Virtual Security: Combating Actual Threats

Learn how to secure your virtual environment from every angle.
Virtual Network

The last area to secure is networking. Securing your virtual networking environment can be divided into two parts: securing management interfaces and guest networking. In most scenarios, the host utilizes one network interface card (NIC) as a management interface and shares the remaining port(s) between the guests. Any management interfaces should be placed on a separate physical network from any network your guests will use. If you are using a proprietary management client, limit access to the client install files and make sure you use some method of authentication or role-based access control (both mentioned earlier). If you are managing a Linux-KVM based system, follow the normal recommendations for securing SSH.

When it comes to networking guests, you have two basic options: bridging with NAT or using a virtual switch. Bridging is simple and quick to set up, but it is less secure and only masquerades the guest's virtual NIC as the host's NIC. Using a virtual switch gives you more flexibility in networking your guests. The default configuration on most solutions is to use a single default virtual switch for all guests that is uplinked to one of the host's NICs. Now, most solutions even have the ability to use VLANs on their virtual switch. The process of VLAN-ing involves labeling a client NIC with a unique ID so it communicates only with other computers that use the same VLAN ID. VLANs on a virtual switch can exist solely on the host or span other guests and devices on the physical network (Figure 7).

Figure 7. VMware's Highly Flexible Networking Options

Although VLANs provide an additional security layer to the virtual network, they are limited to layer 2 (switching) functions. Because of this, vendors have developed products to provide additional protection at a virtual layer 3 (routing) and above. Vyatta's vRouter and vFirewall act as a networking layer between the hypervisor and its guests to provide layer 3 protection for VMware, XenServer and KVM systems. VMware also has developed similar functionality with its vShield technology and the resulting products. When you can extend layer 3 functionality to your virtual environment securely, you can deploy guests safely as edge or even public-facing devices.

Additionally, be sure to monitor virtual network activity. You can monitor external traffic leaving the host using traditional sniffing, IDS and packet capture methods. Things get a little more difficult when you try to sniff interhost or interguest traffic, as the hypervisor makes very different types of network-related calls between guests from what it would with other devices on a network. As a result, traditional methods of sniffing won't work. However, products that can sniff this traffic, like Network Instruments' Observer, are beginning to pop up. Observer can sniff virtual traffic inside the host and redirect it to a physical port for analysis by an IDS, IPS or other external monitoring system.

In this short overview, you can see that securing a virtual environment from every angle requires a lot of work and knowledge. Just like any other new technology, there is a learning curve for administrators. If you add the fact that not all of the technology is fully mature, the curve becomes steeper and the risks greater. Don't be hesitant to embrace virtualization though. For now, it seems to be the future of the industry, so we probably will all have to take the plunge. If you educate yourself about the technology and its limitations, and keep abreast of current trends, you'll be just fine. As you progress in knowledge and experience with virtualization, you will find it easier to identify those areas at risk of exposure and take the appropriate precautions. The recommendations made here are a good start. If you follow them, you should be able to minimize your risks and rest a little bit easier when deploying your virtualized solutions.

Jeramiah Bowling has been a systems administrator and network engineer for more than ten years. He works for a regional accounting and auditing firm in Hunt Valley, Maryland, and holds numerous industry certifications, including the CISSP. Your comments are welcome at