JNCIS-ENT Protocol Independent Routing — 20 Questions

Question 1

An administrator has configured a forwarding-type routing instance to perform filter-based forwarding. Which configuration statement is mandatory under the routing-instances hierarchy to properly define this instance type?

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

Accepted Answer

set routing-instances dept-fwd instance-type forwarding. A forwarding instance requires the instance-type forwarding statement under the routing-instances definition.

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set routing-instances dept-fwd routing-options interface ge-0/0/0.0

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set routing-instances dept-fwd instance-type virtual-router

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set routing-instances dept-fwd instance-type l3vpn

Question 2

By default, what is the Junos routing protocol preference value assigned to static routes?

Accepted Answer

5. Junos OS assigns a default preference of 5 to static routes, making them more preferred than most dynamic interior routing protocols like OSPF.

Answer

170

Answer

10

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150

Question 3

What is the primary function of a Junos routing instance of type 'forwarding'?

Accepted Answer

To support filter-based forwarding without running routing protocols. Forwarding instances are lightweight instances that allow filter-based forwarding without running any independent routing protocols or maintaining separate dynamic routing tables.

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To terminate BGP sessions from multiple external peers

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To run multiple independent OSPF instances

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To provide transparent bridging across WAN circuits

Question 4

You need to create a virtual router routing instance to isolate traffic for a specific department. Which routing-instance type should you configure in the Junos configuration?

Accepted Answer

virtual-router. The 'virtual-router' instance type is used for complete routing isolation where the instance runs its own independent routing protocols and tables, similar to a VRF but without VPN-specific MPLS labels.

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forwarding

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no-structural-instance

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l2vpn

Question 5

An administrator configures an aggregate route for 172.16.0.0/16. However, no contributing routes are present in the routing table. What is the default behavior of this aggregate route in Junos OS?

Accepted Answer

It is suppressed and will not be installed in the routing table.. An aggregate route in Junos requires at least one contributing (more specific) route to be active in the routing table before it is installed in the routing table and advertised.

Answer

It is installed in the routing table with a reject discard next-hop.

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It installs into the routing table with a next-hop pointing to the local loopback.

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It floods a default route to all routing instances.

Question 6

You need to configure a static floating route that will only become active if the primary dynamic route learned via OSPF fails. Which configuration parameter must be adjusted to achieve this behavior?

Accepted Answer

preference. Floating static routes rely on a higher preference (administrative distance) than the primary protocol so that they remain inactive until the primary route is removed from the routing table.

Answer

as-path prepend

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local-preference

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metric

Question 7

You are configuring an aggregate route and want to ensure that a discard next-hop is automatically applied when there are no contributing routes, preventing routing loops. Which configuration statement should you use under routing-options?

Accepted Answer

set routing-options aggregate route 10.0.0.0/16 discard. To secure an aggregate route and silently drop traffic when no more-specific routes exist, the discard option is appended to the aggregate route configuration.

Answer

set routing-options static route 10.0.0.0/16 drop

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set routing-options aggregate route 10.0.0.0/16 passive

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set routing-options aggregate route 10.0.0.0/16 reject

Question 8

An engineer has configured a static route to the 192.168.100.0/24 network via 10.0.1.1. However, the route is not installing into the forwarding table because the recursive next-hop cannot be resolved. Which Junos command should the engineer use to verify the resolution status of the recursive next hop?

Accepted Answer

show route protocol static detail. The show route protocol static detail command displays detailed information about static routes, including the active next-hop and whether recursive resolution has succeeded.

Answer

show route resolution

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show route forwarding-table destination 10.0.1.1

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show system route summary

Question 9

Which command allows you to inspect the active forwarding table entries and verify next-hops on a Junos router?

Accepted Answer

show route forwarding-table. The show route forwarding-table command displays the contents of the Packet Forwarding Engine (PFE) routing tables.

Answer

show interfaces extensive

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show pfe traffic

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show routing-engine status

Question 10

When configuring load balancing on a Junos device, you want to include Layer 4 source and destination ports in the hash calculation to achieve finer-grained load distribution. Which configuration statement achieves this under the forwarding-options hierarchy?

Accepted Answer

set forwarding-options hash-key layer-3 layer-4. The hash-key options under forwarding-options allow administrators to include Layer 3 and Layer 4 header fields in the load-balancing hash algorithm.

Answer

set system services load-balancing ports

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set routing-options forwarding-table export load-balance-policy

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set protocols ospf ecmp-hash-ports

Question 11

You are troubleshooting a load-balancing configuration across multiple equal-cost paths (ECMP) on a Juniper MX Series router. Traffic is hashing persistently onto only one link. Which action should you take to enable per-packet or per-flow load balancing across the ECMP paths?

