JN0-352 Enterprise Routing and Switching, Specialist (JNCIS-ENT) Questions and Answers

A functioning GRE tunnel interface in Junos requires, at minimum, both a tunnel source address and a tunnel destination address configured together under the tunnel statement of the gr- logical unit, since these two values together define the outer, delivery-layer IP header that will encapsulate every passenger packet sent through the tunnel; the source identifies which of the router's own addresses will originate the encapsulated traffic, and the destination identifies the remote tunnel endpoint the encapsulated traffic must be routed toward across the underlying IP network. The first option correctly supplies both required values in a single, complete statement — source 192.168.1.1 (Router A's own address) and destination 192.168.2.1 (Router B's address) — fully defining the tunnel's endpoints and ensuring the encapsulation and route-resolution process can succeed. The fourth option supplies only the destination and omits the source entirely, which is an incomplete configuration; without an explicit source, Junos cannot always reliably determine which local address to use for encapsulation, particularly on multi-address or multi-interface routers, and the tunnel configuration is left non-deterministic or non-functional as shown. The second option enables the IPv6 protocol family on the tunnel's logical unit, which is irrelevant to a scenario explicitly requiring IPv4 passenger traffic support. The third option attempts to assign a family inet address directly using one of the underlying tunnel endpoint addresses, which conflates the tunnel's own transport addressing with logical-unit protocol addressing and does not by itself establish the required source/destination tunnel definition. Reference topics: Junos Enterprise Routing – Tunneling, Configuring GRE Tunnel Source and Destination.

Root bridge election is based on comparing each switch's full Bridge Identifier, which combines the bridge priority value with the switch's MAC address, with priority always evaluated first and MAC address serving strictly as a tiebreaker when two or more switches present identical priority values. In this scenario, the network has been left entirely at the default spanning-tree configuration, meaning every switch is operating at the standard IEEE and Junos default bridge priority of 32768; since all three switches share the exact same priority value, the comparison necessarily falls through to the MAC address tiebreak, where the switch with the numerically lowest MAC address wins the election. Comparing the three addresses shown — 00:1a:2b:3c:4d:01, 00:1a:2b:3c:4d:02, and 00:1a:2b:3c:4d:03 — Switch A's address is the lowest, since only the final octet differs and 01 is less than both 02 and 03, making Switch A the elected root bridge. RSTP uses the identical Bridge ID comparison mechanism as legacy STP for root election, so there is no special 'median MAC address' rule that applies uniquely under RSTP, making that distractor factually invalid regardless of protocol version. The election process also does not require any manual bridge priority configuration to complete; the default priority value is entirely sufficient on its own to allow a deterministic election to occur, since default priorities are still numerically comparable Bridge IDs. Reference topics: Junos Enterprise Switching – Spanning Tree Protocols, Default Priority and MAC Address Tiebreaking.

Each of the 24 end-device-facing interfaces in this scenario needs to carry traffic for exactly one VLAN, and the end devices themselves are ordinary hosts that neither expect nor generate 802.1Q-tagged frames. This is precisely the definition of an access port in Junos: family ethernet-switching interface-mode is set to access, and a single vlan members statement assigns the port to VLAN 70. Access mode ensures frames egressing toward the host are untagged and any frames received are implicitly treated as belonging to the configured VLAN, which is both simpler to manage and more efficient than trunking, since access ports do not carry the 802.1Q tag overhead nor process VLAN pruning logic relevant only to multi-VLAN links. Trunk mode, by contrast, is reserved for switch-to-switch or switch-to-router links that must simultaneously carry frames for multiple VLANs, such as the uplink toward the distribution switch that transports VLANs 30, 50, and 70 together — configuring the 24 host-facing ports as trunks (with or without a native VLAN) would be functionally incorrect and operationally wasteful, since end devices have no need to interpret VLAN tags. There is also no such behavior in Junos where VLAN-ID numeric value dictates default port behavior, making the 'no configuration needed' option a distractor with no basis in EX Series switching architecture. Reference topics: Junos Enterprise Switching – VLANs, Configuring Access and Trunk Port Modes.

