Internet DRAFT - draft-fan-opsawg-packet-loss
draft-fan-opsawg-packet-loss
Network Working Group P. Fan
Internet-Draft L. Huang
Intended status: Informational China Mobile
Expires: January 06, 2014 M. Chen
Huawei Technologies
N. Kumar
Cisco Systems
July 05, 2013
IP Packet Loss Rate Measurement Testing and Problem Statement
draft-fan-opsawg-packet-loss-01
Abstract
This document describes common methods for measuring packet loss rate
and their effectiveness. Issues encountered when using the methods
and necessary considerations are also discussed and recommended.
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 http://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
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 January 06, 2014.
Copyright Notice
Copyright (c) 2013 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
(http://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
Fan, et al. Expires January 06, 2014 [Page 1]
Internet-Draft Packet Loss Measurement July 2013
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Methods for Packet Loss Rate Measurement . . . . . . . . . . 3
2.1. Active Approach . . . . . . . . . . . . . . . . . . . . . 3
2.1.1. Ping . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.2. OWAMP and TWAMP . . . . . . . . . . . . . . . . . . . 3
2.1.3. Proprietary Tools . . . . . . . . . . . . . . . . . . 4
2.2. Passive Approach . . . . . . . . . . . . . . . . . . . . 4
2.2.1. Interface Statistics Report . . . . . . . . . . . . . 4
2.2.2. Coloring Based Performance Measurement . . . . . . . 5
3. Test on Packet Loss Rate Measurement . . . . . . . . . . . . 5
3.1. Basic Test Information . . . . . . . . . . . . . . . . . 5
3.2. Ping with CLI vs. SNMP . . . . . . . . . . . . . . . . . 6
3.3. Ping Behaviors of Routers . . . . . . . . . . . . . . . . 6
3.4. Statistics Report of Routers . . . . . . . . . . . . . . 10
4. Measurement Issues . . . . . . . . . . . . . . . . . . . . . 10
4.1. Issues with Ping . . . . . . . . . . . . . . . . . . . . 10
4.2. Issues with OWAMP and TWAMP . . . . . . . . . . . . . . . 11
4.3. Issues with Proprietary Tools . . . . . . . . . . . . . . 11
4.4. Issues with Interface Statistics Report . . . . . . . . . 12
4.5. Issues with Coloring Based Performance Measurement . . . 12
5. Considerations and Recommendations . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
IP packet loss rate is one of the important metrics that are
frequently used to measure IP performance of a data path or link. A
general framework of IP performance metrics is provided in [RFC2330],
including fundamental concepts definition and issues related to
defining sound metrics and methodologies. [RFC2680] and [RFC6673]
further define metrics for one-way and round-trip packet loss.
In practical network operation, a number of methods are used by
network engineers to calculate packet loss rate, and one of the
common ways is to use ping. By checking ping statistics, people
expect to get the idea of traffic transmission condition on the link.
This document gives an overview of the frequently used methods for
Fan, et al. Expires January 06, 2014 [Page 2]
Internet-Draft Packet Loss Measurement July 2013
measuring IP packet loss rate, and describes a test on packet loss
rate measurement with multiple methods using routers from different
vendors. Issues that should be taken into consideration during the
measurement using different methods are discussed. Causes analysis
and processing mechanisms of routers are also covered. It is
expected that an operable measurement scheme with consistent testing
results and equal treatment of network components can be reached.
2. Methods for Packet Loss Rate Measurement
This section describes common methods for measuring packet loss rate.
2.1. Active Approach
2.1.1. Ping
Ping (ICMP echo request/reply) is a useful tool to examine the
connectivity and performance of a path between two nodes in the
network. The source node generates echo request packets with
configured size, interval, count and other settings, and the
destination node sends back an echo reply packet once it receives a
request. Then we count the packets sent out and received and get the
round-trip packet loss rate on the link between source and
destination. This approach is clear and convenient, and is
frequently used by engineers when packet loss rate is needed.
