Internet Engineering Task Force (IETF) F. Baker
Request for Comments: 6556 Cisco Systems
Category: Informational April 2012
ISSN: 2070-1721
Testing Eyeball Happiness
Abstract
The amount of time it takes to establish a session using common
transport APIs in dual-stack networks and networks with filtering
such as proposed in BCP 38 is a barrier to IPv6 deployment. This
note describes a test that can be used to determine whether an
application can reliably establish sessions quickly in a complex
environment such as dual-stack (IPv4+IPv6) deployment or IPv6
deployment with multiple prefixes and upstream ingress filtering.
This test is not a test of a specific algorithm, but of the external
behavior of the system as a black box. Any algorithm that has the
intended external behavior will be accepted by it.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6556.
Copyright Notice
Copyright (c) 2012 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
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 3
2. Measuring Eyeball Happiness . . . . . . . . . . . . . . . . . 3
2.1. Happy Eyeballs Test-Bed Configuration . . . . . . . . . . 4
2.2. Happy Eyeballs Test Procedure . . . . . . . . . . . . . . 5
2.3. Metrics for Happy Eyeballs . . . . . . . . . . . . . . . . 7
2.3.1. Metric: Session Setup Interval . . . . . . . . . . . . 7
2.3.2. Metric: Maximum Session Setup Interval . . . . . . . . 8
2.3.3. Metric: Minimum Session Setup Interval . . . . . . . . 8
2.3.4. Descriptive Metric: Attempt Pattern . . . . . . . . . 9
3. Security Considerations . . . . . . . . . . . . . . . . . . . 9
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Normative References . . . . . . . . . . . . . . . . . . . 9
5.2. Informative References . . . . . . . . . . . . . . . . . . 10
1. Introduction
The Happy Eyeballs [RFC6555] specification notes an issue in deployed
multi-prefix IPv6-only and dual-stack networks, and proposes a
correction. [RFC5461] similarly looks at TCP's response to so-called
"soft errors" (ICMP host and network unreachable messages), pointing
out an issue and a set of possible solutions.
In a dual-stack network (i.e., one that contains both IPv4 [RFC0791]
and IPv6 [RFC2460] prefixes and routes), or in an IPv6-only network
that uses multiple prefixes allocated by upstream providers that
implement BCP 38 ingress filtering [RFC2827], the fact that two hosts
that need to communicate have addresses using the same architecture
does not imply that the network has usable routes connecting them, or
that those addresses are useful to the applications in question. In
addition, the process of establishing a session using the sockets API
[RFC3493] is generally described in terms of obtaining a list of
possible addresses for a peer (which will normally include both IPv4
and IPv6 addresses) using getaddrinfo() and trying them in sequence
until one succeeds or all have failed. This naive algorithm, if
implemented as described, has the side effect of making the worst-
case delay in establishing a session far longer than human patience
normally allows.
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This has the effect of discouraging users from enabling IPv6 in their
equipment or content providers from offering AAAA records for their
services.
This note describes a test to determine how quickly an application
can reliably open sessions in a complex environment, such as dual-
stack (IPv4+IPv6) deployment or IPv6 deployment with multiple
prefixes and upstream ingress filtering. This is not a test of a
specific algorithm, but a measurement of the external behavior of the
application and its host system as a black box. The "happy eyeballs"
question is this: how long does it take an application to open a
session with a server or peer, under best-case and worst-case
conditions?
The methods defined here make the assumption that the initial
communication setup of many applications can be summarized by the
measuring the DNS query/response and transport-layer handshaking,
because no application-layer communication takes place without these
steps.
The methods and metrics defined in this note are ideally suited for
laboratory operation, as this affords the greatest degree of control
to modify configurations quickly and produce consistent results.
However, if the device under test is operated as a single user with
limited query and stream generation, then there's no concern about
overloading production network devices with a single "set of
eyeballs". Therefore, these procedures and metrics MAY be applicable
to a production network application, as long as the injected traffic
represents a single user's typical traffic load, and the testers
adhere to the precautions of the relevant network with respect to re-
configuration of devices in production.
1.1. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Measuring Eyeball Happiness
This measurement determines the amount of time it takes an
application to establish a session with a peer in the presence of at
least one IPv4 and multiple IPv6 prefixes and a variety of network
behaviors. ISPs are reporting that a host (Mac OS X, Windows, Linux,
FreeBSD, etc.) that has more than one address (an IPv4 and an IPv6
address, two global IPv6 addresses, etc.) may serially try addresses,
allowing each TCP setup to expire, taking several seconds for each
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attempt. There have been reports of lengthy session setup times --
in various application and OS combinations, anywhere from multi-
second to half an hour -- as a result. The amount of time necessary
to establish communication between two entities should be
approximately the same regardless of the type of address chosen or
the viability of routing in the specific network; users will expect
this time to be consistent with their current experience (else,
happiness is at risk).
2.1. Happy Eyeballs Test-Bed Configuration
The configuration of equipment and applications is as shown in
Figure 1.
