VPN service-level agreements - always check the fine print

Here are some tips from a service provider about what to look for in virtual private network service-level agreements.

VPN providers offer money-back guarantees on network availability, delay and throughput. These are key factors, but you need to look a little deeper and ask a few questions, including:

When providers talk about availability, are they talking about their own network or are they including the access link to the network? If the access link fails, you wind up with a downed VPN, but the SLA may offer no recourse for compensation.

Similarly, does the network delay include the access link? Too much delay will hurt VPN performance for some applications. Knowing where the delay was introduced isn't necessarily an important issue for you. Your main concern will involve learning about the total delay the VPN creates between your sites.

How does the service provider measure throughput? Some providers measure the rate of traffic on their networks based on the packets that make it through. They don't mention how many packets are getting dropped somewhere along the way. Work out a guarantee on packet loss. Dropped packets may be re-sent, but they may arrive too late for some applications. And if there are too many re-sends, it degrades effective throughput of data.

Tim Greene is a senior editor at Network World, covering virtual private networking gear, remote access, core switching and local phone companies. You can reach him at tgreene@nww.com.

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