JNCIS-ENT Practice Questions 1 — 50 Questions

Question 1

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 2

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

Accepted Answer

Peers reside in different Autonomous Systems. eBGP peers are typically in different Autonomous Systems and have a default TTL of 1, whereas iBGP peers are in the same AS and have a default TTL of 255.

Answer

Automatic route reflection enabled by default

Answer

Must reside within the same Autonomous System

Answer

Default Local Preference of 200

Question 3

Which TWO actions can be performed using Junos routing policies applied to BGP? (Choose two)

Accepted Answer

Accepting or rejecting routes based on AS_PATH regular expressions.. Routing policies can modify path attributes such as local preference and MED, as well as accept or reject routes.

Answer

Changing the TCP port used for BGP session establishment from 179 to another port.

Answer

Directly modifying the physical interface speed when BGP flaps.

Answer

Encrypting BGP payload data using policy-based IPsec keys.

Question 4

An administrator wants to gracefully restart a BGP routing daemon without dropping the underlying TCP session or causing traffic loss. Which Junos feature should be enabled?

Accepted Answer

BGP Graceful Restart. Graceful Restart allows a BGP speaker to express its ability to preserve forwarding state while restarting the control plane.

Answer

Nonstop Active Routing (NAR)

Answer

TCP MD5 Signature bypass

Answer

BGP Bidirectional Forwarding Detection (BFD)

Question 5

Which TWO statements correctly differentiate eBGP from iBGP? (Choose two.)

Accepted Answer

eBGP routers prepend their own AS number to the AS_PATH attribute when advertising routes.. eBGP sessions are typically established between routers in different autonomous systems and have a default TTL of 1, whereas iBGP sessions are between routers in the same AS and have a default TTL of 255.

Answer

iBGP routes have a default administrative distance (preference in Junos) of 20.

Answer

The default TTL for iBGP packets is 1, requiring explicit multihop configurations for non-directly connected peers.

Answer

iBGP routers modify the next-hop attribute to their own interface address by default when advertising routes to iBGP peers.

Question 6

An MX Series router is configured with BGP Multipath. Two paths have identical Local Preference, AS path length, origin, and MED. Which additional configuration statement is required under protocols bgp to enable multipath load balancing across these iBGP paths?

Accepted Answer

set protocols bgp multipath relaxation. By default, multipath is only for eBGP. To enable iBGP multipath, the 'as-path-multipath relaxation' or 'ibgp multipath' statement must be used.

Answer

set protocols bgp group internal type external

Answer

set routing-options forwarding-table export load-balance

Answer

set protocols bgp group internal multihop

Question 7

You are configuring a Link Aggregation Group (LAG) on an EX series switch. Which statement is correct regarding LACP active mode?

Accepted Answer

The interface will actively transmit LACP packets to initiate and negotiate the aggregation with the peer device.. In LACP active mode, the interface actively transmits LACP packets to the remote peer to negotiate the link aggregation.

Answer

The interface will only respond to LACP packets and never transmit them.

Answer

Active mode can only be used when connecting Juniper switches to non-Juniper servers.

Answer

LACP active mode requires static pinning of member links and disables dynamic hash selection.

Question 8

An engineer wants to configure Nonstop Active Routing (NSR) alongside GRES on an MX204 router running OSPF. What is the primary operational benefit of enabling NSR compared to running GRES alone?

Accepted Answer

NSR synchronizes protocol daemon states between Routing Engines, preventing neighbors from detecting a control plane switchover.. GRES preserves forwarding state during a switchover, but routing protocols must restart and re-converge unless NSR is running, which synchronizes routing protocol states between REs.

Answer

NSR automatically configures VRRP tracking on all local VLAN interfaces.

Answer

NSR allows software upgrades to be performed without ever rebooting either Routing Engine.

Answer

NSR replaces LACP negotiation with static member pinning during link failures.

Question 9

An operator troubleshooting BGP path selection notices two routes have identical Local Preference, AS path length, origin, MED, and both are eBGP routes. Which attribute does the BGP path selection algorithm evaluate next?

Accepted Answer

Lowest IGP cost to the BGP next hop. According to the BGP best path selection algorithm, after comparing local pref, AS path, origin, MED, and iBGP vs eBGP, the router prefers the path with the lowest IGP metric to the BGP next hop.

Answer

Lowest Router ID

Answer

Oldest route

Answer

Lowest peer IP address

Question 10

An engineer needs to verify which BGP routes are currently installed in the forwarding table (FIB). Which command should be used?

Accepted Answer

show route forwarding-table protocol bgp. The forwarding table is viewed using 'show route forwarding-table'.

