Free Juniper JN0-281 Practice Exam with Questions & Answers | Set: 2

In Junos routing and security contexts, martian addresses are IP prefixes that should not appear as valid, routable sources or destinations on normal interfaces because they are reserved, special-purpose, or otherwise not usable for general unicast forwarding. Treating these as invalid helps protect the control plane and prevents leakage of nonsensical routes into the fabric. This is especially relevant in data center underlays where strict routing hygiene is expected and where improper advertisements can cause blackholing or policy confusion.

The multicast range 224.0.0.0/4 is a classic martian example for unicast routing. These addresses are reserved for multicast and should not be accepted as ordinary unicast sources or carried as typical unicast reachability in an IP fabric. The loopback range 127.0.0.0/8 is also martian on physical networks because it is reserved for host self-reference and must never be forwarded by routers. Seeing it on an interface implies misconfiguration or spoofing.

The prefix 192.0.0.0/24 is reserved for special protocol and IETF assignments and is not intended for general use on public or private networks. As a result, it is commonly treated as martian in routing policy and input validation. By contrast, 172.36.0.0/24 and 198.60.0.0/16 are ordinary globally routable unicast space, so they are not martian by definition.

The configuration defines a static route for 192.168.1.0/24 with a primary next hop of 10.20.20.254 and a qualified-next-hop of 10.20.20.253 with preference 25. In Junos, qualified next hop is used to create preference-ranked redundancy for a static route, typically primary and backup forwarding. The key behavior is that the best, lowest preference path is selected as active. For static routes, the default preference for the route and its primary next hop is lower than 25 unless you explicitly raise it. Because the qualified-next-hop is configured with preference 25, it is less preferred than the primary next hop, so 10.20.20.254 remains the selected next hop during normal operation.

This is not load balancing. Junos does not automatically install both next hops for forwarding simply because more than one next hop is configured when one is qualified with a higher preference. Instead, the qualified next hop is held in reserve and is used only when the primary next hop becomes unusable, such as when it is no longer resolvable or the associated forwarding condition fails. Therefore, the route is expected to be installed and active using 10.20.20.254 under normal conditions, with 10.20.20.253 acting as a backup path.

The configuration shown is under protocols bgp and defines a BGP group named service-pod with the statement type internal. In Junos, the BGP group type determines whether the sessions formed by neighbors in that group are treated as internal BGP or external BGP. When the group is set to type internal, the router establishes an iBGP session to the configured neighbor address. That means both peers are expected to be in the same autonomous system, and the session is used to exchange routes within that single AS.

The local-address statement sets the source address that the router will use when initiating the TCP connection for BGP. In data center designs, this is commonly a loopback address so the session can be resilient and independent of any single physical interface. The neighbor statement identifies the remote peer address. With type internal, the session is iBGP even if the neighbor is directly connected, because the relationship is defined by AS scope rather than topology.

OSPF and IS-IS are different routing protocols entirely and are not established through BGP configuration. EBGP would require type external and typically involves different AS numbers across the peering. Therefore, the only correct answer is IBGP.

On Junos switching platforms used in data centers, a VLAN is a Layer 2 broadcast domain. To make a VLAN functional for user traffic, you define the VLAN with a name and typically a VLAN ID, and you associate Layer 2 interfaces with that VLAN so frames arriving on those interfaces are placed into the correct broadcast domain. Without interface membership, the VLAN exists as configuration but does not carry endpoint traffic because no ports participate in it. This is why assigning a VLAN name or ID and associating Layer 2 interfaces to the VLAN is a correct requirement.

Trunk mode interfaces are designed to carry multiple VLANs over a single physical link using 802.1Q tagging. In a data center, trunks are common on leaf-to-spine uplinks, switch-to-switch connections, and server connections where the host or hypervisor tags multiple VLANs. Therefore, assigning one or more VLANs to a trunk port is correct.

An IRB interface is not required for every VLAN. IRB is only needed when the VLAN requires Layer 3 gateway functionality, such as inter-VLAN routing or default gateway services for that subnet. Pure Layer 2 VLANs do not need IRB. Also, an access mode interface is intended to belong to a single VLAN and typically carries untagged traffic, so assigning multiple VLANs to an access mode interface is not correct in standard Ethernet switching behavior.

A link aggregation group combines multiple physical Ethernet interfaces into one logical link layer interface, called an aggregated Ethernet interface on Junos. The primary purpose is to improve availability and increase usable bandwidth between two devices without changing the logical topology. If one member link fails, the aggregate can remain up and continue forwarding traffic over the remaining active members, providing redundancy at the link layer. This is especially valuable in data center designs where loss of a single optic or cable should not interrupt server connectivity, leaf to spine uplinks, or connections to service appliances.

LAG also enables load balancing. Instead of forcing all traffic over one physical link, the forwarding plane distributes flows across member links using a hashing algorithm. This allows the aggregate to use the sum of member bandwidth for multiple concurrent flows while keeping packets for a given flow in order. In leaf spine fabrics, this complements ECMP at Layer 3 by delivering parallelism both at the routed path level and within a single adjacency when multiple physical links exist.

LAG does not encrypt traffic. Encryption is provided by separate security features and protocols. It also does not increase the speed of a single physical interface; rather, it increases the total capacity of the logical bundle across multiple links. Finally, it does not assign IP addresses, which is the role of services like DHCP, not link aggregation.

