Free Practice Questions for the Juniper JNCIS-ENT JN0-352 Exam (2026 Updated)

OSPF's Designated Router election, as defined in RFC 2328 and implemented unchanged in Junos, is explicitly non-preemptive. Router priority is used only at the moment an election actually takes place — that is, when no DR or BDR currently exists on the segment. Once a DR and BDR have been elected and are functioning, a router with a numerically higher priority that joins the segment afterward does not trigger a new election and does not displace the incumbent DR or BDR, no matter how much higher its priority value is. In this scenario, R2 (priority 150) and R3 (priority 100) were already elected DR and BDR respectively while R1 was offline. When R1, whose priority of 200 would have made it the preferred DR had it been present during the original election, returns to the segment, it simply forms a full adjacency with the existing DR and BDR and takes on the DROther role like R4, without any re-election occurring. This design choice exists specifically to prevent unnecessary and disruptive Network LSA regeneration and adjacency churn every time a high-priority router reboots or rejoins a stable broadcast network. The only ways R1 could become DR going forward are if the current DR fails (promoting the BDR to DR and triggering a new BDR election) or if the entire segment's OSPF process is restarted, forcing a fresh election from a clean state. Reference topics: Junos Enterprise Routing – OSPF, Designated Router Election and Non-Preemption.

Root protection (root guard) must always be applied on the ports of the switches you trust to remain root-bridge-eligible, specifically on the interfaces facing away from the legitimate root and toward parts of the network where an untrusted or rogue device could plausibly appear and begin transmitting superior BPDUs. In this topology, Switch-1 is the intended, permanent root bridge (lowest priority, 4k), and Switch-2 is its aggregation-layer peer; both sit above the access layer, where Switch-3 and Switch-4 connect downstream toward end-user-facing infrastructure and where an accidental or malicious rogue switch is realistically most likely to be introduced. The ge-0/0/6 and ge-0/0/8 interfaces on Switch-1 and Switch-2 are precisely the downlink ports facing that access layer, meaning they are the exact points at which a rogue switch's superior BPDU (one advertising a lower priority than the legitimate root) would first be received if such a device appeared beneath Switch-3 or Switch-4. Applying root protection on those specific interfaces causes Junos to immediately block (move to a root-inconsistent, discarding state) any port that receives a superior BPDU, preventing the rogue device from ever being accepted as root, while normal, non-superior BPDUs continue to be processed without disruption. Applying root guard on Switch-1 and Switch-2's peer link (ge-0/0/12/13) would be inappropriate, since that link legitimately connects two trusted, root-eligible switches. Reference topics: Junos Enterprise Switching – Spanning Tree Protocols, Root Protection Placement Strategy.

The Backup Designated Router exists specifically to provide immediate failover redundancy for the Designated Router role on a multi-access broadcast or NBMA segment: the BDR maintains full adjacencies with every other router on the segment concurrently with the DR, precisely so that if the DR ever fails or is withdrawn, the BDR can be promoted directly to DR essentially instantaneously, without needing to wait through a fresh, full DR/BDR election process, and a new BDR election then takes place separately among the remaining DROther routers to fill the now-vacant backup role. This immediate promotion behavior confirms the first statement as correct. The Designated Router's other core responsibility on the segment is originating the Type 2 Network LSA, which describes the multi-access network itself as a pseudonode, listing every router attached to that segment; this LSA type exists specifically to avoid the full-mesh explosion of Router LSA adjacency listings that would otherwise be needed to describe a shared broadcast segment, and only the DR — never the BDR, and never any DROther — is responsible for generating and maintaining this particular LSA under normal, stable conditions, which confirms the third statement while directly ruling out the fourth. There is no such thing as the DR 'electing' an area border router; ABR status is instead a role a router acquires organically by having interfaces in more than one OSPF area, entirely independent of any DR/BDR election process on any individual segment. Reference topics: Junos Enterprise Routing – OSPF, DR/BDR Roles and Type 2 Network LSA Origination.

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.

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.

