUT that is capable of Failure Detection and Failover from a
Primary Path to a Backup Path or Standby Node when a Failover
Event occurs.
Discussion:
The Protection-Switching System must include either a Primary Path
and Backup Path, as shown in Figures 1 through 4, or a Primary
Node and Standby Node, as shown in Figure 5. The Backup Path may
be a Standby Backup Path or a Dynamic Backup Path. The
Protection-Switching System includes the mechanisms for both
Failure Detection and Failover.
Measurement Units:
n/a
Issues:
None.
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See Also:
Primary Path Backup Path Failover
3.3.2. Failover Event
Definition:
The occurrence of a planned or unplanned action in the network
that results in a change in the Path that data traffic traverses.
Discussion:
Failover Events include, but are not limited to, link failure and
router failure. Routing changes are considered Convergence Events
[6] and are not Failover Events. This restricts Failover Events
to sub-IP layers. Failover may be at the PLR or at the ingress.
If the failover is at the ingress, it is generally on a disjoint
path from the ingress to egress.
Failover Events may result from failures such as link failure or
router failure. The change in path after Failover may have a
Backup Span of one or more nodes. Failover Events are
distinguished from routing changes and Convergence Events [6] by
the detection of the failure and subsequent protection switching
at a sub-IP layer. Failover occurs at a PLR or Primary Node.
Measurement Units:
n/a
Issues:
None.
See Also:
Path
Failure Detection
Disjoint Path
3.3.3. Failure Detection
Definition:
The process to identify at a sub-IP layer a Failover Event at a
Primary Node or along the Primary Path.
Discussion:
Failure Detection occurs at the Primary Node or ingress node of
the Primary Path. Failure Detection occurs via a sub-IP mechanism
such as detection of a link down event or timeout for receipt of a
control packet. A failure may be completely isolated. A failure
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may affect a set of links that share a single SRLG (e.g., port
with many sub-interfaces). A failure may affect multiple links
that are not part of the SRLG.
Measurement Units:
n/a
Issues:
None.
See Also:
Primary Path
3.3.4. Failover
Definition:
The process to switch data traffic from the protected Primary Path
to the Backup Path upon Failure Detection of a Failover Event.
Discussion:
Failover to a Backup Path provides Link Protection, Node
Protection, or Path Protection. Failover is complete when Packet
Loss [6], Out-of-order Packets [4], and Duplicate Packets [4] are
no longer observed. Forwarding Delay [4] may continue to be
observed.
Measurement Units:
n/a
Issues:
None.
See Also:
Primary Path Backup Path Failover Event
3.3.5. Restoration
Definition:
The state of failover recovery in which the Primary Path has
recovered from a Failover Event, but is not yet forwarding packets
because the Backup Path remains the Working Path.
Discussion:
Restoration must occur while the Backup Path is the Working Path.
The Backup Path is maintained as the Working Path during
Restoration. Restoration produces a Primary Path that is
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recovered from failure, but is not yet forwarding traffic.
Traffic is still being forwarded by the Backup Path functioning as
the Working Path.
Measurement Units:
n/a
Issues:
None.
See Also:
Primary Path
Failover Event
Failure Recovery
Working Path
Backup Path
3.3.6. Reversion
Definition:
The state of failover recovery in which the Primary Path has
become the Working Path so that it is forwarding packets.
Discussion:
Protection-Switching Systems may or may not support Reversion.
Reversion, if supported, must occur after Restoration. Packet
forwarding on the Primary Path resulting from Reversion may occur
either fully or partially over the Primary Path. A potential
problem with Reversion is the discontinuity in end-to-end delay
when the Forwarding Delays [4] along the Primary Path and Backup
Path are different, possibly causing Out-of-order Packets [4],
Duplicate Packets [4], and increased Jitter [4].
Measurement Units:
n/a
Issues:
None.
See Also:
Protection-Switching System
Working Path
Primary Path
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3.4. Nodes
3.4.1. Protection-Switching Node
Definition:
A node that is capable of participating in a Protection Switching
System.
Discussion:
The Protection-Switching Node may be an ingress or egress for a
Primary Path or Backup Path, such as used for MPLS Fast Reroute
configurations. The Protection-Switching Node may provide
Redundant Node Protection as a Primary Node in a Redundant chassis
configuration with a Standby Node, such as used for VRRP and HA
configurations.
