JN0-106: Junos, Associate (JNCIA-Junos) Certification

Junos OS treats a lower route-preference value as more preferred. Longest-prefix matching identifies the most-specific matching destination, after which route preference is used to select the preferred route for that destination. Route preference ranks route candidates; it does not determine forwarding-table size.

An IPv4 /30 subnet contains four addresses in total. With one network address and one broadcast address reserved, two addresses remain usable for the endpoints of a point-to-point link.

A physical interface can host multiple logical units, enabling multiple logical interfaces such as VLAN-associated interfaces on one physical device. A logical unit can also have more than one IP address configured. Logical units are not limited to management interfaces.

The Routing Engine maintains routing tables and runs routing protocols. It installs active routes into the forwarding table, and Junos OS synchronizes that forwarding information to the Packet Forwarding Engine, which forwards packets. Transit traffic is therefore handled by the PFE rather than the Routing Engine, and exception traffic is not always dropped.

Before a Junos OS upgrade, sufficient disk space must be available, which can be verified with the show system storage command. The active configuration should also be backed up to preserve a recoverable configuration if the upgrade must be rolled back or restored.