Internet Engineering Task Force G. Chen
Internet-Draft China Mobile
Intended status: Informational C. Williams
Expires: September 5, 2014 Consultant
D. Wing
A. Yourtchenko
Cisco Systems, Inc.
March 4, 2014
Happy Eyeballs Extension for Multiple Interfaces
draft-ietf-mif-happy-eyeballs-extension-04
Abstract
Currently the interface selection in multi-interface environment is
exclusive - only one interface can be used at the time, frequently
needing manual intervention. Happy Eyeballs in MIF would make the
selection process smoother by using the connectivity checks over a
pre-filtered interfaces according to defined policy. This would
choose "best" interface with an automatic fallback.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
3. Happiness Parameters . . . . . . . . . . . . . . . . . . . . 4
4. HE Behavior in MIF . . . . . . . . . . . . . . . . . . . . . 5
4.1. First Step, Filter . . . . . . . . . . . . . . . . . . . 6
4.2. Second Step, Sort . . . . . . . . . . . . . . . . . . . . 6
5. Implementation Framework . . . . . . . . . . . . . . . . . . 7
6. Additional Considerations . . . . . . . . . . . . . . . . . . 8
6.1. Usage Scope . . . . . . . . . . . . . . . . . . . . . . . 8
6.2. Fallback Timeout . . . . . . . . . . . . . . . . . . . . 8
6.3. DNS Selections . . . . . . . . . . . . . . . . . . . . . 9
6.4. Flow Continuity . . . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
In multiple interface context, the problems raised by hosts with
multiple interfaces have been discussed. The MIF problem
statement[RFC6418] described the various issues when using a wrong
domain selection on a MIF node. Happy Eyeballs (HE) [RFC6555]
described how a dual-stack client can determine the functioning path
to a dual-stack server. It's using stateful algorithm to help
applications quickly determine if IPv6 or IPv4 is the most fast path
to connect a server. That is a good method to achieve smart path
selection. However, the assumption is a single-homed context. The
interaction with multiple interfaces is deferred for further study.
[I-D.ietf-mif-mpvd-arch] has proposed a multiple provisioning domain
architecture. This memo has been proposed to extend happy eyeballs
algorithm to fit into the multiple interfaces context. Several
additional considerations have been elaborated to analyze the user
demands and initiate HE-MIF connections. It allows a node with
multiple interfaces picking a fast flow path.
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2. Problem Statement
The section enumerates several concrete use cases in existing
networks.
Case 1: WiFi is broken
o [Scenario] A MIF node has both 3G and WiFi interface. When the
node enters a WiFi area, a common practice would always prefer
WiFi because it' cheap and fast-speed normally.
o [Problem] User assumes the WiFi is working, because the node
already got IP address from WiFi. However, he can't run
applications due to Internet connectivity being unavailable. This
may be an authentication required coming into play, or unstable
Layer 2 conditions. In order to figure out the problems, users
have to turn off the WiFi manually.
o [Workaround] Users can indicate their desire with some setting on
the phone. For instance, they may prefer to wait a little bit of
time but not forever. After the timer is expired, users would
finally give up the WiFi path and try to establish connection over
3G path. Users may won't want the wait time too short, because
the 3G path for most people is more expensive than WiFi path.
Case 2: VPN (Virtual Private Network) scenario
o [Scenario] In some cases, a node has multiple interface because of
VPN. Users would only have interests to connect a corporate
network inside VPN. While, connecting to Internet would work
outside the VPN.
o [Problem] That is normally a implementation consideration that
unmanaged interface may be considered less trustworthy than
managed. It results in trusted interfaces having the highest
priority. This setting may steer all traffic to VPN interface.
When this is a traffic heading to a corporate site, everything is
fine. But sometimes, the connections out to Internet sites may
suffer from long-distance path delays.
o [Workaround] It's desirable if routing could be bound to each
interface. However, a node following weak host model[RFC1122]
takes routing tables as node-scoped. A sophisticated VPN software
may configure a specific route setting on each interface to
dispatch traffic in a predetermined network environment. As an
alternative, It may be useful to perform parallel IP connectivity
checks before selecting an interface. Consequently, the fastest
interface would be picked up automatically.
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Case 3: 3G/LTE tethering scenario
o [Scenario] Many mobile phones are equipped with software to offer
tethered Internet access. It shares their Internet connection
with another Internet-capable mobile phone or other devices over
Wi-Fi.
o [Problem] The WiFi link that tethered phone see is not free WiFi
link, i.e. it might be 3G backhaul. The policy of "always WiFi"
leads to all traffic being sent over the tethering WiFi. Usually,
such tethering WiFi link puts sharing limitation to access nodes.
