Virtual interface for multiple interfaces in a host
draft-hong-mif-virtual-interface-01

Abstract

The simultaneous usage of multiple interfaces in a host may cause the interface change. This document discusses how to solve the problems of interface change in a host and proposes a virtual interface which hides the change of network interface from the host IP stack to support simultaneous usage of multiple interfaces in a host.

Status of this Memo

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Table of Contents

1.  Introduction
2.  Introduction of a virtual interface
3.  Mechanism to use a virtual interface in a host
    3.1.  Architecture of a virtual interface in a host
    3.2.  Operations of a host with a virtual interface
4.  Security Considerations
5.  IANA Considerations
6.  Informative References
§  Authors' Addresses

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 access technologies networks and have multiple network interfaces [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,” May 2008.).

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] (Blanchet, M. and P. Seite, “Multiple Interfaces Problem Statement, draft-ietf-mif-problem-statement-05 (work in progress),” July 2010.).

In order to solve the problems mentioned above, we propose a virtual interface scheme for a host with multiple network interfaces. We currently use a virtual interface to provide the duplication of network connections through multiple network interface cards on an important network node such as a server. With a virtual interface scheme, the host with multiple interfaces can operate as it has a single interface irrespective to the number of network interfaces [3] (Melia, T. and S. Gundavelli, “Logical Interface Support for multi-mode IP Hosts, draft-melia-netext-logical-interface-support-00 (work in progress),” July 2010.).

2.  Introduction of a virtual interface

In some operating systems such as Linux (or Unix), most network interfaces, such as eth0, wlan, and ppp, are associated to a physical and/or logical devices that are 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 interface is not a real physical device and it is a logical network interface. It has connections with physical network devices within a network entity and the path between the virtual interface and real physical network devices is determined dynamically according to some policy.

The virtual interface is registered to the network layer and it is regarded as a general network interface. Then real physical interfaces are connected to the virtual interface. The network layer does not know the existence of these physical interfaces.

The virtual interface can be used for the duplication 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 inerface 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 in a host if a virtual interface is used.

3.  Mechanism to use a virtual interface in a host

3.1.  Architecture of a virtual interface in a host

In the following figure, network interfaces if_1, if_2 are real physical interfaces. The network interface VI is a virtual interface. The virtual interface is connected to the physical interfaces and it is shown to the network layer. In this figure, the network layer uses the virtual interface VI instead of physical interfaces if_1, if_2. To handle the virtual interface, the host needs a specific module (e.g., connection manager)to manage the virtual interface and select the path between the virtual interface and physical interfaces.

                  +-------------------------------+
                  |         Applications          |
                  |-------------------------------|
                  |        Transport area         |
                  |-------------------------------|
                  |         network area          |
                  |-------------------------------|
                  |      +------------------+   +------------+
                  |      | Virtual Interface|   | Connection |
                  |      |       (VI)       |   | Manager    |
                  |      +------------------+   +------------+
                  |           /        \          |
                  |          /          \         |
                  | +------------+ +------------+ |
                  | | Interface 1| | Interface 2| |
                  | |   (if_1)   | |   (if_2)   | |
                  | +------------+ +------------+ |
                  +-------------------------------+

3.2.  Operations of a host with a virtual interface

When a network module in a host starts, the virtual interface is configured to send and receive packets. In Figure 1, if the host uses a physical interface if_1, the path between the virtual interface VI and the physical interface if_1 is configured.

When sending packets to another node, packets are delivered to the virtual interface and these packets are also forwarded into physical interface if_1 according to the path configuration. When receiving packets from another node, packets are delivered to if_1 and these packets are also forwarded into VI according to the path configuration.

If the host changes another interface due to movement of a host or the failure of network interface, the host chooses a physical interface if_2 and then makes the path between the virtual interface VI and the physical interface if_2. 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 forwarded into if_2 according to the path configuration. When the host is receiving packets from another node, packets are delivered to if_2 and these packets are also forwarded into VI according to the path configuration.

4.  Security Considerations

TBD

5.  IANA Considerations

This document has no actions for IANA.

6. Informative References

Authors' Addresses