JNCIA-Junos Exam Flashcards

Q: What is the current JNCIA-Junos exam code in 2026?

Juniper announced a JNCIA-Junos update on March 2, 2026. JN0-105 remains the active exam through April 5, 2026, and JN0-106 becomes active on April 6, 2026. The objectives stay centered on Junos OS fundamentals, CLI, configuration, monitoring, routing, and routing policy.

Q: How many questions are on JNCIA-Junos and how long is it?

Juniper lists JNCIA-Junos as 65 multiple-choice questions with a 90-minute time limit, delivered in English through Pearson VUE. That is roughly 80 seconds per question, so plan pacing and leave a few minutes to review.

Q: What is the JNCIA-Junos passing score?

Juniper does not publicly publish a numeric passing score for JNCIA-Junos. Candidates receive an immediate pass or fail status, so the study goal should be broad coverage of all seven objective domains rather than targeting a percentage.

Q: Does Juniper publish official domain weightings?

No. Juniper publishes the seven JNCIA-Junos objective domains and their subtopics but does not publish official percentage weightings. Any percentages seen elsewhere are estimates based on objective breadth, not Juniper figures.

Q: Is there a prerequisite for JNCIA-Junos?

No prerequisite certification is required. Basic networking knowledge is recommended, and the exam is the entry point into the Junos certification track that leads to JNCIS, JNCIP, and JNCIE levels.

Q: How long is the certification valid?

Juniper certifications are valid for 3 years. Recertification keeps the credential active, and passing a higher-level Junos exam can also recertify the associate level.

Question 1

Collision domain vs. broadcast domain

Accepted Answer

A switch port (or full-duplex link) is its own collision domain. A router interface bounds a broadcast domain; a switch by default forwards broadcasts, so all ports on one VLAN are one broadcast domain.

Question 2

TCP vs. UDP

Accepted Answer

TCP is connection-oriented and reliable: it uses a handshake, sequencing, and acknowledgments. UDP is connectionless with no delivery guarantee, used where speed matters more than reliability (DNS, VoIP).

Question 3

Longest-prefix match

Accepted Answer

When multiple routes match a destination, the router selects the route with the most specific (longest) subnet mask. A /32 host route beats a /24, which beats the 0.0.0.0/0 default.

Question 4

IPv6 address length and notation

Accepted Answer

IPv6 addresses are 128 bits, written as eight 16-bit hex groups. A double colon (::) compresses one run of consecutive all-zero groups, and it may appear only once in an address.

Question 5

Junos control plane vs. forwarding plane

Accepted Answer

Junos cleanly separates the two: the Routing Engine (RE) runs the control plane (protocols, CLI, route calculation); the Packet Forwarding Engine (PFE) forwards traffic at high speed using the forwarding table.

Question 6

Routing Engine (RE) role

Accepted Answer

The RE runs the Junos OS kernel, routing protocols, and management interface. It builds the routing table (RIB) and pushes the best routes down to the PFE as the forwarding table (FIB).

Question 7

Transit traffic vs. exception traffic

Accepted Answer

Transit traffic is forwarded by the PFE without involving the RE. Exception traffic (packets to the device itself, options, or that need control handling) is sent to the RE for processing.

Question 8

Junos software architecture benefit

Accepted Answer

A single, modular OS image with one consistent CLI runs across Juniper platforms. Daemon-based modularity means a process failure (e.g., a routing daemon) does not crash the whole system.

Question 9

Operational mode vs. configuration mode

Accepted Answer

Operational mode (prompt ends with >) runs show, ping, and monitoring commands. Configuration mode (prompt ends with #, entered via 'configure') edits the candidate configuration.

Question 10

Candidate vs. active configuration

Accepted Answer

Edits go into the candidate configuration and are not live until 'commit'. The active configuration is what the device is actually running. 'commit' makes the candidate the new active config.

Question 11

commit confirmed

Accepted Answer

Activates the candidate config but auto-rolls back after a timer (default 10 minutes) unless a second 'commit' confirms it. Protects against lockout from a bad remote change.

Question 12

rollback command

Accepted Answer

'rollback n' loads a previous committed configuration into the candidate (0 = last committed, up to 49). You must still 'commit' to make it active. 'rollback' alone discards uncommitted edits.

