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Virtual Routing

Bringing TCP/IP to a New Level

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Virtual routing is one of the hottest new

features in the routing world, and asthe quotation above notes, it will "dra-matically alter network economics."The following pages are designed tohelp you understand how virtual rout-ing works and how it is applied in real- world situations to save enormousamounts of money and resources.

How Routing Works

As we know, Internet Service Providers(ISPs) can have vast numbers of cus-tomers, including organizations thathave their own large networks (withusers connected to each other on a "lo-cal access network" [LAN] via Ethernetor a similar connection scenario). Con-sidering the number of ISPs in the world and the number of networksthese ISPs service, it's easy to imagine

that there is a shortage of IP addresses.

Shortage of IP Addresses

Each ISP customer with its own network must have a static IP address. Suchan address is most likely given to thecustomer by the ISP, and will never beseen by other computers on theInternet. Because of a shortage if IPaddresses (in IPv4), the Internet Engi-neering Task Force (IETF) has defined

The Virtual Router

a limited number of addresses that ISPscan assign to their customers. Given thislimited number, an ISP in New York City and one in Beijing might be as-signing the same addresses to their cus-tomers; this is possible because theseaddresses are never shared with the pub-lic - in other words, they are never vis-ible on the Internet.

The ISPs can easily deal with these

"internal" addresses by NAT (network address translation). NAT enables anISP to translate all the addresses it hasassigned to its customers into addressesvisible on the internet and clearly be-longing to that ISP.

“The virtual router feature creates a paradigm shift in to-day's requirements to insert and deliver value-added services at the edge of the network. This unique capability reduces service providers’ capital investment and operational costs,dramatically altering network economics and enabling new wholesale services.” Jennifer Liscom, principal analyst,

Gartner Inc.

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Routing Tables

The Internet backbone servers maintainrouters and routing tables that identify billions of addresses on the Internet. Ina conventional model, ISPs do muchthe same thing, maintaining routers androuting tables for each network thatthey service. [See Figure 1.]

The Problem Conventional

Routing Creates

In a conventional routing model, arouter is required for each organizationthat the ISP services. This is necessary because the ISP may be using similaraddresses for a number of different or-ganizations (such as 10.1.1.1). Thesame router would not be able to look into two organizations, because it couldnot differentiate between them and would malfunction when seeing dupli-

cate addresses.In the example of Figure 1, a single

router would not be able to know if packets of information are to be deliv-ered to Network A, B or C if these networks had the same addresses.

Figure 1: In a conventional model, ISPs (or other organizations) maintainrouters and routing tables for each network that they service.

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How Virtual Routing Works

A More Efficient Router

Implementation

Of course, given the number of networks that an ISP can service (thou-sands… even tens of thousands), thereis a vast expense associated with havingto purchase and maintain routers foreach network. Yet here is an interesting

problem: there is no logical reason why there have to be that many physicalrouters, and why each network needsto be associated with this piece of hardware. The routing tables that eachrouter has are the critical componentof this model, and these must be dif-ferent. Again, the same routing tablescould not handle having the same ad-dresses. But do we really need separatepieces of hardware to maintain separaterouting tables?

Understanding that it's not the

physical router but rather its routingtable which is the central issue has leadto the conceptualization and creationof the virtual router.

What Is a Virtual Router?

A virtual router is any number of TCP/IP stacks built into one. In our Figure1. example, a virtual router would in-clude three TCP/IP stacks built intoone, though be sure to remember thatthe model is not limited to any par-ticular number (in fact, if your process-

ing power is strong enough, you canhave over 65,000 stacks without any additional physical routers!). The stackslook and behave like independentstacks, yet for our purposes, the only things that really need to be independ-ent are the routing tables.

Virtual routing is made possible by the introduction of a network ID andnetwork interface. The Virtual routerin our example will have three network interfaces to the three customers, andone to the Internet.

The TCP/IP stack will be con-figured with a virtual routing ID foreach network interface. This way, Or-ganization A may have any number of

its own networks with the same ID. ThisID will always be associated with Or-ganization A, and the virtual router willknow it. The ID is administrated by thesystem administrator.

How It Works

When an ISP provides service to an or-

ganization, it assigns an ID to that or-ganization. Any packet from the organi-zation's network is stacked with its ID.For example, any packet coming fromOrganization A will be stacked with ID#1.

Each organization that has its ownID will also have its own routing tableassociated with that ID, and the rout-ing table will only work with that spe-cific ID. This way, routing tables canremain independent and accurate. A system administrator can configure the

router without interfering with otherorganizations' routing tables. See Fig-ure 2 for an illustration of this concept.

