JN0-352 Practice Questions

A BGP Notification message is used to signal a fatal error condition to a BGP peer. When a BGP speaker sends or receives a Notification message, it immediately terminates the BGP session and removes all associated routing entries. The message contains an Error Code and an Error Subcode that explicitly report the specific reason for the error and the subsequent session closure.

A: This describes a BGP UPDATE message, which is used to advertise or withdraw routes while keeping the session active.

D: This describes a BGP Route Refresh message, which requests a re-advertisement of routes without tearing down the session.

- RFC 4271, "A Border Gateway Protocol 4 (BGP-4)", Section 4.5 (NOTIFICATION Message Format) and Section 6.7 (Notification processing). https://doi.org/10.17487/RFC4271

- Juniper Networks TechLibrary, "BGP Message Types" (Understanding BGP Messages).

Based on standard Junos OS IS-IS operational outputs (such as show isis interface), loopback interfaces (e.g., lo0.0) are typically configured as passive. A passive interface in IS-IS advertises its IP address into the routing domain but does not send or receive IS-IS hello packets, meaning it does not form adjacencies. Furthermore, if a physical interface like ge-0/0/2.0 is configured specifically for Level 1 only (or has Level 2 explicitly disabled in the output), it is restricted to Level 1 operations and cannot establish a Level 2 adjacency with a neighbor.

A. A Designated Intermediate System (DIS) is only elected on broadcast network types (like Ethernet LANs), not on point-to-point interfaces.

C. Loopback interfaces are logical, virtual interfaces configured as passive; they do not transmit hello packets and therefore cannot establish IS-IS adjacencies.

- Juniper Networks, "Junos OS Routing Protocols Library," Release 21.4, Chapter: IS-IS Configuration, Section: Configuring Passive Interfaces.

- Juniper Networks, "IS-IS User Guide," Section: Understanding IS-IS Adjacencies and Levels.

In the Junos BGP path selection algorithm, the router evaluates multiple attributes in a strict sequence to select the active route. The route with the shortest AS-path is preferred early in the selection process (Step 3). While the scenario mentions IBGP and EBGP, the other options provided are factually incorrect based on standard BGP rules: EBGP is preferred over IBGP (not the reverse), the lowest (not highest) Router ID is preferred, and the lowest (not highest) peer IP address is preferred. Therefore, selecting the route with the shortest AS-path is the only valid BGP path selection rule among the choices.

- A. The route learned through IBGP: BGP path selection prefers EBGP routes over IBGP routes when all preceding attributes (like Local Preference and AS-path) are equal.

- B. The route learned with the highest next-hop IP address: BGP prefers the route from the peer with the lowest peer IP address as a final tie-breaker, not the highest.

- D. The route learned from the neighbor with highest router ID: BGP prefers the route with the lowest Router ID, not the highest.

- Juniper Networks, "Junos OS Routing Protocols Library," Document ID: Junos OS 21.4, Section

By default, External BGP (EBGP) sessions are established with a Time-to-Live (TTL) value of 1, operating under the assumption that the peering routers are directly connected on the same physical subnet. When establishing an EBGP session using loopback addresses, the IP packets must traverse at least one internal hop (from the physical receiving interface to the logical loopback interface). This requires a TTL greater than 1. The multihop feature must be configured to increase the TTL value of the BGP packets, allowing the EBGP session to establish successfully over the loopback interfaces.

B. Multipath is a feature used for load balancing traffic across multiple equal-cost BGP paths, not for establishing BGP sessions.

C. Damping is a route stability mechanism used to suppress flapping routes and prevent network instability, which is unrelated to session establishment.

D. Passive mode prevents the local router from initiating the TCP connection for BGP, which does not resolve the TTL limitation required for loopback peering.

- Juniper Networks, "Junos OS Routing Protocols Library," Release 21.4, Chapter: BGP Configuration, Section: ebgp-multihop.

- Juniper Networks, "BGP User Guide," Section: EBGP Multihop Configuration and TTL requirements.

Root protection should be configured on designated ports where the STP root bridge should never be seen. To prevent a rogue access-layer switch from sending superior BPDUs and changing root bridge placement, apply root protection on the distribution/root-facing switches’ downstream interfaces toward the access layer. In the exhibit, those are ge-0/0/6 and ge-0/0/8 on Switch-1 and Switch-2.

A. Protecting only Switch-1 leaves Switch-2 access-facing links vulnerable to superior BPDUs.

B. Root protection should be applied on upstream designated ports toward the access layer, not on the access switches’ uplinks.

D. ge-0/0/12 and ge-0/0/13 are not the access-facing downstream interfaces shown for rogue-switch protection.

- Juniper Networks, Understanding Spanning Tree Protocol Root Protection, section “Root Protection”: root protection prevents a port from becoming a root port when superior BPDUs are received.

- Juniper Networks, Configuring STP Root Protection, Junos OS Layer 2 Switching documentation: recommends enabling root protection on interfaces where the root bridge should not appear.

- Juniper Networks, Understanding STP, RSTP, MSTP, and VSTP, section “Root Bridge and Bridge Protocol Data Units”: explains superior BPDUs and root bridge election behavior.

