Network Working Group Y. Hong
Internet-Draft ETRI
Intended status: Informational J. Youn
Expires: September 2, 2009 DONG-EUI Univ.
March 1, 2009
Virtual network interface model for multiple network interfaces in a
host
draft-hong-mif-virtual-interface-00
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Abstract
The use of multiple interfaces in a host with existing TCP/IP stack
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may have some problems. This document discusses how to solve the
problems of multiple interfaces in a host and proposes a virtual
network interface model which describes the use of original TCP/IP
stack to support multiple network interfaces in a host.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction of a Virtual network interface model . . . . . . . 3
3. Motivations of using of a virtual network interface model . . . 4
4. Mechanism to use a virtual network interface in a host . . . . 5
4.1. Architecture of a virtual network interface model in a
host . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Operations of a host with a virtual network interface
model . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
8. Informative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
In traditional TCP/IP network environments, a communication entity
usually has a wire connection with a single network interface and it
is fixed. As an introduction of wireless technologies and
heterogeneous access technologies, a communication entity is able to
move around between different networks and have multiple network
interfaces [1].
Because traditional network applications and TCP/IP stack are
developed for a communication entity which has a single network
interface, the adoption of multiple network interfaces into a general
communication entity makes some problems. Because of the change of
network interface during communication, there may be many
considerations to support multiple interfaces in a host [2] [3].
In order to solve the problems mentioned above, we propose a virtual
network interface model for a host with multiple network interfaces.
We currently use a virtual network interface model to provide the
duplication of network connections with multiple network interface
cards on an important network node such as a server. With a virtual
network interface model, the host with multiple network interfaces
can operate as it has a single network interface irrespective to the
number of network interfaces. We have implemented a host with one
WLAN interface and one CDMA interface using this virtual network
interface model and checked that this approach can be a good solution
to handle multiple network interfaces in a host with using
traditional TCP/IP stack.
2. Introduction of a Virtual network interface model
In some Operating Systems such as Linux (or Unix), most network
interfaces, such as eth0, wlan0, and ppp0, are associated to a
physical and/or logical device that is in charge of transmitting and
receiving data packets. However, there are exceptions to this rule,
and some logical network interfaces do not feature any physical
packet transmission. The virtual network interface model is not a
real physical device and it is a logical network interface. It has
connections with physical devices within a network entity and the
path between the virtual network interface and real physical devices
is determined dynamically according to some policy. The virtual
network interface is registered to the network layer and is regarded
as a general network interface. Then real physical interfaces are
connected to the virtual network interface. The network layer does
not know the existence of these physical interfaces.
The virtual network interface model can be used for the duplication
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of network connections (the duplication of network interface cards)
for fault tolerance or load sharing. If an important server has
multiple physical network interface cards, it can survive even though
one network interface card is down. It can keep a communication
session with other live network interface cards. In this case, the
presence of multiple network interface cards can be hidden to network
layer and network layer regards the virtual network interface as a
general network interface. The traditional network applications and
network modules such as TCP/IP do not need to be modified to support
multiple network interfaces.
We can use this approach in a host which is using IPv6/IPv4 and has
multiple network interfaces. Although the purpose of the above case
is not the same, using a virtual network interface model for a
supporting a multiple network interface host can be sufficiently one
of the solutions to solve the problems of the multiple interfaces in
a host.
3. Motivations of using of a virtual network interface model
In this section, we describe the motivations of the use of a virtual
network interface model. To describe the motivations, we present
some problems of multiple network interfaces in a host which uses
traditional TCP/IP stack. There are some documents to describe the
problems when a host uses multiple network interfaces [2] [3] [4].
Traditional network applications and TCP/IP stack do not consider
about the change of network addresses and the change of network
interfaces. The change of network address can be solved by the use
of Mobile IPv6. But the change of network interfaces is not fully
studied. The one of problems of multiple network interfaces in a
host is the relation between a destination address and a network
interface. When an application sends packets to another node,
firstly looks up the routing table and then finds an appropriate
network interface, according to the destination address. When a host
changes its network interface due to the movement or the failure of
network interface during communicating to a corresponding node, the
destination address is not changed. The destination address is
continually mapped to the previous network interface. If this
situation happens, the communication sessions will be terminated.
When a network interface is newly selected to send/receive packets in
a host, the host should update the relation between a destination
address and a network interface.