Question 13

show | compare

Accepted Answer

In configuration mode, 'show | compare' displays the difference between the candidate and the active configuration, with + for additions and - for deletions before you commit.

Question 14

set vs. delete vs. deactivate

Accepted Answer

'set' adds/modifies a statement. 'delete' removes it entirely. 'deactivate' keeps the statement but marks it inactive (shown as 'inactive:'), so it can be re-enabled with 'activate'.

Question 15

CLI output filtering with the pipe

Accepted Answer

Question 16

edit and top/up/exit navigation

Accepted Answer

'edit <hierarchy>' moves into a subtree; 'up' moves one level up; 'top' returns to the root of the configuration; 'exit' leaves configuration mode (warns if uncommitted changes exist).

Question 17

J-Web

Accepted Answer

Junos' built-in HTTPS web interface for configuration and monitoring. It is an alternative to the CLI for many tasks but the CLI remains the comprehensive management interface.

Question 18

Factory-default configuration

Accepted Answer

Out of the box a device has a minimal factory-default config. 'load factory-default' resets the candidate to it; you must then set a root authentication password before the first commit succeeds.

Question 19

Login classes and permissions

Accepted Answer

A login class defines permission flags (e.g., view, configure, all) and idle timeout. Each user account references a class. Predefined classes include super-user, operator, read-only, and unauthorized.

Question 20

Authentication order

Accepted Answer

Junos tries authentication methods in the configured 'authentication-order' (e.g., radius, tacplus, password). Local password is always checked if it is in the order or if remote servers are unreachable.

Question 21

Configuration groups

Accepted Answer

Reusable config templates applied with 'apply-groups'. Use them to define common settings once (e.g., interface or system parameters) and inherit them, with explicit config overriding the group.

Question 22

Rescue configuration

Accepted Answer

A known-good config saved with 'request system configuration rescue save'. 'rollback rescue' restores it. Unlike rollback 0-49, it is not overwritten by routine commits.

Question 23

Interface naming convention

Accepted Answer

Junos interfaces use type-fpc/pic/port (e.g., ge-0/0/1). A logical unit is added as '.unit' (ge-0/0/1.0). lo0 is the loopback; the unit holds the address and family.

Question 24

NTP, SNMP, and syslog purpose

Accepted Answer

NTP synchronizes the clock (critical for accurate logs and certificates). SNMP exposes monitoring data via communities/v3 users. Syslog records system events to local files or remote servers.

Question 25

Configuration archival

Accepted Answer

'system archival configuration' transfers the config to a remote SCP/FTP server on each commit (transfer-on-commit) or on a timer, providing off-box backups for recovery.

Question 26

show interfaces terse

Accepted Answer

Gives a compact list of every interface with admin status, link status, protocol family, and address. The fastest way to verify which interfaces are up and addressed.

Question 27

Interface 'Admin' vs. 'Link' status

Accepted Answer

Admin status reflects configuration (up unless 'disable' is set). Link status reflects the physical layer. Admin up / Link down typically means a cabling or far-end problem.

Question 28

monitor traffic interface

Accepted Answer

A built-in tcpdump-style capture of control/exception traffic on an interface. It does not show transit traffic forwarded by the PFE, only packets reaching the RE.

Question 29

monitor interface traffic

Accepted Answer

Displays real-time, refreshing input/output packet and error counters for interfaces. Different from 'monitor traffic interface', which captures actual packets.

Question 30

Root password recovery on Junos

Accepted Answer

Reboot, interrupt the boot sequence to enter single-user mode, run the recovery option to get a root shell, set a new root password with 'set system root-authentication', then commit.

Question 31

request system halt vs. reboot

Accepted Answer

'request system halt' safely stops the OS so power can be removed without corrupting the file system. 'request system reboot' performs an orderly restart. Never just pull power on a running RE.

Question 32

request system software add

Accepted Answer

Installs a Junos software package. The 'validate' option checks compatibility with the active config first; a reboot is typically required to run the new version.

Question 33

Routing table (RIB) vs. forwarding table (FIB)

Accepted Answer

The routing table (RIB, inet.0) holds all learned routes from every protocol. The device selects the active route per destination and installs it into the forwarding table (FIB) used by the PFE.