It could cause contention on both that WiFi link and the backhaul
3G link, while it be higher cost than going on the 3G that is
built in the handset.
o [Workaround] To solve that, it is necessary for the node to be
aware of not only the link layer information, but also services
information, like billable or free. That could help to facilitate
the execution of the algorithm. Same concern has been documented
in Section 4.4 of [RFC6418])
Case 4: Policy Conflict
o [Scenario] A node has WiFi and 3G access simultaneously. In
mobile network, IPv6-only may be preferable since IPv6 has the
potential to be simpler than dual-stack. WiFi access still remain
on IPv4.
o [Problem] The problem is caused by policy confliction. The
transition to IPv6 is likely to encourage IPv6 and prefer
IPv6[RFC6724]. If the 3G path has IPv6 on it and the WiFi does
not, a suboptimal interface might be chosen from the cost saving
perspective.
o [Workaround] Users interests should be well understood and
considered before interface selection. The different
preconditions may impact subsequent behaviors. Users concern
about high-reliability or high-speed or less-cost should make
different choice. A flexible mechanism should be provided allow
to make smart decision.
3. Happiness Parameters
To solve the problems, this section provides the design proposal for
HE-MIF. Two sets of "Happiness" parameters have been defined. It
serves upper applications and initiates HE-MIF connections to below
level API subsequently. Going through the process, MIF nodes could
pick an appropriate interface which would correspond to user demands.
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The two sets of "Happiness" parameters are called Hard set and Soft
set respectively.
o Hard set: It contains parameters which have mandatory indications
that interface behavior should comply with. This might provide an
interface for applications constraints or delivering operator's
policies. Basically, parameters in Hard set should be easy-to-use
and easy-to-understand. The potential users would directly use
those. When several hard parameters were conflicted, user's
preference should override.
* User's preference: users would express preferences which may
not have a formally technical language , like "No 3G while
roaming", "Only use free WiFi", etc.
* Operator policies: operators would deliver the customized
policies in particular network environments due to geo-location
or services regulation considerations. One example in 3GPP
network is that operator could deliver policies from access
network discovery and selection function (ANDSF).
o Soft set: It's a factor contributing to the best path. The
following is considered as for the justification.
* Next hop: [RFC4191] allows configuration of specific routes to
a destination.
* DNS selection: [RFC6731] could configure nodes with information
to indicate DNS server address for a particular namespace.
* Source address selection: the information provided by [RFC6724]
would be considered.
* Other factors: There is a common practice may impact interface
selection, e.g. WiFi is preferable. Such conventional
experiences should also be considered.
4. HE Behavior in MIF
Corresponding to the two sets of parameters, a HE-MIF node may take a
two-step approach. One is to do "hard" decision to synthesize
policies from different actors (e.g., users and network operator).
In a nutshell, that is a filter which will exclude the interfaces
from any further consideration. The second is to adjust how we make
a connection on multiple interfaces after the filter. It's a sorting
behavior. In the multiple provisioning domain architecture,
Provisioning Domain ( PVD) selection is performed based on "hard" and
"soft" inputs. Connections intend to be initiated on the resultant
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PVDs in parallel. Those two steps are described as following sub-
sections. It should be noted that HE-MIF doesn't prescribe such two-
step model. It will be very specific to particular cases and
implementations. For example, if one interface or PVD is left after
the first step, the process would be closed.
4.1. First Step, Filter
One goal of filter is to reconcile multiple selection policies from
users or operators. Afterwards, the merged demands would be mapped
to a set of candidate interfaces, which is judged as qualified.
Decision on reconciliation of different policies will depend very
much on the deployment scenario. An implementation may not be able
to determine priority for each policies without explicit
configuration provided by users or administrator. For example, an
implementation may by default always prefer the WiFi due to cost
saving consideration. Whereas, users may dedicatedly prefer 3G
interface to seek high-reliability or security benefits even to
actively turn off WiFi interface. The decision on mergence of
policies may be made by implementations, by node administrators, even
by other standards investigating customer behavior. However, it's
worth to note that a demand from users should be normally considered
higher priority than from other actors.
The merged policies would serve as a filter principle doing iterate
across the list of all known interfaces. Qualified interface would
be selected to sort processing at next step.
