Juniper Updated JN0-352 Exam Questions and Answers by mia-rose

A native VLAN is a trunk-port concept, not an access-port concept. On an 802.1Q trunk, every frame is normally expected to carry a VLAN tag identifying its membership; the native VLAN is the single exception that Junos permits an administrator to define using the native-vlan-id statement under the trunk interface's family ethernet-switching hierarchy. Any untagged frame arriving on that trunk port is automatically classified into the configured native VLAN, and conversely, outbound frames belonging to the native VLAN are transmitted untagged rather than with an 802.1Q header. This behavior exists chiefly for interoperability with legacy or third-party devices that either cannot generate 802.1Q tags or intentionally send management or default traffic untagged across an otherwise tagged trunk. Access ports, by definition, only ever carry a single VLAN's traffic and never receive tagged frames in normal operation, so the native VLAN mechanism has no relevance there — which eliminates the access-port-oriented answer choices. The native VLAN also does not restrict a trunk to a single VLAN; the trunk continues to carry all configured tagged VLANs simultaneously, with the native VLAN simply being the designated untagged exception. Misconfiguring or mismatching native VLAN IDs between two trunk peers is a classic Layer 2 troubleshooting scenario on the exam. Reference topics: Junos Enterprise Switching – VLANs, Configuring the Native VLAN on a Trunk Interface.

On EX Series switches, aggregated Ethernet (ae) interfaces do not exist by default; before any ae interface can be created, referenced, or brought into service, an administrator must first reserve the desired number of aggregated Ethernet device slots by configuring set chassis aggregated-devices ethernet device-count number at the [edit chassis] hierarchy. This statement allocates the internal resources needed for that many ae interfaces to exist as valid, configurable objects; until it is committed, any interface-level configuration referencing ae0 (such as the aggregated-ether-options and family ethernet-switching stanzas shown in the exhibit) is accepted syntactically by the CLI but never actually instantiates a live ae0 device, which is exactly why show interfaces ae0.0 returns 'device ae0 not found' despite the interface appearing fully configured. Increasing the device-count to at least 1 (or higher, to cover the number of LAG bundles planned) immediately resolves this and allows ae0 to appear as an operational interface once its member links are also associated with it. This is a foundational and frequently overlooked prerequisite step in LAG deployment on Juniper switches. There is no separate licensing requirement for aggregated Ethernet functionality on EX Series switches, a reboot is not needed since the chassis statement takes effect upon commit, and the LACP mode (active versus passive) is unrelated to whether the ae interface object itself exists in the first place. Reference topics: Junos Enterprise Switching – Link Aggregation, Configuring the Aggregated Ethernet Device Count.

VLAN 5 and VLAN 7 are two entirely separate Layer 2 broadcast domains, each with its own distinct IP subnet, and devices in one VLAN can never reach devices in the other through switching alone — Layer 3 routing between the two subnets is mandatory for any inter-VLAN communication to occur, regardless of how the VLANs are configured at Layer 2. On a single EX Series switch, the correct and standard mechanism for enabling this routing without an external router is to create one integrated routing and bridging (IRB) logical interface for each VLAN, assign each IRB the appropriate gateway IP address for its respective subnet (192.168.5.1 for VLAN 5's irb.5 and 192.168.7.1 for VLAN 7's irb.7, for example), and ensure routing is active on the switch so that traffic arriving at one IRB's gateway address destined for the other VLAN's subnet is routed internally between the two IRB interfaces. Attempting to bind a single family inet interface with two distinct subnet addresses via secondary addressing conflates two separate broadcast domains onto one Layer 3 interface incorrectly and is not how VLAN routing is architected in Junos. Spanning tree exists purely to prevent Layer 2 loops and has no routing function whatsoever, so configuring it cannot enable inter-VLAN reachability. Placing both VLANs on a single trunk with Multiple VLAN Registration Protocol (MVRP) only automates VLAN membership propagation across trunk links; it does not provide any Layer 3 routing capability between the VLANs either. Reference topics: Junos Enterprise Switching – Routing VLANs, Configuring IRB Interfaces for Inter-VLAN Routing.

The L column in this output identifies which IS-IS levels are active on each interface, using the standard bitmask where 1 represents Level 1 only and 3 represents both Level 1 and Level 2 combined. Interface ge-0/0/2.0 shows an L value of 1 and its Level 2 DR field explicitly reads Disabled, meaning Level 2 has not been enabled on that circuit at all; consequently no Level 2 adjacency can ever form there, regardless of what the neighboring router advertises, which confirms that statement as correct. The lo0.0 loopback interface shows Passive under both the Level 1 DR and Level 2 DR columns. A passive IS-IS interface is deliberately excluded from adjacency formation — no IIH PDUs are sent or expected on it — but its associated prefix is still injected into the router's own LSP and flooded throughout the area, which is precisely why loopbacks are configured as passive: to guarantee the router ID/loopback prefix is reachable network-wide without wasting adjacency overhead on an interface with no real neighbor. This confirms that R3 advertises its loopback address, while ruling out the claim that the loopback is used to form an adjacency. Regarding designated routers, all circuits shown here report 'Point to Point' rather than an actual DR system ID, because DR election in IS-IS is a construct exclusive to broadcast (LAN) circuits; point-to-point circuits never elect a DR, so the first statement is false. Reference topics: Junos Enterprise Routing – IS-IS, Interface Levels and Passive Interfaces.