In practical network operation, the ping testing can be initiated
manually and directly on the node by engineers, for example through
the command line interface (CLI) of a router, or activated indirectly
by instructions, for example through SNMP messages sent from network
management system.
No matter through CLI or SNMP, ping testing can be conducted directly
on the endpoint devices of the link to be tested, or other nodes as
long as the request/reply packets pass through the link. Those nodes
are often referred to as probes, which can be a router or a PC
server, directly connected or indirectly reachable to the endpoints.
Usually the probes and paths to the endpoints are not supposed to be
congested to avoid affecting the ping testing result.
2.1.2. OWAMP and TWAMP
The One-way Active Measurement Protocol (OWAMP, [RFC4656]) and Two-
Way Active Measurement Protocol (TWAMP, [RFC5357]) are defined by the
IP Performance Metrics (IPPM) working group. They provide a method
and protocol for measuring delay and packet loss of IP flows, and are
designed for wide scale deployment in the network to provide
ubiquitous performance data. Both OWAMP and TWAMP use control
Fan, et al. Expires January 06, 2014 [Page 3]
Internet-Draft Packet Loss Measurement July 2013
protocol and test protocol. The control protocol is used to
negotiate test session between test endpoints, start and stop the
test, and fetch the test result for OWAMP. The test protocol runs
over UDP and conducts the test.
OWAMP can be used to perform one-way packet loss measurement, and
requires synchronized time defined by GPS. The test results are
collected at the receiving endpoints and returned using the control
protocol. TWAMP is more simplified, and used for two-way packet loss
measurement. The opposite endpoint is regarded as a reflector, and
the test results are collected at the sender.
2.1.3. Proprietary Tools
There are some other proprietary performance measurement tools
incorporating embedded and external probes. The probes generate and
inject extra packets into the network to mimic the service flows that
are intended to be tested. The performance of the target service
flows can be evaluated by measuring the performance of the injected
packets. Compared with Ping, these proprietary tools normally
support more services, which include not only ICMP, but TCP, UDP,
HTTP, etc.
The embedded proprietary tools have been widely implemented by
routers to provide automatic detection of IP performance. Examples
of this kind of tools include RPM (Juniper), IPSLA (Cisco), NQA
(Huawei/H3C), SAA (ALU), etc. By necessary configurations on the
router, the embedded tools support multi-service testing of multiple
queues on an interface. Packet loss rate can be measured with ICMP
ping function of the tool. Routers send out ICMP packets
automatically according to the configured parameters, so the embedded
tool is working in a similar way as ping method described above.
2.2. Passive Approach
2.2.1. Interface Statistics Report
Forwarding devices maintain statistics report of every interface.
The report shows the detailed status of the interface as well as
traffic information, including inbound and outbound speed and packet
count. For a typical router, traffic statistics show number of
packets transmitted and discarded by an interface, and even on the
basis of QoS queue, so the entire packet loss rate of a link or
packet loss rates regarding different queues can be calculated.
Traffic data on the report can be displayed through CLI or obtained
using SNMP which allows automatic packet loss sampling.
Fan, et al. Expires January 06, 2014 [Page 4]
Internet-Draft Packet Loss Measurement July 2013
2.2.2. Coloring Based Performance Measurement
The concept of coloring based performance measurement is introduced
in [I-D.tempia-opsawg-p3m], and [I-D.chen-coloring-based-ipfpm-
framework] defines a framework for coloring based IP Flow Performance
Measurement (IPFPM). By periodically setting/changing one or more
bits of the IP header of the packets that belong to an IP flow to
"color" the packets into different colors, the IP flow is split into
different consecutive blocks. Packets in the same block have the
same color and packets in consecutive blocks have different colors.
This method gives a way to a measurement node to count and calculate,
without inserting any extra auxiliary OAM packets, packet loss based
on each color block. Since the measurement is based on the real
traffic data, the measurement results will reflect the real
performance of the tested flow.
