JN0-106 Practice Test 23 — 15 Questions

Question 1

Which TWO commands can be used to view the current active configuration on a Junos device? (Choose two.)

Accepted Answer

show configuration | display set. Option C, `show configuration`, is correct because it displays the active configuration in Junos's hierarchical (curly-brace) format, which is the standard way to view the currently committed configuration. Option A, `show configuration | display set`, is also correct because it renders that same active configuration as flat `set` commands, which is useful for viewing or copying the configuration in a script-friendly form. Both commands read the committed active configuration, so they satisfy the requirement. Option B, `show system configuration`, is not a valid Junos operational command for displaying the configuration. Option D, `show | compare`, only shows the difference between the candidate configuration and the active configuration (a diff), not the full active configuration. Option E, `show interfaces`, displays interface status and statistics rather than the device configuration.

Answer

show system configuration

Answer

show | compare

Answer

show interfaces

Question 2

Which THREE CLI features are available in Junos OS to assist with command entry?

Accepted Answer

? (question mark) for context-sensitive help.. Option A is correct because in Junos OS CLI, typing ? at any point displays context-sensitive help listing valid commands, keywords, or options available at that position. Option C is correct because the Up arrow key scrolls backward through the command history buffer, allowing the user to recall and re-execute previously entered commands. Option E is correct because the Tab key performs command and option completion, automatically finishing a partially typed command or keyword when the entry is unambiguous. Option B is incorrect because Ctrl+R is not a Junos OS command-recall feature; command history is navigated with the Up/Down arrow keys or the show cli history command. Option D is incorrect because Ctrl+Z is not an undo function in Junos OS; it is not a supported command-entry aid in the CLI.

Answer

Ctrl+R to repeat the last command.

Answer

Ctrl+Z to undo the last command.

Question 3

Which THREE statements about the Junos OS file system are true? (Choose three.)

Accepted Answer

The active configuration is stored in the /config directory. Option C is correct because the active Junos configuration is saved as juniper.conf.gz in the /config directory, which is a separate partition from the root file system. Option D is correct because Junos OS writes its log files, such as messages and interactive-commands, into the /var/log directory. Option E is correct because the Junos OS file system is a FreeBSD-based, UNIX-like hierarchy containing standard directories including /, /var, and /config. Option A is incorrect because /etc holds system configuration files, not log files, which reside in /var/log. Option B is incorrect because /altroot is a backup root partition used for alternate boot images, not for user-uploaded files, which are typically placed in /var/tmp or /var/home.

Answer

The /etc directory contains all log files

Answer

The /altroot directory is used for user-uploaded files

Question 4

Which TWO statements are true about the 'commit confirmed' command? (Choose two.)

Accepted Answer

The default timeout is 10 minutes.. Option B is correct because the 'commit confirmed' command in Junos OS uses a default rollback timeout of 10 minutes, during which the configuration is active but not yet permanent. Option E is correct because the commit only becomes permanent if the administrator issues a confirming 'commit' command within that timeout window; otherwise, the device automatically rolls back to the previous configuration. Option A is incorrect because scheduling a commit for a future time is done with the 'commit at' command, not 'commit confirmed'. Option C is incorrect because 'commit confirmed' does not save the configuration to a file before applying; it applies the candidate configuration with an automatic rollback timer. Option D is incorrect because the timeout can be set to any value from 1 to 65,535 minutes using the 'commit confirmed <minutes>' syntax, not only in multiples of 5 minutes.

Answer

It is used to schedule a commit at a future time.

Answer

It saves the configuration to a file before applying.

Answer

The timeout can be set only in multiples of 5 minutes.

Question 5

Which TWO statements about ARP are correct? (Select two.)

Accepted Answer

ARP request is sent to the broadcast MAC address. Option A is correct because an ARP request must reach every device on the local segment, so it is encapsulated in a frame with the broadcast destination MAC address FF:FF:FF:FF:FF:FF. Option E is correct because the ARP reply is unicast: the responding host already knows the requester's MAC address from the sender hardware address field in the request, so it sends the reply directly to that MAC address. Option B is wrong because ARP requests use the broadcast MAC address, not a multicast address (IPv6 uses multicast with Neighbor Discovery instead of ARP). Option C is wrong because the reply is unicast to the requester, not broadcast, which would waste bandwidth and force all hosts to process it. Option D is wrong because ARP resolves IPv4 addresses to MAC addresses; IPv6 uses Neighbor Discovery (NDP) with ICMPv6 rather than ARP.

Answer

ARP request is sent to a multicast MAC address

Answer

ARP reply is sent to the broadcast MAC address

Answer

ARP is used for both IPv4 and IPv6

Question 6

Which THREE statements are true about VLANs on Juniper EX switches? (Select three.)

