Alternate-Marking Method for Passive and Hybrid Performance Monitoring
draft-ietf-ippm-alt-mark-14
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8321.
|
|
|---|---|---|---|
| Authors | Giuseppe Fioccola , Alessandro Capello , Mauro Cociglio , Luca Castaldelli , Mach Chen , Lianshu Zheng , Greg Mirsky , Tal Mizrahi | ||
| Last updated | 2018-01-29 (Latest revision 2017-12-07) | ||
| Replaces | draft-tempia-opsawg-p3m, draft-tempia-ippm-p3m, draft-chen-ippm-coloring-based-ipfpm-framework, draft-cociglio-mboned-multicast-pm | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Experimental | ||
| Formats | |||
| Reviews |
INTDIR Last Call review
(of
-10)
by Brian Haberman
Ready w/nits
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Carlos Pignataro | ||
| Shepherd write-up | Show Last changed 2017-09-21 | ||
| IESG | IESG state | Became RFC 8321 (Experimental) | |
| Action Holders |
(None)
|
||
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Spencer Dawkins | ||
| Send notices to | Carlos Pignataro <cpignata@cisco.com> | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | No IANA Actions |
draft-ietf-ippm-alt-mark-14
Network Working Group G. Fioccola, Ed.
Internet-Draft A. Capello
Intended status: Experimental M. Cociglio
Expires: June 10, 2018 L. Castaldelli
Telecom Italia
M. Chen
L. Zheng
Huawei Technologies
G. Mirsky
ZTE
T. Mizrahi
Marvell
December 7, 2017
Alternate Marking method for passive and hybrid performance monitoring
draft-ietf-ippm-alt-mark-14
Abstract
This document describes a method to perform packet loss, delay and
jitter measurements on live traffic. This method is based on
Alternate Marking (Coloring) technique. A report is provided in
order to explain an example and show the method applicability. This
technology can be applied in various situations as detailed in this
document and could be considered passive or hybrid depending on the
application.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 10, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview of the method . . . . . . . . . . . . . . . . . . . 5
3. Detailed description of the method . . . . . . . . . . . . . 6
3.1. Packet loss measurement . . . . . . . . . . . . . . . . . 6
3.1.1. Coloring the packets . . . . . . . . . . . . . . . . 11
3.1.2. Counting the packets . . . . . . . . . . . . . . . . 11
3.1.3. Collecting data and calculating packet loss . . . . . 12
3.2. Timing aspects . . . . . . . . . . . . . . . . . . . . . 13
3.3. One-way delay measurement . . . . . . . . . . . . . . . . 14
3.3.1. Single marking methodology . . . . . . . . . . . . . 14
3.3.2. Double marking methodology . . . . . . . . . . . . . 16
3.4. Delay variation measurement . . . . . . . . . . . . . . . 17
4. Considerations . . . . . . . . . . . . . . . . . . . . . . . 18
4.1. Synchronization . . . . . . . . . . . . . . . . . . . . . 18
4.2. Data Correlation . . . . . . . . . . . . . . . . . . . . 19
4.3. Packet Re-ordering . . . . . . . . . . . . . . . . . . . 20
5. Applications, implementation and deployment . . . . . . . . . 20
5.1. Report on the operational experiment . . . . . . . . . . 21
5.1.1. Metric transparency . . . . . . . . . . . . . . . . . 23
6. Hybrid measurement . . . . . . . . . . . . . . . . . . . . . 24
7. Compliance with RFC6390 guidelines . . . . . . . . . . . . . 24
8. Security Considerations . . . . . . . . . . . . . . . . . . . 26
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
11.1. Normative References . . . . . . . . . . . . . . . . . . 28
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11.2. Informative References . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction
Nowadays, most Service Providers' networks carry traffic with
contents that are highly sensitive to packet loss [RFC7680], delay
[RFC7679], and jitter [RFC3393].
In view of this scenario, Service Providers need methodologies and
tools to monitor and measure network performances with an adequate
accuracy, in order to constantly control the quality of experience
perceived by their customers. On the other hand, performance
monitoring provides useful information for improving network
management (e.g. isolation of network problems, troubleshooting,
etc.).
A lot of work related to OAM, that includes also performance
monitoring techniques, has been done by Standards Developing
Organizations(SDOs): [RFC7276] provides a good overview of existing
OAM mechanisms defined in IETF, ITU-T and IEEE. Considering IETF, a
lot of work has been done on fault detection and connectivity
verification, while a minor effort has been dedicated so far to
performance monitoring. The IPPM WG has defined standard metrics to
measure network performance; however, the methods developed in this
WG mainly refer to focus on active measurement techniques. More
recently, the MPLS WG has defined mechanisms for measuring packet
loss, one-way and two-way delay, and delay variation in MPLS
networks[RFC6374], but their applicability to passive measurements
has some limitations, especially for pure connection-less networks.
The lack of adequate tools to measure packet loss with the desired
accuracy drove an effort to design a new method for the performance
monitoring of live traffic, easy to implement and deploy. The effort
led to the method described in this document: basically, it is a
passive performance monitoring technique, potentially applicable to
any kind of packet based traffic, including Ethernet, IP, and MPLS,
both unicast and multicast. The method addresses primarily packet
loss measurement, but it can be easily extended to one-way delay and
delay variation measurements as well.
The method has been explicitly designed for passive measurements but
it can also be used with active probes. Passive measurements are
usually more easily understood by customers and provide a much better
accuracy, especially for packet loss measurements.
RFC 7799 [RFC7799] defines passive and hybrid methods of measurement.
In particular, Passive Methods of Measurement are based solely on
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observations of an undisturbed and unmodified packet stream of
interest; Hybrid Methods are Methods of Measurement that use a
combination of Active Methods and Passive Methods.
Taking into consideration these definitions, Alternate Marking Method
could be considered Hybrid or Passive depending on the case. In case
the marking method is obtained by changing existing field values of
the packets (e.g. DSCP field), the technique is Hybrid. In case the
marking field is dedicated, reserved and is included in the protocol
specification Alternate Marking technique can be considered as
Passive (e.g. RFC6374 Synonymous Flow Label or OAM Marking Bits in
BIER Header).
The advantages of the method described in this document are:
o easy implementation: it can be implemented or by using features
already available on major routing platforms as described in
Section 5.1 or by applying an optimized implementation of the
method for both legacy and newest technologies;
o low computational effort: the additional load on processing is
negligible;
o accurate packet loss measurement: single packet loss granularity
is achieved with a passive measurement;
o potential applicability to any kind of packet/frame -based
traffic: Ethernet, IP, MPLS, etc., both unicast and multicast;
o robustness: the method can tolerate out of order packets and it's
not based on "special" packets whose loss could have a negative
impact;
o flexibility: all the timestamp formats are allowed, because they
are managed out-of-band. The format (the Network Time Protocol
(NTP) RFC 5905 [RFC5905] or the IEEE 1588 Precision Time Protocol
(PTP) [IEEE-1588]) depends on the precision you want;
o no interoperability issues: the features required to experiment
and test the method (as described in Section 5.1) are available on
all current routing platforms. Both a centarlized or distributed
solution can be used to harvest data from the routers.