3. Test on Packet Loss Rate Measurement
This section describes test result on packet loss rate measurement
using different methods. Test equipment covers routers from several
vendors. Results show the diverse outcome of the methods used, and
the diverse responding mechanism of routers.
3.1. Basic Test Information
The basic topology of testing can be depicted as follows.
+--------+ +---------+ +---------+ +--------+
| Probe1 |------| Router1 |-----------| Router2 |------| Probe2 |
+--------+ GE +---------+ 10G POS +---------+ GE +--------+
| | | |
10GE | | 10GE 10GE | | 10GE
| | | |
Port1 | | Port2 Port3 | | Port4
+---------------------------+
| Tester |
+---------------------------+
Figure 1: Basic topology for packet loss rate test
Two routers are connected by a 10G POS link, and each router is
connected to the tester by two 10GE links. The tester generates
unidirectional/bidirectional traffic between port 1 and port 3, and
between port 2 and port 4, with frame length of 400 bytes. The total
volume of traffic injected into a router by the tester is more than
10G, leading to congestion when the traffic passes through the 10G
POS link between the two routers. Routers and probes generate ping
packets for testing, with frame length of 400 and DSCP field of 0.
Fan, et al. Expires January 06, 2014 [Page 5]
Internet-Draft Packet Loss Measurement July 2013
We tested routers from 3 vendors, indicated as A, B, and C in the
following parts of discussion. The tester generated different levels
of congestion, and we tested packet loss rates on the 10G POS
interconnection link on those congestion levels with CLI, SNMP, and
interface statistics report.
3.2. Ping with CLI vs. SNMP
Some routing boxes by default treat ping packets generated with CLI
and SNMP in different ways. The following is a test on this issue.
to tester +---------+ +---------+ to tester
---10G----| Router1 |-----------| Router2 |----10G---
---10G----| | 10G | |----10G---
+---------+ +---------+
ping with CLI ---------->
ping with SNMP---------->
test traffic
---------------------------------------------------->
The tester generates test traffic at 20 Gbps, and sends the traffic
into a router of vendor A. The traffic goes through the 10G
interconnecting link and past the router of vendor B on the other
end. We use ping with CLI and SNMP on router A to test packet loss
rate on the interconnecting link. The DSCP fields of test traffic
and ping packets are all left to be 0..
By default, router A forwards the test traffic with the basic
priority, like BE class. The ping packets with CLI are also treated
as of best effort class, but ping packets with SNMP are given a
higher priority, some class like network control. So the two kinds
of ping are actually testing packet loss of streams in different
classes. The test result verifies the issue. Ping with SNMP shows
no packet loss, and ping with CLI shows a packet loss rate of around
50%.
The forwarding class of ICMP packets can be configured on router A.
In the following tests we put all traffic in the same basic class.
3.3. Ping Behaviors of Routers
We considered the following test cases (TCs) when investigating
packet loss rate with ping on the link between two different routers.
TC 1: Router sends ICMP echo request packets with SNMP instruction
to the peering router.
Fan, et al. Expires January 06, 2014 [Page 6]
Internet-Draft Packet Loss Measurement July 2013
+---------+ +---------+
| Router1 |-----------| Router2 |
+---------+ +---------+
ping with SNMP---------->
TC 2: Router sends ICMP echo request packets with CLI to the peering
router.
+---------+ +---------+
| Router1 |-----------| Router2 |
+---------+ +---------+
ping with CLI ---------->
TC 3: Router sends ICMP echo request packets with SNMP instruction
to the probe behind the peering router.
+---------+ +---------+ +--------+
| Router1 |-----------| Router2 |------| Probe2 |
+---------+ +---------+ +--------+
ping with SNMP--------------------------->
TC 4: Router sends ICMP echo request packets with CLI to the probe
behind the peering router.
+---------+ +---------+ +--------+
| Router1 |-----------| Router2 |------| Probe2 |
+---------+ +---------+ +--------+
ping with CLI --------------------------->
TC 5: Probe behind router sends ICMP echo request packets to the
probe behind the peering router.
