JNCIS-ENT Practice Test 18 — 15 Questions

Question 1

Which TWO statements are true regarding Junos tunnel interface naming conventions? (Choose two)

Accepted Answer

GRE tunnel interfaces begin with the prefix 'gr-'.. Option A is correct because Junos names GRE (Generic Routing Encapsulation) tunnel interfaces with the 'gr-' prefix, for example gr-0/0/0, which is the standard convention for GRE tunnels. Option D is correct because IP-IP (IP-in-IP) tunnel interfaces use the 'ip-' prefix, such as ip-0/0/0, distinguishing them from GRE tunnels. Option B is incorrect because IPsec secure tunnel interfaces are not named with 'gr-'; they are configured as st0 (secure tunnel) interfaces. Option C is incorrect because logical tunnel (lt-) interfaces use the 'lt-' prefix, not 'ip-'. Option E is incorrect because 'xe-' is the prefix for 10-Gigabit Ethernet physical interfaces, not tunnel interfaces.

Answer

Secure tunnel interfaces (IPsec) begin with the prefix 'gr-'.

Answer

Logical tunnel interfaces begin with the prefix 'ip-'.

Answer

All tunnel interfaces must start with the prefix 'xe-'.

Question 2

An administrator wants to modify the Local Preference attribute for all routes received from a specific external BGP peer. Where must this policy be applied in Junos?

Accepted Answer

Import policy applied to the eBGP neighbor or group. Inbound routing policies on Junos affect attributes like Local Preference before path selection occurs.

Answer

Export policy applied to the eBGP group

Answer

Forwarding plane firewall filter

Answer

Global system-level static route policy

Question 3

An enterprise network design requires implementing private VLANs (PVLANs) on an EX Series switch. Which THREE components or port types are characteristic of a private VLAN architecture? (Choose three.)

Accepted Answer

Community ports that can communicate with other ports in the same community and promiscuous ports.. In a private VLAN architecture on EX Series switches, community ports (option A) are secondary-VLAN member ports that may communicate with other ports in the same community VLAN and with promiscuous ports, but not with isolated ports or other communities. Isolated ports (option B) belong to an isolated secondary VLAN and can communicate only with promiscuous ports, providing the strictest Layer 2 isolation among host ports. Promiscuous ports (option C) are members of the primary VLAN and can communicate with all ports across both the primary VLAN and its associated secondary VLANs, typically serving as the gateway or uplink port. Option D is incorrect because RIB-only routing instance interfaces are a Layer 3 routing construct unrelated to PVLAN port roles and do not define PVLAN behavior. Option E is incorrect because PVLANs do not use fully meshed trunk ports to bypass isolation; trunk ports simply carry the primary and secondary VLAN tags while preserving the PVLAN isolation rules.

Answer

Routing instance interfaces (RIB-only) that automatically disable Layer 2 bridging.

Answer

Fully meshed trunk ports that bypass all isolation rules for inter-VLAN routing.

Question 4

Which TWO characteristics describe eBGP compared to iBGP? (Choose two)

Accepted Answer

Peers reside in different Autonomous Systems. Option C is correct because eBGP (External BGP) is specifically designed to exchange routing information between routers in different Autonomous Systems, whereas iBGP peers must be within the same AS. Option D is correct because eBGP sessions between directly connected external peers use a default IP TTL of 1 (multihop eBGP requires explicitly raising the TTL with the ebgp-multihop command), while iBGP sessions default to TTL 255. Option A is incorrect because route reflection is an iBGP mechanism (used to avoid the full-mesh requirement) and is not enabled by default on eBGP. Option B is incorrect because residing within the same Autonomous System describes iBGP, not eBGP. Option E is incorrect because the default Local Preference in BGP is 100, not 200, and this value is not a distinguishing eBGP-versus-iBGP characteristic.

Answer

Automatic route reflection enabled by default

Answer

Must reside within the same Autonomous System

Answer

Default Local Preference of 200

Question 5

What happens if you have an area address mismatch in a Level 1 adjacency?

Accepted Answer

The adjacency will fail to form.. Level 1 adjacencies require the routers to share at least one area address.

Answer

The DIS will override the mismatch.

Answer

The adjacency will form but no routes will be exchanged.

Answer

The router will automatically adopt the neighbor's area address.