+--------+ | |198.51.100.0/24
|Protocol| |192.0.2.0/24 |2001:db8:0:2::/64
|Analyzer+-+2001:db8:1:0::/64 |2001:db8:1:4::/64
+--------+ |2001:db8:0:1::/64 |2001:db8:2:4::/64
| |
+-----+ | | +-----+
|Alice+-+ +-+ Bob |
+-----+ | +-------+ +-------+ | +-----+
+-+Router1| |Router2+-+
+-----+ | +-----+-+ +-+-----+ |
| DNS +-+ | | |
+-----+ | -+------+- |
| 203.0.113.0/24 |
| 2001:db8:0:3::/64 |
Figure 1: Generic Test Environment
Alice is the unit being measured, the computer running the process
that will establish a session with Bob for the application in
question. DNS is represented in the diagram as a separate system, as
is the protocol analyzer that will watch Alice's traffic. This is
not absolutely necessary; if one computer can run tcpdump and a DNS
server process -- and for that matter, can subsume the routers --
that is acceptable. The units are separated in the test for purposes
of clarity.
On each test run, configuration is performed in Router 1 to permit
only one route to work. There are various ways this can be
accomplished, including but not limited to installing:
o a filter that drops datagrams to Bob resulting in an ICMP
"administratively prohibited",
o a filter that silently drops datagrams to Bob,
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o a null route or removing the route to one of Bob's prefixes,
resulting in an ICMP "destination unreachable", and
o a middleware program that responds with a TCP RST.
o Path MTU issues
The Path MTU Discovery [RFC1191] [RFC1981] matter requires some
explanation. With IPv6, and with IPv4, when "Do Not Fragment" is
set, a router with a message too large for an interface discards it
and replies with an ICMPv4 "Destination Unreachable: Datagram Too
Big" or ICMPv6 "Packet Too Big". If this packet is lost, the source
doesn't know what size to fragment to and has no indication that
fragmentation is required. A configuration for this scenario would
set the MTU on 203.0.113.0/24 or 2001:db8:0:3::/64 to the smallest
allowed by the address family (576 or 1280) and disable generation of
the indicated ICMP message. Note that [RFC4821] is intended to
address these issues.
The tester should try different methods to determine whether
variances in this configuration make a difference in the test. For
example, one might find that the application under test responds
differently to a TCP RST than to a silent packet loss. Each of these
scenarios should be tested; if doing so is too difficult, the most
important is the case of silent packet loss, as it is the worst case.
2.2. Happy Eyeballs Test Procedure
Consider a network as described in Section 2.1. Alice and Bob each
have a set of one or more IPv4 and two or more IPv6 addresses. Bob's
are in DNS, where Alice can find them; Alice's and others' may be
there as well, but they are not relevant to the test. Routers 1 and
2 are configured to route the relevant prefixes. Different
measurement trials revise an access list or null route in Router 1
that would prevent traffic Alice->Bob using each of Bob's addresses.
If Bob has a total of N addresses, we run the measurement at least N
times, permitting exactly one of the addresses to enjoy end-to-end
communication each time. If the DNS service randomizes the order of
the addresses, this may not result in a test requiring establishment
of a connection to all of the addresses; in this case, the test will
have to be run repeatedly until in at least one instance a TCP SYN or
its equivalent is seen for each relevant address. The tester either
should flush the resolver cache between iterations, to force repeated
DNS resolution, or should wait for at least the DNS RR TTL on each
resource record. In the latter case, the tester should also observe
DNS re-resolving; if not, the application is not correctly using DNS.
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This specification assumes common LAN technology with no competing
traffic and nominal propagation delays, so that they are not a factor
in the measurement.
The objective is to measure the amount of time required to establish
a session. This includes the time from Alice's initial DNS request
through one or more attempts to establish a session to the session
being established, as seen in the LAN trace. The simplest way to
measure this will be to put a traffic analyzer on Alice's point of
attachment and capture the messages exchanged by Alice.
DNS Server Alice Bob
| | |
1. |<--www.example.com A------| |
2. |<--www.example.com AAAA---| |
3. |---198.51.100.1---------->| |
4. |---2001:db8:0:2::1------->| |
5. | | |
6. | |--TCP SYN, IPv6--->X |<***********
7. | |--TCP SYN, IPv6--->X | |
8. | |--TCP SYN, IPv6--->X | TCP 3wHS
9. | | | Time
10. | |--TCP SYN, IPv4------->|(any family)
11. | |<-TCP SYN+ACK, IPv4----| |
12. | |--TCP ACK, IPv4------->|<***********
Figure 2: Message Flow Using TCP
In a TCP-based application (Figure 2), that would be from the DNS
request (line 1) through the first completion of a TCP three-way
handshake (line 12), which is abbreviated "3wHS" above.
DNS Server Alice Bob
| | |
1. |<--www.example.com A------| |
2. |<--www.example.com AAAA---| |
3. |---198.51.100.1---------->| |
4. |---2001:db8:0:2::1------->| |
5. | | |
6. | |--UDP Request, IPv6-->X|<---------
7. | |--UDP Request, IPv6-->X| first
8. | |--UDP Request, IPv6-->X| request/
9. | | | response
10. | |--UDP Request, IPv4--->| success
11. | |<-UDP Response, IPv4---|<---------
Figure 3: Message Flow Using UDP
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In a UDP-based application (Figure 3), that would be from the DNS
request (line 1) through one or more UDP Requests (lines 6-10) until
a UDP Response is seen (line 11).
When using other transports, the methodology will have to be
specified in context; it should measure the same event.
2.3. Metrics for Happy Eyeballs
The measurements taken are the duration of the interval from the
initial DNS request until the session is seen to have been
established, as described in Section 2.2. We are interested in the
shortest and longest durations (which will most likely be those that
send one SYN and succeed and those that send a SYN to each possible
address before succeeding in one of the attempts), and the pattern of
attempts sent to different addresses. The pattern may be simply to
send an attempt every
RFC, FYI, BCP