Internet Area M.Hui
Internet Draft H.Deng
Intended status: Informational China Mobile
Expires: September 9, 2009 March 9, 2009
Problem Statement and Requirement of Simple IP Multi-homing of the
Host
draft-hui-ip-multiple-connections-ps-02
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Abstract
This document discusses current issues with simple IP multi-homing.
In order to have deep understanding of the issue, the document also
analyzes related works in IETF. In the end gives the requirements of
the simple IP multi-homing in concern of technical implements. Simple
IP multi-homing focuses on simultaneous multiple IP connections of
the host.
Table of Contents
1. Introduction................................................3
2. Problem statements of Simple IP Multi-homing.................4
2.1. Default Gateway.........................................4
2.2. Merging of parameters...................................4
2.3. Source address selection for IPv4.......................5
3. Analysis of Related Work in IETF.............................6
3.1. Multi6.................................................6
3.2. Shim6..................................................6
3.3. Monami6................................................7
3.4. Netlmm.................................................7
4. Requirements for Simple IP Multi-homing......................9
5. Security Considerations.....................................10
6. IANA Considerations........................................11
7. References.................................................12
7.1. Normative References...................................12
7.2. Informative References.................................12
Author's Addresses............................................13
Intellectual Property Statement....................
Disclaimer of Validity............................
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1. Introduction
Simple IP Multi-homing means the host connects to more than one
physical network through different network interfaces, and assigns
different network flows to each interface, and ensure all the
interfaces can deliver the flow simultaneously.
Simple IP Multi-homing is a necessary part of daily life, i.e., you
have to connect to your company office network through VPN connection
by your Ethernet interface, at the same time you want to watch the
stock market, which is not allowed through office network. And you
have a GPRS card, so you would like to use ethernet and GPRS at the
same time.
Current the operating systems only allow one default network
connection. If there are multiple connections of the host, all the
flows will go to the default gateway based on RFC1122 description.
One default gateway guarantees the host always has one entry to the
network, but lead to the multiple connections be difficult. The most
convenient way to make the host work under several networks at the
same time is to add specific static route in the host route table, so
that certain flow can use the assigned interface while others use the
default one, but it is not easy for the ordinary users to handle it.
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2. Problem statements of Simple IP Multi-homing
As description above, simple IP multi-homing can not work based on
the current specification. There are several reasons cause it invalid,
and this section analyzes them in detail.
2.1. Default Gateway
The Windows operating system in the host follows the default gateway
mechanism, which will choose the unify gateway among more than one
default routes ('0.0.0.0'), the detail is described in RFC1122. The
default gateway guarantees there always has a route to network when
the host can not find a specific route for a datagram in the route
table.
But when it comes to multi-homing, the default gateway also causes
all the flows go out through one interface, although there has more
than one network connections. Nowadays there are diverse networks
can be chosen by the user, and the terminal have the capability and
interfaces to connect to more than one networks at the same time. It
is possible and necessary for the user to require connecting to
different networks to ensure the best user experiences of different
services, but the default gateway mechanism only allows one
connection at once. Although you can connect your host to several
networks physically, and each network has already assigned a IP
address for your host interface, even you can see different default
routes in the route table, all the flow goes to the default gateway
chosen by the operation system other than different gateways actually.
2.2. Merging of parameters
In multiple interfaces host, each interface will get its own IP
parameters in the procedure of IP address allocation all other policy
deployment, such as DNS, metrics of routings, TOS. How to merge the
same type of parameters derived form multiple interfaces to act
harmoniously in the host is the problem presented in multiple
interfaces host.
2.2.1. DNS consideration
DNS will be configured to the interface manually or by DHCP procedure,
and multiple interfaces will obtain multiple DNS. The host will
reserve several DNS in this situation. Referring to different domain
names the host should query proper DNS so that the domain names can
be resolved. The problem is current DNS selection mechanism is lack
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to choose a right one for specific visited domain name, so that we
need to merge multiple DNS to provide the host with the best
connectivity.