4.2. Second Step, Sort
Sort process would guarantee "best" interface selection with fallback
capacities. As soon as a node connects to a network at bootstrap or
changes to a different network, network connectivity status probes
have been performed in some existing implementations, e.g. Windows
Vista, Windows 7, Windows Server 2008 and iOS. In the process, a
pre-configured URL have been connected to examine a certain answer.
If anything is abnormal, it assumes there is a proxy on the path.
This status detection is recommended to be used in HE-MIF to detect
DNS interception or HTTP proxy that forces a login or a click-
through. The unexamined interfaces should be accounted as
"unconnected" . Those interfaces should not join the sort process.
For a PVD-aware node, it could instinctively avoid the mismatch of
provisioning information. Those status detection behaviors may not
be applied to such node.
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Two phases normally are involved in a sort process, i.e. name
resolving and data session establishing. Parameters in soft set
should considered at this stage.
When the node initiates name requests, it should follow the
instruction in [RFC6731]if DNS server selection DHCP option is
provided. Otherwise, DNS queries would be sent out on multiple
interfaces on relevant PVDs in parallel. More discussions of DNS
selection in HE-MIF are elaborated at Section 6.3.
Once a peer address was resolved, a connection would be intended to
setup. Heading to a destination, a particular interface on relevant
PVDs may comply with the configuration of soft parameters, e.g. next
hop[RFC4191] , source address selection[RFC6724] or a common
practice. A particular interface should be treated with higher
priority compared to others. And, it should be choose to initiate
the connection in advance. This could avoid thrashing the network,
by not (always) making simultaneous connection attempts on multiple
interfaces. After making a connection attempt on the preferred
interface and failing to establish a connection within a certain time
period (see Section 6.2), a HE-MIF implementation will decide to
initiate connection attempt using rest of interfaces in parallel.
This fallback consideration may make subsequent connection attempts
successful on non-preferable interface.
The node would cache information regarding the outcome of each
connection attempt. Cache entries would be flushed periodically. A
system-defined timeout may take place to age the state. Maximum on
the order of 10 minutes defined in [RFC6555] is recommended to keep
the interface state changes synchronizing with IP filmily states. So
long as new connections are being attempted by the MIF-node, such an
implementation should occasionally make connection attempts using the
soft-parameter's preferred interface, as it may have become
functional again.
If there are no specific soft-parameters provided, all selected
interface on relevant PVDs should be equally treated. The
connections would initiate on several interface simultaneously. The
goal here is to provide fast connection for users, by quickly
attempting to connect using one of interfaces. Afterwards, the node
would do the same caching and flushing process as described above.
5. Implementation Framework
The simplest way for the implementation is within the application
itself. The mechanism described in the document would not require
any specific support from the operating system beyond the commonly
available APIs that provide transport service. It could also be
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implemented as high-level API approach, linking to MIF-API
[I-D.ietf-mif-api-extension]. A number of enhancements could be
added, making the use of the high-level APIs much more productive in
building applications.
6. Additional Considerations
6.1. Usage Scope
Connection-oriented transports (e.g., TCP, SCTP) could be directly
applied as scoped in [RFC6555]. For connectionless transport
protocols (e.g., UDP), it was also described "a similar mechanism can
be used if the application has request/ response semantics (e.g., as
done by Interactive Connectivity Establishment (ICE) to select a
working IPv6 or IPv4 media path[RFC6157])."
6.2. Fallback Timeout
When the preferred interface was failed, HE-MIF would trigger
fallback process to start connection initiation on several candidate
interfaces. It should set a reasonable wait time to comfort user
experiences. Aggressive timeouts may achieve quick interface
handover, but at the cost of traffic that may be chargeable on
certain networks. E.g. the handover from WiFi to 3G would bring a
bill to customers. Considering the reasons, it is recommended to
prioritize the input from users(e.g. real customers or applications)
through UI(user interface). For default-setting on a system, a hard
error[RFC1122] in replied ICMP could serve as a trigger for the
fallback process. When the ICMP soft error is present or non-
response was received, it's recommended that the timeout should be
large enough to allow connection retransmission. [RFC1122] states
that such timer MUST be at least 3 minutes to provide TCP
retransmission. Several minutes delay may not inappropriate for user
experiences. A widespread practice[RFC5461] sets 75 seconds to
optimize connection process.
More optimal timer may be expected. The particular setting will be
very specific to implementations and cases. The memo didn't try to
provide a concrete value due to following concerns.
o RTT(Round-Trip Time) on different interfaces may vary quite a lot.