Measurement Units:
n/a
Issues:
None.
See Also:
Protection-Switching System
3.4.2. Non-Protection-Switching Node
Definition:
A node that is not capable of participating in a Protection
Switching System, but may exist along the Primary Path or Backup
Path.
Discussion:
None.
Measurement Units:
n/a
Issues:
None.
See Also:
Protection-Switching System
Primary Path
Backup Path
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3.4.3. Headend Node
Definition:
The ingress node of the Primary Path.
Discussion:
The Headend Node may also be a PLR when it is serving in the dual
role as the ingress to the Backup Path.
Measurement Units:
n/a
Issues:
None.
See Also:
Primary Path
PLR
Failover
3.4.4. Backup Node
Definition:
A node along the Backup Path.
Discussion:
The Backup Node can be any node along the Backup Path. There may
be one or more Backup Nodes along the Backup Path. A Backup Node
may be the ingress, midpoint, or egress of the Backup Path. If
the Backup Path has only one Backup Node, then that Backup Node is
the ingress and egress of the Backup Path.
Measurement Units:
n/a
Issues:
None.
See Also:
Backup Path
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3.4.5. Merge Node
Definition:
A node along the Primary Path where Backup Path terminates.
Discussion:
The Merge Node can be any node along the Primary Path except the
ingress node of the Primary Path. There can be multiple Merge
Nodes along a Primary Path. A Merge Node can be the egress node
for a single Backup Path or multiple Backup Paths. The Merge Node
must be the egress to the Backup Path. The Merge Node may also be
the egress of the Primary Path or Point of Local Repair (PLR).
Measurement Units:
n/a
Issues:
None.
See Also:
Primary Path
Backup Path
PLR
Failover
3.4.6. Primary Node
Definition:
A node along the Primary Path that is capable of Failover to a
redundant Standby Node.
Discussion:
The Primary Node may be used for Protection-Switching Systems that
provide Redundant Node Protection, such as VRRP and HA.
Measurement Units:
n/a
Issues:
None.
See Also:
Protection-Switching System Redundant Node Protection Standby Node
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3.4.7. Standby Node
Definition:
A redundant node to a Primary Node; it forwards traffic along the
Primary Path upon Failure Detection of the Primary Node.
Discussion:
The Standby Node must be used for Protection-Switching Systems
that provide Redundant Node Protection, such as VRRP and HA. The
Standby Node must provide protection along the same Primary Path.
If the failover is to a Disjoint Path, then it is a Backup Node.
The Standby Node may be configured for 1:1 or N:1 protection.
The communication between the Primary Node and Standby Node may be
in-band or across an out-of-band State Control Interface. The
Standby Node may be geographically dispersed from the Primary
Node. When geographically dispersed, the number of hops of
separation may increase failover time.
The Standby Node may be passive or active. The Passive Standby
Node is not offered traffic and does not forward traffic until
Failure Detection of the Primary Node. Upon Failure Detection of
the Primary Node, traffic offered to the Primary Node is instead
offered to the Passive Standby Node. The Active Standby Node is
offered traffic and forwards traffic along the Primary Path while
the Primary Node is also active. Upon Failure Detection of the
Primary Node, traffic offered to the Primary Node is switched to
the Active Standby Node.
Measurement Units:
n/a
Issues:
None.
See Also:
Primary Node
State Control Interface
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3.5. Benchmarks
3.5.1. Failover Packet Loss
Definition:
The amount of packet loss produced by a Failover Event until
Failover completes, where the measurement begins when the last
unimpaired packet is received by the Tester on the Protected
Primary Path and ends when the first unimpaired packet is received
by the Tester on the Backup Path.
Discussion:
Packet loss can be observed as a reduction of forwarded traffic
from the maximum forwarding rate. Failover Packet Loss includes
packets that were lost, reordered, or delayed. Failover Packet
Loss may reach 100% of the offered load.
Measurement Units:
Number of Packets
Issues:
None.
See Also:
Failover Event
Failover
3.5.2. Reversion Packet Loss
Definition:
The amount of packet loss produced by Reversion, where the
measurement begins when the last unimpaired packet is received by
the Tester on the Backup Path and ends when the first unimpaired
packet is received by the Tester on the Protected Primary Path.