IEEE 802.3ad LACP defines two distinct negotiation modes, active and passive, and the standard's fundamental requirement for successful negotiation is that at least one end of the point-to-point link must be configured in active mode; an actively configured device initiates LACPDU transmission on its own, while a passively configured device waits and only responds once it receives an LACPDU from its peer. If both ends of the bundle were left in passive mode simultaneously, neither side would ever initiate the exchange, and no negotiation — and therefore no functioning aggregated bundle — would ever occur; at least one active participant is therefore mandatory, though having both sides active (active-active) is also fully valid and is in fact the most common production deployment. Junos does not enable LACP automatically on aggregated Ethernet interfaces; unlike some competing platforms, LACP must be explicitly configured under the aggregated-ether-options lacp hierarchy, and specifying no LACP configuration at all results in a 'static' LAG that relies purely on physical link-state rather than any protocol negotiation — there is no implicit default active mode. There is likewise no requirement to configure differing LACP system priority values between the two peer switches; system priority is used only to determine which side of the link controls port selection during negotiation and has no bearing on whether the bundle can form. Both sides being mandatorily active is a stricter requirement than the actual standard specifies. Reference topics: Junos Enterprise Switching – Link Aggregation, LACP Active and Passive Mode Negotiation.

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.

A link aggregation group bundles multiple physical Ethernet links into a single logical interface (an ae interface) specifically to provide both increased aggregate bandwidth and link-level redundancy. By default, the aeX interface remains operationally up as long as at least one member link within the bundle remains active and passing traffic; the LAG does not require every member link to be functional to continue operating. When one of the four 1-GbE member links in this scenario fails, LACP (if in use) or the underlying link-status monitoring detects the failure, removes that specific link from the active forwarding set, and redistributes traffic hashing across the three remaining healthy member links automatically and without operator intervention. End devices and upper-layer protocols continue to see a single, continuously up ae interface throughout this process, experiencing only a proportional reduction in available aggregate bandwidth rather than any interruption in connectivity. This default behavior is precisely why LAG is a foundational building block for resilient EX Series switch interconnects in enterprise and data center designs, since it allows individual optic, cable, or transceiver failures to be absorbed transparently. None of the distractor behaviors — full administrative shutdown of the bundle, forwarding limited to broadcast traffic only, or a temporary disabling of all member links during renegotiation — reflect actual Junos LAG behavior, which is designed explicitly to avoid any such disruption. Reference topics: Junos Enterprise Switching – Layer 2 Switching, Link Aggregation Group Resiliency.

RSTP, as defined in IEEE 802.1w, introduces explicit, well-defined port roles that go beyond legacy 802.1D STP's simpler root/designated/blocking model, and the alternate port role is one of RSTP's key refinements. An alternate port is a port that receives BPDUs from a bridge other than the one through which the local switch's actual root port reaches the root bridge — in other words, it represents a second, redundant path toward the root bridge learned from a different upstream bridge than the one currently providing the best (root port) path. Because the existing root port already provides the lowest-cost, actively used path to the root, the alternate port is deliberately held in the discarding (non-forwarding) state during normal, stable operation, functioning purely as a pre-computed, ready-to-use backup; critically, RSTP's major performance advantage over legacy STP is that if the current root port fails, the switch can transition its alternate port directly and almost instantly into the forwarding root port role without needing to pass through the lengthy listening and learning timer-based states that classic STP required, since the alternate port's suitability as a backup was already continuously verified through ongoing BPDU reception. It is not simply 'not receiving BPDUs' (an alternate port receives BPDUs continuously, just inferior ones relative to the current root port), it is not itself the least-cost path (that describes the root port), and it does not forward based on designated-port overload, which is not a concept that exists in RSTP's port-role logic at all. Reference topics: Junos Enterprise Switching – Spanning Tree Protocols, RSTP Port Roles: Alternate and Backup Ports.

Because Server A resides in VLAN 10 and Server B resides in VLAN 20, traffic between them cannot remain a purely Layer 2 switched flow; it must be routed between the two VLANs, which on Switch 1 means the packet traverses the switch's internal routing engine (via an IRB interface) between the ingress and egress switching stages. Junos processes firewall filters along this path in a strict, layered order that mirrors the packet's actual journey through the device. First, any filter applied at the physical ingress port level (Rx-Port) is evaluated as the frame first arrives on ge-0/0/10. Next, any filter applied to the ingress VLAN (Rx-VLAN, i.e., VLAN 10) is evaluated as the frame is classified into its source broadcast domain. Because the destination subnet requires routing, the packet is then handed to the routing engine, where any input/ingress routed filter (Rx-Router) applied to the receiving IRB interface is evaluated next, followed by any output/egress routed filter (Tx-Router) applied as the now-routed packet is handed from the routing engine back out toward VLAN 20. Finally, the packet passes through any egress VLAN filter (Tx-VLAN, for VLAN 20) and then the egress physical port filter (Tx-Port) on ge-0/0/20 immediately before transmission to Server B. This complete six-stage sequence — Rx-Port, Rx-VLAN, Rx-Router, Tx-Router, Tx-VLAN, Tx-Port — reflects every filter-evaluation checkpoint a routed, inter-VLAN packet passes through on an EX Series Layer 3 switch. Reference topics: Junos Enterprise Switching – Layer 2 Switching and Firewall Filter Processing Order for Routed VLAN Traffic.