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.

The destination address 172.16.200.5 falls within the 172.16.0.0/16 aggregate's summarized range but does not fall within either of the two active, more-specific contributing routes actually present in the table — 172.16.10.0/24 and 172.16.99.0/24 — meaning no route more specific than the /16 itself exists to cover it. Under Junos's longest-match forwarding logic, the lookup for 172.16.200.5 therefore resolves to the aggregate route itself, and since aggregate routes are installed by default with a reject next hop rather than any real forwarding path, the router drops the packet and simultaneously generates an ICMP destination-unreachable message back to the originating source, explicitly signaling that no valid path exists for that specific destination even though a covering summary is being advertised. This reject behavior is precisely why aggregate routes are valuable for reducing the number of routes advertised upstream while still providing clear, immediate feedback for traffic aimed at address space within the summary that has no genuine underlying route, rather than silently black-holing it or misdirecting it toward an unrelated contributing route's next hop. The aggregate route itself remains active and installed throughout this process — a gap in contributing coverage does not deactivate the aggregate, since the aggregate's activation depends only on at least one contributing route being active, which is satisfied here by both existing /24 blocks. There is also no default route present in this scenario to fall back upon. Reference topics: Junos Enterprise Routing – Protocol Independent Routing, Aggregate Route Reject Behavior for Uncovered Address Space.

The virtual-router routing-instance type in Junos is a general-purpose instance type intended for creating isolated, independent routing and forwarding contexts within a single physical device for applications that have nothing to do with MPLS-based VPN services — common use cases include multi-tenant network segmentation, filter-based forwarding deployments, and simple traffic isolation between departments or customers on a shared switch or router, all of which are non-VPN-related applications by nature. Layer 2 and Layer 3 VPN services, by contrast, rely on a different, dedicated routing-instance type specifically named vrf, which integrates with MPLS/BGP-based VPN signaling, route distinguishers, route targets, and PE-CE routing exchange; virtual-router instances do not participate in that VPN signaling framework at all, which is why the statement associating virtual-router with VPN use is incorrect. Whenever an administrator creates any user-configured routing instance — regardless of its specific type — Junos automatically allocates and generates a brand-new, dedicated routing table for that instance, named according to the pattern instance-name.inet.0 (or the appropriate address-family suffix), which is entirely separate from and independent of the default master inet.0 table used by the global/default routing context. Because each new routing instance receives its own distinct table rather than sharing or defaulting into the master inet.0 table, the statement claiming instances automatically fall back to using inet.0 unless configured otherwise is factually incorrect; instances are isolated by design from the outset. Reference topics: Junos Enterprise Routing – Protocol Independent Routing, Routing Instance Types and Table Allocation.

The show spanning-tree bridge command is specifically designed to surface exactly the two pieces of information required in this scenario within a single output. Its Root ID field reports the full Bridge Identifier (priority and MAC address) of whichever switch has been elected root bridge for the spanning-tree instance in question, immediately answering which switch in the campus network is currently acting as root, regardless of whether that happens to be the local device or a remote one. In the same output, the command's Root port field explicitly names the specific local interface (for example, ge-0/0/1.0) that the local switch has selected as its path toward that root bridge, directly answering the second part of the requirement without needing to cross-reference a separate command. Together, these two fields give a complete, immediate picture of both root bridge identity and local root port selection from one operational command. show spanning-tree interface instead presents a per-interface breakdown of STP role (root, designated, alternate, backup) and state across all local ports, which can indirectly reveal the root port by looking for the 'Root' role, but it does not directly report the Root ID/root bridge identity in the same structured way that show spanning-tree bridge does. show ethernet-switching table and show ethernet-switching interface pertain entirely to MAC address learning and switching-specific interface configuration respectively, and neither surfaces any spanning-tree topology or root bridge information at all. Reference topics: Junos Enterprise Switching – Spanning Tree Protocols, Verifying Root Bridge and Root Port with show spanning-tree bridge.