Discussion:
Packet loss can be observed as a reduction of forwarded traffic
from the maximum forwarding rate. Reversion Packet Loss includes
packets that were lost, reordered, or delayed. Reversion Packet
Loss may reach 100% of the offered load.
Measurement Units:
Number of Packets
Issues:
None.
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See Also:
Reversion
3.5.3. Failover Time
Definition:
The amount of time it takes for Failover to successfully complete.
Discussion:
Failover Time can be calculated using the Time-Based Loss Method
(TBLM), Packet-Loss-Based Method (PLBM), or Timestamp-Based Method
(TBM). It is RECOMMENDED that the TBM is used.
Measurement Units:
milliseconds
Issues:
None.
See Also:
Failover
Failover Time
Time-Based Loss Method (TBLM)
Packet-Loss-Based Method (PLBM)
Timestamp-Based Method (TBM)
3.5.4. Reversion Time
Definition:
The amount of time it takes for Reversion to complete so that the
Primary Path is restored as the Working Path.
Discussion:
Reversion Time can be calculated using the Time-Based Loss Method
(TBLM), Packet-Loss-Based Method (PLBM), or Timestamp-Based Method
(TBM). It is RECOMMENDED that the TBM is used.
Measurement Units:
milliseconds
Issues:
None.
See Also:
Reversion
Primary Path
Working Path
Reversion Packet Loss
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Time-Based Loss Method (TBLM)
Packet-Loss-Based Method (PLBM)
Timestamp-Based Method (TBM)
3.5.5. Additive Backup Delay
Definition:
The amount of increased Forwarding Delay [4] resulting from data
traffic traversing the Backup Path instead of the Primary Path.
Discussion:
Additive Backup Delay is calculated using Equation 1 as shown
below:
(Equation 1)
Additive Backup Delay =
Forwarding Delay(Backup Path) -
Forwarding Delay(Primary Path)
Measurement Units:
milliseconds
Issues:
Additive Backup Latency may be a negative result. This is
theoretically possible but could be indicative of a sub-optimum
network configuration.
See Also:
Primary Path
Backup Path
Primary Path Latency
Backup Path Latency
3.6. Failover Time Calculation Methods
The following Methods may be assessed on a per-flow basis using at
least 16 flows spread over the routing table (using more flows is
better). Otherwise, the impact of a prefix-dependency in the
implementation of a particular protection technology could be missed.
However, the test designer must be aware of the number of packets per
second sent to each prefix, as this establishes sampling of the path
and the time resolution for measurement of Failover time on a per-
flow basis.
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3.6.1. Time-Based Loss Method (TBLM)
Definition:
The method to calculate Failover Time (or Reversion Time) using a
time scale on the Tester to measure the interval of Failover
Packet Loss.
Discussion:
The Tester must provide statistics that show the duration of
failure on a time scale based on occurrence of packet loss on a
time scale. This is indicated by the duration of non-zero packet
loss. The TBLM includes failure detection time and time for data
traffic to begin traversing the Backup Path. Failover Time and
Reversion Time are calculated using the TBLM as shown in Equation
2:
(Equation 2)
(Equation 2a)
TBLM Failover Time = Time(Failover) - Time(Failover Event)
(Equation 2b)
TBLM Reversion Time = Time(Reversion) - Time(Restoration)
Where
Time(Failover) = Time on the tester at the receipt of the first
unimpaired packet at egress node after the backup path became the
working path
Time(Failover Event) = Time on the tester at the receipt of the
last unimpaired packet at egress node on the primary path before
failure
Measurement Units:
milliseconds
Issues:
None.
See Also:
Failover
Packet-Loss-Based Method
3.6.2. Packet-Loss-Based Method (PLBM)
Definition:
The method used to calculate Failover Time (or Reversion Time)
from the amount of Failover Packet Loss.
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Discussion:
PLBM includes failure detection time and time for data traffic to
begin traversing the Backup Path. Failover Time can be calculated
using PLBM from the amount of Failover Packet Loss as shown below
in Equation 3. Note: If traffic is sent to more than 1
destination, PLBM gives the average loss over the measured
destinations.
