The Generic Routing Encapsulation (GRE) is a transport protocol that transmits other protocol packets. The GRE tunnels act as a virtual point-to-point connection identified by the tunnel source and the tunnel destination configuration. A tunnel interface can be associated with an IP interface. A GRE tunnel acts as a transport medium for the IP interface. In SLX-OS, a VE interface is associated with a GRE tunnel. The properties such as the IP address, routing protocol that are configured in the VE interface are be applied for the GRE tunnel.
Before configuring a GRE tunnel, a point-to-point tunnel configuration, GRE requires both the ends of the tunnel to be configured.
The diagram below illustrates the GRE tunnel.
The IP address of a tunnel is derived from the VE interface. After a VE is associated with a tunnel, all the configuration under the VE such as IP address, routing protocol configurations are applied to the GRE tunnel interface. GRE tunnels support pipe and uniform QoS mode. By default, the QoS mode is set to pipe mode for all the tunnels.
By default, statistics for a tunnel is disabled. You can enable statistics for each tunnel by using the statistics command. Note that traffic loss might occur when enabling or disabling statistics on a tunnel. GRE keep alive is an optional configuration. The minimum granularity of the GRE keep alive time is 1 second.