RFC 2328 specifies a precise set of parameters that two OSPF routers on a broadcast network must agree upon before a valid neighbor relationship can be established, and a mismatch in any of these mandatory fields causes the routers to reject each other's Hello packets outright rather than forming even a basic 2-Way state. The network mask carried in each Hello packet must match between neighbors on a broadcast segment, since OSPF uses this field to confirm both routers agree on the subnet boundaries of the shared segment; a mismatched mask (for example, one router configured with a /24 and its neighbor with a /25 on the same physical wire) is treated as a configuration error and blocks adjacency formation. The router dead interval, which defines how long a router will wait without receiving a Hello before declaring a neighbor down, must likewise match exactly between neighbors, alongside the closely related hello interval, since these timers govern the shared expectations both sides have for how frequently Hellos should arrive and how quickly a failure should be detected; Junos explicitly checks and rejects Hello packets carrying a mismatched dead interval value. Router priority, by contrast, is intentionally allowed to differ between neighbors on the same segment — it exists precisely so that administrators can differentiate router preference for the DR/BDR election, and differing values are expected and normal rather than being blocked. The designated router field, as advertised within each Hello, is informational about the sender's current view of the segment's DR and is not a value that must be identical between the two Hello senders to permit adjacency formation. Reference topics: Junos Enterprise Routing – OSPF, Required Hello Parameter Matching on Broadcast Networks.

The show route advertising-protocol bgp command displays exactly what would be transmitted to a specific BGP neighbor after all configured export routing policy has already been evaluated and applied, meaning any prefixes shown in this output have successfully passed through the export policy chain — confirming the export routing policy has been processed. The command header explicitly states '7 destinations, 7 routes (7 active, ...)' and every listed prefix is preceded by an asterisk, Junos's standard marker for an active route, confirming all seven displayed routes are active in the local routing table. The routing table name shown, XYZ.inet.0, indicates these routes reside in a named routing instance called XYZ rather than the default master routing instance, whose table would instead be labeled simply inet.0; this rules out the statement claiming the routes belong to the default instance. The AS path column shows only the origin code 'I' (IGP) with no AS numbers prepended ahead of it, meaning the AS path is empty, which indicates these prefixes were originated locally within R1's own AS (through redistribution or local origination) rather than having been learned from and passed through an external AS, ruling out that statement as well. Finally, the Nexthop column explicitly shows 'Self' for every route rather than an actual peer or learned address, confirming R1 is rewriting the next-hop attribute to its own address before advertising — a deliberate next-hop-self policy action typically applied toward IBGP peers. Reference topics: Junos Enterprise Routing – BGP, Verifying Advertised Routes and Export Policy Effects.

Nonstop active routing is specifically engineered to be completely transparent to the rest of the network: rather than relying on neighboring routers to preserve state during a Routing Engine switchover the way graceful restart does, NSR keeps a fully synchronized instance of the routing protocol process (rpd) running continuously on the backup Routing Engine, mirroring protocol adjacencies, the RIB, and session state in real time. Because neighbors never observe a session reset or restart signal during an NSR-driven switchover, there is no dependency on those neighbors supporting or enabling graceful restart extensions at all — this is the core architectural advantage that distinguishes NSR from GR and is precisely why the first and third answer choices are incorrect distractors. What NSR does require locally is Graceful Routing Engine Switchover (GRES) enabled first, since NSR is built as an extension on top of GRES and depends on it to synchronize kernel and interface state between the two Routing Engines before protocol-level synchronization can occur. Additionally, Juniper's official guidance mandates that both Routing Engines run the identical Junos OS software version; mismatched versions between the primary and backup Routing Engine can introduce incompatible internal data structures or feature behavior during state replication, jeopardizing the integrity of a switchover and is explicitly called out as a hard operational requirement rather than a mere best practice. Reference topics: Junos Enterprise Routing – High Availability, Nonstop Active Routing Requirements and GRES Dependency.

