The exhibit illustrates the use of the apply-path feature within a prefix list configuration. In Junos OS, apply-path is a dynamic configuration utility that allows a prefix list to be automatically populated with values derived from other parts of the configuration—in this case, all IPv4 addresses assigned to interfaces with the xe-* prefix. This is particularly useful for building automated firewall filters or routing policies that stay updated as interfaces are added or modified.
When viewing the standard configuration using show configuration, the CLI only displays the literal apply-path statement. To verify the actual list of IP addresses that the system has inherited and populated into the DIRECT-IP list, the administrator must use the | display inheritance pipe filter. This command instructs the Junos OS parser to expand all inherited values and dynamic paths, showing the effective configuration as it is seen by the Packet Forwarding Engine. Based on the exhibit, this would reveal the subnets associated with xe-0/1/0, xe-0/1/1, and xe-0/1/2, while ignoring ge-0/0/0 because it does not match the xe-* wildcard. This verification is a critical troubleshooting step before applying such a prefix list to a transit firewall filter like Export-Direct.
[Reference: Routing Policy and Firewall Filters, Prefix Lists, and the apply-path statement., , ]
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