Accepted Answer

A single VLAN can extend across multiple switches via trunk ports. Option B is correct because a VLAN is a Layer 2 broadcast domain that can span multiple Juniper EX switches when the inter-switch links are configured as trunk ports carrying 802.1Q tags, allowing the same VLAN ID to be present on each switch. Option C is correct because within a single switch the VLAN ID (1–4094) must be unique; you cannot create two distinct VLANs with the same ID on one EX device, as the ID is the local identifier for that broadcast domain. Option D is correct because VLANs segment a switch into separate broadcast domains, so broadcast, unknown unicast, and multicast traffic from one VLAN is not flooded into another VLAN, providing broadcast isolation. Option A is not correct because hosts in different VLANs are in separate Layer 3 subnets and require a router or Layer 3 interface (e.g., an IRB/RVI) to communicate; no communication occurs by default. Option E is not correct because on Juniper EX switches, assigning an interface to a VLAN requires the VLAN to already exist (or be created with 'set vlans vlan-id '); it is not automatically created by the interface assignment.

Answer

Hosts in different VLANs can communicate without any additional configuration

Answer

VLANs are automatically created when you assign an interface to an untagged VLAN

Question 7

Which THREE fields are part of an Ethernet frame header? (Select three.)

Accepted Answer

Destination MAC address. The Ethernet frame header always begins with the Destination MAC address (Option A), a 6-byte field identifying the intended recipient's hardware address, which is essential for Layer 2 forwarding. The Source MAC address (Option E) is the next 6-byte field, identifying the sending NIC so replies and switch MAC-address-table entries can be built. The EtherType field (Option C) follows (or follows the optional 802.1Q tag) and is a 2-byte value such as 0x0800 for IPv4 or 0x86DD for IPv6, telling the receiver which upper-layer protocol is encapsulated. Option B (VLAN tag 802.1Q) is not part of the standard Ethernet header; it is an optional 4-byte tag inserted only on trunk links, so it is not one of the three basic header fields. Option D (FCS) is a 4-byte CRC trailer appended to the end of the frame for error detection, not a header field.

Answer

VLAN tag (802.1Q)

Answer

Frame Check Sequence (FCS)

Question 8

Which TWO statements about VLANs are correct? (Choose two.)

Accepted Answer

Trunk links can carry traffic for multiple VLANs.. Option C is correct because a trunk link (typically 802.1Q) tags frames so it can carry traffic for multiple VLANs between switches or to a router/switch, unlike an access port. Option D is correct because each VLAN defines its own broadcast domain, so broadcasts are confined within the VLAN and do not propagate to other VLANs, which is the core purpose of VLAN segmentation. Option A is incorrect because MAC addresses are not shared across VLANs; each VLAN maintains its own MAC address table and forwarding domain. Option B is incorrect because a VLAN does not strictly require a unique IP subnet — VLANs can be Layer 2 only, and multiple VLANs can theoretically share a subnet in unusual designs, though best practice is one subnet per VLAN. Option E is incorrect because a single switch port can belong to multiple VLANs when configured as a trunk (or in some vendor-specific modes), not only one VLAN.

Answer

MAC addresses are shared across VLANs.

Answer

Each VLAN must be assigned a unique IP subnet.

Answer

A single switch port can belong to only one VLAN.

Question 9

An administrator configures a static route to 192.168.2.0/24 with next-hop 10.0.0.1. The route does not appear in the routing table. What is the most likely cause?

Accepted Answer

The next-hop 10.0.0.1 is not reachable.. A static route will only be installed in the routing table if the next-hop address is reachable via an active route in the routing table. If 10.0.0.1 is not reachable (e.g., no route to that subnet, or the interface is down), Junos will reject the static route and not place it in the inet.0 table. This is a fundamental validation check in Junos that prevents black-hole routing.

Answer

The static route has a higher preference than an existing dynamic route.

Answer

The configuration was not committed.

Answer

The prefix 192.168.2.0/24 already exists in the forwarding table.

Question 10

Which TWO statements about configuration groups in Junos are correct? (Choose two.)

Accepted Answer

Configuration groups are defined under the [edit groups] hierarchy.. Option A is correct because configuration groups in Junos are created and stored under the [edit groups] hierarchy, where each group is defined by a name and contains configuration statements that can be inherited elsewhere. Option C is correct because the apply-groups statement is the mechanism used to insert a group's configuration at a specific point in the configuration hierarchy, causing the group's statements to be inherited at that level. Option B is incorrect because configuration groups are not stored in separate files imported with the file statement; the file statement is used for loading configuration snippets from files, not for defining groups. Option D is incorrect because the replace tag is used to override inherited configuration values, not to reference a configuration group. Option E is incorrect because configuration groups can be applied at many hierarchy levels, not only at [edit interfaces].

Answer

Configuration groups are stored in separate files that are imported using the 'file' statement.

Answer

The 'replace' tag is used to reference a configuration group.

Answer

Configuration groups are applied only at the [edit interfaces] hierarchy level.

Question 11

Which three characteristics are true for OSPF? (Choose three.)