Question 6

Which THREE actions occur when a Junos router with GRES and NSR enabled performs a manual Routing Engine switchover while running OSPF and BGP? (Choose three)

Accepted Answer

OSPF and BGP daemon states synchronized via NSR allow routing sessions to remain established without neighbor drop.. Option A is correct because NSR (Nonstop Routing) synchronizes OSPF and BGP daemon state (adjacencies, databases, and session information) from the master to the backup Routing Engine, so protocol sessions stay up across the switchover without neighbors dropping. Option B is correct because, with sessions preserved by NSR, external OSPF and BGP peers observe no adjacency state change and therefore do not flap or trigger route recalculation. Option C is correct because GRES (Graceful Routing Engine Switchover) lets the backup Routing Engine take over control-plane mastership while the Packet Forwarding Engine keeps forwarding using its existing state, avoiding a forwarding reset. Option D is wrong because GRES/NSR specifically avoid resetting the PFE and interfaces, so there is no 30-second blackout. Option E is wrong because VRRP virtual IPs are not reverted to physical interface addresses during a Routing Engine switchover; VRRP mastership is unaffected by GRES/NSR.

Answer

All physical interfaces are reset and re-initialized, causing a 30-second traffic blackout.

Answer

All VRRP virtual gateway IPs revert to their physical interface fallback addresses.

Question 7

Which TWO factors must be carefully managed when running OSPF over a GRE tunnel interface on Junos devices? (Choose two.)

Accepted Answer

Interface MTU settings to account for the additional GRE header size and prevent packet drops or fragmentation issues.. Option B is correct because a GRE tunnel adds an outer IP header (typically 24 bytes for GRE + IPv4, or more with additional options), which reduces the effective payload MTU on the gr- interface; if the tunnel interface MTU is not lowered accordingly (e.g., to 1476 or less) or TCP MSS clamping is not applied, OSPF hello packets and other traffic can be dropped or fragmented, breaking adjacency. Option D is correct because OSPF over a GRE tunnel is normally configured with the point-to-point network type, since a point-to-point link does not require DR/BDR election and avoids the multicast/unicast adjacency issues that can arise on a broadcast-type tunnel; this ensures reliable adjacency formation between the two tunnel endpoints. Option A is not required because BGP multipath on the physical transit interface is unrelated to running OSPF over GRE and is not a prerequisite for OSPF adjacency. Option C is incorrect because LDP is an MPLS label distribution protocol and is not configured on a gr- interface to run OSPF. Option E is incorrect because proprietary Junos Layer 2 bridging protocols are not used to run OSPF over GRE.

Answer

Mandatory activation of BGP multipath routing on the physical transit interface.

Answer

Configuring MPLS Label Distribution Protocol (LDP) directly on the gr- interface.

Answer

Enabling proprietary Junos Layer 2 bridging protocols over the gr- interface.

Question 8

What is the primary function of the RSTP port role known as the 'Backup' port?

Accepted Answer

It acts as a backup for a designated port on the same segment.. An RSTP Backup port is a discarding port that provides a backup path to a designated port on the same shared segment. It exists only on shared (multi-access) segments where a switch has multiple ports connected to the same LAN, and it can quickly transition to forwarding if the designated port on that segment fails.

Answer

It forwards traffic when the primary trunk fails without triggering a topology change.

Answer

It acts as a backup for the root port towards the root bridge.

Answer

It is an operational state used exclusively during edge port transitions.

Question 9

An operator configures RSTP across multiple EX Series switches. A rogue switch running legacy STP is connected to an RSTP switch. How does the RSTP switch handle interaction with the legacy STP switch?

Accepted Answer

The RSTP switch falls back to legacy STP behavior on that specific interface.. RSTP (IEEE 802.1w) is backward compatible with legacy STP (802.1D). When an RSTP switch receives legacy STP BPDUs on a port, it detects the neighbor as an STP bridge and falls back to legacy STP behavior on that specific interface only. The rest of the RSTP domain continues to operate in RSTP mode, ensuring interoperability without disrupting the entire network.

Answer

The port receiving legacy BPDUs is immediately placed into a permanent error-disabled state.

Answer

The legacy STP BPDUs are dropped and logged as protocol violations.

Answer

The entire switch converts its spanning tree mode to legacy STP.

Question 10

You need to ensure that traffic entering interface ge-0/0/1 is forced into a specific forwarding routing instance named 'corp-fwd', regardless of the destination IP address in the packet header. Which configuration steps must you perform?

Accepted Answer

Create a forwarding instance, write a firewall filter with 'then routing-instance corp-fwd', and apply the filter as input on ge-0/0/1.. To force traffic from an interface into a specific forwarding routing instance regardless of destination, you create a forwarding instance (type 'forwarding'), define a firewall filter with the action 'then routing-instance corp-fwd', and apply that filter as an input filter on ge-0/0/1. This is the standard Junos method for policy-based routing into a forwarding instance, often used for service chaining or VRF selection.

Answer

Create a virtual-router instance and apply a static default route pointing to ge-0/0/1.