IS-IS is a link-state protocol that, like OSPF, runs Dijkstra's Shortest Path First algorithm independently on each router against its own copy of the synchronized link-state database to compute the best path toward every reachable destination. Each link within the topology carries an administrator-assigned or default metric, and as the SPF algorithm walks the topology graph from the local router outward, it sums the metrics of every link traversed along a candidate path to produce that path's total accumulated cost. Among all possible paths to a given destination prefix, IS-IS always selects and installs the path (or, in the case of equal-cost multipath, the set of paths) with the numerically lowest total accumulated metric, exactly mirroring the 'lowest cost wins' principle shared by essentially all link-state IGPs. A higher accumulated metric value is by definition a less preferred, more costly path, making that option the direct inverse of correct IS-IS behavior. Level 2 proximity to the destination has no independent bearing on path selection beyond however it happens to be reflected in the accumulated metric itself — IS-IS does not apply a separate rule preferring paths merely for passing near a Level 2 router. Likewise, LSP recency (sequence number or freshness) governs which version of a given LSP is trusted and flooded during database synchronization, ensuring the topology database itself is accurate and loop-free, but it plays no role in the SPF cost comparison once the database is synchronized and consistent. Reference topics: Junos Enterprise Routing – IS-IS, SPF Calculation and Metric-Based Path Selection.

By default, EBGP sessions are built with the expectation that peers are directly connected at Layer 3, and Junos enforces this by sending EBGP packets with a TTL of 1. When loopback addresses are used as the session endpoints instead of the directly connected physical interface addresses, the resulting IP packets must traverse at least one additional router hop between the two loopbacks, and a TTL of 1 will expire in transit before reaching the remote loopback, causing the TCP handshake — and therefore the BGP session — to fail even though a valid route to the peer's loopback exists. The multihop statement (configured as an EBGP multihop parameter with an accompanying TTL value, most commonly set to 2 for a single intermediate hop) instructs Junos to increase the TTL used for that peer's BGP packets so they survive the extra hop count between loopbacks. This is a mandatory addition any time an EBGP session is deliberately built against non-directly-connected addresses, whereas IBGP sessions, by contrast, do not have this default restriction because IBGP already assumes peers may be multiple hops apart within the same AS. Multipath affects load-balancing across equal-cost paths, damping suppresses flapping routes, and passive controls whether a router waits for the remote peer to initiate the TCP connection — none of these resolve the TTL expiration problem inherent to loopback-based EBGP peering. Reference topics: Junos Enterprise Routing – BGP, Configuring EBGP Multihop Sessions.

A floating static route is a backup static route that remains present in the configuration but stays inactive in the routing table under normal conditions, only becoming active if the primary, preferred route to the same destination is withdrawn or otherwise becomes unavailable. Junos determines which of several competing routes to the same prefix becomes active strictly by comparing each route's preference value (administrative distance), with the numerically lowest preference always winning; every routing protocol and static routes themselves carry a default preference (5 for standard static routes), and this value can be explicitly overridden per route using the preference statement under the static route's configuration. To create a floating static route, the administrator deliberately configures a preference value higher (that is, numerically worse, less preferred) than the preference of the primary route it is meant to back up — for example, a value higher than the 5 default of an ordinary static route, or higher than a dynamic protocol's preference such as OSPF's 10 — ensuring the floating route only becomes active once the more-preferred primary route disappears from the table entirely. This preference-based mechanism is the essential, defining configuration element of a floating static route. Priority is not a valid Junos static-route statement, next-hop simply defines where matching traffic is forwarded without controlling route selection behavior, and qualified-next-hop is a related but distinct mechanism used to assign a per-next-hop preference within a single multi-next-hop static route statement rather than between the standalone static route and its dynamic counterpart. Reference topics: Junos Enterprise Routing – Protocol Independent Routing, Configuring Floating Static Routes with Preference.