On Junos Ethernet switching, access and trunk ports serve different purposes and therefore treat VLAN tags differently by default. An access port is intended for a single VLAN and is designed to connect to endpoints that do not tag their frames. Because of that, access ports forward traffic as untagged on the wire and internally associate those untagged frames to the configured access VLAN. This makes access ports the standard choice for single-VLAN server NICs, management devices, and any endpoint expecting a plain Ethernet connection.

A trunk port is intended to carry traffic for multiple VLANs over a single link, which is typical for switch-to-switch uplinks, leaf-to-spine connectivity where VLAN services are extended, and hosts or appliances that use VLAN tagging. By default, trunk ports forward tagged traffic and require VLAN tags to identify the VLAN membership of each frame. Untagged behavior on a trunk is not assumed by default and is typically governed by configuring a native VLAN or equivalent untagged VLAN handling, depending on platform and design. Without such configuration, untagged frames are not treated as a normal expected case for a trunk link in data center fabrics.

Therefore, the correct default statements are that access ports forward untagged traffic and trunk ports forward tagged traffic, matching options B and D.

The configuration is applied under the routing-options hierarchy and specifically under graceful-restart with the statement disable. In Junos, routing-options graceful-restart is the global control point used to enable or manage graceful restart behavior at the system routing level. When graceful restart is enabled, the router can continue forwarding and temporarily suppress certain routing protocol update behavior during a routing process restart or control-plane event, allowing the network to avoid unnecessary reconvergence and route churn.

Placing disable under routing-options graceful-restart turns off graceful restart globally. This means the device will not attempt to use graceful restart mechanisms for routing protocols at the global level. Protocol-specific graceful restart configuration exists under each routing protocol hierarchy, but the exhibit shows the global routing-options location, which impacts overall graceful restart behavior for the routing subsystem.

Option A is incorrect because disabling BGP graceful restart only would be done under the BGP protocol hierarchy, not routing-options. Option C is incorrect because graceful restart is a routing protocol restart behavior, not something applied only to static routes. Option D is also incorrect because the setting is not scoped to specific route statements under routing-options; it disables the graceful restart feature itself, not individual routes.

In data center environments, globally disabling graceful restart may be chosen when an operator prefers deterministic, immediate reconvergence behavior or when interoperability testing indicates graceful restart helper or restart behavior is undesired with specific peers.

In the BGP finite state machine, OpenConfirm indicates that the TCP session is already established and the BGP OPEN message exchange has successfully completed. At this point, both peers have agreed on critical session parameters such as BGP version, autonomous system numbers, hold time, and the BGP identifier. Because the OPEN messages have been processed, BGP transitions from OpenSent to OpenConfirm and then waits for the next control message that validates the session is operational.

Specifically, in OpenConfirm the local BGP process is waiting to receive a KEEPALIVE message from the neighbor, which confirms that the neighbor accepted the OPEN and is ready to bring the session to the Established state. If instead a NOTIFICATION message is received, it indicates an error condition and the session will be torn down. This is why option D is correct.

Option A describes OpenSent, where the router is waiting to receive an OPEN after sending its own OPEN. Option B aligns more closely with Connect, where BGP is still trying to complete the transport connection. Option C relates to Idle, where BGP waits for a start event or configuration to initiate the session. In data center BGP underlays and EVPN control planes, being stuck in OpenConfirm commonly points to policy mismatch, capability negotiation issues, or keepalive handling problems, rather than basic IP reachability.

A Layer 2 switch builds its Ethernet switching table through a learning process based on the source MAC addresses of incoming frames. When a frame arrives on an interface within a VLAN or bridge domain, the switch examines the source MAC address and associates it with the ingress interface and VLAN context. If the MAC address is new, the switch creates a new entry; if it already exists but is seen on a different interface, the switch updates the entry to reflect the new location. This dynamic learning is fundamental to efficient unicast forwarding and is why option A is correct.

Once the switch has learned MAC-to-port mappings, it can forward subsequent frames destined to those MAC addresses as known unicast out the specific egress interface rather than flooding them. If the destination MAC is unknown, the switch typically floods the frame within the VLAN or bridge domain to discover the correct destination. When the destination replies, the switch learns that MAC as a source, completing the learning cycle.

Spanning Tree Protocol does not provide a MAC table and there is no concept of downloading an Ethernet switching table from a root bridge. STP’s role is loop prevention and topology control at Layer 2, not MAC learning distribution. Firewall filters can enforce policy but do not create the switching table. Recording destination MAC addresses would not correctly learn endpoint locations because the destination can be unknown when the first frames are sent; source learning is reliable because every received frame carries the sender’s MAC address.

In a spine-leaf fabric architecture, which is commonly used in data center designs, each device has a distinct role to ensure efficient and scalable network traffic flow.

Step-by-Step Breakdown:

Spine Nodes:

The spine nodes form the backbone of the fabric and are responsible for transit traffic between leaf nodes. They connect to every leaf switch and provide multiple paths for traffic between leaf nodes, ensuring redundancy and load balancing.

Leaf Nodes:

The leaf nodes are used for host connectivity. These switches connect to servers, storage, or edge routers. They also connect to the spine switches to reach other leaf switches.

Juniper Reference:

Spine-Leaf Architecture: In Juniper's IP fabric designs, spine switches handle inter-leaf communication, while leaf switches manage host and endpoint connectivity.