Free Practice Questions for Juniper JN0-352 Exam

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 Complete Sequence Number PDU (CSNP) is the IS-IS mechanism used to summarize the entire contents of a router's link-state database, listing the LSP ID, sequence number, checksum, and remaining lifetime for every LSP the sending router currently believes should exist in the database for that level. On broadcast (LAN) circuits, the elected Designated Intermediate System periodically transmits CSNPs to all routers on the segment as a database-synchronization mechanism; any receiving router compares the summarized list against its own local database, and any discrepancy — an LSP it is missing entirely, or one for which it holds an older sequence number — triggers a targeted request for the specific, updated LSP content. On point-to-point circuits, a single CSNP is exchanged once when the adjacency first comes up, serving the identical synchronization purpose without needing periodic repetition. The Partial Sequence Number PDU (PSNP), by contrast, is used to acknowledge receipt of specific LSPs or to explicitly request specific LSPs identified as missing or outdated after a CSNP comparison, making it a partial, targeted PDU rather than a complete database listing. The LSP itself is the PDU that actually carries the detailed topology and reachability information being advertised, rather than a database summary. The IS-IS Hello PDU (IIH) is used purely for neighbor discovery and adjacency maintenance and carries no link-state database summary information whatsoever. Reference topics: Junos Enterprise Routing – IS-IS, CSNP and Link-State Database Synchronization.

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.

The intent of this filter is to match and discard traffic from one single, specific host MAC address, which requires the source-mac-address match condition to reference the complete, exact 48-bit address using an explicit /48 mask (or no mask at all, which Junos treats as an implicit full match) so that only that one precise address is matched. As configured, the term instead specifies a /40 mask on 00:12:34:56:00:07, meaning only the first 40 bits (the first five octets, 00:12:34:56:00) are actually significant to the match, while the sixth octet is effectively wildcarded across its full range; this produces an imprecise, overly broad match criterion rather than the single-host match the administrator intended, and is a common configuration mistake that undermines the predictability and correctness of MAC-based filtering. The lesson tested here is that source and destination MAC address match conditions in Junos firewall filters must be specified with the correct, deliberate, and explicit prefix length appropriate to the intended scope — typically /48 for a single exact host — rather than an arbitrary or miscalculated mask value. Firewall filters under family ethernet-switching are fully capable of matching on both source-mac-address and destination-mac-address, which rules out that option entirely. Layer 2 MAC-based filters function correctly on both access and trunk interface modes, so interface type is not a limiting factor here. There is no indication in the exhibit that the filter's application direction (input versus output) is reversed. Reference topics: Junos Enterprise Switching – Layer 2 Security, MAC Address Match Conditions and Prefix Length Precision.

An integrated routing and bridging interface, configured as irb.x on an EX Series switch, is the mechanism that bridges the Layer 2 and Layer 3 forwarding planes for a given bridge domain or VLAN. By assigning an irb logical unit to a VLAN and configuring an IP address on that unit, the switch gains a routable Layer 3 gateway address that hosts within that VLAN can use as their default gateway, enabling traffic destined for other subnets to be routed off the local broadcast domain. Internally, when a frame destined for the gateway's MAC address arrives on any port belonging to that VLAN, the switch's integrated circuitry hands the packet from the Layer 2 bridging domain to the Layer 3 routing engine associated with the corresponding irb interface, and vice versa for the return path — hence the name 'integrated routing and bridging.' IRB does not eliminate the need for routing instances, which remain a separate mechanism for isolating routing tables; it does not itself perform inter-VLAN switching, since switching still happens strictly within a VLAN's own broadcast domain; and it has no relationship to trunk ports, which remain necessary for carrying multiple tagged VLANs between switches. IRB is the standard method for enabling inter-VLAN routing on a single EX Series switch without an external router. Reference topics: Junos Enterprise Switching – Routing VLANs, Configuring Integrated Routing and Bridging.

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.

GRE is fundamentally a stateless encapsulation protocol: the encapsulating router simply wraps the passenger packet in a GRE header and an outer delivery IP header and forwards it based on ordinary IP routing table lookups toward the configured tunnel destination address. For that forwarding to succeed, the underlying (global or routing-instance) routing table on each endpoint must contain a valid, reachable route to the far-end tunnel address; without such a route, the tunnel interface will not come up or will be unable to deliver traffic, since GRE relies entirely on the existing IP infrastructure rather than any tunnel-specific signaling to establish reachability. Because GRE has no built-in state machine or session negotiation, it does not natively track whether the remote endpoint is alive — that requires an optional add-on such as GRE keepalives or BFD, neither of which is enabled by default; an operator must explicitly configure them if failure detection is required. GRE is also protocol-agnostic rather than IPv4-only: it can encapsulate IPv4, IPv6, MPLS, and other network-layer protocols as the passenger, which is one of its defining advantages over IP-in-IP tunneling. Finally, because GRE keeps no per-session state about the peer, it cannot detect or report tunnel failures on its own, reinforcing why route reachability is the one true prerequisite for tunnel operation. Reference topics: Junos Enterprise Routing – Tunneling, Understanding Generic Routing Encapsulation.

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.

TLV 22, the Extended IS Reachability TLV defined in RFC 5305, is the modern and Junos-preferred mechanism for advertising a router's adjacent neighbors together with the metric associated with each link. It carries the seven-octet system ID and pseudonode number of each neighbor along with a 24-bit wide metric field, and supports an extensible set of sub-TLVs used for traffic-engineering data such as interface and neighbor IP addresses, bandwidth, and administrative groups. The original IS Reachability TLV, TLV 2, defined in the base ISO 10589 standard, carries similar neighbor and metric information but is constrained to a 6-bit narrow metric with a maximum value of 63, which is inadequate for expressing meaningful cost differentiation in modern, high-capacity enterprise and service-provider topologies; consequently, Junos deployments are commonly configured for wide-metrics-only, favoring TLV 22 over the legacy TLV 2 whenever traffic-engineering-capable or simply more granular metric representation is desired. TLV 132, the IP Interface Address TLV, only advertises the IPv4 addresses configured on the originating router's interfaces and carries no neighbor-adjacency or metric information. TLV 129, the Protocols Supported TLV, merely lists which network-layer protocols (such as IPv4 or IPv6) the originating router is capable of routing, and likewise has nothing to do with neighbor reachability or link cost. Reference topics: Junos Enterprise Routing – IS-IS, Extended IS Reachability and Wide Metrics.