+--------+ +---------+ +---------+ +--------+
| Probe1 |------| Router1 |-----------| Router2 |------| Probe2 |
+--------+ +---------+ +---------+ +--------+
ping with CLI-------------------------------------------->
Fan, et al. Expires January 06, 2014 [Page 7]
Internet-Draft Packet Loss Measurement July 2013
The link between the two routers is injected bidirectional or
unidirectional test traffic to cause congestion. The packet loss
rate of test traffic is calculated with the Rx and Tx rate on the
tester. We use router A, B and C in pairs and get the ICMP packet
loss rate in each test case. The comparison of the packet loss rate
of ICMP and test traffic shows diverse behaviors of ping process on
routers. The following tables show the test results
+------------------------------------------------------------------+
| Pkt loss rate of | ICMP pkt loss rate | ICMP pkt loss rate |
| test traffic |(echo req drct: A->B)|(echo req drct: B->A)|
|----------------------|---------------------|---------------------|
| A->B B->A | TC1 TC2 TC3 TC4 TC5 | TC1 TC2 TC3 TC4 TC5 |
|----------------------|---------------------|---------------------|
| 48.60% 48.60% | 54% 56% 80% 76% 73% | 54% 54% 58% 58% 77% |
| 28% 28% | 27% 30% 61% 58% 47% | 32% 32% 27% 21% 53% |
| 7.60% 7.60% | 9% 12% 15% 18% 21% | 13% 15% 11% 11% 21% |
| 48.60% No traffic | 54% 56% 57% 54% 54% | 62% 56% 54% 48% 56% |
| 28% No traffic | 31% 33% 32% 33% 33% | 36% 34% 34% 35% 35% |
| 7.60% No traffic | 14% 13% 12% 9% 14% | 14% 13% 11% 12% 14% |
|No traffic 48.60% | 1% 0% 54% 50% 47% | 1% 1% 0% 1% 50% |
|No traffic 28% | 0% 0% 26% 31% 28% | 0% 0% 0% 0% 28% |
|No traffic 7.60% | 0% 0% 10% 9% 9% | 0% 0% 0% 0% 8% |
+------------------------------------------------------------------+
Table 1: Test result when interconnecting router A and router B
+------------------------------------------------------------------+
| Pkt loss rate of | ICMP pkt loss rate | ICMP pkt loss rate |
| test traffic |(echo req drct: A->B)|(echo req drct: C->A)|
|----------------------|---------------------|---------------------|
| A->C C->A | TC1 TC2 TC3 TC4 TC5 | TC1 TC2 TC3 TC4 TC5 |
|----------------------|---------------------|---------------------|
| 48.70% 44.70% | 58% 54% 57% 58% 53% | 57% 55% 48% 57% 56% |
| 28% 22.40% | 38% 31% 37% 33% 35% | 30% 33% 33% 37% 35% |
| 7.70% 7.30% | 14% 13% 13% 13% 12% | 16% 13% 15% 16% 14% |
| 48.80% No traffic | 50% 54% 51% 53% 55% | 54% 56% 55% 59% 57% |
| 28% No traffic | 27% 29% 32% 32% 33% | 35% 30% 35% 33% 33% |
| 7.60% No traffic | 11% 10% 15% 15% 13% | 11% 11% 15% 15% 13% |
|No traffic 44.50% | 0% 0% 0% 0% 0% | 0% 0% 0% 0% 0% |
|No traffic 22.60% | 0% 0% 0% 0% 0% | 0% 0% 0% 0% 0% |
|No traffic 7.74% | 0% 0% 0% 0% 0% | 0% 0% 0% 0% 0% |
+------------------------------------------------------------------+
Table 2: Test result when interconnecting router A and router C
+------------------------------------------------------------------+
| Pkt loss rate of | ICMP pkt loss rate | ICMP pkt loss rate |
Fan, et al. Expires January 06, 2014 [Page 8]
Internet-Draft Packet Loss Measurement July 2013
| test traffic |(echo req drct: C->B)|(echo req drct: B->C)|
|----------------------|---------------------|---------------------|
| C->B B->C | TC1 TC2 TC5 | TC1 TC2 TC5 |
|----------------------|---------------------|---------------------|
| 48.76% 44.69% | 1% 0% 54% | 0% 1% 50%|
| 28.04% 22.29% | 0% 0% 40% | 0% 1% 29%|
| 7.62% 7.62% | 0% 0% 11% | 0% 0% 8%|
| 48.69% No traffic | 0% 0% 0% | 0% 0% 0%|