2.2.2. Metrics consideration
Metrics are used to measure the performance of routings, the lower
metric it owns, the higher priority it has. For example, the default
gateway is chosen based on the metric rule as RFC1122 description,
The one have the lowest metric value becomes to the default gateway
among several connected gateways, and the interface correspond to
this gateway turns to be the default interface.
Metric rules are different depending on the access technology and
routing protocol, if the multiple interfaces connect to multiple
access networks which have different measurements of metrics, the
metric will not reflect the routing performances correctly. For
example, current metric rules define the 100M bps Ethernet network
card to be 20 and 10M bps to be 30, but the CDMA data card set its
metric value as 1, although its speed is lower than 100M bps Ethernet
network card. The merging of metrics is necessary in multiple
interfaces condition.
2.2.3. TOS consideration
TOS can be a parameter of routing item to indicate which kind of IP
data is suitable to deliver by this routing. The multiple interfaces
will connect to multiple access networks, so that the preference of
TOS need to be merged to have a better performance of data delivery.
For example, the WiFi access could indicate itself has broader
bandwidth comparing with 2G access, and set the TOS as broad
bandwidth. When another interface connects the Ethernet, the TOS is
also set as broad bandwidth preferred. In this situation, it needs
some mechanism to merge and reorder the TOS getting form multiple
interfaces.
2.3. Source address selection for IPv4
For the host has more than one IP addresses which are obtained by
multiple interfaces, the source address selection is the key issue in
order to use multiple interfaces reasonably. The application needs to
select right source address so that the data will be delivered by the
corresponding interface. This mechanism is lack currently which needs
to be solved in multiple interfaces situation.
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3. Analysis of Related Work in IETF
Multi-homing is a wide topic contains different aspects, and there
are some work groups in IETF worked on a certain aspect of multi-
homing.
This section explains their work, and compares the covered field with
the simple IP multi-homing. In the end we will find the simple IP
multi-homing is still a problem which is not solved yet.
3.1. Multi6
Multi6 WG in IETF focuses on the multi-homed site, which has more
than one connection to the public internet with those connections
through either the same or different ISPs. The reasons to choose
site multi-homing are to improve fault tolerance, perform load
balancing, etc.
The Multi6 WG mainly focuses on site multi-homing solutions that tend
to minimize adverse impacts on the end-to-end routing system and
limit the number of prefixes that need to be advertised in the
Default-Free Zone (DFZ). The background is site multi-homing today
is done largely by having a site obtain a dedicated block of address
space and then advertising a route for its prefix through each of its
ISP connections. A site's ISPs in turn advertise the prefix to some
or all of their upstream connections and the route for the prefix may
propagate to all of the routers connected to the default-free zone.
As the number of sites multi-homing in this manner increase, the
number of routes propagated throughout the DFZ increases and overall
routing stability decreases because of the burden on convergence time.
Multi6 WG tries to solve this by defining a set of goals for IPv6
site multi-homing architecture, and analyzing the current limitations
and the approaches to the site multi-homing. What's need to notice
is that the working group is not chartered to make significant
changes to the nature of IP addresses or to inter-domain routing.
Obviously, the site multi-homing does not consider the host multiple
connection which is the key problem of this document.
3.2. Shim6
Shim6 is another WG in IETF aims at site multi-homing. Shim6 work is
based on the architecture developed by the Multi6 WG, and completes
the required protocol developments and the architecture and security
analysis of the required protocols. Different form Multi6, Shim6
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focuses on surviving hosts on the multi-homing site from the changes
or for creating new associations, when one or more of the site's
address prefixes becomes unreachable.
Shim6 WG produces specifications for an IPv6-based site multi-homing
solution that inserts a new sub-layer (shim) into the IP stack of
end-system hosts. It enables hosts on multi-homed sites to use a set
of provider-assigned IP address prefixes and switch between them
without upsetting transport protocols or applications. But it can
not support connecting to all the ISPs simultaneously.
3.3. Monami6
The objective of the Monami6 WG is to produce a clear problem
statement and to produce standard track specifications to the
straight-forward problems associated with the simultaneous use of
multiple addresses for either mobile hosts using Mobile IPv6 or
mobile routers using NEMO Basic Support and their variants (FMIPv6,
HMIPv6,etc).