Accepted Answer

Configure a routing policy with 'then load-balance' action and apply it to forwarding-options.. By default, Junos performs destination-based forwarding. To enable load balancing across multiple paths, you must explicitly configure a load-balance policy action with per-packet or per-flow load-balancing options.

Answer

Increase the router's MTU across all core interfaces.

Answer

Enable BGP multipath under protocols bgp.

Answer

Configure a static discard route for the loopback interface.

Question 12

You are configuring Filter-Based Forwarding (FBF) on an interface. You apply a firewall filter that matches specific source addresses and uses 'then routing-instance' as an action. What must be configured in that target routing instance to ensure return traffic is handled correctly?

Accepted Answer

A default route pointing back to the core gateway within that routing instance's routing table.. Filter-based forwarding only intercepts packets leaving an interface. To ensure traffic can route properly within the target instance and return, routes (such as a default route) must be present in that instance's routing table.

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A static ARP entry for every device on the network.

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An RSVP LSP bridging the source and destination instances.

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A BGP peering session with the loopback address.

Question 13

An administrator implements filter-based forwarding and applies a firewall filter on the ingress interface. However, traffic matching the filter is dropped rather than routed to the alternate routing instance. Upon investigation, what is the most likely cause of this issue?

Accepted Answer

The destination IP address does not have a matching route in the alternate routing instance's table.. If the routing instance specified in the firewall filter action does not have an active route for the destination, the packet is discarded.

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The ingress interface is configured as a trunk port.

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The firewall filter term lacks a 'count' action statement.

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The routing instance type is set to virtual-router instead of forwarding.

Question 14

What is the key difference between a 'discard' static route and a 'reject' static route in Junos OS?

Accepted Answer

Discard drops packets silently, whereas reject returns an ICMP unreachable message.. Discard drops packets silently, while reject drops packets and returns an ICMP destination unreachable message to the sender.

Answer

Reject installs the route into the forwarding table, while discard does not.

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Discard is used for IPv4 and reject is exclusively used for IPv6.

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Discard requires an active next-hop interface, while reject does not.

Question 15

You need to configure a static route that acts as a discard route, ensuring that any traffic destined for a specific unassigned subnet is silently dropped. Which configuration syntax should you use?

Accepted Answer

set routing-options static route 192.168.50.0/24 discard. Discard static routes are configured by appending the 'discard' keyword to the static route definition.

Answer

set routing-options static route 192.168.50.0/24 drop

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set routing-options static route 192.168.50.0/24 reject

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set routing-options static route 192.168.50.0/24 null0

Question 16

You are configuring a qualified next-hop for a static route in Junos to provide redundancy. Which parameter allows you to specify a secondary next-hop with a different preference value?

Accepted Answer

qualified-next-hop. Qualified next-hops allow administrators to assign specific preferences or metrics to individual next-hops of a static route.

Answer

alternate-path

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secondary-route

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backup-next-hop

Question 17

An engineer configures a static route pointing to an interface rather than an IP address. What potential issue can occur with interface-based static routes on multi-access Ethernet networks in Junos OS?

Accepted Answer

The router will generate an ARP request for every destination IP, potentially exhausting ARP cache.. On multi-access networks (like Ethernet), pointing a static route directly to an interface causes the router to ARP for every destination IP address it receives, potentially exhausting ARP tables (Proxy ARP behavior or ARP storm).

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The packet forwarding engine will crash due to unresolvable MAC addresses.

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The static route will immediately enter a hidden state due to missing next-hop IP.

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BGP will automatically re-advertise the interface route into external ASNs.

Question 18

You configure an aggregate route and want to control which specific attributes or policies are applied when the aggregate is advertised by BGP. Which routing option is used to assign a specific contributing route tag or policy to an aggregate route?

Accepted Answer

set routing-options aggregate route 10.10.0.0/16 metric 100. Aggregate routes can have specific attributes like preference, metric, and tags assigned using the routing-options aggregate hierarchy.

Answer

set routing-instances aggregate-property

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set protocols bgp aggregate-attribute 10.10.0.0/16

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set routing-options aggregate route 10.10.0.0/16 policy

Question 19

Which command is used to display all configured static routes along with their active/inactive status in Junos?

Accepted Answer

show route protocol static. The show route protocol static command displays routes learned or defined via the static routing protocol.

Answer

show static routes summary

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show configuration routing-options static

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show route table inet.0 static

Question 20

When configuring a routing instance of type 'virtual-router', what is required to allow communication between the virtual router instance and the default routing instance?

Accepted Answer

Configure leaking routes between instances using rib-groups or routing policies.. Routing instances are isolated. To share routes between a virtual-router and the default instance, you must explicitly configure route leakage using export and import policies under routing-instances.

Answer

Connect a physical cable between two ports on the router (cable-patch).

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Configure static routes with identical preferences in both instances.

Answer

Disable firewall filters on all loopback interfaces.