draft-fan-opsawg-packet-loss-00:
IP Packet loss rate measurement testing and problem statement
Author(s): Lu Huang, Peng Fan
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....
Network Working Group P. Fan
Internet-Draft L. Huang
Intended status: Informational China Mobile
Expires: August 22, 2013 February 18, 2013
IP Packet loss rate measurement testing and problem statement
draft-fan-opsawg-packet-loss-00
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
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This Internet-Draft will expire on August 22, 2013.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Methods for packet loss rate measurement . . . . . . . . . . . 3
3. Test on packet loss rate measurement . . . . . . . . . . . . . 4
4. Measurement Issues . . . . . . . . . . . . . . . . . . . . . . 4
5. Considerations and recommendations . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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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 describes a test on packet loss rate measurement with
multiple methods using routers from different vendors, followed by
issues that should be taken into consideration during the
measurement. 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 frequently used methods nowadays for measuring
packet loss rate.
1. Ping
Ping (ICMP echo request/reply) is a useful tool to examine the
connectivity and performance of the link 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
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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. Diagnosis toolset
Routers have diagnosis toolsets to provide automatic detection of IP
performance. An example of the toolsets is Juniper's RPM. By
necessary configurations on the router, toolset support multi-service
testing of multiple queues on an interface, including ICMP, TCP/UDP,
and HTTP. Packet loss rate can be measured with ICMP ping function
of the toolset. Routers send out ping packets automatically
according to the configured parameters, so toolset is working in a
similar way as ping method described above.
3. 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.
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.
Details are to be added.
4. Measurement Issues
This section describes issues encountered when measuring the packet
loss rate of a link using different testing methods.
1. Ping
Routers from every vendors have their unique processing procedure
when sending and receiving ICMP packets, thus resulting in diverse
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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:
a) 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.
b) 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 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.
c) 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.
2. Diagnosis toolset
Although diagnosis toolsets provide integrated automatic testing
method, the basic principle is still to ping from the router itself.
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So it is believed toolset method will experience the same issues
about class and priority as local ping from router does. We did not
test diagnosis toolsets, and the discussion is left to be further
continued.
3. 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.
5. Considerations and recommendations
TBD.
6. Security Considerations
TBD.
7. IANA Considerations
This memo includes no request to IANA.
8. Normative References
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC2330,
May 1998.
[RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Packet Loss Metric for IPPM", RFC2680, September 1999.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC4443, March 2006.
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[RFC6673] Morton, A., "Round-Trip Packet Loss Metrics", RFC6673,
August 2012.
[RFC0792] Postel, J., "Internet Control Message Protocol", RFC0792,
September 1981.
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
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