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 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.

The diagnostic output explicitly states the root cause: the local router has only the inet6-unicast address family configured for this peer, while the remote router advertised inet-unicast and inet-vpn-unicast in its OPEN message, and BGP requires at least one common negotiated address family (NLRI type) between two peers for a session to remain established; with zero overlap between the two sides' configured families, the session is torn down immediately after the OPEN exchange, which is precisely why the peer state shows Active rather than Established. This confirms the mismatched-address-family statement directly and unambiguously from the exhibit's own Down reason and Detail reason fields. The diagnostic tool's own embedded Suggestion text goes further, explicitly advising the administrator to additionally verify that the local-address configured for the peer matches the remote router's configured neighbor address and vice versa — a secondary, commonly encountered condition in which mismatched or effectively duplicated/incorrect address bindings between the two sides' neighbor statements can independently prevent a session from completing correctly, even once the family mismatch is resolved. This is why address-configuration consistency between the peers is flagged as a second concern worth checking in this scenario. Nothing in the exhibit references NTP or time synchronization at all, nor does anything in the output reference authentication, an MD5 mismatch, or any related failure signature; both of those conditions would present through entirely different diagnostic messages than the one shown here. Reference topics: Junos Enterprise Routing – BGP, Address Family Negotiation and the show bgp diagnostics neighbor Command.

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.

Layer 2 MAC learning on an EX Series switch, as on any standard Ethernet bridge, is a passive, frame-driven process rather than an active polling or query-based mechanism. Every time a frame arrives on any interface, the switch inspects the frame's source MAC address field and, if that address is not already present in the Ethernet switching (bridge) table for the associated VLAN, creates a new dynamic entry recording the source MAC address, the VLAN it was learned on, and the specific ingress interface through which the frame arrived. Junos also stamps each learned entry with an aging timestamp, which is refreshed every time a subsequent frame from that same source MAC is received; entries that receive no refreshing traffic within the configured MAC aging interval (300 seconds by default) are eventually purged from the table to keep it current and to reclaim table space from hosts that have moved or gone offline. This source-address-driven, per-frame learning process happens continuously and automatically with no dependency on spanning-tree state changes — although a topology change notification can trigger accelerated aging of the table to flush potentially stale entries faster, learning itself is not gated by or contingent upon such an event occurring. The switch never learns addresses from the destination field of a frame, since the destination address, if already known, is used purely for the forwarding lookup decision, not for populating new table entries. Reference topics: Junos Enterprise Switching – Layer 2 Switching Fundamentals, Source MAC Learning and Table Aging.

Correctly blocking SSH traffic originating from a specific network requires matching three precise conditions simultaneously in the from clause: the traffic's source-address must equal the 192.168.10.0/24 network, since the requirement is to block traffic coming from that network rather than traffic destined to it; the protocol must be explicitly set to tcp, since SSH operates exclusively over TCP; and the destination-port must be set to 22, because an inbound SSH connection request is always directed at the well-known SSH listening port 22 on the receiving side, regardless of which ephemeral source port the initiating client happens to use. The first option satisfies all three conditions correctly and pairs them with a discard action, cleanly dropping matching traffic. The second option incorrectly substitutes destination-address for source-address, which would match traffic heading toward that /24 rather than traffic originating from it, inverting the intended match direction. The third option incorrectly uses source-port 22 instead of destination-port 22; since the SSH client's source port is a randomly assigned ephemeral value rather than a fixed 22, this term would almost never match real SSH session-initiation traffic. The fourth option relies on a service ssh match condition, which is not valid syntax within the standard Junos firewall filter grammar for family inet; there is no such application-based keyword available at that hierarchy, making the term invalid regardless of the reject action chosen. Reference topics: Junos Enterprise Switching – Firewall Filters, Matching on Address, Protocol, and Port Conditions.