Internet Area M.Hui
Internet Draft H.Deng
Intended status: Informational China Mobile
Expires: May 3, 2009 November 4, 2008
Scenario and Solution: Simple IP Multi-homing of the Host
draft-hui-ip-multiple-connections-01.txt
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Copyright (C) The IETF Trust (2008).
Abstract
Current host routing mechanism doesn't allow simple IP multi-homing
for the default gateway consideration. This document proposes a
solution to make multiple connections can work simultaneously.
Table of Contents
1. Introduction................................................3
2. Scenario....................................................4
3. Solution....................................................5
3.1. Routing policy.........................................5
3.2. DHCP extension.........................................5
3.3. Configuration procedure.................................6
4. Security Considerations......................................8
5. IANA Considerations.........................................9
6. References.................................................10
6.1. Normative References...................................10
6.2. Informative References.................................10
Author's Addresses............................................11
Intellectual Property Statement................................12
Disclaimer of Validity........................................12
Copyright Statement...........................................12
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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.
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.
We analyze this problem statement in another IETF draft 'draft-hui-
ip-multiple-connections-ps-01'.
In this document we will illustrate the specific scenario and give a
probable solution by extending DHCPv4.
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2. Scenario
Simple IP Multi-homing is a necessary part of daily life. For example,
Mike must connect with the VPN by Ethernet interface when he is at
work, at the same time he wants to watch the stock market, which is
prohibited in the VPN, so he needs another connection to the GPRS
network simultaneously.
The problem is Mike can not use two connections at the same time for
his different service requirement, because all the IP flows go to the
same interface which is related to the default gateway in the host
routing table. That is the point need to be solved in simple IP
multi-homing.
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3. Solution
The default gateway problem can be solved by applying routing policy
in the host.
3.1. Routing policy
The routing policy can be applied in the host so that different IP
flows can go to different interfaces depending on the polices. To
maintain a simple host routing table, the policy can be allocated by
the network side, i.e. the gateway. The policy is distributed to the
host as soon as it attaches to the gateway, and the policy will be
applied in the initial procedure of the host.
The routing policy information should contain the proper interface
allocation according to IP destination and service type. For doing
this, IP flows can go to the appropriate network, and all connections
can work simultaneously.
3.2. DHCP extension
DHCP is a proper message to carry the host routing policy information,
for DHCP take effect when host first attach to the network, and DHCP
is a universal protocol used in the host IP deployment between
network gateway and host.
To carry the host routing information, DHCP should make an extension
in the DHCP option field. The format is showed as follow:
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Code Len Destination 1 Mask 1
+-----+-----+-----+-----+-----+-----+-----+
| x | n | d1 | d2 | d3 | d4 | m1 |
+-----+-----+-----+-----+-----+-----+-----+
TOS1 Router1
+-----+-----+-----+-----+-----+-----+-----+
| m2 | m3 | m4 | t1 | r1 | r2 | r3 |
+-----+-----+-----+-----+-----+-----+-----+
Destination 2 Mask2
+-----+-----+-----+-----+-----+-----+-----+
| r4 | d1 | d2 | d3 | m1 | m2 | m3 |
+-----+-----+-----+-----+-----+-----+-----+
TOS2 Router2
+-----+-----+-----+-----+-----+-----+-----
| m4 | t2 | t1 | t2 | t3 | t4 | ...
+-----+-----+-----+-----+-----+-----+-----
Figure 1 DHCP extension format.
Code is a number represents the specific DHCP option, which needs to
be assigned by IANA.
Len represents the length of the option form the byte after the Len
field.
Destination is the Destination IP address of the datagram, occupying
4 byte. Mask field represents the subnet mask of the destination.
TOS follows the definition in RFC1349, and it represents the
requirement of specific IP flow, such as bandwidth and delay.
Router is the IP address of the network gateway. Either the router
interface address or the corresponding host interface address is
suitable.
3.3. Configuration procedure
The DHCP routing policy is carried in the DHCP message, when host
requires IP configuration as soon as it first attaches the network,
DHCP server will send the routing policy together with the IP
configuration to the host.
Then the routing policy carried on the DHCP message is obtained by
the host, and applied as the static routing entries in the host
routing table.
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When it comes to the source address selection of the datagram, the
host operating system will look up the routing table according to the
destination IP address first, if it finds an available routing, the
interface of this routing will be used to send out the datagram, and
the IP address of this interface is selected to be the source address
of the datagram. The detail of the source address selection is
described in RFC1122 and RFC3484.
So that the static routing entry can constrain specific IP flow to
certain interface. Depending on the destination and TOS, the IP flow
can find a proper router as the next hop, and goes out through the
corresponding interface. Thus different IP flows can use multiple
connections properly and simultaneously.
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4. Security Considerations
This document doesn't propose any new protocol.
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5. IANA Considerations
This document requires a new number for DHCP option code x described
in section 3.2.
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6. References
6.1. 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.
[RFC2132] S. Alexander, Silicon Graphics, Inc., and R. Droms, " DHCP
Options and BOOTP Vendor Extensions ", RFC 2132, March 1997.
[RFC3484] R. Draves, "Default Address Selection for Internet Protocol
version 6 (IPv6)", RFC3484, February 2003.
[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", RFC4191, November 2005
6.2. 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)>.
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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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