JNCIS-ENT Practice Test 13 — 15 Questions

Question 1

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. In Junos, route preference (also called administrative distance) determines which route wins when multiple protocols offer a path to the same destination. OSPF's default preference is 10, while a static route's default preference is 5 — meaning the static route would normally win. To make the static route a floating (backup) route, you must raise its preference above OSPF's (e.g., 'set routing-options static route 10.0.0.0/24 next-hop x.x.x.x preference 200') so it is only installed when the OSPF route disappears.

Answer

as-path prepend

Answer

local-preference

Answer

metric

Question 2

Which command is used to verify the IS-IS adjacency state on a Junos device?

Accepted Answer

show isis adjacency. The command 'show isis adjacency' on Junos devices displays the IS-IS adjacency table, including the system ID of each neighbor, the interface, the adjacency state (e.g., Up, Down, Init), and other details like hold time and priority. This is the direct and standard way to verify IS-IS adjacency state. Other commands provide different IS-IS information, such as interface configuration or link-state database contents.

Answer

show isis interface

Answer

show isis database

Answer

show protocols isis neighbors

Question 3

An administrator configures Dynamic ARP Inspection (DAI) on an access switch. To ensure legitimate ARP packets from the default gateway (which uses a statically configured IP address on a core router) are not dropped, what must be configured?

Accepted Answer

Configure the interface connected to the default gateway as a trusted interface for DAI.. Dynamic ARP Inspection (DAI) validates ARP packets by comparing them against the DHCP snooping binding database, and by default all interfaces are untrusted. Since the default gateway uses a statically configured IP address, no DHCP snooping binding exists for it, so its ARP packets would be dropped on an untrusted interface. Configuring the interface connected to the gateway as trusted bypasses DAI inspection for that port, allowing legitimate ARP traffic from the gateway to pass. This is the standard Juniper configuration using 'set ethernet-switching-options secure-access-port interface ge-0/0/1.0 arp-inspection trust'.

Answer

Enable DHCP snooping on the core router's interface.

Answer

Configure a static DHCP binding for the gateway IP on the access switch.

Answer

Apply a Layer 2 firewall filter permitting ARP broadcasts from the gateway MAC.

Question 4

When configuring a Link Aggregation Group (LAG) on a Juniper switch, what is the naming convention used for the aggregated interface in the Junos CLI?

Accepted Answer

ae0, ae1, ae2, etc.. Junos uses the 'aeX' naming convention (Aggregated Ethernet) for LAG interfaces.

Answer

lag0, lag1, lag2, etc.

Answer

eth-trunk0, eth-trunk1, etc.

Answer

bond0, bond1, bond2, etc.

Question 5

Which of the following are valid IS-IS interface types? (Choose TWO)

Accepted Answer

point-to-point. In IS-IS, the two valid interface (circuit) types are point-to-point and broadcast, so options C and D are correct. A point-to-point interface (C) is used on links such as serial or point-to-point Ethernet subinterfaces, where IS-IS forms an adjacency without a DIS election and uses the Point-to-Point Three-Way Handshake (RFC 5303). A broadcast interface (D) is used on multi-access media like Ethernet, where IS-IS elects a Designated Intermediate System (DIS) and uses Level 1/Level 2 LAN IIHs. The other options are not IS-IS interface types: mesh (A) and star (B) describe topology shapes, not IS-IS circuit types, and passive (E) is an interface state/configuration (passive-interface) that suppresses adjacency formation, not a valid IS-IS interface type.