| 28.03% No traffic | 0% 0% 0% | 0% 0% 0%|
| 7.62% No traffic | 0% 0% 0% | 0% 0% 0%|
|No traffic 44.50% | 1% 0% 51% | 0% 1% 51%|
|No traffic 22.29% | 0% 0% 29% | 0% 0% 29%|
|No traffic 7.74% | 0% 0% 9% | 0% 0% 10%|
+------------------------------------------------------------------+
Table 3: Test result when interconnecting router C and router B
The behaviors of the three vendors' routers are summarized here, and
we leave the discussion on reasons for the behaviors to the next
section.
Router A: Ping by router A with SNMP, CLI and by the probe behind
router A lead to similar usable results. However, all the methods
encounter larger errors when the test traffic is less congested.
Router B: Ping by router B with SNMP and CLI will not report
correctly the packet loss rate of test traffic. Ping by the probe
behind router B gives usable result of packet loss rate, but also
with certain errors.
Router C: Ping by router C with SNMP, CLI and by the probe behind
router C will not report correctly the packet loss rate of test
traffic.
We can further highlight the outcomes when testing the packet loss
rate on the interconnection link between each pair of routers.
Router A - router B: If one wants to get relatively accurate value
of packet loss rate in all congestion scenarios, he is advised to
use ping between probes (test case 5), or have A generate ping to
the probe behind B.
Router A - router C: All the test methods will only reflect the
outbound packet loss rate of A.
Router B - router C: Packet loss rate is difficult to measure with
this combination- only using ping between probes (test case 5) can
reflect the outbound packet loss rate of B.
Fan, et al. Expires January 06, 2014 [Page 9]
Internet-Draft Packet Loss Measurement July 2013
3.4. Statistics Report of Routers
We also checked the interface statistics reports given with CLI on
the 3 routers, and we confirmed that the outbound packet loss rate of
an interface obtained from the statistics report was in accordance
with the actual packet loss rate of test traffic. The following
table shows the test result.
+----------------------------------------------------------------+
| Router | Outbound pkt loss rate of | Outbound pkt loss rate |
| | test traffic |shown on statistics report |
|--------|---------------------------|---------------------------|
| A | 48.52% | 48.52% |
| B | 48.52% | 48.52% |
| C | 44.60% | 44.60% |
+----------------------------------------------------------------+
Table 4: Test result when referring to the statistics report on
routers
4. Measurement Issues
This section describes issues encountered when measuring the packet
loss rate of a link using different testing methods.
4.1. Issues with Ping
Routers from every vendor have their unique processing procedure when
sending and receiving ICMP packets, thus resulting in diverse ping
packet loss rates, as described in the section above. Errors exist
using the ping method, and in some cases ping no longer reflects the
actual packet loss rate correctly. Relevant issues that have to be
taken into account include:
Forwarding class: When sending ping packets locally, routers are
likely to put the packets into a certain QoS queue/class although
the DSCP field of ICMP packets is kept zero. QoS queue of ping
may be different than that of the traffic to be measured, and even
ping packets sent by CLI commands and SNMP are in different queues
by default. Usually forwarding class can be adjusted by CLI or
SNMP commands.