Question) To update the information for the relation between a
destination address and a network interface, which module
(layer)should do that job? (In Linux, making a network interface up
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and down (e.g. ifconfig eth0 down, ifconfig eth1 up) automatically
updates the relation between a destination address and a network
interface. But, we think that this approach is not reasonable.)
4. Mechanism to use a virtual network interface in a host
To answer the question in the previous section, we think that there
are many answers. To choose the best answer, there are also many
considerations (The considerations are out of the scope of this
document).
To answer the questions, we propose a virtual network interface
model. In this section, we describe a mechanism to use a virtual
network interface in a host which uses traditional TCP/IP stack.
4.1. Architecture of a virtual network interface model in a host
In the following figure, network interfaces I1, I2 are real network
interfaces. The network interface VI is a virtual network interface.
The virtual network interface is connected to the real network
interfaces and it is shown to the network layer. In this model, the
network layer uses the virtual network interface VI instead of real
network interfaces I1, I2. To handle the virtual network interface,
the host needs a specific module (e.g., connection manager) to manage
the virtual network interface and select the path between the virtual
network interface and real network interfaces.
+-------------------------------+
| Applications |
|-------------------------------|
| TCP/UDP/SCTP |
|-------------------------------|
| IPv6 / IPv4 |
|-------------------------------|
| +------------------+ +------------+
| | Virtual Interface| | Connection |
| | (VI) | | Manager |
| +------------------+ +------------+
| / \ |
| / \ |
| +------------+ +------------+ |
| | Interface 1| | Interface 2| |
| | (I1) | | (I2) | |
| +------------+ +------------+ |
+-------------------------------+
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Figure 1: Architecture of a virtual network interface model in a host
with two network interfaces
4.2. Operations of a host with a virtual network interface model
When a network module in a host starts, the virtual network interface
module is configured to send and receive packets. In the above
figure, if the host uses a network interface I1, the path between the
virtual network interface VI and the real network interface I1 is
made. When sending packets to another node, packets are delivered to
VI and these packets are also flowed into I1 according to the path
configuration. When receiving packets from another node, packets are
delivered to I1 and these packets are also flowed into VI according
to the path configuration. The packets which are delivered to VI are
processed by network layer. If the host changes another network
interface due to node movement or the failure of network interface,
the host chooses network interface I2 and then makes the path between
the virtual network interface VI and the real network interface I2.
At this time, the connection manager updates the relation between a
destination address and a network interface. When the host is
sending packets to another node, packets are delivered to VI and
these packets are flowed into I2 according to the path configuration.
When the host is receiving packets from another node, packets are
delivered to I2 and these packets are also flowed into VI according
to the path configuration.
5. Conclusions
In traditional TCP/IP network environments, a communication entity
does not consider the change of network interfaces. To support
multiple network interfaces in a host used at traditional TCP/IP
network environments, we propose a virtual network interface model.
The proposed mechanism can solve the problems of multiple network
interfaces in a host without modifying original network layer,
transport layer, and application layer.
6. Security Considerations
If a host does not properly manage virtual interface, the
communication (send and receiving packets) may disrupt. Because the
virtual interface may be implemented in a host's kernel, it seems
that it is safe from outside security attack.
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7. IANA Considerations
This document has no actions for IANA.
8. Informative References
[1] Ernst, T., Montavont, N., Wakikawa, R., Ng, C., and K.
Kuladinithi, "Motivations and Scenarios for Using Multiple
Interfaces and Global Addresses,
draft-ietf-monami6-multihoming-motivation-scenario-03 (work in
progress)", May 2008.
[2] Blanchet, M., "Multiple Interfaces Problem Statement,
draft-blanchet-mif-problem-statement-00 (work in progress)",
December 2009.
[3] Hui, M. and H. Deng, "Problem Statement and Requirement of
Simple IP Multi-homing of the Host,
draft-hui-ip-multiple-connections-ps-01 (work in progress)",
November 2008.
[4] Hong, Y. and J. Youn, "Analysis and scenarios of multiple
interfaces in a host, draft-hong-mif-analysis-scenario-00 (work
in progress)", February 2009.
Authors' Addresses
Yong-Geun Hong
ETRI
161 Gajeong-Dong Yuseung-Gu
Daejeon, 305-700
Korea
Phone: +82 42 860 6557
Email: yonggeun.hong@gmail.com
Joo-Sang Youn
DONG-EUI Univ.
Busan,
Korea
Phone: +82 51 890 1993
Email: joosang.youn@gmail.com
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