Question 34

Route preference (administrative distance)

Accepted Answer

Lower preference wins when routes to the same prefix come from different sources. Defaults: Direct 0, Local 0, Static 5, OSPF internal 10, BGP 170. It is the Junos equivalent of Cisco admin distance.

Question 35

Static route configuration

Accepted Answer

Configured under 'routing-options static route'. A next-hop can be an IP, an interface, or 'discard'/'reject'. 'reject' returns ICMP unreachable; 'discard' drops silently.

Question 36

inet.0 vs. inet6.0

Accepted Answer

inet.0 is the default IPv4 unicast routing table; inet6.0 is the IPv6 unicast routing table. mpls.0 holds MPLS label routes. Routing instances create their own tables.

Question 37

Routing instances

Accepted Answer

Logical, separate routing tables on one device (e.g., a virtual-router instance) providing traffic separation. The main (default) instance uses inet.0 unless an instance is specified.

Question 38

Why use dynamic routing protocols

Accepted Answer

They automatically learn and adapt to topology changes and scale better than static routes. JNCIA tests the role and concepts of OSPF/BGP rather than deep protocol configuration.

Question 39

Routing policy: import vs. export

Accepted Answer

Import policy filters routes coming INTO the routing table from a protocol. Export policy filters routes leaving the routing table to a protocol (advertising). Direction is relative to the routing table.

Question 40

Policy term structure: from / then

Accepted Answer

A policy is an ordered list of terms. 'from' defines match conditions; 'then' defines the action (accept, reject, next term, or modify attributes). Terms are evaluated top-down.

Question 41

Default routing policy actions

Accepted Answer

If no term matches, the protocol's default policy applies (e.g., OSPF accepts and exports OSPF routes; BGP accepts all from peers and exports active BGP routes). Custom policy overrides defaults.

Question 42

Policy chain evaluation

Accepted Answer

When multiple policies are applied as a chain, they are evaluated left to right. The first terminating action (accept or reject) stops evaluation; 'next policy' continues to the next one.

Question 43

Routing policy vs. firewall filter

Accepted Answer

Routing policy controls which ROUTES are accepted/advertised (control plane). A firewall filter controls which PACKETS are permitted, discarded, or actioned (data plane). They operate on different things.

Question 44

Firewall filter term evaluation

Accepted Answer

Filter terms are evaluated in order; the first matching term's action applies and evaluation stops. Any traffic not matching any term hits an implicit discard at the end.

Question 45

Firewall filter actions

Accepted Answer

Terminating actions: accept, discard (silent drop), reject (drop + send ICMP). Non-terminating actions like 'count', 'log', and 'policer' can be combined with a terminating action.

Question 46

Applying a firewall filter: input vs. output

Accepted Answer

A filter is applied to an interface unit's family as 'filter input' (ingress) or 'filter output' (egress). Direction is from the device's perspective on that interface.

Question 47

Unicast Reverse Path Forwarding (uRPF)

Accepted Answer

Checks that a packet's source address is reachable via the interface it arrived on, dropping spoofed-source packets. A loose mode only requires the source to be in the routing table at all.

Question 48

Loopback filter for control-plane protection

Accepted Answer

Applying a firewall filter to lo0 filters traffic destined to the Routing Engine itself, protecting the control plane from DoS while not affecting transit traffic.

Question 49

Prefix list vs. route filter in policy

Accepted Answer

A prefix-list is a reusable named set of prefixes referenced in 'from'. A route-filter matches prefixes with match types like exact, longer, orlonger, upto, and through for granular control.

Question 50

show route command

Accepted Answer

Displays the routing table: prefix, protocol source, preference (in brackets), and next hop. '*' marks the active route installed in the forwarding table. Add a prefix to filter the output.

Free JNCIA-Junos Exam Flashcards

Filter by Topic

Jump to Card

About These JNCIA-Junos Flashcards

Topics Covered

Frequently Asked Questions

JNCIA-Junos

Explore More Juniper Certifications

JNCIA-Cloud Juniper Associate Cloud

JNCIA-DC Juniper Associate Data Center

JNCIA-Design Juniper Associate Design

JNCIA-DevOps Juniper Associate DevOps

JNCIA-SEC Juniper Associate Security

JNCIE-DC Juniper Expert Data Center

More From This Family