Answer

Configure a routing policy with 'then export corp-fwd' and apply it under protocols.

Answer

Enable proxy-ARP on ge-0/0/1 and assign the corp-fwd routing instance to the physical port.

Question 11

During an audit of an IS-IS routing network, an engineer examines the Type-Length-Value (TLV) structures used in IS-IS PDUs. Which TLV is specifically responsible for carrying IPv4 internal and external reachability information when using wide metrics?

Accepted Answer

TLV 135. TLV 135 is specifically used in IS-IS to carry IPv4 internal and external reachability information when wide metrics are enabled. It supports extended IP reachability with wider metric values.

Answer

TLV 128

Answer

TLV 1

Answer

TLV 2

Question 12

Which TWO features characterize OSPFv3 compared to OSPFv2? (Choose two)

Accepted Answer

OSPFv3 router IDs remain 32-bit unsigned integers, formatted identically to IPv4 addresses.. Option B is correct because OSPFv3, like OSPFv2, still uses a 32-bit unsigned router ID that is written in dotted-decimal IPv4 format, even though OSPFv3 runs over IPv6; the router ID is not an IPv6 address. Option D is correct because OSPFv3 forms adjacencies and sends hello packets using IPv6 link-local addresses (fe80::/10) on each interface, which is a key operational difference from OSPFv2's use of interface IPv4 addresses. Option A is incorrect because OSPFv3 does not exclusively use MD5 in the OSPF header; it relies on IPv6 IPsec (AH/ESP) for authentication, and later RFCs also define OSPFv3 authentication trailer options. Option C is incorrect because OSPFv3 still requires a backbone area, Area 0, for multi-area topologies just like OSPFv2. Option E is incorrect because OSPFv3 dynamically learns inter-area routes through LSAs and the SPF calculation; it does not require manual static routes for inter-area paths.

Answer

OSPFv3 exclusively uses MD5 authentication embedded in the OSPF packet header.

Answer

OSPFv3 eliminates the need for Area 0 in multi-area topologies.

Answer

OSPFv3 requires manual static routing for all inter-area paths.

Question 13

Which of the following are true regarding IS-IS authentication? (Choose TWO)

Accepted Answer

It secures the PDUs exchanged between neighbors.. IS-IS authentication is used to secure the PDUs exchanged between neighbors, such as Hello PDUs, LSPs, and SNPs, which is why option C is correct. It can also be configured at different levels, including per interface, which makes option D correct. IS-IS authentication is not mandatory for all deployments, so option A is incorrect. It is not limited to the entire area, since it can be applied at the interface, area, or domain level, so option B is incorrect. It does not encrypt the entire link traffic; it only authenticates routing protocol PDUs, so option E is incorrect.

Answer

It is mandatory for all IS-IS deployments.

Answer

It can only be configured for the entire area.

Answer

It encrypts the entire link traffic.

Question 14

An enterprise network runs MSTP. Instance 0 is always reserved for which specific purpose?

Accepted Answer

The Common and Internal Spanning Tree (CIST) instance. In MSTP, Instance 0 is always reserved for the Common and Internal Spanning Tree (CIST). The CIST is the spanning tree that connects all MST regions and also includes the IST (Internal Spanning Tree) within a region. Therefore, option C is correct.

Answer

The Internal Regional Boundary instance (IRBI)

Answer

The Designated Root Backup instance (DRB)

Answer

The Vlan-to-Instance Mapping table (VIM)

Question 15

Which THREE conditions can cause a Virtual Chassis primary Routing Engine election or switchover to occur unexpectedly? (Choose three)

Accepted Answer

Manual modification of member priority values followed by a mastership switchover command or reboot.. Option A is correct because Virtual Chassis primary RE election is influenced by the member priority value; changing priorities and then issuing a mastership switchover command or rebooting forces a new election that can unexpectedly move mastership. Option C is correct because Virtual Chassis relies on the stacking/VCP links for control and election communication; a cable failure or disconnection can split the fabric, trigger a new election, or cause topology restructuring that changes which member becomes primary. Option E is correct because a hardware crash or kernel panic on the current primary Routing Engine switch causes the backup RE to take over mastership, resulting in an unexpected switchover. Option B is not correct because VRRP preemption affects VRRP master election on a VLAN interface, not Virtual Chassis primary Routing Engine election. Option D is not correct because LACP timeout interval mismatches affect link aggregation behavior and can cause LACP bundling issues, but they do not directly trigger Virtual Chassis primary RE election or switchover.

Answer

Configuring VRRP preemption on a VLAN interface.

Answer

A mismatch in LACP timeout intervals on aggregated Ethernet interfaces.