Testing Eyeball Happiness
draft-baker-bmwg-testing-eyeball-happiness-01

Abstract

The amount of time it takes to open 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 open 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

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Table of Contents

1.  Introduction
2.  Measuring eyeball happiness
    2.1.  Happy Eyeballs test bed configuration
    2.2.  Happy Eyeballs test procedure
    2.3.  Happy Eyeballs metrics
        2.3.1.  Metric: Maximum Session Setup Interval
        2.3.2.  Metric: Minimum Session Setup Interval
        2.3.3.  Descriptive Metric: Attempt pattern
3.  IANA Considerations
4.  Security Considerations
5.  Acknowledgements
6.  Change Log
7.  References
    7.1.  Normative References
    7.2.  Informative References
§  Author's Address

1.  Introduction

The Happy Eyeballs (Wing, D. and A. Yourtchenko, “Happy Eyeballs: Trending Towards Success with Dual-Stack Hosts,” October 2010.) [I‑D.wing‑v6ops‑happy‑eyeballs‑ipv6] specification observes on an issue in deployed multi-prefix IPv6-only and dual stack networks, and proposes a correction. [RFC5461] (Gont, F., “TCP's Reaction to Soft Errors,” February 2009.) 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 solutions. In a network that contains both IPv4 (Postel, J., “Internet Protocol,” September 1981.) [RFC0791] and IPv6 (Deering, S. and R. Hinden, “Internet Protocol, Version 6 (IPv6) Specification,” December 1998.) [RFC2460] prefixes and routes or that uses multiple prefixes allocated by upstream providers that implement BCP 38 Ingress Filtering (Ferguson, P. and D. Senie, “Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing,” May 2000.) [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 opening a session using the Sockets API (Gilligan, R., Thomson, S., Bound, J., McCann, J., and W. Stevens, “Basic Socket Interface Extensions for IPv6,” February 2003.) [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 opening a session far longer than human patience normally allows.

This note describes a test that can be used to determine whether an application can reliably open sessions quickly 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 system as a black box. The question is how long it takes an application, best case and worst case, to open a session with a server or peer.

2.  Measuring eyeball happiness

This measurement determines the amount of time it takes an application to open 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 (MacOSX, 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 attempt. There have been reports of a session setup taking as long as 40 seconds 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.

2.1.  Happy Eyeballs test bed configuration

The configuration of equipment and applications is as shown in Figure 1 (Generic Test Environment).

+--------+ |                      |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 |

Alice is the unit being measured, the computer running the process that will open 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 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

• a filter that drops datagrams to Bob resulting in an ICMP "administratively prohibited",
• a filter that drops datagrams to Bob silently,
• a null route or removing the route to one of Bob's prefixes, resulting in an ICMP "destination unreachable", and
• a middleware program that responds with a TCP RST.

The tester should try different methods to determine whether differences 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.

2.2.  Happy Eyeballs test procedure

Consider a network as described in Section 2.1 (Happy Eyeballs test bed configuration). Alice and Bob each have a set of one or more IPv4 and two or more IPv6 addresses in DNS, and routers 1 and 2 are configured to route the relevant prefixes. The measurement plays with 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 opening 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 should either 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.

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 open a session. This includes the time from Alice's initial DNS request through one or more attempts to open a session to the session being opened, 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.  |---192.0.2.1------------->|                       |
 4.  |---2001:dba::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------->|<***********

In a TCP-based application (Figure 2 (Message flow using TCP)), that would be from the DNS request on line 1 through the first completion of a TCP three-way handshake, the transmission on line 12.

 DNS Server                   Alice                    Bob
     |                          |                       |
 1.  |<--www.example.com A------|                       |
 2.  |<--www.example.com AAAA---|                       |
 3.  |---192.0.2.1------------->|                       |
 4.  |---2001:dba::1----------->|                       |
 5.  |                          |                       |
 6.  |                          |--UDP Request, IPv6-->X|
 7.  |                          |--UDP Request, IPv6-->X|
 8.  |                          |--UDP Request, IPv6-->X|
 9.  |                          |                       |
10.  |                          |--UDP Request, IPv4--->|
11.  |                          |<-UDP Response, IPv4---|

In a UDP-based application (Figure 3 (Message flow using UDP)), 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.  Happy Eyeballs metrics

The measurements taken are the duration of the interval from the initial DNS request until the session is seen to be open, as described in Section 2.2 (Happy Eyeballs test procedure). 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 to simply send an attempt every <time interval>, or may be more complex; as a result, this is in part descriptive.

2.3.1.  Metric: Maximum Session Setup Interval

Name:

Maximum Session Setup Interval

Description:

The maximum session setup interval is the longest period of time observed for the opening of a session.

Methodology:

In the LAN analyzer trace, note the times of the initial DNS request and the confirmation that the session is open as described in Section 2.2 (Happy Eyeballs test procedure). Several instances of the test will be run, in at least one of which an attempt is seen to each of Bob's addresses. The setup interval is the difference between those times, and the maximum setup interval is the largest of those intervals.

Units:

Session setup time is measured in milliseconds.

Measurement Point(s):

The measurement point is at Alice's LAN interface, observed using a program such as tcpdump running on Alice or an external analyzer.

Timing:

Continuous.

2.3.2.  Metric: Minimum Session Setup Interval

Name:

Minimum Session Setup Interval

Description:

The minimum session setup interval is the shortest period of time observed for the opening of a session.

Methodology:

In the LAN analyzer trace, note the times of the initial DNS request and the confirmation that the session is open as described in Section 2.2 (Happy Eyeballs test procedure). Several instances of the test will be run, in at least one of which an attempt is seen to exactly one of Bob's addresses. The setup interval is the difference between those times, and the minimum setup interval is the smallest of those intervals.

Units:

Session setup time is measured in milliseconds.

Measurement Point(s):

The measurement point is at Alice's LAN interface, observed using a program such as tcpdump running on Alice or an external analyzer.

Timing:

Continuous.

2.3.3.  Descriptive Metric: Attempt pattern

Name:

Attempt pattern

Description:

The Attempt Pattern is a description of the observed pattern of attempts to open the session. In simple cases, it may be something like "Initial TCP SYNs to a new address were observed every <so many> milliseconds"; in more complex cases, it might be something like "Initial TCP SYNs in IPv6 were observed every <so many> milliseconds, and other TCP SYNs using IPv4 were observed every <so many> milliseconds, but the two sequences were independent." It may also comment on retransmission patterns if observed.

Methodology:

The traffic trace is analyzed to determine the pattern of initiation.

Units:

milliseconds.

Measurement Point(s):

The measurement point is at Alice's LAN interface, observed using a program such as tcpdump running on Alice or an external analyzer.

Timing:

Continuous.

3.  IANA Considerations

This memo asks the IANA for no new parameters.

Note to RFC Editor: This section will have served its purpose if it correctly tells IANA that no new assignments or registries are required, or if those assignments or registries are created during the RFC publication process. From the author"s perspective, it may therefore be removed upon publication as an RFC at the RFC Editor"s discretion.

4.  Security Considerations

This note doesn't address security-related issues.

5.  Acknowledgements

This note was discussed with Dan Wing, Andrew Yourtchenko, and Fernando Gont. In the Benchmark Methodology Working Group, Al Morton, David Newman, and Sarah Banks made comments.

6.  Change Log

-00 Version:

Initial version - November, 2010

-01 Version:

Rewritten per suggestions by Al Morton and David Newman.

7.  References

7.1. Normative References

7.2. Informative References

Author's Address