A particular value of timeout may not accurately help to make a
decision that this interface doesn't work at all. On the
contrary, it may cause a misjudgment on a interface, which is not
very fast. In order to compensate the issues, the timeout setting
based on past experiences of a particular interface may help to
make a fair decision. Whereas, it's going beyond the capability
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of Happy Eyeballs [RFC6555]. Therefore, it's superior to leave it
to a particular implementation.
o In some cases, fast interface may not be treated as "best". For
example, a interface could be evaluated in the principle of
bandwidth-delay, termed "Bandwidth-Delay-Product ". Happy
Eyeballs measures only connection speed. That is, how quickly a
TCP connection is established . It does not measure bandwidth. If
the fallback has to take various factors into account and make
balanced decision, it's better to resort to a specific context and
implementation.
6.3. DNS Selections
In the sort process, HE-MIF prioritizes [RFC6731]inputs to select a
proper server. [RFC6731]could help to address following two cases
that HE-MIF failed to address.
o A DNS answer may be only valid on a specific provisioning domain,
but HE-MIF may not be aware of that mapping because DNS reply may
not be kept with the provisioning from which the answer comes.
The situation may become worse if asking internal name with public
address response or asking public name with private address
answers.
o Some FQDNs can be resolvable only by sending queries to the right
server (e.g., intranet services). Otherwise, a response with
NXDOMAIN is replied. HE-MIF treats the DNS answer with fast
response as optimal only if the record is valid. That may cause
messy for data connections, since NXDOMAIN doesn't provide useful
information.
By doing HE-MIF, it can help to solve the issues of DNS interception
with captive portal. The DNS server modified and replied the answer
with the IP address of captive portal rather than the intended
destination address. In those cases, TCP connection may succeed, but
Internet connectivity is not available. It results in lack of
service unless user has authenticated. HE-MIF recommended using
network connectivity status probes to examine a pre-configured URL
for detecting DNS interception on the path (see more in Section 4.2).
The node will be able to automatically rely upon other interfaces to
select right DNS servers by excluding the unexamined interfaces.
It should be noticed that both [RFC6731]and HE-MIF can't fully solve
the problems of DNS resolution issues, which was described in
Section 2.3 of [RFC6731]. In order to handle the issues, a MIF-node
should have PVD-aware capability to explicitly differentiate various
provisioning domains.
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6.4. Flow Continuity
Interface changing should only happen at the beginning of new session
in order to keep flow continuity for ongoing TCP session. Dynamic
movement of traffic flows are beyond the scope of this document.
7. IANA Considerations
This memo includes no request to IANA.
8. Security Considerations
The security consideration is following the statement in [RFC6555]and
[RFC6418].
9. Acknowledgements
The authors would like to thank Margaret Wasserman, Hui Deng, Erik
Kline, Stuart Cheshire, Teemu Savolainen, Jonne Soininen, Simon
Perreault, Zhen Cao, Dmitry Anipko and Ted Lemon for their helpful
comments.
10. References
10.1. Normative References
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, April 2012.
[RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, September 2012.
[RFC6731] Savolainen, T., Kato, J., and T. Lemon, "Improved
Recursive DNS Server Selection for Multi-Interfaced
Nodes", RFC 6731, December 2012.
10.2. Informative References
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[I-D.ietf-mif-api-extension]
Liu, D., Lemon, T., Ismailov, Y., and Z. Cao, "MIF API
consideration", draft-ietf-mif-api-extension-05 (work in
progress), February 2014.
[I-D.ietf-mif-mpvd-arch]
Anipko, D., "Multiple Provisioning Domain Architecture",
draft-ietf-mif-mpvd-arch-00 (work in progress), February
2014.
[RFC5461] Gont, F., "TCP's Reaction to Soft Errors", RFC 5461,
February 2009.
[RFC6157] Camarillo, G., El Malki, K., and V. Gurbani, "IPv6
Transition in the Session Initiation Protocol (SIP)", RFC
6157, April 2011.
[RFC6418] Blanchet, M. and P. Seite, "Multiple Interfaces and
Provisioning Domains Problem Statement", RFC 6418,
November 2011.
Authors' Addresses
Gang Chen
China Mobile
53A,Xibianmennei Ave.,
Xuanwu District,
Beijing 100053
China
Email: phdgang@gmail.com
Carl Williams
Consultant
El Camino Real
Palo Alto, CA 94306
USA
Email: carlw@mcsr-labs.org
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Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
USA
Email: dwing@cisco.com
Andrew Yourtchenko
Cisco Systems, Inc.
De Kleetlaan, 7
Diegem B-1831
Belgium
Email: ayourtch@cisco.com
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