Generic Routing Encapsulation

(redirected from GRE tunnels)

Generic Routing Encapsulation

(networking, protocol)
(GRE) A protocol which allows an arbitrary network protocol A to be transmitted over any other arbitrary network protocol B, by encapsulating the packets of A within GRE packets, which in turn are contained within packets of B.

Defined in RFC 1701 and RFC 1702 (GRE over IP).
This article is provided by FOLDOC - Free Online Dictionary of Computing (


(Generic Routing Encapsulation) A tunneling protocol developed by Cisco that allows network layer packets to contain packets from a different protocol. It is widely used to tunnel protocols inside IP packets for virtual private networks (VPNs). For example, the point-to-point tunneling protocol (PPTP) is based on GRE, and GRE is used with IPsec to transmit routing protocol data from one router to another, which IPsec does not natively support. See tunneling protocol, PPTP and IPsec.
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References in periodicals archive ?
Advantage of GRE tunnels is that the traffic other than Internet Protocol (IP) would also be routed through it and by using Internet Protocol Security (IPsec) in conjunction with GRE tunnel it is possible to secure the data travelling through it.
"The only way to do that is establish a tunnel from one end to the other, and GRE tunnels solve this problem."
"Because the new design required that packets be sent through the GRE tunnels, we were losing visibility of the diffserv code-point flag on the packet, which tells the MPLS (multiprotocol label switching) network what priority the packet has," explains White.