Configuring Gre; Overview; Gre Encapsulation Format; Gre Tunnel Operating Principle - HPE FlexNetwork 10500 Series Configuration Manual

Configuring GRE

Overview

Generic Routing Encapsulation (GRE) is a tunneling protocol that can encapsulate a protocol (such
as IP, MPLS, or Ethernet) into a virtual point-to-point tunnel over a network (such as an IP network).
Packets are encapsulated at one tunnel end and de-encapsulated at the other tunnel end. The
network layer protocol of the packets before encapsulation and after encapsulation can be the same
or different.

GRE encapsulation format

Figure 100 GRE encapsulation format
Delivery header
(Transport protocol)
(Encapsulation protocol)
Payload packet
(Passenger protocol)
As shown in
•
Payload packet—Original packet. The protocol type of the payload packet is called the
passenger protocol. The passenger protocol can be any network layer protocol.
•
GRE header—Header that is added to the payload packet to change the payload packet to a
GRE packet. A GRE header includes the number of encapsulations, version, and passenger
protocol type. GRE is called the encapsulation protocol.
•
Delivery header—Header that is added to the GRE packet to deliver it to the tunnel end. The
transport protocol (or delivery protocol) is the network layer protocol that transfers GRE
packets.
The device supports GRE tunnels with IPv4 and IPv6 as the transport protocols. When the transport
protocol is IPv4, the GRE tunnel mode is GRE over IPv4 (GRE/IPv4). When the transport protocol is
IPv6, the GRE tunnel mode is GRE over IPv6 (GRE/IPv6).

GRE tunnel operating principle

Figure 101 IPv6 networks interconnected through a GRE tunnel
IPv6 payload
IPv6 network 1
GRE header
Figure 100, a GRE-tunneled packet includes the following parts:
IPv4 header
GE1/0/1
Tunnel1
Device A
GRE header IPv6 payload
GE1/0/1
IPv4 network
GRE tunnel
Tunnel1
Device B
270
IPv6 payload
IPv6 network 2