The method doesn't raise any specific need for protocol extension,
but it could be further improved by means of some extension to
existing protocols. Specifically, the use of DiffServ bits for
coloring the packets could not be a viable solution in some cases: a
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standard method to color the packets for this specific application
could be beneficial.
2. Overview of the method
In order to perform packet loss measurements on a production traffic
flow, different approaches exist. The most intuitive one consists in
numbering the packets, so that each router that receives the flow can
immediately detect a packet missing. This approach, though very
simple in theory, is not simple to achieve: it requires the insertion
of a sequence number into each packet and the devices must be able to
extract the number and check it in real time. Such a task can be
difficult to implement on live traffic: if UDP is used as the
transport protocol, the sequence number is not available; on the
other hand, if a higher layer sequence number (e.g. in the RTP
header) is used, extracting that information from each packet and
process it in real time could overload the device.
An alternate approach is to count the number of packets sent on one
end, the number of packets received on the other end, and to compare
the two values. This operation is much simpler to implement, but
requires that the devices performing the measurement are in sync: in
order to compare two counters it is required that they refer exactly
to the same set of packets. Since a flow is continuous and cannot be
stopped when a counter has to be read, it can be difficult to
determine exactly when to read the counter. A possible solution to
overcome this problem is to virtually split the flow in consecutive
blocks by inserting periodically a delimiter so that each counter
refers exactly to the same block of packets. The delimiter could be
for example a special packet inserted artificially into the flow.
However, delimiting the flow using specific packets has some
limitations. First, it requires generating additional packets within
the flow and requires the equipment to be able to process those
packets. In addition, the method is vulnerable to out of order
reception of delimiting packets and, to a lesser extent, to their
loss.
The method proposed in this document follows the second approach, but
it doesn't use additional packets to virtually split the flow in
blocks. Instead, it "marks" the packets so that the packets
belonging to the same block will have the same color, whilst
consecutive blocks will have different colors. Each change of color
represents a sort of auto-synchronization signal that guarantees the
consistency of measurements taken by different devices along the path
(see also [I-D.cociglio-mboned-multicast-pm] and
[I-D.tempia-opsawg-p3m], where this technique was introduced).
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Figure 1 represents a very simple network and shows how the method
can be used to measure packet loss on different network segments: by
enabling the measurement on several interfaces along the path, it is
possible to perform link monitoring, node monitoring or end-to-end
monitoring. The method is flexible enough to measure packet loss on
any segment of the network and can be used to isolate the faulty
element.
Traffic flow
========================================================>
+------+ +------+ +------+ +------+
---<> R1 <>-----<> R2 <>-----<> R3 <>-----<> R4 <>---
+------+ +------+ +------+ +------+
. . . . . .
. . . . . .
. <------> <-------> .
. Node Packet Loss Link Packet Loss .
. .
<--------------------------------------------------->
End-to-End Packet loss
Figure 1: Available measurements
3. Detailed description of the method
This section describes in detail how the method operate. A special
emphasis is given to the measurement of packet loss, that represents
the core application of the method, but applicability to delay and
jitter measurements is also considered.
3.1. Packet loss measurement
The basic idea is to virtually split traffic flows into consecutive
blocks: each block represents a measurable entity unambiguously
recognizable by all network devices along the path. By counting the
number of packets in each block and comparing the values measured by
different network devices along the path, it is possible to measure
packet loss occurred in any single block between any two points.
As discussed in the previous section, a simple way to create the
blocks is to "color" the traffic (two colors are sufficient) so that
packets belonging to different consecutive blocks will have different
colors. Whenever the color changes, the previous block terminates
and the new one begins. Hence, all the packets belonging to the same
block will have the same color and packets of different consecutive
blocks will have different colors. The number of packets in each
block depends on the criterion used to create the blocks:
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o if the color is switched after a fixed number of packets, then
each block will contain the same number of packets (except for any
losses);
o if the color is switched according to a fixed timer, then the
number of packets may be different in each block depending on the
packet rate.
The following figure shows how a flow looks like when it is split in
traffic blocks with colored packets.
A: packet with A coloring
B: packet with B coloring
| | | | |
| | Traffic flow | |
------------------------------------------------------------------->
BBBBBBB AAAAAAAAAAA BBBBBBBBBBB AAAAAAAAAAA BBBBBBBBBBB AAAAAAA
------------------------------------------------------------------->
... | Block 5 | Block 4 | Block 3 | Block 2 | Block 1
| | | | |
Figure 2: Traffic coloring
Figure 3 shows how the method can be used to measure link packet loss
between two adjacent nodes.
Referring to the figure, let's assume we want to monitor the packet
loss on the link between two routers: router R1 and router R2.
According to the method, the traffic is colored alternatively with
two different colors, A and B. Whenever the color changes, the
transition generates a sort of square-wave signal, as depicted in the
following figure.
Color A ----------+ +-----------+ +----------
| | | |
Color B +-----------+ +-----------+
Block n ... Block 3 Block 2 Block 1
<---------> <---------> <---------> <---------> <--------->
Traffic flow
===========================================================>
Color ...AAAAAAAAAAA BBBBBBBBBBB AAAAAAAAAAA BBBBBBBBBBB AAAAAAA...
===========================================================>
Figure 3: Computation of link packet loss
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Traffic coloring could be done by R1 itself or it is already done
before. R1 needs two counters, C(A)R1 and C(B)R1, on its egress
interface: C(A)R1 counts the packets with color A and C(B)R1 counts
those with color B. As long as traffic is colored A, only counter
C(A)R1 will be incremented, while C(B)R1 is not incremented; vice
versa, when the traffic is colored as B, only C(B)R1 is incremented.
C(A)R1 and C(B)R1 can be used as reference values to determine the
packet loss from R1 to any other measurement point down the path.
Router R2, similarly, will need two counters on its ingress
interface, C(A)R2 and C(B)R2, to count the packets received on that
interface and colored with color A and B respectively. When an A
block ends, it is possible to compare C(A)R1 and C(A)R2 and calculate
the packet loss within the block; similarly, when the successive B
block terminates, it is possible to compare C(B)R1 with C(B)R2, and
so on for every successive block.
Likewise, by using two counters on R2 egress interface it is possible
to count the packets sent out of R2 interface and use them as
reference values to calculate the packet loss from R2 to any
measurement point down R2.
Using a fixed timer for color switching offers a better control over
the method: the (time) length of the blocks can be chosen large
enough to simplify the collection and the comparison of measures
taken by different network devices. It's preferable to read the
value of the counters not immediately after the color switch: some
packets could arrive out of order and increment the counter
associated to the previous block (color), so it is worth waiting for
some time. A safe choice is to wait L/2 time units (where L is the
duration for each block) after the color switch, to read the still
counter of the previous color, so the possibility to read a running
counter instead of a still one is minimized. The drawback is that
the longer the duration of the block, the less frequent the
measurement can be taken.
The following table shows how the counters can be used to calculate
the packet loss between R1 and R2. The first column lists the
sequence of traffic blocks while the other columns contain the
counters of A-colored packets and B-colored packets for R1 and R2.
In this example, we assume that the values of the counters are reset
to zero whenever a block ends and its associated counter has been
read: with this assumption, the table shows only relative values,
that is the exact number of packets of each color within each block.