Answer

mesh

Answer

star

Answer

passive

Question 6

Which TWO actions occur during OSPF link-state database flooding on a Junos routing device? (Choose two)

Accepted Answer

The router updates its link-state database (LSDB) with the received LSA and acknowledges it.. Option D is correct because when a Junos router receives an LSA during OSPF flooding, it installs the LSA into its link-state database (LSDB), runs the SPF algorithm if the topology changed, and sends a Link State Acknowledgment back to the sender to confirm reliable receipt. Option E is correct because OSPF flooding requires the router to forward (flood) the received LSA out all other OSPF-enabled interfaces in the same area, excluding the interface on which the LSA was received, so that every router in the area maintains an identical LSDB. Option A is wrong because OSPF LSAs are never converted into BGP path attributes; OSPF and BGP are separate protocols with independent databases and attributes. Option B is wrong because flooding an LSA does not cause static routes to be deleted from the routing table. Option C is wrong because OSPF flooding does not reset all neighbor adjacencies on the device; adjacencies remain up and only the LSDB is updated and the LSA is re-flooded.

Answer

The router converts the link-state database into BGP path attributes.

Answer

The router immediately deletes all static routes from the routing table.

Answer

The router resets all active neighbor adjacencies across the entire device.

Question 7

Which actions occur during an IS-IS SPF calculation? (Choose THREE)

Accepted Answer

Calculating the shortest path to each destination.. Option B is correct because the core purpose of the IS-IS SPF (Dijkstra) computation is to determine the shortest path from the calculating router to every reachable destination in the topology. Option D is correct because SPF operates on the Link State Database, using it to build a Shortest Path Tree rooted at the local router before deriving routes. Option C is correct because once the SPT is built and best paths are selected, the results are installed into the IP routing table (RIB), making the routes usable for forwarding. Option A is not part of SPF: IIH (IS-IS Hello) packets are generated by the Hello protocol to form and maintain adjacencies, which happens independently of the SPF calculation. Option E is also not part of SPF: DIS election on broadcast networks is driven by Hello packet exchanges and priority values, not by the SPF algorithm.

Answer

Generating new IIH packets.

Answer

Re-electing the DIS.

Question 8

You are configuring multi-topology IS-IS. What does this allow?

Accepted Answer

Running separate topologies for different address families.. Multi-topology IS-IS allows for separate routing topologies for different protocol families (e.g., IPv4 and IPv6).

Answer

Load balancing over different physical paths.

Answer

Creating multiple areas within a single instance.

Answer

Increasing the maximum MTU.

Question 9

An engineer is troubleshooting IS-IS adjacency formation failures on a Junos device. Which THREE parameters must match or be compatible between neighboring routers to successfully establish an IS-IS adjacency? (Choose three)

Accepted Answer

Link-level MTU size, as oversized IIH packets may be dropped if they exceed the interface MTU.. Option A is correct because IS-IS IIH (Intermediate System-to-Intermediate System Hello) PDUs are sent at Layer 2 and must fit within the link MTU; if the MTU is mismatched or too small, oversized IIH packets are dropped and the adjacency never forms. Option B is correct because Level 1 routers must share at least one common area address in their area address list to form a Level 1 adjacency, while Level 2 adjacencies are formed between routers in the same routing domain regardless of area. Option D is correct because when authentication is enabled, the authentication type (cleartext, MD5, or HMAC-MD5) and the password/key must match on both neighbors, otherwise the IIH PDUs fail authentication and the adjacency is rejected. Option C is not required because IS-IS system IDs must be unique, not identical — duplicate system IDs actually cause adjacency and routing problems. Option E is not required because DIS priority only influences which router becomes the Designated Intermediate System on a multi-access network; mismatched priorities do not prevent adjacency formation.

Answer

Identical system IDs configured on both neighboring nodes

Answer

Identical DIS priority values on multi-access networks

Question 10

Which TWO parameters can be modified within a static route configuration to control path selection and backup behavior? (Choose two)

Accepted Answer

Qualified next-hop with custom preference. Option B is correct because in a static route you can specify a qualified next-hop and assign it a custom preference, allowing the router to prefer one next-hop over another for the same destination and thereby influence path selection and provide backup behavior. Option E is correct because the preference (administrative distance) value on a static route determines how it competes with routes from other protocols and with other static routes, so modifying it directly controls which route is installed and which serves as backup. Options A, C, and D are incorrect because MED, AS-path length, and local preference are BGP path attributes used in BGP route selection, not parameters that can be configured within a static route.

