Description

This article explains the configuration of a GRE tunnel in two scenarios:

  1. When the tunnel destination is in default routing-instance
  2. When the tunnel destination is in non-default routing-instance

Symptoms

Configuration of a GRE (Generic Routing Encapsulation) tunnel requires defining the tunnel source and tunnel destination addresses. It is important to note that the tunnel destination address is by default considered to be reachable using the default routing table "inet.0".

If the tunnel destination is in a routing-instance, there may be a need to specify the correct routing-instance and also the routing table to be used to reach the configured tunnel destination address.

Solution

There are two possible scenarios:

  1. Physical interface, which is used to reach tunnel destination address, is in default routing-instance
  2. Physical interface, which is used to reach tunnel destination address, is in non-default routing-instance

Physical interface, which is used to reach tunnel destination address, is in default routing-instance:

In this scenario, the gr-0/0/0 interface does not need to have configured the routing-instance that is going to be used to reach the tunnel destination, as by default, the routing table inet.0 will be used.

An example of the relevant configuration for this scenario:

interfaces {
    gr-0/0/0 {
        unit 0 {
            tunnel {
                source 172.16.0.1;
                destination 10.10.1.2;
            }
            family inet {
                address 192.168.100.1/30;
            }
        }
    }
    ge-0/0/0 {
        unit 0 {
            family inet {
                address 172.30.73.56/24;
            }
        }
    }
    lo0 {
        unit 0 {
            family inet {
                address 172.16.0.1/32;
            }
        }
    }
    ...
}
routing-options {
    static {
        route 10.10.1.2/32 next-hop 172.30.73.57;                   # Tunnel destination is reachable from default routing-instance
        ...
    }
}
routing-instances {
    test {
        instance-type virtual-router;
        interface gr-0/0/0.0;
        routing-options {
            ...
        }
    }
}

Physical interface, which is used to reach tunnel destination address, is in non-default routing-instance:

In this scenario, the gr-0/0/0 interface has to be configured with routing-instance that should be used to reach the tunnel destination. Also the correct routing table to be used must be configured. These should be done with following commands:

set interface gr-0/0/0 unit 0 tunnel routing-instance destination <routing-instance-name>
set routing-options static route 10.10.1.2/32 next-table <routing-table-name>

An example of relevant configuration for this scenario:

interfaces {
    gr-0/0/0 {
        unit 0 {
            tunnel {
                source 172.16.0.1;
                destination 10.10.1.2;
                routing-instance {
                    destination test;                               # Routing-instance to reach tunnel destination
                }
            }
            family inet {
                address 192.168.100.1/30;
            }
        }
    }
    ge-0/0/0 {
        unit 0 {
            family inet {
                address 172.30.73.56/24;
            }
        }
    }
    lo0 {
        unit 0 {
            family inet {
                address 172.16.0.1/32;
            }
        }
    }
    ...
}

routing-options {
     static {
         route 10.10.1.2/32 next-table test.inet.0;                 # Tunnel destination is reachable via test.inet.0
     ...
     }
}

routing-instances {
     test {
         instance-type virtual-router;
         interface ge-0/0/0;
         routing-options {
             static {
                 route 10.10.1.2/32 next-hop 172.30.73.57;          # Tunnel destination is reachable from non-default routing-instance
                 ...
             }
         }
     }
}

Note: When SRX is in packet mode, you do not need to configure a static route to make the tunnel destination reachable from inet.0. However, you still need to specify the correct routing-instance under the gr-0/0/0 interface.