343
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 133 GRE encapsulation format
As shown in Figure 133, a GRE-tunneled packet includes the following parts:
• 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, passenger
protocol type, checksum, and key. 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 134 IPv6 networks interconnected through a GRE tunnel
To Next Page
Loading...
Need help?
General
