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The science behind virtual routers and their emerging roles

The evolution of virtualization has now hit the router market. Here's what you need to know to make virtual routers work for you.

Editor's note: In this three-part series, Kevin Tolly examines the virtual router marketplace. In part one, Tolly...

explains the evolution of virtual routers. Upcoming installments will look at virtual routers from four manufacturers -- Brocade, Cisco, HP and Juniper -- and discuss their features and benefits.

By now, the notion of "virtual" anything is a familiar concept. The most common, the virtual machine, appears to users as if it were a real computer -- with an actual hard drive and memory. In reality, however, these elements don't exist on their own. Rather, the virtual operating system environment --usually VMware vSphere, Citrix Xen Server or Microsoft Hyper-V -- presents these elements to us.

Virtual routers are no different. A virtual router has all the components of a physical router and it works the same way. But, like a virtual machine, a virtual router doesn't exist as a standalone box with physical connections.

To understand a virtual router, it's important to understand the elements of a physical router. In its simplest form, a router links two LANs together via a protocol that implements and understands sub-networks and the routes between those subnets. That is, a routable protocol. Moving up a step, routers also link subnets -- via a wide area network (WAN) -- to subnets that are based in different geographic locations.

Thus, three components are needed: a LAN interface, a WAN interface and the routing code that can decide which traffic needs to traverse the WAN and how to package it accordingly.

When WAN routing first became a viable way to connect geographically dispersed corporate LANs in the 1990s, the routing world was in its "Wild West" phase. While we might think of our current networks as complex, they are quite simple insofar as basic routing is concerned, since both the Internet and routers run over IP.

Connecting locations aren't as simple as first-generation routers

For early routers, it was not so simple. Many of these routers were connected using private WANs (rather than the Internet) and might run any number of routable protocols such DECNet, Novell's IPX and even Banyan VINES. (Back then, Cisco's marketing team used to claim the vendor's products routed over a dozen protocols.) Thus, the processing power and memory required to handle this set of protocols could be significant -- especially with respect to the generally available compute power of the time.

The WAN connection wasn't simple either. The wide area interface would typically be high-level data control or frame relay. These required specialized hardware interfaces that would only be available in purpose-built routers.

Fast forward to today. Our world is vastly simpler. Not only do we have but a single protocol to route, but CPU power has increased while memory has blossomed -- even on standard, commercial servers.

The WAN interface -- as implemented by cable and DSL providers -- has become just another standard Ethernet connection. And with 10 Gigabit Ethernet cards readily available even for off-the-shelf servers, carving out the bandwidth needed to handle Internet speeds that rarely exceed 100 Mbps is no challenge.

Basic routing requirements well within the sphere of commodity PCs

What does this mean? Today's basic router requirements (for a simple, branch-office class router) are well within the performance levels of a commodity PC with two Ethernet connections. And, of course, that commodity PC doesn't have to be real -- it can be virtualized.

Even before virtualization became popular, Vyatta, now part of Brocade, built business-class routers that ran on standard Dell PCs. More recently, vendors such as Cisco, HP and others have implemented code on their platforms that allow the generation of multiple, standalone routers on a single physical server. This translates into a virtualization approach that is especially attractive in multi-tenant environments as each tenant can have a dedicated, albeit virtual, router.

Next: Stacking up the virtual routers: Brocade and Cisco.

Next Steps

Assessing virtual routers with Cisco Modeling Labs

Is it the end of low-end routers?

Understanding Hyper-V networking and the three virtual switches behind Microsoft virtualization

This was last published in May 2015

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