Answer

MED (Multi-Exit Discriminator)

Answer

AS-path length

Answer

Local preference attribute

Question 11

Which statement accurately describes port security MAC-limit behavior?

Accepted Answer

It restricts the maximum number of MAC addresses that can be learned on a secure interface.. Port security MAC-limit restricts the maximum number of MAC addresses learned on a secure interface.

Answer

It statically assigns all learned MAC addresses to the switch configuration file automatically.

Answer

It defines the maximum bandwidth a single MAC address can consume on a port.

Answer

It prevents MAC address spoofing by validating IP bindings against DHCP tables.

Question 12

An administrator is configuring a new point-to-point link between two Junos routers running IS-IS. By default, how does IS-IS handle adjacency establishment on a point-to-point link compared to a broadcast link?

Accepted Answer

It uses a 3-way handshake TLV in IIH packets and bypasses the DIS election process entirely.. On point-to-point (P2P) IS-IS links, adjacency is established using a 3-way handshake via the Point-to-Point Three-Way Adjacency TLV (TLV 240) carried in IIH packets, which confirms bidirectional communication before the adjacency reaches Up state. Because there is no multi-access segment, there is no DIS election — that process only exists on broadcast (LAN) interfaces where a pseudonode is needed.

Answer

It relies strictly on CSNPs sent every 10 seconds to establish the adjacency.

Answer

It requires manual mapping of neighbor system IDs using static ARP bindings.

Answer

It initiates a DIS election using priority values identical to broadcast segments.

Question 13

What is the purpose of the 'lsp-generation-interval'?

Accepted Answer

To limit the frequency of LSP updates.. The 'lsp-generation-interval' controls how often a router can generate new LSPs (Link State PDUs) in IS-IS. It sets a minimum interval between consecutive LSP generations, thereby limiting the frequency of LSP updates and reducing flooding and SPF churn.

Answer

To set the hello interval.

Answer

To define the authentication key rotation.

Answer

To set the time for database aging.

Question 14

You are analyzing a core Juniper MX router after an ISSU upgrade procedure completed. You notice that BGP sessions dropped immediately after the final routing engine rebooted. What post-upgrade verification step should have been performed to prevent unexpected protocol drops during ISSU?

Accepted Answer

Verify that all external BGP peers negotiated Graceful Restart capability and that helper mode was active on both ends prior to initiating the upgrade.. Verifying that BGP graceful restart and helper modes were fully operational and peer routers had acknowledged the capability before starting ISSU.

Answer

Confirm that LACP minimum-links is set to zero.

Answer

Check that the Virtual Chassis cable is connected between the MX Routing Engines.

Answer

Ensure VRRP preemption is turned off on all core interfaces.

Question 15

An administrator wants to configure an OSPF Not-So-Stubby Area (NSSA) on a Junos router. Which THREE characteristics distinguish an NSSA from a standard OSPF Stub Area? (Choose three)

Accepted Answer

An NSSA blocks incoming Type 5 AS-external LSAs from the backbone area.. Option A is correct because, like a standard stub area, an NSSA blocks Type 5 AS-external LSAs from entering the area from the backbone, keeping the area's LSDB free of external routes. Option C is correct because the defining feature of an NSSA is that routers within it can originate external routes as Type 7 NSSA-external LSAs, which is not permitted in a standard stub area. Option D is correct because the NSSA ABR translates those Type 7 LSAs into Type 5 LSAs before flooding them into the backbone, allowing external reachability to propagate beyond the NSSA. Option B is wrong because NSSA is an area-type attribute and has nothing to do with automatically converting internal links to broadcast point-to-multipoint networks. Option E is wrong because an NSSA can support multiple ABRs; there is no such prohibition.

Answer

An NSSA automatically converts all internal links into broadcast point-to-multipoint networks.

Answer

An NSSA is prohibited from supporting multiple ABRs.