GRE (Generic Routing Encapsulation)
Generic Routing Encapsulation (GRE) is a protocol that
allows data packets to be transported over a network by wrapping one packet inside
another:
How it works
GRE encapsulates a payload packet inside a GRE packet,
which is then encapsulated in a transport protocol like IP. The packet is then
redirected to an intermediary host, where it is de-encapsulated and routed to
its final destination.
Benefits
GRE can simplify connections between separate networks
and enable the use of protocols that are not normally supported by a network.
Limitations
GRE tunnels are stateless, meaning the tunnel's endpoint has no information about the far end. GRE also adds two headers to the
packet, which could violate maximum transmission unit (MTU) rules.
Use cases
GRE tunnels are ideal for forwarding internet-bound
traffic from a corporate network to a service.
GRE is similar to a VPN, but without encryption. It can
be used to bypass open filtering systems, which hackers can use to set up
distributed denial of service (DDoS) attacks.
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