JN0-106 Routing Fundamentals — 25 Questions

Question 1

A network engineer is troubleshooting a connectivity issue and wants to see the active routes in the routing table. Which Junos CLI command should they use?

Accepted Answer

show route. The 'show route' command displays the active routing table entries, including directly connected, static, and dynamic routes learned via protocols like OSPF, BGP, or IS-IS. This is the correct command to view the active routes the device uses for forwarding traffic.

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show log messages

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show configuration

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show interface

Question 2

During a routing table lookup, a packet matches both a static route and an OSPF route to the same destination. Which route will be installed in the forwarding table?

Accepted Answer

The static route, because it has a lower preference value.. In Junos, the route with the lowest preference value is installed in the forwarding table. Static routes have a default preference of 5, while OSPF internal routes have a default preference of 10. Therefore, the static route is preferred and installed.

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Both routes, if they are equal-cost.

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The route with the higher preference value.

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The OSPF route, because OSPF is a dynamic routing protocol.

Question 3

Which TWO statements about active routes in the Junos routing table are correct?

Accepted Answer

An active route is installed in the forwarding table.. An active route in Junos is one that is selected as the best route for a given prefix and is installed in the forwarding table (the FIB). The forwarding table is used by the Packet Forwarding Engine (PFE) to make actual forwarding decisions, so only active routes are placed there.

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All routes in the routing table are active.

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Multiple active routes can exist for the same prefix.

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An active route is always preferred over a passive route.

Question 4

Which THREE statements about static routes in Junos are correct?

Accepted Answer

Static routes have a default preference of 5.. Static routes in Junos have a default preference of 5, which is lower (more preferred) than routes learned from most dynamic routing protocols like OSPF (preference 10) or IS-IS (preference 18). This default value ensures that static routes are preferred over dynamically learned routes unless explicitly overridden.

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The preference of a static route cannot be changed.

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Static routes automatically update if the next hop becomes unreachable.

Question 5

Which THREE route types are considered protocol-independent in Junos?

Accepted Answer

Direct routes. Direct, local, and static routes are considered protocol-independent because they are not learned or installed by any dynamic routing protocol. Direct routes are automatically created for directly connected interfaces, local routes represent the interface's own IP address, and static routes are manually configured by an administrator. These routes exist in the routing table regardless of whether any routing protocol is running, hence the term 'protocol-independent'.

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BGP routes

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OSPF routes

Question 6

Refer to the exhibit. How many static default routes are configured?

Accepted Answer

2. The exhibit shows two static routes with a next-hop of 0.0.0.0, which are static default routes. In JUNOS, a static default route is defined by a destination prefix of 0.0.0.0/0 (or ::/0 for IPv6). The configuration lists two such routes, each with a different next-hop address, confirming two static default routes.

Answer

1

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0

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3

Question 7

Refer to the exhibit. Which route is active for the 192.168.1.0/24 prefix?

Accepted Answer

The OSPF route because it is marked with an asterisk.. In JUNOS, the active route for a prefix is determined by route preference (administrative distance) and route validation. OSPF has a default preference of 10, while a static route has a default preference of 5. However, the exhibit shows the OSPF route with an asterisk (*), which indicates it is the active route in the routing table. The static route, despite its lower preference, is not marked with an asterisk, meaning it is not active. This can occur if the static route's next-hop is unreachable or if the static route was configured with a higher preference value, causing JUNOS to select the OSPF route instead. Thus, Option D is correct because the asterisk directly identifies the active route, and the OSPF route is active while the static route is not.

Answer

Both routes are active.

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The static route because it has a lower preference.

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Neither route is active.

Question 8

Which Junos command displays the route to a specific IP address, including the active route and any backup routes?

Accepted Answer

show route 192.168.1.1. The 'show route 192.168.1.1' command in Junos displays all routes in the routing table that match the specified destination, including the active route (marked with '>') and any backup routes (marked with a space). This command provides a comprehensive view of the forwarding table entries for that prefix, which is essential for understanding both primary and failover paths.

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show route protocol

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show route active

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show route table

Question 9

A network administrator wants to filter routes from being installed in the routing table based on certain criteria. Which Junos feature should be used?

Accepted Answer

Routing policy (import). B is correct because a routing policy with an import term is the Junos mechanism to control which routes are accepted into the routing table from a routing protocol or a peer. By defining match conditions (e.g., prefix, community, AS path) and an action (accept or reject), the administrator can filter routes before they are installed. This is the standard Junos approach for route filtering at the routing table level.

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Community list

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Prefix list

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Firewall filter

Question 10

Which TWO attributes are used by Junos to select the active route among multiple routes to the same destination?

Accepted Answer

Metric. Junos uses the route preference (also known as administrative distance) as the primary attribute to select the active route among multiple routes to the same destination. If multiple routes have the same preference, Junos then compares the metric (also called cost or protocol-specific metric) to break the tie. Preference is a local, configurable value that ranks the trustworthiness of the routing protocol source, while metric is a protocol-specific value (e.g., OSPF cost, RIP hop count) used within the same protocol.

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Protocol type

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Next hop address

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AS path length

Question 11

What is the default preference of a direct route in Junos?

Accepted Answer

0. Direct routes in Junos have a default preference of 0, which is the highest possible preference (lowest numerical value). This ensures that directly connected routes are always preferred over any other route type, including static routes (preference 5) and OSPF internal routes (preference 10). The preference value is used by Junos to select the best route when multiple routes exist to the same destination.

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10

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5

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15

Question 12

A network engineer is troubleshooting a connectivity issue and wants to see the active routes in the routing table. Which Junos CLI command should they use?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

show route. The 'show route' command displays the routing table, which contains all active routes learned via static configuration, direct connections, or dynamic routing protocols. To verify the routing table entry for a specific remote network, this command shows the next-hop IP address, interface, and route preference/metric, directly confirming whether the remote network is reachable. Command 'show arp' (option D) only shows IP-to-MAC address mappings and does not display routing table information.

