This KB explains the types of software and hardware GRE interfaces available for M-series and T-series Routers.

In M- and T- Series routers there are two types of GRE interfaces. With the software GRE interface, the packets are sent to the RE for the GRE encapsulation. With the hardware gr-x/y/z interface, the packets are sent to the Tunnel PIC or AS PIC for the GRE encapsulation.

• Hardware GRE interface:
  
  This interface needs a Tunnel PIC or AS-PIC. When show interface terse , is run these are shown as gr-x/y/z.
  

  lab@trinity> show interfaces terse
      gr-1/2/0                up    up
      

• Software GRE interface:
  
  This is a software GRE interface. It is used as a point-to-point control channel in GMPLS signaling  when a multi-access interface (Ethernet) is used as a physical interface for the control channel. No additional hardware is needed to use this interface.
  
  When show interface terse , is run these are shown as gre.
  

  lab@trinity> show interfaces terse
      gre                     up    up