Juniper Data Center, Associate (JNCIA-DC) JN0-280 Exam Dumps: Updated Questions & Answers (October 2025)

In the exhibit, we see two next-hop addresses for the default static route (0.0.0.0/0):

The first next hop is172.25.11.254, with no specified preference.

The second next hop is172.25.11.200, with a specified preference of140.

Step-by-Step Breakdown:

Default Static Route Preference:If no preference is explicitly set for a next hop in Junos, it defaults to5for static routes.

Determining Preference:In this case, the next hop172.25.11.254does not have an explicit preference defined, so it will use the default value of5. The second next hop has a preference of140, which is higher,meaning it will only be used if the primary next hop is unavailable.

Juniper Reference:

Static Route Preference: In Junos, the default preference for static routes is5, and this value is applied unless overridden by the preference parameter.

The exhibit shows aFolded IP Clos Architecture, which is also referred to as a3-stage Closnetwork design. This architecture typically consists of two layers of switches:

Spine Layer: The top row of switches.

Leaf Layer: The bottom row of switches.

Step-by-Step Breakdown:

Clos Architecture:A 3-stage Clos network has two types of devices: spine and leaf. In this design, each leaf switch connects to every spine switch, providing a high level of redundancy and load balancing.

Stage Explanation:

Stage 1: The first set of leaf switches.

Stage 2: The spine switches.

Stage 3: The second set of leaf switches.

TheFolded Closarchitecture shown here effectively "folds" the 3-stage design by combining the ingress and egress leaf layers into one, reducing it to two visible layers, but still maintaining the overall3-stage architecture.

Juniper Reference:

IP Clos Architecture: The 3-stage Clos design is commonly used in modern data centers for high availability, redundancy, and scalability.

The BGP session in the exhibit shows the state asConnect, which indicates that theTCP sessionbetween the BGP peers has not been fully established.

Step-by-Step Breakdown:

BGP State "Connect":

TheConnectstate is the second stage in the BGP finite state machine (FSM). At this stage, BGP is trying to establish aTCP sessionwith the peer, but the session has not yet been successfully established.

A successful TCP three-way handshake (SYN, SYN-ACK, ACK) is required before BGP can progress to theOpenSentstate, where the peers exchange BGP Open messages.

Possible Causes:

A firewall blocking TCP port179.

Incorrect IP addresses or network connectivity issues between the BGP peers.

Juniper Reference:

BGP Troubleshooting: In Junos, if a BGP session is stuck in theConnectstate, the issue is likely due to a failure in establishing the underlying TCP connection.

The primary purpose of anIRB (Integrated Routing and Bridging)interface is to enableinter-VLAN routingin a Layer 3 environment. An IRB interface in Junos combines the functionality of both Layer 2 bridging (switching) and Layer 3 routing, allowing devices in different VLANs to communicate with each other.

Step-by-Step Breakdown:

VLANs and Layer 2 Switching:Devices within the same VLAN can communicate directly through Layer 2 switching. However, communication between devices in different VLANs requires Layer 3 routing.

IRB Interface for Inter-VLAN Routing:The IRB interface provides a Layer 3 gateway for each VLAN, enabling routing between VLANs. Without an IRB interface, devices in different VLANs would not be able to communicate.

Configuration:In Juniper devices, the IRB interface is configured by assigning Layer 3 IP addresses to it. These IP addresses serve as the default gateway for devices in different VLANs.

Example configuration:

set interfaces irb unit 0 family inet address 192.168.1.1/24

set vlans vlan-10 l3-interface irb.0

This allows VLAN 10 to use the IRB interface for routing.

Juniper Reference:

IRB Use Case: Inter-VLAN routing is essential in data centers where multiple VLANs are deployed, and Juniper's EX and QFX series switches support IRB configurations for this purpose.

In Junos, thedefault export policyforOSPFis toreject all routesfrom being exported.

Step-by-Step Breakdown:

Default Export Policy:By default,OSPFin Junos does not export any routes to other routing protocols or neighbors. This is a safety mechanism to prevent unintended route advertisements.

Custom Export Policies:

If you need to export routes, you must create a customexport policythat explicitly defines which routes to advertise.