If the values of the counters were not reset, the table would contain
cumulative values, but the relative values could be determined simply
by difference from the value of the previous block of the same color.
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The color is switched on the basis of a fixed timer (not shown in the
table), so the number of packets in each block is different.
+-------+--------+--------+--------+--------+------+
| Block | C(A)R1 | C(B)R1 | C(A)R2 | C(B)R2 | Loss |
+-------+--------+--------+--------+--------+------+
| 1 | 375 | 0 | 375 | 0 | 0 |
| | | | | | |
| 2 | 0 | 388 | 0 | 388 | 0 |
| | | | | | |
| 3 | 382 | 0 | 381 | 0 | 1 |
| | | | | | |
| 4 | 0 | 377 | 0 | 374 | 3 |
| | | | | | |
| ... | ... | ... | ... | ... | ... |
| | | | | | |
| 2n | 0 | 387 | 0 | 387 | 0 |
| | | | | | |
| 2n+1 | 379 | 0 | 377 | 0 | 2 |
+-------+--------+--------+--------+--------+------+
Table 1: Evaluation of counters for packet loss measurements
During an A block (blocks 1, 3 and 2n+1), all the packets are
A-colored, therefore the C(A) counters are incremented to the number
seen on the interface, while C(B) counters are zero. Vice versa,
during a B block (blocks 2, 4 and 2n), all the packets are B-colored:
C(A) counters are zero, while C(B) counters are incremented.
When a block ends (because of color switching) the relative counters
stop incrementing and it is possible to read them, compare the values
measured on router R1 and R2 and calculate the packet loss within
that block.
For example, looking at the table above, during the first block
(A-colored), C(A)R1 and C(A)R2 have the same value (375), which
corresponds to the exact number of packets of the first block (no
loss). Also during the second block (B-colored) R1 and R2 counters
have the same value (388), which corresponds to the number of packets
of the second block (no loss). During blocks three and four, R1 and
R2 counters are different, meaning that some packets have been lost:
in the example, one single packet (382-381) was lost during block
three and three packets (377-374) were lost during block four.
The method applied to R1 and R2 can be extended to any other router
and applied to more complex networks, as far as the measurement is
enabled on the path followed by the traffic flow(s) being observed.
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It's worth mentioning two different strategies that can be used when
implementing the method:
o flow-based: the flow-based strategy is used when only a limited
number of traffic flows need to be monitored. According to this
strategy, only a subset of the flows is colored. Counters for
packet loss measurements can be instantiated for each single flow,
or for the set as a whole, depending on the desired granularity.
A relevant problem with this approach is the necessity to know in
advance the path followed by flows that are subject to
measurement. Path rerouting and traffic load-balancing increase
the issue complexity, especially for unicast traffic. The problem
is easier to solve for multicast traffic where load balancing is
seldom used and static joins are frequently used to force traffic
forwarding and replication.
o link-based: measurements are performed on all the traffic on a
link by link basis. The link could be a physical link or a
logical link. Counters could be instantiated for the traffic as a
whole or for each traffic class (in case it is desired to monitor
each class separately), but in the second case a couple of
counters is needed for each class.
As mentioned, the flow-based measurement requires the identification
of the flow to be monitored and the discovery of the path followed by
the selected flow. It is possible to monitor a single flow or
multiple flows grouped together, but in this case measurement is
consistent only if all the flows in the group follow the same path.
Moreover if a measurement is performed by grouping many flows, it is
not possible to determine exactly which flow was affected by packets
loss. In order to have measures per single flow it is necessary to
configure counters for each specific flow. Once the flow(s) to be
monitored have been identified, it is necessary to configure the
monitoring on the proper nodes. Configuring the monitoring means
configuring the rule to intercept the traffic and configuring the
counters to count the packets. To have just an end-to-end
monitoring, it is sufficient to enable the monitoring on the first
and the last hop routers of the path: the mechanism is completely
transparent to intermediate nodes and independent from the path
followed by traffic flows. On the contrary, to monitor the flow on a
hop-by-hop basis along its whole path it is necessary to enable the
monitoring on every node from the source to the destination. In case
the exact path followed by the flow is not known a priori (i.e. the
flow has multiple paths to reach the destination) it is necessary to
enable the monitoring system on every path: counters on interfaces
traversed by the flow will report packet count, counters on other
interfaces will be null.
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3.1.1. Coloring the packets
The coloring operation is fundamental in order to create packet
blocks. This implies choosing where to activate the coloring and how
to color the packets.
In case of flow-based measurements, the flow to monitor can be
defined by a set of selection rules (e.g. headers fields) used to
match a subset of the packets; in this way it is possible to control
the number of involved nodes, the path followed by the packets and
the size of the flows. it is possible, in general, to have multiple
coloring nodes or a single coloring node that is easier to manage and
doesn't rise any risk of conflict. Coloring in multiple nodes can be
done and the requirement is that the coloring must change
periodically between the nodes according to the timing considerations
in Section 3.2; so every node, that is designated as a measurement
point along the path, should be able to identify unambiguously the
colored packets. Furthermore [I-D.fioccola-ippm-multipoint-alt-mark]
generalizes the coloring for multipoint to multipoint flow. In
addition, it can be advantageous to color the flow as close as
possible to the source because it allows an end-to-end measure if a
measurement point is enabled on the last-hop router as well.
For link-based measurements, all traffic needs to be colored when
transmitted on the link. If the traffic had already been colored,
then it has to be re-colored because the color must be consistent on
the link. This means that each hop along the path must (re-)color
the traffic; the color is not required to be consistent along
different links.
Traffic coloring can be implemented by setting a specific bit in the
packet header and changing the value of that bit periodically. How
to choose the marking field depends on the application and is out of
scope here. However some applications are reported in Section 5.
3.1.2. Counting the packets
For flow-based measurements, assuming that the coloring of the
packets is performed only by the source nodes, the nodes between
source and destination (included) have to count the colored packets
that they receive and forward: this operation can be enabled on every
router along the path or only on a subset, depending on which network
segment is being monitored (a single link, a particular metro area,
the backbone, the whole path). Since the color switches periodically
between two values, two counters (one for each value) are needed: one
counter for packets with color A and one counter for packets with
color B. For each flow (or group of flows) being monitored and for
every interface where the monitoring is active, a couple of counters
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is needed. For example, in order to monitor separately 3 flows on a
router with 4 interfaces involved, 24 counters are needed (2 counters
for each of the 3 flows on each of the 4 interfaces). Furthermore
[I-D.fioccola-ippm-multipoint-alt-mark] generalizes the counting for
multipoint to multipoint flow.
In case of link-based measurements the behaviour is similar except
that coloring and counting operations are performed on a link by link
basis at each endpoint of the link.
Another important aspect to take into consideration is when to read
the counters: in order to count the exact number of packets of a
block the routers must perform this operation when that block has
ended: in other words, the counter for color A must be read when the
current block has color B, in order to be sure that the value of the
counter is stable. This task can be accomplished in two ways. The
general approach suggests to read the counters periodically, many
times during a block duration, and to compare these successive
readings: when the counter stops incrementing means that the current
block has ended and its value can be elaborated safely.