Inner priority: For some routers, although ping traffic and service
traffic will not be treated differently by QoS, packets sent out
by the router itself, for example ping packets, are put into an
inner high priority while other forwarding service traffic into
low priority. These kinds of inner priority are valid within the
interior of routers and do not rewrite the packets. One of the
Fan, et al. Expires January 06, 2014 [Page 10]
Internet-Draft Packet Loss Measurement July 2013
purposes of using the priorities is to get the protocol packets
(ping included) processed in prior. These priorities are set by
vendor and may not be able to adjust, so in this case ping will
not give the correct packet loss rate as ping packets are not
processed and discarded together with service traffic.
Ingress line card: If the ping testing is conducted on a probe which
is connected or IP reachable to the router, then the ping packets
will be treated by the router as forwarding traffic, eliminating
the queue and priority issues. However, the location of
interfaces through which ingress traffic is received matters when
using some types of routers. In this case, the router employs a
polling schedule which allows traffic from different line cards or
modules to get forwarding chance. For a card with small volume of
traffic, the chance will be little but not none. So if ping
packets come through a card different from the high-volume service
traffic, the packets would probably get enough forwarding
resources as ping traffic itself requires little bandwidth. As a
result, ping will suffer little from congestion and shows
disaccord in packet loss rate.
Internal rate limitation: Routers normally have rate limitation
towards CPU, which is considered a kind of protection to the
control plane of routers. So if a packet is sent to CPU for
processing rather than line card ASIC (e.g. in many routers, an
ICMP echo reply packet received in response to an earlier echo
request packet sent by the router will be sent to the CPU), it
might be influenced by the rate limiter. Typical rate limitation
of ICMP packets would be 1000 pps, though the value is highly
dependent on vendor implementation and can be configured. In
practical deployment, if there is a large number of ICMP packets
sending to a router, the ping test packets may be dropped, causing
test errors. This problem did not arise in our test in section 3
as the ICMP traffic is rather small.
4.2. Issues with OWAMP and TWAMP
OWAMP and TWAMP fall into the category of active measurement, so the
general issues of active measurement apply to them. When using the
two methods, one is advised to make sure that the measurement traffic
will have the same drop probability as non-measurement traffic.
However, it is usually difficult to guarantee this, as too many
factors effect the behavior of traffic.
4.3. Issues with Proprietary Tools
Since the proprietary tools are implemented by vendors independently,
interoperability is one of the major issues when using the tools,
Fan, et al. Expires January 06, 2014 [Page 11]
Internet-Draft Packet Loss Measurement July 2013
especially for one-way measurement. Besides, these tools also share
the common issues of active measurement. The accuracy of results
depends on the rate, numbers and interval of the injected packets.
It also needs to guarantee that the injected packets follows the same
path as the tested packets, otherwise the results cannot reflect the
real performance.
Although these tools provide automatic testing method, the basic
principle is still to ping from the router itself. So it is believed
toolset method will experience the same issues about class and
priority as local ping from router does. However, we did not test
diagnosis toolsets, and the discussion is left to be further
continued.
4.4. Issues with Interface Statistics Report
Interface statistic is the most direct and accurate way to get
performance of an interface. Packet loss rate calculated from
traffic statistics is in accordance with the expected value. By
referring to statistics collected from the endpoint routers,
bidirectional packet loss rate can easily be obtained.
However, this approach requires access to routers, while in some
scenarios it is difficult to do that. For example, if we would like
to know the inbound packet loss rate of the interconnection link to
another service operator, we may have to rely on statistics provided
by the peering router. Normally, this information is not easily
shared by interworking operators.
4.5. Issues with Coloring Based Performance Measurement
The challenge for coloring based performance measurement is that
there are not so many bits in the IP header that can be used for IP
packet coloring. Operators have to carefully think of the color bits
selection to make sure that the setting and changing of the color
bits will not affect the normal packet forwarding and process.