The WG does not define a tunnel selection mechanism, but document how
to use existing mechanisms based upon preferences or policies. They
explain the limitations for mobile hosts using multiple simultaneous
Care-of Addresses and Home Agent addresses using Mobile IPv6, whether
issues are specific to Mobile IPv6 or not. They also deliver a
protocol extension to Mobile IPv6 (RFC 3775) and NEMO Basic Support
(RFC 3963) to support the registration of multiple Care-of Addresses
at a given Home Agent address [Standard Track]. What's more, Monami6
WG makes a "Flow/binding policies exchange" solution for an exchange
of policies from the mobile host/router to the Home Agent and from
the Home Agent to the mobile host/router influencing the choice of
the Care-of Address and Home Agent address.
Monami6 focus the same field with simple IP multi-homing, which is
ensuring simultaneous use of multiple addresses for the host. The
difference is Monami6 puts this aim to under a certain condition, the
mobile host using MIP6, while the simple IP multi-homing focuses on
ordinary host using IPv4/6.
3.4. Netlmm
Netlmm WG studies Proxy Mobile IPv6 (PMIPv6) which supports multiple
interfaces binding, by maintaining multiple binding cache entries for
a given MN. The scenario concerned by PMIPv6 is each interfaces gets
different prefix form others, however, there are many other scenarios
associated with multiple interface attachment are not covered. The
specific scenario needs specific solutions which require some
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enhancement/modification to the current PMIPv6 protocol, and the
simple IP multi-homing hasn't supported in the PMIPv6 environment as
well.
What's more, the multi-homing in PMIPv6 lacks flow filtering support.
The LMA must has filter rules to allocate certain flow to traverse
via a certain care-of address, but the mechanism in PMIPv6 is
currently not supported.
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4. Requirements for Simple IP Multi-homing
Based on problem statements and related work analysis, the
requirements for simple IP multi-homing is concluded and listed as
follows:
1) The host with multiple network interfaces should be capable to
connect with different networks simultaneously.
2) The default gateway mechanism needs to be improved to support
several gateways working at the same time.
3) New metric mechanism must be defined to adapt to various network
cards nowadays.
4) The policies to assign different flows to the appropriate
interface are required, and how to apply the policies to the host
need to be considered as well.
5 Network side should be capable of distributing the IP flow
according to some parameters, such as IP address prefix, network type
and so on.
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5. Security Considerations
This document doesn't propose any new protocol.
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6. IANA Considerations
This document doesn't require any new number from IANA.
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7. References
7.1. Normative References
[RFC1122] Braden, R., "Requirements for Internet Hosts-communication
Layers", STD 3, RFC 1122, October 1989.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3582] Abley, J., Black, B., and V. Gill, "Goals for IPv6 Site-
Multihoming Architectures", RFC 3582, August 2003.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC4177] Huston, G., "Architectural Approaches to Multi-homing for
IPv6", RFC 4177, September 2005.
[RFC4191] R. Draves, D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC5213] S. Gundavelli, Ed., K. Leung, ''Proxy Mobile IPv6'', RFC5213,
August 2008
7.2. Informative References
[MONAMI6] Ernst, T., "Motivations and Scenarios for Using Multiple
Interfaces and global Addresses", May 2008, <draft-ietf-
monami6-multihoming-motivation-scenario-03(work in
progress)>.
[NETLMM] M. Jeyatharan, C. Ng, J. Hirano, "Multiple Interfaced
Mobile Nodes in NetlMM", June 2008, <draft-jeyatharan-
netlmm-multi-interface-ps-02(work in progress)>.
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Author's Addresses
Min Hui
China Mobile
53A,Xibianmennei Ave.,
Xuanwu District,
Beijing 100053
China
Email: huimin.cmcc@gmail.com
Hui Deng
China Mobile
53A,Xibianmennei Ave.,
Xuanwu District,
Beijing 100053
China
Email: denghui02@gmail.com
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