(Equation 3)
(Equation 3a)
PLBM Failover Time =
(Number of packets lost / Offered Load rate) * 1000)
(Equation 3b)
PLBM Restoration Time =
(Number of packets lost / Offered Load rate) * 1000)
Units are packets/(packets/second) = seconds
Measurement Units:
milliseconds
Issues:
None.
See Also:
Failover Time-Based Loss Method
3.6.3. Timestamp-Based Method (TBM)
Definition:
The method to calculate Failover Time (or Reversion Time) using a
time scale to quantify the interval between unimpaired packets
arriving in the test stream.
Discussion:
The purpose of this method is to quantify the duration of failure
or reversion on a time scale based on the observation of
unimpaired packets. The TBM is calculated from Equation 2 with
the values obtained from the timestamp in the packet payload,
rather than from the Tester clock (which are used with the TBLM).
Unimpaired packets are normal packets that are not lost,
reordered, or duplicated. A reordered packet is defined in
Section 3.3 of [7]. A duplicate packet is defined in Section
3.3.5 of [4]. Unimpaired packets may be detected by checking a
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sequence number in the payload, where the sequence number equals
the next expected number for an unimpaired packet. A sequence gap
or sequence reversal indicates impaired packets.
For calculating Failover Time, the TBM includes failure detection
time and time for data traffic to begin traversing the Backup
Path. For calculating Reversion Time, the TBM includes Reversion
Time and time for data traffic to begin traversing the Primary
Path.
Measurement Units:
milliseconds
Issues:
None.
See Also:
Failover
Failover Time
Reversion
Reversion Time
4. Security Considerations
Benchmarking activities as described in this memo are limited to
technology characterization using controlled stimuli in a laboratory
environment, with dedicated address space and the constraints
specified in the sections above.
The benchmarking network topology will be an independent test setup
and MUST NOT be connected to devices that may forward the test
traffic into a production network or misroute traffic to the test
management network.
Further, benchmarking is performed on a "black-box" basis, relying
solely on measurements observable external to the DUT/SUT.
Special capabilities SHOULD NOT exist in the DUT/SUT specifically for
benchmarking purposes. Any implications for network security arising
from the DUT/SUT SHOULD be identical in the lab and in production
networks.
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5. References
5.1. Normative References
[1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
[2] Bradner, S., "Benchmarking Terminology for Network
Interconnection Devices", RFC 1242, July 1991.
[3] Mandeville, R., "Benchmarking Terminology for LAN Switching
Devices", RFC 2285, February 1998.
[4] Poretsky, S., Perser, J., Erramilli, S., and S. Khurana,
"Terminology for Benchmarking Network-layer Traffic Control
Mechanisms", RFC 4689, October 2006.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[6] Poretsky, S., Imhoff, B., and K. Michielsen, "Terminology for
Benchmarking Link-State IGP Data Plane Route Convergence", RFC
6412, November 2011.
[7] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov, S., and
J. Perser, "Packet Reordering Metrics", RFC 4737, November 2006.
[8] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
Version 3 for IPv4 and IPv6", RFC 5798, March 2010.
5.2. Informative References
[9] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May 2005.
[10] Nichols, K., Blake, S., Baker, F., and D. Black, "Definition of
the Differentiated Services Field (DS Field) in the IPv4 and
IPv6 Headers", RFC 2474, December 1998.
6. Acknowledgments
We would like thank the BMWG and particularly Al Morton and Curtis
Villamizar for their reviews, comments, and contributions to this
work.
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Authors' Addresses
Scott Poretsky
Allot Communications
300 TradeCenter
Woburn, MA 01801
USA
Phone: + 1 508 309 2179
EMail: sporetsky@allot.com
Rajiv Papneja
Huawei Technologies
2330 Central Expressway
Santa Clara, CA 95050
USA
Phone: +1 571 926 8593
EMail: rajiv.papneja@huawei.com
Jay Karthik
Cisco Systems
300 Beaver Brook Road
Boxborough, MA 01719
USA
Phone: +1 978 936 0533
EMail: jkarthik@cisco.com
Samir Vapiwala
Cisco System
300 Beaver Brook Road
Boxborough, MA 01719
USA
Phone: +1 978 936 1484
EMail: svapiwal@cisco.com
Poretsky, et al. Informational PAGE 33
RFC TOTAL SIZE: 55563 bytes
PUBLICATION DATE: Tuesday, November 22nd, 2011
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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