Description

This article explains the difference between the GRE interfaces of the form gr-x/x/x or gre for M Series and T Series routers

Symptoms


Solution

There are two types of GRE interfaces available for the J Series, MX Series, M Series and T Series routers.

Hardware GRE interface

This interface needs a Tunnel PIC, AS-PIC or MS-PIC on M Series and T Series routers.. For MX Series routers tunnel-serives must be configured. On J Series routers, the interface is automatically present. When show interfaces terse , is run these are shown as gr-x/y/z . These are configurable interfaces and is used for GRE tunnel creation. 
lab@Nobelium> show interfaces terse gr-1/2/0  
Interface               Admin Link Proto    Local                 Remote
gr-1/2/0                up    up
Software GRE interface
This is a software GRE interface which is non configurable. No additional hardware is needed to use this interface. This interface cannot be used for GRE tunnel creation instead this is used by some protocols which would require a software tunnel interface.

When running CLI command show interfaces terse this is shown as gre . 
lab@Nobelium> show interfaces terse gre         
Interface               Admin Link Proto    Local                 Remote
gre                     up    up