Alternatively, if the coloring operation is performed on the basis of
a fixed timer, it is possible to configure the reading of the
counters according to that timer: for example, reading the counter
for color A every period in the middle of the subsequent block with
color B is a safe choice. A sufficient margin should be considered
between the end of a block and the reading of the counter, in order
to take into account any out-of-order packets.
3.1.3. Collecting data and calculating packet loss
The nodes enabled to perform performance monitoring collect the value
of the counters, but they are not able to directly use this
information to measure packet loss, because they only have their own
samples. For this reason, an external Network Management System
(NMS) can be used to collect and elaborate data and to perform packet
loss calculation. The NMS compares the values of counters from
different nodes and can calculate if some packets were lost (even a
single packet) and also where packets were lost.
The value of the counters needs to be transmitted to the NMS as soon
as it has been read. This can be accomplished by using SNMP or FTP
and can be done in Push Mode or Polling Mode. In the first case,
each router periodically sends the information to the NMS, in the
latter case it is the NMS that periodically polls routers to collect
information. In any case, the NMS has to collect all the relevant
values from all the routers within one cycle of the timer.
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it would be also possible to use a protocol to exchange values of
counters between the two endpoints in order to let them perform the
packet loss calculation for each traffic direction.
A possible approach for the performance measurement architecture is
explained in [I-D.chen-ippm-coloring-based-ipfpm-framework], while
[I-D.chen-ippm-ipfpm-report] introduces new information elements of
IPFIX (RFC 7011 [RFC7011]).
3.2. Timing aspects
This document introduces two color switching method: one is based on
fixed number of packet, the other is based on fixed timer. But the
method based on fixed timer is preferable because is more
deterministic, and will be considered in the rest of the dcoument.
By considering the clock error between network devices R1 and R2,
they must be synchronized to the same clock reference with an
accuracy of +/- L/2 time units, where L is the time duration of the
block. So each colored packet can be assigned to the right batch by
each router. This is because the minimum time distance between two
packets of the same color but belonging to different batches is L
time units.
In practice, there are also out of order at batch boundaries,
strictly related to the delay between measurement points. This means
that, without considering clock error, we wait L/2 after color
switching to be sure to take a still counter.
In summary we need to take into account two contributions: clock
error between network devices and the interval we need to wait to
avoid out of order because of network delay.
The following figure explains both issues.
...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB...
|<======================================>|
| L |
...=========>|<==================><==================>|<==========...
| L/2 L/2 |
|<===>| |<===>|
d | | d
|<==========================>|
available counting interval
Figure 4: Timing aspects
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It is assumed that all network devices are synchronized to a common
reference time with an accuracy of +/- A/2. Thus, the difference
between the clock values of any two network devices is bounded by A.
The guardband d is given by:
d = A + D_max - D_min,
where A is the clock accuracy, D_max is an upper bound on the network
delay between the network devices, and D_min is a lower bound on the
delay.
The available counting interval is L - 2d that must be > 0.
The condition that must be satisfied and is a requirement on the
synchronization accuracy is:
d < L/2.
3.3. One-way delay measurement
The same principle used to measure packet loss can be applied also to
one-way delay measurement. There are three alternatives, as
described hereinafter.
3.3.1. Single marking methodology
The alternation of colors can be used as a time reference to
calculate the delay. Whenever the color changes (that means that a
new block has started) a network device can store the timestamp of
the first packet of the new block; that timestamp can be compared
with the timestamp of the same packet on a second router to compute
packet delay. Considering Figure 2, R1 stores a timestamp TS(A1)R1
when it sends the first packet of block 1 (A-colored), a timestamp
TS(B2)R1 when it sends the first packet of block 2 (B-colored) and so
on for every other block. R2 performs the same operation on the
receiving side, recording TS(A1)R2, TS(B2)R2 and so on. Since the
timestamps refer to specific packets (the first packet of each block)
we are sure that timestamps compared to compute delay refer to the
same packets. By comparing TS(A1)R1 with TS(A1)R2 (and similarly
TS(B2)R1 with TS(B2)R2 and so on) it is possible to measure the delay
between R1 and R2. In order to have more measurements, it is
possible to take and store more timestamps, referring to other
packets within each block.
In order to coherently compare timestamps collected on different
routers, the clocks on the network nodes must be in sync.
Furthermore, a measurement is valid only if no packet loss occurs and
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if packet misordering can be avoided, otherwise the first packet of a
block on R1 could be different from the first packet of the same
block on R2 (f.i. if that packet is lost between R1 and R2 or it
arrives after the next one).
The following table shows how timestamps can be used to calculate the
delay between R1 and R2. The first column lists the sequence of
blocks while other columns contain the timestamp referring to the
first packet of each block on R1 and R2. The delay is computed as a
difference between timestamps. For the sake of simplicity, all the
values are expressed in milliseconds.
+-------+---------+---------+---------+---------+-------------+
| Block | TS(A)R1 | TS(B)R1 | TS(A)R2 | TS(B)R2 | Delay R1-R2 |
+-------+---------+---------+---------+---------+-------------+
| 1 | 12.483 | - | 15.591 | - | 3.108 |
| | | | | | |
| 2 | - | 6.263 | - | 9.288 | 3.025 |
| | | | | | |
| 3 | 27.556 | - | 30.512 | - | 2.956 |
| | | | | | |
| | - | 18.113 | - | 21.269 | 3.156 |
| | | | | | |
| ... | ... | ... | ... | ... | ... |
| | | | | | |
| 2n | 77.463 | - | 80.501 | - | 3.038 |
| | | | | | |
| 2n+1 | - | 24.333 | - | 27.433 | 3.100 |
+-------+---------+---------+---------+---------+-------------+
Table 2: Evaluation of timestamps for delay measurements
The first row shows timestamps taken on R1 and R2 respectively and
referring to the first packet of block 1 (which is A-colored). Delay
can be computed as a difference between the timestamp on R2 and the
timestamp on R1. Similarly, the second row shows timestamps (in
milliseconds) taken on R1 and R2 and referring to the first packet of
block 2 (which is B-colored). Comparing timestamps taken on
different nodes in the network and referring to the same packets
(identified using the alternation of colors) it is possible to
measure delay on different network segments.
For the sake of simplicity, in the above example a single measurement
is provided within a block, taking into account only the first packet
of each block. The number of measurements can be easily increased by
considering multiple packets in the block: for instance, a timestamp
could be taken every N packets, thus generating multiple delay
measurements. Taking this to the limit, in principle the delay could
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be measured for each packet, by taking and comparing the
corresponding timestamps (possible but impractical from an
implementation point of view).
3.3.1.1. Mean delay
As mentioned before, the method previously exposed for measuring the
delay is sensitive to out of order reception of packets. In order to
overcome this problem, a different approach has been considered: it
is based on the concept of mean delay. The mean delay is calculated
by considering the average arrival time of the packets within a
single block. The network device locally stores a timestamp for each
packet received within a single block: summing all the timestamps and
dividing by the total number of packets received, the average arrival
time for that block of packets can be calculated. By subtracting the
average arrival times of two adjacent devices it is possible to
calculate the mean delay between those nodes. When computing the
mean delay, measurement error could be augmented by accumulating
measurement error of a lot of packets. This method is robust to out
of order packets and also to packet loss (only a small error is
introduced). Moreover, it greatly reduces the number of timestamps
(only one per block for each network device) that have to be
collected by the management system. On the other hand, it only gives
one measure for the duration of the block (f.i. 5 minutes), and it
doesn't give the minimum, maximum and median delay values (RFC 6703
[RFC6703]). This limitation could be overcome by reducing the
duration of the block (f.i. from 5 minutes to a few seconds), that
implicates an highly optimized implementation of the method.