In Junos OS, when multiple firewall filters are applied to a packet traversing a switch, they are processed in a specific hierarchical order. For ingress (Rx) traffic, the switch processes Port (PACL), then VLAN (VACL), and finally Router (RACL) filters. For egress (Tx) traffic, the order is reversed: Router (RACL), then VLAN (VACL), and finally Port (PACL) filters. Therefore, the complete processing sequence for a routed packet encountering all possible filters is Rx-Port, Rx-VLAN, Rx-Router, Tx-Router, Tx-VLAN, and Tx-Port.

B. This option omits the Tx-Router filter, which is processed first on the egress path before the Tx-VLAN filter.

C. This option completely omits the Router (RACL) filters, which are necessary for routed traffic between different subnets.

D. This option omits the VLAN (VACL) filters, which are processed between Port and Router filters.

- Juniper Networks, "Junos OS Routing Policies, Firewall Filters, and Traffic Policers User Guide," Understanding the Order of Firewall Filters Applied to a Packet. Section: Filter Processing Order.

In the Spanning Tree Protocol (STP), the root bridge is determined by the lowest Bridge ID. The Bridge ID is a 64-bit value consisting of a 16-bit bridge priority and a 48-bit system MAC address. Because the bridge priority is the most significant portion of the Bridge ID, configuring a switch with the lowest bridge priority (e.g., 0 or 4096) guarantees that it will win the election and always be designated as the root bridge, regardless of its MAC address.

- A: STP prefers the lowest system MAC address, not the highest, and bridge priority takes precedence over the MAC address anyway.

- C: Port priority is used to determine the root port on non-root bridges, not to elect the root bridge itself.

- D: Port costs are used to calculate the shortest path to the root bridge, not to elect the root bridge.

- Juniper Networks. "Spanning Tree Protocol User Guide." Understanding STP, RSTP, and MSTP, Section: Root Bridge Election.

- IEEE 802.1D-2004. "IEEE Standard for Local and metropolitan area networks - Media Access Control (MAC) Bridges." Section 17: Rapid Spanning Tree Protocol.

In the Junos OS command-line interface, when an administrator views the OSPF link-state database using the show ospf database command, an asterisk () placed next to a Link State Advertisement (LSA) entry signifies that the LSA was originated by the local router itself. This visual indicator is a built-in feature of the Junos OS CLI designed to help network administrators quickly distinguish locally generated routing information from LSAs received from other routers in the OSPF domain.

A. LSAs advertised by remote devices are listed in the database but do not have an asterisk next to them in the local router's output.

C. While the Designated Router (DR) originates Network LSAs, the asterisk specifically denotes local origination, regardless of whether the local router is the DR.

D. The Backup Designated Router (BDR) does not have a specific marker like an asterisk for its LSAs; the asterisk strictly means the LSA is locally originated.

- Juniper Networks, "Junos OS Routing Protocols Library," Release 21.4, Chapter: OSPF Operational Commands, Section: show ospf database.

- Juniper Networks, "OSPF User Guide," Section: Verifying the OSPF Link-State Database.

Juniper EX Series switches dynamically learn MAC addresses by inspecting the source MAC address of incoming Ethernet frames. When a frame is received, the switch records the source MAC address, the ingress interface on which it was received, and a timestamp in its Ethernet switching table (MAC table). The timestamp is utilized to age out inactive entries to maintain an accurate and efficient forwarding table.

A: Switches learn from the source MAC address of incoming frames, not the destination MAC address.

B: Switches do not actively poll hosts to learn MAC addresses; learning is a passive, traffic-driven process.

C: MAC address learning is a continuous process during normal forwarding operations, not restricted to spanning-tree topology changes.

- Juniper Networks TechLibrary, "Understanding MAC Address Learning and Aging on EX Series Switches".

- IEEE 802.1D-2004, "IEEE Standard for Local and metropolitan area networks: Media Access Control (MAC) Bridges", Section 7.8 (Learning Process). https://doi.org/10.1109/IEEESTD.2004.94569

On Juniper Networks EX Series switches, a trunk port is designed to carry traffic for multiple VLANs by utilizing 802.1Q tagging. By default, a trunk port will drop any untagged frames it receives. The primary purpose of the native VLAN feature (configured via the native-vlan-id statement) is to enable a trunk port to accept untagged incoming traffic and logically assign it to the specified native VLAN. It also ensures that outgoing traffic belonging to that specific VLAN is forwarded as untagged frames.

A. Access ports inherently accept and forward untagged traffic by default; they do not require the native VLAN feature to perform this function.

B. The native VLAN feature does not assign a VLAN tag to access ports; it is a feature specifically configured on trunk ports to handle untagged traffic.

D. The native VLAN feature does not restrict or filter traffic on a trunk port; it simply dictates how untagged frames are categorized and processed.

- Juniper Networks, "Understanding Bridging and VLANs," Junos OS Layer 2 Configuration Guide, Section: Native VLANs on Trunk Ports.

- Juniper Networks, "Configuring VLANs for EX Series Switches," Junos OS Ethernet Switching, Section: Trunk Ports and Untagged Traffic.