GRE tunnels: getting transit without a physical presence

To benefit from an operator's transit, people often assume you need a dedicated physical link to it — a cable in the same datacenter, a fibre access. That's the ideal case, but it isn't the only option. The GRE tunnel lets you establish logical connectivity over any existing Internet access.

What is a GRE tunnel?

GRE (Generic Routing Encapsulation) creates a virtual "tunnel" between two routers across the Internet: packets are encapsulated on one side and decapsulated on the other, as if a direct link existed between them. You can then run a BGP session inside that tunnel and announce your prefixes, exactly as on a physical link.

What it's actually for

• Getting transit without a physical presence: you're hosted elsewhere but want a specific operator's transit and routing.
• Adding a second operator (multihoming) quickly, without waiting for a physical connection.
• Bringing DDoS protection back home: carrying the "cleaned" traffic through the tunnel.
• Testing or starting fast: bringing up a session in hours rather than weeks.

The limits to know

A GRE tunnel still depends on the quality of the underlying Internet access: its latency and capacity depend on the path taken to the operator. Encapsulation slightly reduces the usable packet size (MTU), which requires proper tuning to avoid fragmentation. For very demanding needs or high volumes, a physical link is still preferable — but to get started, recover quickly or diversify, GRE is an excellent tool.

In practice at Connect-IX

We provision IPv4/IPv6 BGP sessions including over GRE tunnels, which lets you benefit from our IP transit and DDoS protection even without a physical presence with us. Once the session is up, you can view your announcements in the Looking Glass and steer your traffic with our BGP communities.