Accepted Answer

Supports VLSM (Variable Length Subnet Masks). OSPF is a link-state routing protocol that supports VLSM (Variable Length Subnet Masks), so option B is correct because it carries subnet mask information in its LSAs, allowing classless, hierarchical addressing. Option C is correct because OSPF's default metric is cost, which is derived from interface bandwidth (reference bandwidth divided by interface bandwidth). Option D is correct because OSPF uses the Dijkstra Shortest Path First (SPF) algorithm to compute the loop-free shortest-path tree from the link-state database. Option A is incorrect because the Bellman-Ford algorithm is used by distance-vector protocols such as RIP, not OSPF. Option E is incorrect because OSPF is classless and explicitly supports VLSM, contradicting the statement.

Answer

Uses the Bellman-Ford algorithm

Answer

Is classful and does not support VLSM

Question 12

Which TWO statements about static routes in Junos OS are correct? (Choose two.)

Accepted Answer

A static route can have a next-hop specified as an interface name for point-to-point interfaces.. Option B is correct because in Junos OS a static route may specify a next-hop as an interface name (for example, set routing-options static route 10.0.0.0/24 next-hop ge-0/0/0.0), which is valid and commonly used on point-to-point interfaces such as PPP, HDLC, or GRE tunnels where no remote address resolution is needed. Option C is correct because Junos supports the reject next-hop (set routing-options static route 10.0.0.0/24 reject), which installs a route that discards matching traffic and returns an ICMP unreachable message to the sender, unlike discard which silently drops packets. Option A is wrong because two static routes to the same destination with equal preference are both eligible and, depending on next-hop type, can be installed as multipath (ECMP) or one selected by tie-breaking, not an automatic active/backup pair; active/backup requires different preferences. Option D is wrong because the default preference for static routes in Junos is 5, not 10 (10 is the default for OSPF internal routes). Option E is wrong because a static route does not always require a next-hop address; it can instead use an interface name, a discard, reject, or receive next-hop, or be qualified with options such as no-readvertise.

Answer

Two static routes to the same destination with the same preference will result in an active/backup scenario.

Answer

The default preference for a static route is 10.

Answer

A static route must always include a next-hop address.

Question 13

Which THREE factors influence the selection of the active route in the Junos routing table when multiple routes exist for the same destination? (Choose three.)

Accepted Answer

Route preference (administrative distance).. Option A is correct because Junos uses route preference (the equivalent of administrative distance) as the primary tiebreaker: when routes to the same destination come from different sources, the route with the lowest preference value (e.g., Direct 0, Static 5, OSPF 10, RIP 100, BGP 170) is installed as active. Option B is correct because the route's originating protocol determines its default preference and thus directly influences which route wins when multiple protocols advertise the same prefix. Option D is correct because when multiple routes come from the same routing protocol (equal preference), Junos compares the metric and selects the route with the lowest metric as active. Option C is not a selection criterion — Junos does not choose a route based on how many next-hops it has; multiple next-hops can be retained for load balancing only after a route is already selected. Option E is not a factor because interface bandwidth is not used as a tiebreaker in the Junos route selection process; metric values are protocol-specific and not derived from raw interface bandwidth.

Answer

Number of next-hops available for each route.

Answer

Bandwidth of the outgoing interface.

Question 14

Which TWO statements are true about the default route in JunOS? (Choose two.)

Accepted Answer

It has a prefix of 0.0.0.0/0. Option A is correct because the default route in JunOS (and IP generally) is the all-zeros prefix 0.0.0.0/0, which matches any destination not covered by a more specific route. Option D is correct because a default route can be manually configured as a static route, e.g., 'set routing-options static route 0.0.0.0/0 next-hop <ip>', making it a common way to provide a gateway of last resort. Option B is wrong because the default route can be either statically configured or dynamically learned (e.g., via OSPF, BGP, or IS-IS), not only dynamically. Option C is wrong because the default preference for a static route in JunOS is 5, not 0 (0 is reserved for directly connected routes). Option E is wrong because the default route is not automatically present in the routing table; it must be explicitly configured or learned.

Answer

It can only be learned dynamically

Answer

Its default preference is 0

Answer

It is always present in the routing table

Question 15

Refer to the exhibit. An engineer notices high error counts on the interface. Based on the output, what is the most likely cause?

Accepted Answer

The interface is connected to a device configured for half-duplex.. The output shows high error counts on the interface, which is a classic symptom of a duplex mismatch. When one end of an Ethernet link operates in full-duplex and the other in half-duplex, collisions occur on the half-duplex side because it expects to wait for the carrier to be clear before transmitting, while the full-duplex side transmits at any time. This leads to frame check sequence (FCS) errors, alignment errors, and runts on the half-duplex interface. Option D is correct because the local interface is likely full-duplex (default on modern Juniper devices), and the connected device is configured for half-duplex, causing the mismatch.

Answer

The interface has a hardware fault.

Answer

The interface is experiencing excessive broadcasts.

Answer

The interface is operating in half-duplex mode.