Check out the new USENIX Web site. next up previous
Next: 3 Virtuoso model Up: Towards Virtual Networks for Previous: 1 Introduction

2 Related work

Our work builds on operating-system level virtual machines, of which there are essentially two kinds. Virtual machine monitors, such as VMware [37], IBM's VM [17], and Microsoft's Virtual Server [27] present an abstraction that is identical to a physical machine. For example, VMWare, which we use, provides the abstraction of an Intel IA32-based PC (including one or more processors, memory, IDE or SCSI disk controllers, disks, network interface cards, video card, BIOS, etc.) On top of this abstraction, almost any existing PC operating system and its applications can be installed and run. The overhead of this emulation can be made to be quite low [33,11]. Our work is also applicable to virtual server technology such as UML [4], Ensim [9], Denali [38], and Virtuozzo [36]. Here, existing operating systems are extended to provide a notion of server id (or protection domain) along with process id. Each OS call is then evaluated in the context of the server id of the calling process, giving the illusion that the processes associated with a particular server id are the only processes in the OS and providing root privileges that are effective only within that protection domain. In both cases, the virtual machine has the illusion of having network adaptors that it can use as it sees fit, which is the essential requirement of our work.

The Stanford Collective is seeking to create a compute utility in which ``virtual appliances'' (virtual machines with task-specialized operating systems and applications that are intended to be easy to maintain) can be run in a trusted environment [30,13]. Part of the Collective middleware is able to create ``virtual appliance networks'' (VANs), which essentially tie a group of virtual appliances to an Ethernet VLAN. Our work is similar in that we also, in effect, tie a group of virtual machines together as a LAN. However, we differ in that the collective middleware attempts also to solve IP address and routing, while we remain completely at layer 2 and push this administration problem back to the user's site. Another difference is that we expect to be running in a wide area environment in which remote sites are not under our administrative control. Hence, we make the administrative requirements at the remote site extremely simple and focused almost entirely on the machine that will host the virtual machine. Finally, because the nature of the applications and networking hardware in grid computing tend to be different (parallel scientific applications running on clusters with very high speed wide area networks) from virtual appliances, the nature of the adaptation problems and the exploitation of resource reservations made possible by VNET are also different. A contribution of this paper is to describe these problems. However, we do point out that one adaptation mechanism that we plan to use, migration, has been extensively studied by the Collective group [31].

Perhaps closest to our work is that of Purdue's SODA project, which aims to build a service-on-demand grid infrastructure based on virtual server technology [21] and virtual networking [22]. Similar to VANs in the Collective, the SODA virtual network, VIOLIN, allows for the dynamic setup of an arbitrary private layer 2 and layer 3 virtual network among virtual servers. In contrast, VNET works entirely at layer 2 and with the more general virtual machine monitor model. Furthermore, our model has been much more strongly motivated by the need to deal with unfriendly administrative policies at remote sites and to perform adaptation and exploit resource reservations, as we describe later. This paper also includes detailed performance results for VNET, which are not currently available, to the best of our knowledge, for VAN or VIOLIN.

VNET is a virtual private network (VPN [10,14,19]) that implements a virtual local area network (VLAN [18]) spread over a wide area using layer 2 tunneling [35]. We are extending VNET to act as an adaptive overlay network [1,3,16,20] for virtual machines as opposed to for specific applications. The adaptation problems introduced are in some ways generalizations (because we have control over machine location as well as the overlay topology and routing) of the problems encountered in the design of and routing on overlays [32]. There is also a strong connection to parallel task graph mapping problems [2,23].

next up previous
Next: 3 Virtuoso model Up: Towards Virtual Networks for Previous: 1 Introduction
Ananth Sundararaj 2004-02-17