5. Considerations and Recommendations
We summarize the above analysis here and come to the following
considerations:
a. The ping method to measure packet loss rate is easy to be
influenced by the diverse processing mechanism of ICMP packet
within routers. If this method is to be used on a router, one is
advised to make sure that the ICMP packets experience the same
forwarding and discarding courses as the service traffic (of
which the packet loss rate is to be measured) does, otherwise the
Fan, et al. Expires January 06, 2014 [Page 12]
Internet-Draft Packet Loss Measurement July 2013
measurement will not make sense. When measuring with ping, the
following points are also worth reminding:
* Packet loss rate given by measurement with ping is a value
related to a certain forwarding class in which the ICMP
packets are forwarded. So it is not a scientific way to say
what the packet loss rate is on a link if traffic is
transmitted in more than one class on the link.
* Measurement with ping is enough if one only wants to get a
general, qualitative picture of packet loss. But if one is to
measure precisely and quantitatively, possible errors
(sometimes very large errors) should be taken into account.
* If configured in the right way on router, ping with CLI and
SNMP lead to similar results.
b. It is more likely to get good results if a probe is used to
perform ping measurement (though not 100% guaranteed), but
following issues also need to be considered.
* If the probe is directly connected to a router, then a router
port is occupied. This will be a problem for routers with
limited or expensive port resources, as the probing traffic is
usually extremely small.
* If the probe is more than one hop away from a router, load of
the path to the router is supposed to be under the congestion
level.
c. Interface statistics report gives us the most accurate value of
pack loss rate, and the value is irrelevant to router platforms.
From the report we can find numbers of packets being received,
transmitted, and discarded in different classes within a period
of time, thus we get packet loss rate. Actually this is indeed
how packet loss rate is defined.
* Referring to report requires access to routers, which may be
easier if routers are within a single administrative area.
However it gets annoying if more routers are evolved, for
instance measurement on a long path with a number of routers.
* Router interface report only gives the outbound packet loss
rate. If we want to see if traffic in the other direction is
congested, we'll have to check the upstream routers in that
direction. This will be difficult on certain links, say,
interconnection link to another provider.
Fan, et al. Expires January 06, 2014 [Page 13]
Internet-Draft Packet Loss Measurement July 2013
6. Security Considerations
TBD.
7. IANA Considerations
This memo includes no request to IANA.
8. Acknowledgements
The authors would like to thank Brian Trammell for the kind comments.
9. References
9.1. Normative References
[RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Packet Loss Metric for IPPM", RFC 2680, September 1999.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC4656] Shalunov, S. and B. Teitelbaum, "A One-way Active
Measurement Protocol (OWAMP)", RFC 4656, September 2006.
[RFC5357] Hedayat, K. and R. Krzanowski, "A Two-Way Active
Measurement Protocol (TWAMP)", RFC 5357, October 2008.
[RFC6673] Morton, A., "Round-Trip Packet Loss Metrics", RFC 6673,
August 2012.
[RFC792] Postel, J., "Internet Control Message Protocol", RFC 792,
September 1981.
9.2. Informative References
[I-D.chen-coloring-based-ipfpm-framework]
Chen, M., Liu, H., and Y. Yin, "Coloring based IP Flow
Performance Measurement Framework", draft-chen-coloring-
based-ipfpm-framework-01 (Work in Progress), February
2013.
[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-03 (Work in
Progress), February 2013.
Fan, et al. Expires January 06, 2014 [Page 14]
Internet-Draft Packet Loss Measurement July 2013
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330, May
1998.
Authors' Addresses
Peng Fan
China Mobile
32 Xuanwumen West Street, Xicheng District
Beijing 100053
P.R. China
Email: fanpeng@chinamobile.com
Lu Huang
China Mobile
32 Xuanwumen West Street, Xicheng District
Beijing 100053
P.R. China
Email: huanglu@chinamobile.com
Mach(Guoyi) Chen
Huawei Technologies
Email: mach.chen@huawei.com
Nagendra Kumar
Cisco Systems
Email: naikumar@cisco.com
Fan, et al. Expires January 06, 2014 [Page 15]