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show interfaces terse

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show configuration interfaces

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show arp

Question 13

Which THREE statements are true regarding static routes in Junos?

Accepted Answer

A static route can have a next-hop of a directly connected interface.. A static route can have a next-hop of a directly connected interface, meaning the router will consider the destination as directly reachable out that interface without needing an explicit IP next-hop. This is valid in Junos and is often used for point-to-point links or when the next-hop address is not required.

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Static routes require OSPF to be enabled on the router.

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Static routes automatically generate ICMP redirect messages.

Question 14

Refer to the exhibit. The router has three static routes configured. Which route will be used to forward a packet destined to 172.16.1.100?

Accepted Answer

The static route to 172.16.0.0/16. The router will use the most specific matching route for the destination 172.16.1.100. The static route to 172.16.0.0/16 has a prefix length of 16, which is more specific than the default route (0.0.0.0/0) and the route to 10.0.0.0/8 (which does not match the destination). Therefore, the route to 172.16.0.0/16 is selected based on the longest-prefix-match rule.

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The default route (0.0.0.0/0)

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The router will drop the packet.

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The static route to 10.0.0.0/8

Question 15

You are managing a small enterprise network with one Juniper router and two switches. The router connects to an ISP via ge-0/0/0 and to the internal network via ge-0/0/1. The internal network uses the 192.168.1.0/24 subnet. You need to configure a default route on the router to send all Internet-bound traffic to the ISP gateway at 203.0.113.1. You also want to ensure that internal hosts can reach the Internet. After configuring the default route, you test connectivity from a host on the internal network to an external website, but the ping fails. You verify that the host has an IP address of 192.168.1.100/24 and a default gateway of 192.168.1.1 (the router's internal interface). On the router, you run 'show route 0.0.0.0/0' and see the default route active. You also run 'ping 203.0.113.1' from the router and it succeeds. However, pinging from the host to the ISP gateway fails. What is the most likely cause?

Accepted Answer

The host's default gateway is incorrectly configured.. The host's default gateway is configured as 192.168.1.1, which is the router's internal interface. However, if the host's gateway is incorrectly set (e.g., to a different IP or a non-existent router), it cannot send packets to the router. The router's default route and ping to the ISP gateway succeed from the router itself, indicating the router's configuration is correct. The failure from the host points to an issue at the host's network configuration, most likely the default gateway setting. Other possibilities include NAT or return route issues, but these are not listed as options. Proxy ARP is not required for directly connected hosts and is not the most likely cause.

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DNS resolution is failing on the host.

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The default route is not active on the router.

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Proxy ARP is not enabled on the router's internal interface.

Question 16

Which TWO statements are true about static routes in Junos?

Accepted Answer

Static routes remain in the routing table even if the next hop is unreachable.. Static routes in Junos have a default preference of 5, not 10 (which is the default for OSPF internal routes). They remain in the routing table even if the next hop becomes unreachable because Junos uses a 'passive' route model; the route is only removed if explicitly deleted or if a better route is learned via a routing protocol. This behavior is controlled by the 'no-readvertise' and 'passive' attributes of static routes.

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Static routes have a default preference value of 10.

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Static routes require a routing protocol to be activated.

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Static routes are automatically updated if the network topology changes.

Question 17

Refer to the exhibit. The router has a default static route and a static route to 10.0.0.0/24. An engineer updates the next-hop for the default route from 192.168.1.1 to 192.168.1.2. Which command should the engineer use to verify that the change is active?

Accepted Answer

show route 0.0.0.0/0. The command 'show route 0.0.0.0/0' displays the routing table entry for the default route, including its next-hop address. After changing the next-hop from 192.168.1.1 to 192.168.1.2, this command confirms the active route has the updated next-hop. It directly verifies the specific prefix that was modified.

Answer

show route 192.168.1.2

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ping 192.168.1.2

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show route protocol static

Question 18

Match each Junos routing protocol to its primary characteristic.

Accepted Answer

OSPF: Uses link-state advertisements to build a topology database. OSPF and IS-IS are link-state protocols. BGP is path-vector. RIP is distance-vector. Static routes are manually configured. Common confusions include mixing link-state with distance-vector or mislabeling BGP.

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IS-IS: Uses a distance-vector algorithm with split horizon

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Static route: Learned dynamically through routing protocols

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BGP: Uses distance-vector algorithm with link-state updates

Question 19

Match each Junos configuration hierarchy to its function.

Accepted Answer

system: Configures system-wide parameters such as hostname and time.. In Junos, 'system' manages hostname and time, 'interfaces' configures ports, 'protocols' handles routing protocols, and 'security' manages firewall policies. Common confusions include swapping these definitions.

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system: Configures routing protocols like OSPF and BGP.

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interfaces: Configures security policies and zones.

Question 20

An engineer observes that traffic destined to 203.0.113.0/24 is being load-balanced across two equal-cost paths via OSPF. The engineer wants to ensure that all traffic for this prefix uses only one path unless the primary path fails. Which configuration change should be made?

Accepted Answer

Set the OSPF metric on the backup interface to a higher value.. Increasing the OSPF metric on the backup interface makes that path less preferred in the SPF calculation, breaking the equal-cost multipath (ECMP) condition. OSPF selects routes based on the lowest metric; by raising the metric on one interface, the engineer ensures only the lower-metric path is used for forwarding, with automatic failover to the backup path if the primary fails.

Answer

Configure a static route for 203.0.113.0/24 with a lower preference.

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Use policy-options to set a higher preference for one of the paths.

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Modify the load-balance configuration under forwarding-options.