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Figure 2: The virtual router replaces potentially thousands of conventional routers.

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Virtual Routing Advantages

Advantages

The primary advantage of using virtualrouters is the tremendous cost savingsthey create. Instead of having threerouters (hardware) assigned to organi-zations A, B and C, we have only one.In the case of many ISPs, we're not talk-ing about three organizations but rather

thousands. Therefore, an implementa-tion of virtual routing can save the costof thousands of pieces of hardware, notto mention maintenance and upgrades.

Upgrading becomes especially easy when dealing with a software-centricmodel (consider upgrading a single boxinstead of thousands), and there areadded benefits with ease of configura-tion and space savings. For the custom-ers, however, it will always appear as if they have their own router. In effect,they do; it just doesn't have any hard-

ware.

Why Interpeak Implemented

Virtual Routing:

Interpeak was immediately recognizedin the market for the robustness andversatility of its IPNET TCP/IP stack. We found that while the stack was origi-nally designed as a terminating hoststack for dual IPv4 and IPv6, our cus-tomers were using IPNET for routingpurposes. Indeed the stack worked

beautifully for routing, and one cus-tomer asked that we increase its rout-ing capabilities. We set out to make astate-of-the art router out of an already feature-rich TCP/IP stack.

Most TCP/IP stacks are rather lim-ited in their functionality and features. Why then would we want to developsuch a feature-rich stack as IPNET?

What People Want in a Stack

IPNET is the result of a great deal of customer interaction and market re-search. We found that when customersof ours were considering the purchaseof a TCP/IP stack, they asked three pri-mary questions:

How fast is it compared to other

stacks on the same OS?• What features does it include?• How big is it?

Interpeak's Solution

Because IPNET was already a fast, fea-ture-rich and scalable TCP/IP solution, we decided to create a complete solu-tion for virtual routing at the TCP/IPstack level. To guarantee ease of use andadaptability, we ensured that IPNET,our virtual-routing capable TCP/IPstack, would be ready to run on RTOSs

such as INTEGRITY, OSE, Linux, VX Works, Nucleus, Itron, and others. Atthe same time, we ensured that ourstack could easily be ported to propri-etary RTOSs by creating a porting API.This API makes IPNET consistent withall Interpeak products, which are de-signed for portability to any operatingsystem. In turn, this portability enablesour customers maximum flexibility, whether they are selling into ISPs orTelcos.

A Real-Life Virtual Routing

Scenario

Here is a real-life scenario that we haveexperienced. An Interpeak customer ismaking modems and testing them forour TCP/IP stack. In a traditional situ-ation, this customer would need onehardware router box per modem. Us-

ing IPNET's virtual routing feature, ourcustomer can use a single router to testhundreds, and even thousands, of mo-dems. This is possible because the du-plicate IPNET stacks can operate sepa-rately and independently.

Multiple Routing Tables - Not

Stacks

The most efficient virtual routers en-sure the multiplication of routing ta-bles, not of TCP/IP stacks. WhileIPNET is fully capable of being multi-

plied many times in a system, it alsooffers extreme efficiency by enablingvirtual routing with multiple instancesof routing tables only. Some virtualrouting implementations are performed with the reproduction and concurrentrunning of TCP/IP stacks, which canbe a significant drain on system re-sources. IPNET was made with this inmind; the use of multiple routing ta-bles rather than multiple stacks requiresvery little memory to implement.

Table 1: List of protocols, features, and APIs to be considered in a TCP/IP stack.

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All Interpeak products are trademarks or registered trademarks of Interpeak AB. Other brand and product names are trademarks or registered trademarks of their respective holders. The information in this docu-

ment has been carefully reviewed, and is believed to be accurate and reliable. However, Interpeak AB assumes no liabilities for inaccuracies in this document. Furthermore, Interpeak AB reserves the right tochange specifications embodied in this document without prior notice.

Version 1.21-r5. Copyright © 2005, Interpeak AB. All rights reserved.

Interpeak Secure Networking Software

Interpeak provides state-of-the-art networking solutions specifically designed forembedded systems. The company´s embedded networking and security softwareis currently used in thousands of applications across the globe.

Headquartered in Stockholm, Sweden, Interpeak operates through a globalnetwork of distribution channels and has its own sales and field application forcedispersed in strategic locations worldwide, including the USA, Europe, and Asia.For additional information, please visit our homepage www.interpeak.com.

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