When storm control on an EX Series switch is configured with an action of interface-shutdown (rather than the default of simply dropping excess traffic), exceeding the configured bandwidth threshold for broadcast, multicast, or unknown-unicast traffic causes Junos to administratively disable the offending interface to protect the rest of the switching fabric. Recovery from this condition can happen automatically if a recovery-timeout interval has been configured, but when immediate manual recovery is required, the operational command clear ethernet-switching recovery-timeout interface interface-name explicitly clears the storm-control-triggered violation and re-enables the port without waiting for the timer to expire. This command is purpose-built for this exact condition and is distinct from more general troubleshooting commands: clear ethernet-switching table purges the learned MAC address database and has no bearing on a storm-control-disabled port; clear interface statistics resets traffic counters for diagnostic baselining but does not touch administrative state; and clear log messages simply flushes the local system log buffer. Administrators should also verify the underlying cause of the storm — a switching loop, a misbehaving host, or a misconfigured device — before manually clearing the condition, since without addressing the root cause the port is likely to trip again. This command and workflow are commonly tested as part of the Layer 2 security and resiliency features on EX platforms. Reference topics: Junos Enterprise Switching – Storm Control and Port Security, Recovering Interfaces Disabled by Storm Control.

The BGP finite state machine defined in RFC 4271 progresses through Idle, Connect, Active, OpenSent, OpenConfirm, and finally Established. The Active state is entered either directly after Idle, when the local router begins retrying a TCP connection setup toward the configured peer, or after a previous Connect attempt has failed and the ConnectRetry timer has expired, prompting the router to keep trying to complete the underlying TCP three-way handshake. Seeing a peer parked in Active therefore means the local device has a fully valid neighbor configuration and is persistently attempting to reach the remote address on TCP port 179, but the handshake is not succeeding — common root causes include a firewall or ACL blocking TCP 179 between the two endpoints, an unreachable or incorrect peer IP address, the remote BGP process not running or not listening, or an asymmetric routing path preventing the SYN/ACK from returning. It does not indicate a misconfiguration on the local box in the sense of a missing statement (that would typically leave the session as Idle), nor does it indicate an established, functioning session exchanging UPDATE messages (that state is Established), and it is not a deliberately idle/disabled condition, which Junos reports plainly as Idle. Recognizing Active as 'trying to connect' rather than 'connected' is essential for correct BGP troubleshooting sequencing. Reference topics: Junos Enterprise Routing – BGP Fundamentals, BGP Finite State Machine and Session Verification.

The metric that OSPF assigns to a destination is visible from two complementary vantage points in Junos. The show route protocol ospf command displays the main routing table filtered to OSPF-learned prefixes, and each entry shows the computed cost alongside the next hop, exactly as it was installed after SPF calculation. The show ospf route command (which accepts filters such as intra-area, inter-area, and extern) presents the OSPF-specific routing table, organized by route type, and explicitly lists the metric column for every intra-area, inter-area, and external route the local router has calculated. Together these two commands give both the RIB-level and the protocol-level view of route cost. By contrast, show ospf database extensive dumps the raw link-state advertisements, where metrics appear only as link-level values buried inside Router or Network LSAs rather than as a resolved route cost, so it is not the direct tool for viewing a route's metric. show ospf interface reports interface operational state, area, and DR/BDR information but does not present a cost or metric field at all in its standard output. Candidates should be comfortable distinguishing the RIB-oriented and protocol-table-oriented verification commands, since JNCIS-ENT scenarios frequently test whether a candidate reaches for the correct show command layer during troubleshooting. Reference topics: Junos Enterprise Routing – OSPF Operation and Verification, Monitoring OSPF.