Juniper: Commit operation fails when inheriting port-mirroring instance parameters from another instance

This article explains why a commit operation fails when inheriting port-mirroring instance parameters from another instance, and reveals how to fix this problem.

A commit operation fails when inheriting port-mirroring instance parameters from another instance if the inherited instance is defined later in the configuration.

For example:

If instance-c inherits parameters from instance-d, and
If instance-d is defined after instance-c,

The commit fails, as shown in the example below.

lab@R1# show chassis 
fpc 3 {
    port-mirror-instance instance-d;
}

lab@R1# show firewall 
filter mirror-c {
    term a {
        then {
            count mirror-c;
            port-mirror-instance instance-c;
            accept;
        }
    }
}
filter mirror-d {
    term a {
        then {
            count mirror-d;
            port-mirror-instance instance-d;
            accept;
        }
    }                                   
}

lab@R1# show forwarding-options 
port-mirroring {
    instance {
        instance-c {
            input-parameters-instance instance-d;
            family inet {
                output {
                    interface ge-0/0/9.3 {
                        next-hop 10.1.3.2;
                    }
                }
            }                           
        }
        instance-d {
            input {
                rate 1;
                run-length 1;
                maximum-packet-length 2000;
            }
            family inet {
                output {
                    interface ge-0/0/9.4 {
                        next-hop 10.1.4.2;
                    }
                }
            }
        }
    }
}

lab@R1# commit check
[edit forwarding-options port-mirroring instance instance-c]
  Input parameters instance not defined

error: configuration check-out failed

Forward referencing of port-mirroring instances is not supported in the Junos OS.

You must configure a port-mirroring instance from which parameters are inherited before the instance inheriting the parameters.

To fix the issue in the example in the Problem section above, insert instance-d before instance-c, as shown below. The commit operation will then succeed.

[edit forwarding-options port-mirroring instance]
lab@R1# insert instance-d before instance-c  

[edit forwarding-options port-mirroring instance]
lab@R1# show | compare 
[edit forwarding-options port-mirroring instance]
+instance-d {
+    input {
+        rate 1;
+        run-length 1;
+        maximum-packet-length 2000;
+    }
+    family inet {
+        output {
+            interface ge-0/0/9.4 {
+                next-hop 10.1.4.2;
+            }
+        }
+    }
+}
+instance-c {
+    input-parameters-instance instance-d;
+    family inet {
+        output {
+            interface ge-0/0/9.3 {
+                next-hop 10.1.3.2;
+            }
+        }
+    }                                  
+}

[edit forwarding-options port-mirroring instance]
lab@R1# commit check 
configuration check succeeds

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