By summing the mean delays of the two directions of a path, it is
also possible to measure the two-way mean delay (round-trip delay).
3.3.2. Double marking methodology
The Single marking methodology for one-way delay measurement is
sensitive to out of order reception of packets. The first approach
to overcome this problem is described before and is based on the
concept of mean delay. But the limitation of mean delay is that it
doesn't give information about the delay values distribution for the
duration of the block. Additionally it may be useful to have not
only the mean delay but also the minimum, maximum and median delay
values and, in wider terms, to know more about the statistic
distribution of delay values. So in order to have more information
about the delay and to overcome out of order issues, a different
approach can be introduced: it is based on double marking
methodology.
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Basically, the idea is to use the first marking to create the
alternate flow and, within this colored flow, a second marking to
select the packets for measuring delay/jitter. The first marking is
needed for packet loss and mean delay measurement. The second
marking creates a new set of marked packets that are fully identified
over the network, so that a network device can store the timestamps
of these packets; these timestamps can be compared with the
timestamps of the same packets on a second router to compute packet
delay values for each packet. The number of measurements can be
easily increased by changing the frequency of the second marking.
But the frequency of the second marking must be not too high in order
to avoid out of order issues. Between packets with the second
marking there should be a security time gap (e.g. this gap could be,
at the minimum, the mean network delay calculated with the previous
methodology) to avoid out of order issues and also to have a number
of measurement packets that is rate independent. If a second marking
packet is lost, the delay measurement for the considered block is
corrupted and should be discarded.
Mean delay is calculated on all the packets of a sample and is a
simple computation to be performed for single marking method. In
some cases the mean delay measure is not sufficient to characterize
the sample, and more statistics of delay extent data are needed, e.g.
percentiles, variance and median delay values. The conventional
range (maximum-minimum) should be avoided for several reasons,
including stability of the maximum delay due to the influence by
outliers. RFC 5481 [RFC5481] Section 6.5 highlights how the 99.9th
percentile of delay and delay variation is more helpful to
performance planners. To overcome this drawback the idea is to
couple the mean delay measure for the entire batch with double
marking method, where a subset of batch packets are selected for
extensive delay calculation by using a second marking. In this way
it is possible to perform a detailed analysis on these double marked
packets. Please note that there are classic algorithms for median
and variance calculation, but are out of the scope of this document.
The comparison between the mean delay for the entire batch and the
mean delay on these double marked packets gives an useful information
since it is possible to understand if the double marking measurements
are actually representative of the delay trends.
3.4. Delay variation measurement
Similarly to one-way delay measurement (both for single marking and
double marking), the method can also be used to measure the inter-
arrival jitter. We refer to the definition in RFC 3393 [RFC3393].
The alternation of colors, for single marking method, can be used as
a time reference to measure delay variations. In case of double
marking, the time reference is given by the second marked packets.
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Considering the example depicted in Figure 2, R1 stores a timestamp
TS(A)R1 whenever it sends the first packet of a block and R2 stores a
timestamp TS(B)R2 whenever it receives the first packet of a block.
The inter-arrival jitter can be easily derived from one-way delay
measurement, by evaluating the delay variation of consecutive
samples.
The concept of mean delay can also be applied to delay variation, by
evaluating the average variation of the interval between consecutive
packets of the flow from R1 to R2.
4. Considerations
This section highlights some considerations about the methodology.
4.1. Synchronization
The Alternate Marking technique does not require a strong
synchronization, especially for packet loss and two-way delay
measurement. Only one-way delay measurement requires network devices
to have synchronized clocks.
The color switching is the reference for all the network devices, and
the only requirement to be achieved is that all network devices have
to recognize the right batch along the path.
If the length of the measurement period is L time units, then all
network devices must be synchronized to the same clock reference with
an accuracy of +/- L/2 time units (without considering network
delay). This level of accuracy guarantees that all network devices
consistently match the color bit to the correct block. For example,
if the color is toggeled every second (L = 1 second), then clocks
must be synchronized with an accuracy of +/- 0.5 second to a common
time reference.
This synchronization requirement can be satisfied even with a
relatively inaccurate synchronization method. This is true for
packet loss and two-way delay measurement, instead, for one-way delay
measurement clock synchronization must be accurate.
Therefore, a system that uses only packet loss and two-way delay
measurement does not require synchronization. This is because the
value of the clocks of network devices does not affect the
computation of the two-way delay measurement.
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4.2. Data Correlation
Data Correlation is the mechanism to compare counters and timestamps
for packet loss, delay and delay variation calculation. It could be
performed in several ways depending on the alternate marking
application and use case.
o A possibility is to use a centralized solution using Network
Management System (NMS) to correlate data;
o Another possibility is to define a protocol based distributed
solution, by defining a new protocol or by extending the existing
protocols (e.g. RFC6374, TWAMP, OWAMP) in order to communicate
the counters and timestamps between nodes.
In the following paragraphs an example data correlation mechanism is
explained and could be use independently of the adopted solutions.
When data is collected on the upstream and downstream node, e.g.,
packet counts for packet loss measurement or timestamps for packet
delay measurement, and periodically reported to or pulled by other
nodes or NMS, a certain data correlation mechanism SHOULD be in use
to help the nodes or NMS to tell whether any two or more packet
counts are related to the same block of markers, or any two
timestamps are related to the same marked packet.
The alternate marking method described in this document literally
split the packets of the measured flow into different measurement
blocks, in addition a Block Number could be assigned to each of such
measurement block. The BN is generated each time a node reads the
data (packet counts or timestamps), and is associated with each
packet count and timestamp reported to or pulled by other nodes or
NMS. The value of BN could be calculated as the modulo of the local
time (when the data are read) and the interval of the marking time
period.
When the nodes or NMS see, for example, same BNs associated with two
packet counts from an upstream and a downstream node respectively, it
considers that these two packet counts corresponding to the same
block, i.e. that these two packet counts belong to the same block of
markers from the upstream and downstream node. The assumption of
this BN mechanism is that the measurement nodes are time
synchronized. This requires the measurement nodes to have a certain
time synchronization capability (e.g., the Network Time Protocol
(NTP) RFC 5905 [RFC5905], or the IEEE 1588 Precision Time Protocol
(PTP) [IEEE-1588]). Synchronization aspects are further discussed in
Section 4.
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4.3. Packet Re-ordering
Due to ECMP, packet re-ordering is very common in IP network. The
accuracy of marking based PM, especially packet loss measurement, may
be affected by packet re-ordering. Take a look at the following
example:
Block : 1 | 2 | 3 | 4 | 5 |...
--------|---------|---------|---------|---------|---------|---
Node R1 : AAAAAAA | BBBBBBB | AAAAAAA | BBBBBBB | AAAAAAA |...
Node R2 : AAAAABB | AABBBBA | AAABAAA | BBBBBBA | ABAAABA |...