Example: You can create an export policy to redistribute static or connected routes into OSPF.

Juniper Reference:

OSPF Export Behavior: In Juniper devices, the default policy for OSPF is to reject route advertisements unless explicitly configured otherwise through custom policies.

Agenerated routein Junos OS is configured under the[edit routing-options]hierarchy.

Step-by-Step Breakdown:

Generated Routes:A generated route is created based on the presence of more specific routes in the routing table. It acts as a summary route and is generated when any of its contributing routes are active. This is commonly used to create aggregate routes in OSPF, BGP, or other protocols.

Configuration Hierarchy:The configuration for generated routes is placed under[edit routing-options], where other static and routing policies are also defined.

Command Example:

set routing-options generate route 10.10.0.0/16

Juniper Reference:

Routing Options: Juniper routers use the routing-options hierarchy to configure generated routes and other static routing behaviors.

In the exhibit, R2 receives the same OSPF update from both R1 and R3. OSPF has mechanisms toprevent unnecessary processing of duplicate LSAs (Link-State Advertisements).

Step-by-Step Breakdown:

OSPF LSA Processing:

OSPF uses LSAs to exchange link-state information between routers. When a router receives an LSA, it checks if it already has a copy of the LSA in its Link-State Database (LSDB).

Duplicate LSAs:If R2 has already received and processed the update from R1, it willignore the update from R3because it already has the same LSA in its database. OSPF uses the concept of flooding, but it does not reprocess LSAs that it already knows about.

R2 Behavior:R2 will keep the update from R1 (the first one it received) and will ignore the same LSA from R3, as it is already in the LSDB.

Juniper Reference:

OSPF LSA Processing: Junos adheres to OSPF standards, ensuring that duplicate LSAs are not processed multiple times to avoid unnecessary recalculations.

AnIP fabricis a network architecture commonly used in data centers to provide scalable, high-throughput connectivity using aspine-leaf topology.

Step-by-Step Breakdown:

Layer 3 Routing Protocol:An IP fabric relies on aLayer 3 routing protocol, typically BGP or OSPF, to provide routing between the leaf and spine switches. This ensures efficient traffic forwarding across the network.

Single Connection Between Spine and Leaf:In an IP fabric, each leaf switch connects toevery spine switchwith a single connection. This ensures that traffic between any two leaf switches can travel through the spine layer in just two hops.

Juniper Reference:

Spine-Leaf Design: Juniper’s IP fabric implementations are designed for scalability and low-latency routing, often using protocols like BGP for Layer 3 control.

In the exhibit, BGP is configured withlocal AS 65101and a neighbor at172.16.1.1inpeer AS 65201. This setup involves two different Autonomous Systems (AS), indicating anExternal BGP (EBGP)configuration.

Step-by-Step Breakdown:

EBGP vs. IBGP:

EBGPis used between routers in different ASes. In this case, the local AS is65101and the peer AS is65201, meaning the BGP session isEBGP.

IBGPis used between routers within the same AS, which is not applicable here as the AS numbers are different.

BGP Group Configuration:

The configuration does not require a type external parameter because Junos OSautomatically recognizes the session asEBGPwhen the local and peer AS numbers are different.

The BGP session will operate as EBGP, and the configuration will commit successfully.

Juniper Reference:

BGP Configuration: In Juniper, EBGP is automatically recognized when the local and peer AS numbers differ, without needing to specify type external.

IBGP (Internal Border Gateway Protocol)is used to exchange routing information betweenrouters within the same AS (Autonomous System).

Step-by-Step Breakdown:

TTL of 255:

By default, IBGP sessions are established with aTTL (Time to Live)value of255. This allows IBGP neighbors to communicate over multiple hops within the AS without requiring any additional configuration.

Full Mesh Requirement:

IBGP requires alogical full meshbetween all IBGP routers to ensure that routing information is fully distributed within the AS. Since IBGP does not propagate routes learned from one IBGP peer to another by default, a full mesh topology is needed unlessroute reflectorsorBGP confederationsare used.

Juniper Reference:

IBGP Full Mesh: Juniper recommends using route reflectors in large networks to simplify IBGP full-mesh requirements.