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Explaining concurrent tunnels

"VPN allows up to 10,000 concurrent tunnels."

Above is a common phrase found in many technical manuals of networking companies. Please could you define the meaning of a "concurrent tunnel?" What does it mean when one opens 10,000 concurrent tunnels? Is one opening 10,000 parallel tunnels or 10,000 simultaneous connections?
This common terminology means that there are 10k tunnels terminating on the device. This could be 10k users with remote access VPN IPSec tunnels, or a combination of 4.8k users with remote access VPN IPSec tunnels plus 200 tunnels coming from branch offices using CPE devices to provide site-to-site connectivity. You do need to be careful with these specifications as there are other factors that affect the real capacity of VPN devices such as throughput of each tunnel, number of policies being set, and other features being used such as firewalling or NAT/PAT. Many devices with this type of spec were developed for dial-up users and don?t really support that many tunnels once you add more traffic and features. Network based VPN platforms are the only platforms built to scale and support well beyond 10k tunnels.

This was last published in May 2002

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