Figure 5: Packet Reordering
In Figure 5 the packet stream for Node R1 isn't being reordered, and
can be safely assigned to interval blocks, but the packet stream for
Node R2 is being reordered, so, looking at the packet with the marker
of "B" in block 3, there is no safe way to tell whether the packet
belongs to block 2 or block 4.
In general there is the need to assign packets with the marker of "B"
or "A" to the right interval blocks. Most of the packet re-ordering
occur at the edge of adjacent blocks, and they are easy to handle if
the interval of each block is sufficient large. Then, it can assume
that the packets with different marker belong to the block that they
are more close to. If the interval is small, it is difficult and
sometime impossible to determine to which block a packet belongs.
To choose a proper interval is important and how to choose a proper
interval is out of the scope of this document. But an implementation
SHOULD provide a way to configure the interval and allow a certain
degree of packet re-ordering.
5. Applications, implementation and deployment
The methodology described in the previous sections can be applied in
various situations. Basically Alternate Marking technique could be
used in many cases for performance measurement. The only requirement
is to select and mark the flow to be monitored; in this way packets
are batched by the sender and each batch is alternately marked such
that can be easily recognized by the receiver.
Some recent alternate marking method applications are listed below:
o IP flow performance measurement (IPFPM): this application of
marking method is described in
[I-D.chen-ippm-coloring-based-ipfpm-framework]. As an example, in
this document, the last reserved bit of the Flag field of the IPv4
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header is proposed to be used for marking, while a solution for
IPv6 could be to leverage the IPv6 extension header for marking.
o OAM Passive Performance Measurement: In
[I-D.ietf-bier-mpls-encapsulation] two OAM bits from Bit Index
Explicit Replication (BIER) Header are reserved for the passive
performance measurement marking method. [I-D.ietf-bier-pmmm-oam]
details the measurement for multicast service over BIER domain.
In addition, the alternate marking method could also be used in a
Service Function Chaining (SFC) domain. Lastly the application of
the marking method to Network Virtualization Overlays (NVO3)
protocols is considered by [I-D.ietf-nvo3-encap].
o RFC6374 Use Case: RFC6374 [RFC6374] uses the LM packet as the
packet accounting demarcation point. Unfortunately this gives
rise to a number of problems that may lead to significant packet
accounting errors in certain situations.
[I-D.ietf-mpls-flow-ident] discusses the desired capabilities for
MPLS flow identification in order to perform a better in-band
performance monitoring of user data packets. A method of
accomplishing identification is Synonymous Flow Labels (SFL)
introduced in [I-D.bryant-mpls-sfl-framework], while
[I-D.ietf-mpls-rfc6374-sfl] describes RFC6374 performance
measurements with SFL.
o active performance measurement:
[I-D.fioccola-ippm-alt-mark-active] describes how to extend the
existing Active Measurement Protocol, in order to implement
alternate marking methodology.
[I-D.fioccola-ippm-rfc6812-alt-mark-ext] describes an extension to
the Cisco SLA Protocol Measurement-Type UDP-Measurement.
An example of implementation and deployment is explained in the next
section, just to clarify how the method can work.
5.1. Report on the operational experiment
The method described in this document, also called PNPM (Packet
Network Performance Monitoring), has been invented and engineered in
Telecom Italia.
It is important to highlight that the general description of the
methodology in this document is a consequence of the operational
experiment. The foundational elements of the technique have been
tested and the lessons learnt from the operational experiment
inspired the formalization of the Alternate Marking Method as
detailed in the previous sections.
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The methodology is experimented in Telecom Italia's network and is
applied to multicast IPTV channels or other specific traffic flows
with high QoS requirements (i.e. Mobile Backhauling traffic realized
with a VPN MPLS).
This technology has been employed by leveraging functions and tools
available on IP routers and it's currently being used to monitor
packet loss in some portions of the Telecom Italia's network. The
application of the method to delay measurement has also been
evaluated in Telecom Italia's labs.
This Section describes how the experiment has been executed, in
particular how the features currently available on existing routing
platforms can be used to apply the method, in order to give an
example of implementation and deployment.
The operational test, here described, uses the flow-based strategy,
as defined in Section 3. Instead the link-based strategy could be
applied to physical link or a logical link (e.g. Ethernet VLAN or a
MPLS PW).
The implementation of the method leverages the available router
functions, since the experiment has been done by a Service Provider
(as Telecom Itlaia is) on its own network. So, with current router
implementations, only QoS related fields and features offer the
required flexibility to set bits in the packet header. In case a
Service Provider only uses the three most significant bits of the
DSCP field (corresponding to IP Precedence) for QoS classification
and queuing, it is possible to use the two less significant bits of
the DSCP field (bit 0 and bit 1) to implement the method without
affecting QoS policies. That is the approach used for the
experiment. One of the two bits (bit 0) could be used to identify
flows subject to traffic monitoring (set to 1 if the flow is under
monitoring, otherwise it is set to 0), while the second (bit 1) can
be used for coloring the traffic (switching between values 0 and 1,
corresponding to color A and B) and creating the blocks.
The experiment considers a flow as all the packets sharing the same
source IP address or the same destination IP address, depending on
the direction. In practice, once the flow has been defined, coloring
the traffic using the DSCP field can be implemented by configuring on
the router output interface an access list that intercepts the
flow(s) to be monitored and applies to them a policy that sets the
DSCP field accordingly. Since traffic coloring has to be switched
between the two values over time, the policy needs to be modified
periodically: an automatic script is used to perform this task on the
basis of a fixed timer. The automatic script is loaded on board of
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the router and automatizes the basic operations that are needed to
realize the methodology.
After the traffic is colored using the DSCP field, all the routers on
the path can perform the counting. For this purpose an access-list
that matches specific DSCP values can be used to count the packets of
the flow(s) being monitored. The same access-list can be installed
on all the routers of the path. In addition, network flow
monitoring, such as provided by IPFIX (RFC 7011 [RFC7011]), can be
used to recognize timestamps of first/last packet of a batch in order
to enable one of the alternatives to measure the delay as detailed in
Section 3.3.
In the Telecom Italia's experiment the timer is set to 5 minutes, so
the sequence of actions of the script is also executed every 5
minutes. This value has showed to be a good compromise between
measurement frequency and stability of the measurement (i.e.
possibility to collect all the measures referring to the same block).
For this expertiment, both counters and any other data are collected
by using the automatic script that sends out these to a Network
Management System (NMS). The NMS is responsible for packet loss
calculation, performed by comparing the values of counters from the
routers along the flow(s) path. 5 minutes timer for color switching
is a safe choice for reading the counters and is also coherent with
the reporting window of the NMS.
Note that the use of the DSCP field for marking implies that the
method in this case works reliably only within a single management
and operation domain.
Lastly, the Telecom Italia experiment scales up to 1000 flows
monitored together on a single router, while an implementation on
dedicated hardware scales more, but it was tested only in labs for
now.
5.1.1. Metric transparency
Since a Service Provider application is described here, the method
can be applied to end-to-end services supplied to Customers. So it
is important to highlight that the method MUST be transparent outside
the Service Provider domain.
In Telecom Italia's implementation the source node colors the packets
with a policy that is modified periodically via an automatic script
in order to alternate the DSCP field of the packets. The nodes
between source and destination (included) have to count with an
access-list the colored packets that they receive and forward.
