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Boosting Internet Access Resilience, ISP Multihoming Explained

Abstract: Internet access for organizations today is no longer about email and web browsing connectivity. A stable Internet connection is a vital component in the chain of IT systems required to conduct business. Traditionally, the focus around Internet connectivity has been on cost, with vendors providing solutions allowing organizations to spread their traffic across consumer and enterprise products.

This approach is all good and can provide significant cost savings, especially when employee traffic is directed over low-cost consumer products such as ADSL. However, when you conduct B2B business through front-end servers hosted in your DMZ, resilience becomes a major concern.

A dead Internet link can mean loss of revenue and even, potentially more serious, brand damage in this scenario. In this paper, we discuss some methods that can improve the resilience of an Internet link. While this sounds like it should be a simple case of connecting to multiple Internet Service Providers, the devil, as they say, is in the detail.

Mission-critical Internet

Business networks have been mission-critical for some time now, and the focus on resilience and business continuity has always been top of any CIO’s mind. However, this focus’s general areas of interest were restricted to internal networks and systems. With more and more business being conducted directly via the web or B2B over Internet links to systems hosted in DMZs, it is simply no longer permissible for an Internet link to be down. Loss of access to the Internet can directly impact revenue generation, especially today, as the business operating models begin shifting towards offsite cloud computing and software as a service.

A solution to the problem

Multihoming is a method whereby a company can connect to multiple ISPs simultaneously. The concept was born from the need to protect Internet access in either an ISP link failure or an ISP internal failure. In the earlier days of Internet access, most traffic was outbound, except email.

An Internet link failure left internal users with no browsing capability and email backing up on inbound ISP mail gateways. Once the link was restored, so was browsing and email delivery. The direct impact on the business was relatively small and mostly not revenue-effective. Early solutions to this problem were to connect multiple links to the same ISP, but while this offered some level of link resilience, it could provide no safeguards against an internal ISP failure.

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Today, however, most organizations deploy on-site Internet-access services such as VPNs, voice services, webmail, and secure internal system access while using business-critical offsite services such as software as a service (SaaS) and other cloud-based solutions. Furthermore, while corporate front-end websites are traditionally hosted offsite with web hosting firms, the real-time information on the corporate websites and B2B sites is provided by back-end systems based in the corporate data center or DMZ. Without a good quality Internet connection, these vital links would be severed.

Varied requirements and complexity

The multihoming requirement varies and could range from the simple need for geographic link diversity (single ISP) to full link and ISP resilience, where separate links are run from separate data centers to different ISPs. While the complexity varies for each option, the latter forms the most complex deployment option but affords the highest availability. The former provides some degree of protection but requires a higher ISP grade.

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