JNCIA-JUNOS Routing Fundamentals — Timed 20 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.

Answer

show log messages

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show configuration

Answer

show interface

Question 2

An organization has two ISPs and wants to load-balance traffic equally across both links for all outbound traffic. Which routing configuration approach should be used?

Accepted Answer

Configure two static default routes with equal metric values and enable ECMP.. Option C is correct because configuring two static default routes with equal metric values and enabling Equal-Cost Multi-Path (ECMP) allows the Juniper device to load-balance outbound traffic equally across both ISP links. ECMP uses per-flow or per-packet load balancing based on the hash of source/destination IP addresses and ports, ensuring traffic is distributed evenly without relying on dynamic routing protocols.

Answer

Configure two static default routes with different metric values.

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Configure policy-based routing to match all traffic and forward to both ISPs.

Answer

Establish BGP sessions with both ISPs and rely on BGP path selection.

Question 3

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.

Answer

Both routes, if they are equal-cost.

Answer

The route with the higher preference value.

Answer

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

Question 4

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

Accepted Answer

An active route is installed in the forwarding table.. Option C is correct because 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.

Answer

All routes in the routing table are active.

Answer

Multiple active routes can exist for the same prefix.

Answer

An active route is always preferred over a passive route.

Question 5

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.

Answer

The preference of a static route cannot be changed.

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Static routes automatically update if the next hop becomes unreachable.

Question 6

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'.

Answer

BGP routes

Answer

OSPF routes

Question 7

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

Accepted Answer

2. Option D is correct because 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

Answer

0

Answer

3

Question 8

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 the route preference (administrative distance). 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 in JUNOS indicates the active route in the routing table. Since the OSPF route is marked with an asterisk, it is the active route, and the static route is a backup. Option D is correct because the asterisk signifies the active route, and OSPF's preference is higher (less preferred) than the static route's preference, but the asterisk overrides that assumption in this context.

Answer

Both routes are active.

Answer

The static route because it has a lower preference.

Answer

Neither route is active.

Question 9

You are the network engineer for a mid-sized enterprise with a Juniper MX router running Junos. The router has two uplinks to the internet: one to ISP-A via ge-0/0/0 (10.0.0.1/30) and one to ISP-B via ge-0/0/1 (10.0.0.5/30). You have configured static default routes to both ISPs: one to 10.0.0.2 and one to 10.0.0.6. Both routes have the same preference (default 5) and metric. You enabled ECMP to load-balance outbound traffic. After testing, you notice that all traffic is being sent only to ISP-A, and none to ISP-B. You verify that both interfaces are up and that the next-hop addresses are reachable. You check the routing table and see both routes are active but with different next-hop counts. What is the most likely cause of the traffic not being load-balanced?

Accepted Answer

One of the static routes resolves to multiple next hops, causing imbalance.. When both static default routes have the same preference and metric, Junos installs both in the routing table. However, ECMP load-balancing requires that each route resolve to a single next hop. If one static route resolves to multiple next hops (e.g., through a recursive lookup to a prefix with multiple paths), the route with a single next hop (ISP-A) becomes the sole active path for forwarding, while the multi-next-hop route (ISP-B) is not used for load balancing. This explains why all traffic goes to ISP-A despite both routes being present.

Answer

ECMP is not enabled in the forwarding-options.

Answer

The route to ISP-B is not active.

Answer

Hash-based load balancing requires per-packet configuration.

Question 10

Your Juniper router is running OSPF with multiple neighbors. You have a prefix 10.10.10.0/24 that is being learned via OSPF from two different routers: Router A with metric 30 and Router B with metric 20. The OSPF route from Router B is active. You want to ensure that traffic to 10.10.10.0/24 uses the path through Router A instead, even though it has a higher metric. You cannot change the OSPF metric on Router A. Which action should you take?

Accepted Answer

Use a routing policy to increase the preference of the OSPF route from Router B.. In JUNOS, route preference (administrative distance) determines which route is installed in the routing table when multiple protocols or sources provide the same prefix. By default, OSPF internal routes have a preference of 10. You can use a routing policy to increase the preference of the OSPF route from Router B (making it less preferred), which will cause the route from Router A (with its default preference of 10) to become active, even though its metric is higher. This approach does not require changing the OSPF metric or removing the route from Router A.

Answer

Increase the metric on Router B for that prefix.

Answer

Use a routing policy to reject the OSPF route from Router A.

Answer

Configure a static route to 10.10.10.0/24 pointing to Router A.

Question 11

A router has two routes to the same destination: one with preference 10 and metric 5, and another with preference 15 and metric 3. Which route will be installed in the forwarding table?

Accepted Answer

The route with preference 10.. In Junos, the route preference (administrative distance) is the primary criterion for selecting the best route to a destination. The route with preference 10 is preferred over the route with preference 15, regardless of metric values. The route with preference 10 is installed in the forwarding table.

Answer

The route with metric 3.

Answer

Neither route is installed.

Answer

Both routes are installed if ECMP is enabled.

Question 12

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. Option A is correct because 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.

Answer

show route protocol

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show route active

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show route table

Question 13

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.

Answer

Community list

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Prefix list

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Firewall filter

Question 14

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.

Answer

Protocol type

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Next hop address

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AS path length

Question 15

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.

Answer

10

Answer

5

Answer

15

Question 16

A network engineer is troubleshooting a reachability issue between two directly connected routers. Both routers have IP addresses configured on their interfaces and the interfaces are up. Which command would the engineer use to verify the routing table entry for the remote network?

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.

Answer

show interfaces terse

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show configuration interfaces

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show arp

Question 17

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.

Answer

Static routes require OSPF to be enabled on the router.

Answer

Static routes automatically generate ICMP redirect messages.

Question 18

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.

Answer

The default route (0.0.0.0/0)

Answer

The router will drop the packet.

Answer

The static route to 10.0.0.0/8

Question 19

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

Proxy ARP is not enabled on the router's internal interface.. Option D is correct because the host's default gateway (192.168.1.1) is correctly configured, and the router has a working default route to the ISP gateway (203.0.113.1). However, when the host sends a ping to an external IP (e.g., the ISP gateway), the router receives the packet on ge-0/0/1 and routes it out ge-0/0/0. The reply from 203.0.113.1 arrives back at the router's ge-0/0/0, but the router does not have a route for the host's source IP (192.168.1.100) in its routing table (since it's directly connected to ge-0/0/1, but the router needs to send an ARP request for that IP on ge-0/0/1). If Proxy ARP is not enabled on ge-0/0/1, the router will not respond to ARP requests for the host's IP, so the reply packet cannot be delivered to the host. Proxy ARP allows the router to answer ARP requests on behalf of hosts that are not on the same subnet, which is necessary here because the ISP gateway's reply is destined to 192.168.1.100, and the router must act as a proxy to forward that reply to the correct host.

Answer

DNS resolution is failing on the host.

Answer

The host's default gateway is incorrectly configured.

Answer

The default route is not active on the router.

Question 20

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.

Answer

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.