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Moreover the destination node has an important role: the colored
packets are intercepted and a policy restores and sets the DSCP field
of all the packets to the initial value. In this way the metric is
transparent because outside the section of the network under
monitoring the traffic flow is unchanged.
In such a case, thanks to this restoring technique, network elements
outside the Alternate Marking monitoring domain (e.g. the two
Provider Edge nodes of the Mobile Backhauling VPN MPLS) are totally
anaware that packets were marked. So this restoring technique makes
Alternate Marking completely transparent outside its monitoring
domain.
6. Hybrid measurement
The method has been explicitly designed for passive measurements but
it can also be used with active measurements. In order to have both
end to end measurements and intermediate measurements (hybrid
measurements) two end points can exchanges artificial traffic flows
and apply alternate marking over these flows. In the intermediate
points artificial traffic is managed in the same way as real traffic
and measured as specified before. So the application of marking
method can simplify also the active measurement, as explained in
[I-D.fioccola-ippm-alt-mark-active].
7. Compliance with RFC6390 guidelines
RFC6390 [RFC6390] defines a framework and a process for developing
Performance Metrics for protocols above and below the IP layer (such
as IP-based applications that operate over reliable or datagram
transport protocols).
This document doesn't aim to propose a new Performance Metric but a
new method of measurement for a few Performance Metrics that have
already been standardized. Nevertheless, it's worth applying
[RFC6390] guidelines to the present document, in order to provide a
more complete and coherent description of the proposed method. We
used a subset of the Performance Metric Definition template defined
by [RFC6390].
o Metric name and description: as already stated, this document
doesn't propose any new Performance Metric. On the contrary, it
describes a novel method for measuring packet loss [RFC7680]. The
same concept, with small differences, can also be used to measure
delay [RFC7679], and jitter [RFC3393]. The document mainly
describes the applicability to packet loss measurement.
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o Method of Measurement or Calculation: according to the method
described in the previous sections, the number of packets lost is
calculated by subtracting the value of the counter on the source
node from the value of the counter on the destination node. Both
counters must refer to the same color. The calculation is
performed when the value of the counters is in a steady state.
The steady state is an intrinsic characteristic of the marking
method counters because the alternation of color makes the
counters associated to each color still one at a time for the
duration of a marking period.
o Units of Measurement: the method calculates and reports the exact
number of packets sent by the source node and not received by the
destination node.
o Measurement Points: the measurement can be performed between
adjacent nodes, on a per-link basis, or along a multi-hop path,
provided that the traffic under measurement follows that path. In
case of a multi-hop path, the measurements can be performed both
end-to-end and hop-by-hop.
o Measurement Timing: the method have a constraint on the frequency
of measurements. This is detailed in Section 3.2, where it is
specified that the marking period and the guardband interval are
strictly related each other to avoid out of order issues. That is
because, in order to perform a measure, the counter must be in a
steady state and this happens when the traffic is being colored
with the alternate color. As an example in the experiment of the
method the time interval is set to 5 minutes, while other
optimized implementations can also use a marking period of a few
seconds.
o Implementation: the experiment of the method uses two encodings of
the DSCP field to color the packets; this enables the use of
policy configurations on the router to color the packets and
accordingly configure the counter for each color. The path
followed by traffic being measured should be known in advance in
order to configure the counters along the path and be able to
compare the correct values.
o Verification: both in the Lab and in the operational network the
methodology has been tested and experimented for packet loss and
delay measurements by using traffic generators together with
precision test instruments and network emulators.
o Use and Applications: the method can be used to measure packet
loss with high precision on live traffic; moreover, by combining
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end-to-end and per-link measurements, the method is useful to
pinpoint the single link that is experiencing loss events.
o Reporting Model: the value of the counters has to be sent to a
centralized management system that perform the calculations; such
samples must contain a reference to the time interval they refer
to, so that the management system can perform the correct
correlation; the samples have to be sent while the corresponding
counter is in a steady state (within a time interval), otherwise
the value of the sample should be stored locally.
o Dependencies: the values of the counters have to be correlated to
the time interval they refer to; moreover, as far the experiment
of the method is based on DSCP values, there are significant
dependencies on the usage of the DSCP field: it must be possible
to rely on unused DSCP values without affecting QoS-related
configuration and behavior; moreover, the intermediate nodes must
not change the value of the DSCP field not to alter the
measurement.
o Organization of Results: the method of measurement produces
singletons.
o Parameters: currently, the main parameter of the method is the
time interval used to alternate the colors and read the counters.
8. Security Considerations
This document specifies a method to perform measurements in the
context of a Service Provider's network and has not been developed to
conduct Internet measurements, so it does not directly affect
Internet security nor applications which run on the Internet.
However, implementation of this method must be mindful of security
and privacy concerns.
There are two types of security concerns: potential harm caused by
the measurements and potential harm to the measurements.
o Harm caused by the measurement: the measurements described in this
document are passive, so there are no new packets injected into
the network causing potential harm to the network itself and to
data traffic. Nevertheless, the method implies modifications on
the fly to a header or encapsulation of the data packets: this
must be performed in a way that doesn't alter the quality of
service experienced by packets subject to measurements and that
preserve stability and performance of routers doing the
measurements. One of the main security threats in OAM protocols
is network reconnaissance; an attacker can gather information
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about the network performance by passively eavesdropping to OAM
messages. The advantage of the methods described in this document
is that the marking bits are the only information that is
exchanged between the network devices. Therefore, passive
eavesdropping to data plane traffic does not allow attackers to
gain information about the network performance.
o Harm to the measurement: the measurements could be harmed by
routers altering the marking of the packets, or by an attacker
injecting artificial traffic. Authentication techniques, such as
digital signatures, may be used where appropriate to guard against
injected traffic attacks. Since the measurement itself may be
affected by routers (or other network devices) along the path of
IP packets intentionally altering the value of marking bits of
packets, as mentioned above, the mechanism specified in this
document can be applied just in the context of a controlled
domain, and thus the routers (or other network devices) are
locally administered and this type of attack can be avoided. In
addition, an attacker can't gain information about network
performance from a single monitoring point, and must use
synchronized monitoring points at multiple points on the path,
because they have to do the same kind of measurement and
aggregation that Service Providers using Alternate Marking must
do.
The privacy concerns of network measurement are limited because the
method only relies on information contained in the header or
encapsulation without any release of user data.Although information
in the header or encapsulation is metadata that can be used to
compromise the privacy of users, the limited marking technique in
this document seems unlikely to substantially increase the existing
privacy risks from header or encapsulation metadata.It might be
theoretically possible to modulate the marking to serve as a covert
channel, but it would have a very low data rate if it is to avoid
adversely affecting the measurement systems that monitor the marking.
Delay attacks are another potential threat in the context of this
document. Delay measurement is performed using a specific packet in
each block, marked by a dedicated color bit. Therefore, a man-in-
the-middle attacker can selectively induce synthetic delay only to
delay-colored packets, causing systematic error in the delay
measurements. As discussed in previous sections, the methods
described in this document rely on an underlying time synchronization
protocol. Thus, by attacking the time protocol an attacker can
potentially compromise the integrity of the measurement. A detailed
discussion about the threats against time protocols and how to
mitigate them is presented in RFC 7384 [RFC7384].
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9. IANA Considerations
There are no IANA actions required.
10. Acknowledgements
The previous IETF drafts about this technique were:
[I-D.cociglio-mboned-multicast-pm] and [I-D.tempia-opsawg-p3m].
The authors would like to thank Alberto Tempia Bonda, Domenico
Laforgia, Daniele Accetta and Mario Bianchetti for their contribution
to the definition and the implementation of the method.
The authors would also thank Spencer Dawkins, Carlos Pignataro, Brian
Haberman and Eric Vyncke for their assistance and their detailed and
precious reviews.
11. References
11.1. Normative References
[IEEE-1588]
IEEE 1588-2008, "IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and
Control Systems", July 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393,
DOI 10.17487/RFC3393, November 2002,
<https://www.rfc-editor.org/info/rfc3393>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC7679] Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
Ed., "A One-Way Delay Metric for IP Performance Metrics
(IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January
2016, <https://www.rfc-editor.org/info/rfc7679>.
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[RFC7680] Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
Ed., "A One-Way Loss Metric for IP Performance Metrics
(IPPM)", STD 82, RFC 7680, DOI 10.17487/RFC7680, January
2016, <https://www.rfc-editor.org/info/rfc7680>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
11.2. Informative References
[I-D.bryant-mpls-sfl-framework]
Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S.,
and G. Mirsky, "Synonymous Flow Label Framework", draft-
bryant-mpls-sfl-framework-05 (work in progress), June
2017.
[I-D.chen-ippm-coloring-based-ipfpm-framework]
Chen, M., Zheng, L., Mirsky, G., Fioccola, G., and T.
Mizrahi, "IP Flow Performance Measurement Framework",
draft-chen-ippm-coloring-based-ipfpm-framework-06 (work in
progress), March 2016.
[I-D.chen-ippm-ipfpm-report]
Chen, M., Zheng, L., and G. Mirsky, "IP Flow Performance
Measurement Report", draft-chen-ippm-ipfpm-report-01 (work
in progress), April 2016.
[I-D.cociglio-mboned-multicast-pm]
Cociglio, M., Capello, A., Bonda, A., and L. Castaldelli,
"A method for IP multicast performance monitoring", draft-
cociglio-mboned-multicast-pm-01 (work in progress),
October 2010.
[I-D.fioccola-ippm-alt-mark-active]
Fioccola, G., Clemm, A., Bryant, S., Cociglio, M.,
Chandramouli, M., and A. Capello, "Alternate Marking
Extension to Active Measurement Protocol", draft-fioccola-
ippm-alt-mark-active-01 (work in progress), March 2017.
[I-D.fioccola-ippm-multipoint-alt-mark]
Fioccola, G., Cociglio, M., Sapio, A., and R. Sisto,
"Multipoint Alternate Marking method for passive and
hybrid performance monitoring", draft-fioccola-ippm-
multipoint-alt-mark-01 (work in progress), October 2017.
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[I-D.fioccola-ippm-rfc6812-alt-mark-ext]
Fioccola, G., Clemm, A., Cociglio, M., Chandramouli, M.,
and A. Capello, "Alternate Marking Extension to Cisco SLA
Protocol RFC6812", draft-fioccola-ippm-rfc6812-alt-mark-
ext-01 (work in progress), March 2016.
[I-D.ietf-bier-mpls-encapsulation]
Wijnands, I., Rosen, E., Dolganow, A., Tantsura, J.,
Aldrin, S., and I. Meilik, "Encapsulation for Bit Index
Explicit Replication in MPLS and non-MPLS Networks",
draft-ietf-bier-mpls-encapsulation-12 (work in progress),
October 2017.
[I-D.ietf-bier-pmmm-oam]
Mirsky, G., Zheng, L., Chen, M., and G. Fioccola,
"Performance Measurement (PM) with Marking Method in Bit
Index Explicit Replication (BIER) Layer", draft-ietf-bier-
pmmm-oam-03 (work in progress), October 2017.
[I-D.ietf-mpls-flow-ident]
Bryant, S., Pignataro, C., Chen, M., Li, Z., and G.
Mirsky, "MPLS Flow Identification Considerations", draft-
ietf-mpls-flow-ident-05 (work in progress), July 2017.
[I-D.ietf-mpls-rfc6374-sfl]
Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S.,
Mirsky, G., and G. Fioccola, "RFC6374 Synonymous Flow
Labels", draft-ietf-mpls-rfc6374-sfl-01 (work in
progress), December 2017.
[I-D.ietf-nvo3-encap]
Boutros, S., Ganga, I., Garg, P., Manur, R., Mizrahi, T.,
Mozes, D., Nordmark, E., Smith, M., Aldrin, S., and I.
Bagdonas, "NVO3 Encapsulation Considerations", draft-ietf-
nvo3-encap-01 (work in progress), October 2017.
[I-D.tempia-opsawg-p3m]
Capello, A., Cociglio, M., Castaldelli, L., and A. Bonda,
"A packet based method for passive performance
monitoring", draft-tempia-opsawg-p3m-04 (work in
progress), February 2014.
[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation
Applicability Statement", RFC 5481, DOI 10.17487/RFC5481,
March 2009, <https://www.rfc-editor.org/info/rfc5481>.
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[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374,
DOI 10.17487/RFC6374, September 2011,
<https://www.rfc-editor.org/info/rfc6374>.
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390,
DOI 10.17487/RFC6390, October 2011,
<https://www.rfc-editor.org/info/rfc6390>.
[RFC6703] Morton, A., Ramachandran, G., and G. Maguluri, "Reporting
IP Network Performance Metrics: Different Points of View",
RFC 6703, DOI 10.17487/RFC6703, August 2012,
<https://www.rfc-editor.org/info/rfc6703>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<https://www.rfc-editor.org/info/rfc7011>.
[RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
Weingarten, "An Overview of Operations, Administration,
and Maintenance (OAM) Tools", RFC 7276,
DOI 10.17487/RFC7276, June 2014,
<https://www.rfc-editor.org/info/rfc7276>.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <https://www.rfc-editor.org/info/rfc7384>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/info/rfc7799>.
Authors' Addresses
Giuseppe Fioccola (editor)
Telecom Italia
Via Reiss Romoli, 274
Torino 10148
Italy
Email: giuseppe.fioccola@telecomitalia.it
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Alessandro Capello
Telecom Italia
Via Reiss Romoli, 274
Torino 10148
Italy
Email: alessandro.capello@telecomitalia.it
Mauro Cociglio
Telecom Italia
Via Reiss Romoli, 274
Torino 10148
Italy
Email: mauro.cociglio@telecomitalia.it
Luca Castaldelli
Telecom Italia
Via Reiss Romoli, 274
Torino 10148
Italy
Email: luca.castaldelli@telecomitalia.it
Mach(Guoyi) Chen
Huawei Technologies
Email: mach.chen@huawei.com
Lianshu Zheng
Huawei Technologies
Email: vero.zheng@huawei.com
Greg Mirsky
ZTE
USA
Email: gregimirsky@gmail.com
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Tal Mizrahi
Marvell
6 Hamada st.
Yokneam
Israel
Email: talmi@marvell.com
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