Answer

show bgp forwarding

Answer

show route table inet.0

Answer

show route summary

Question 11

Which TWO BGP attributes are strictly internal to an Autonomous System and are never advertised to external eBGP peers? (Choose two)

Accepted Answer

ORIGINATOR_ID. Local Preference and MED (by default, unless propagated) or internal-only attributes like cluster list are restricted. Specifically, Local Preference is never sent to eBGP peers.

Answer

NEXT_HOP

Answer

ORIGIN

Answer

AS_PATH

Question 12

A Junos router receives four identical routes via BGP. Reviewing the routing table, path selection picked route 3. Route 1 has a lower MED, Route 2 has a higher Local Preference, Route 4 is from an eBGP peer while Route 3 is iBGP. Assuming standard default path selection, why was Route 3 chosen over Route 4?

Accepted Answer

Junos prefers iBGP paths over eBGP paths during the tie-breaking steps.. In Junos BGP path selection, after comparing local preference, AS path length, origin type, and MED, Junos prefers internal (iBGP) paths over external (eBGP) paths, provided all other tie-breakers are equal.

Answer

Route 3 had a lower router ID than Route 4.

Answer

Route 3 had a lower MED value.

Answer

Route 3 was received from a peer with a lower peer IP address.

Question 13

You need to configure authentication for a BGP peering session on a Junos device to prevent spoofing attacks. Where is the MD5 authentication key configured?

Accepted Answer

protocols bgp group name authentication-key. BGP MD5 authentication keys are configured under the specific neighbor or group definition using the authentication-key statement.

Answer

firewall family inet filter bgp-auth

Answer

system authentication-algorithm md5

Answer

routing-options md5-key

Question 14

Which level is enabled by default in Junos when configuring IS-IS on an interface?

Accepted Answer

Level 1 and Level 2. By default, interfaces in Junos IS-IS are enabled for both Level 1 and Level 2.

Answer

None

Answer

Level 2 only

Answer

Level 1 only

Question 15

How does an IS-IS router identify the DIS in its hello packets?

Accepted Answer

By the router's System ID followed by a non-zero pseudonode ID.. The DIS is identified by the System ID and a pseudonode number (the 7th byte of the LSP ID).

Answer

By a special flag in the header.

Answer

By the area address.

Answer

By the MAC address only.

Question 16

When evaluating the BGP path selection algorithm on a Junos device, which THREE attributes are evaluated BEFORE the router considers the IGP metric to the BGP next hop? (Choose three)

Accepted Answer

Multi-Exit Discriminator (MED). The path selection order in Junos is: 1. Local Preference, 2. AS Path length, 3. Origin type, 4. MED, 5. iBGP over eBGP, 6. IGP metric to next hop. Therefore, local preference, AS path length, and MED are evaluated before the IGP metric.

Answer

IGP metric to next hop

Answer

Router ID

Question 17

You are verifying BGP Graceful Restart helper mode on a Juniper router. A peering router restarts its control plane. What output or verification command confirms that your router is acting as a Graceful Restart helper for the peer?

Accepted Answer

Run 'show bgp neighbor' and verify that the 'Graceful Restart' capability is advertised and received, and observe the restart state flags.. Using 'show bgp neighbor' displays the graceful restart capabilities negotiated and whether the peer is currently in restart state.

Answer

Run 'show chassis routing-engine' to verify that the remote neighbor has updated its local RE priority.

Answer

Run 'show lacp statistics ae0' to see if LACP packets are being suppressed during restart.

Answer

Run 'show vrrp summary' to check if the BGP neighbor has assumed the master VRRP role.

Question 18

A network engineer wants to verify IS-IS link-state database entries, specifically checking for TLVs that carry extended IP reachability information with wide metrics. Which Junos operational command should be used?

Accepted Answer

show isis database detail. To view the IS-IS link-state database with detailed TLV and metric information on Junos devices, the command 'show isis database detail' is used.

Answer

show isis adjacency extensive

Answer

show ospf database

Answer

show route protocols isis

Question 19

An engineer configures iBGP peering between two routers in the same AS. Route reflection is not used. The engineer notices that routes learned from an eBGP peer by Router A are not being advertised by Router A to Router B (its iBGP peer). Why is this happening?

Accepted Answer

BGP split-horizon prevents a router from advertising routes learned from one iBGP peer to another iBGP peer.. BGP split-horizon rule dictates that routes learned from an iBGP peer cannot be advertised to another iBGP peer to prevent routing loops. (Note: standard iBGP to iBGP split horizon applies; to share routes, full mesh, route reflectors, or confederations must be used).

Answer

External routes cannot be carried over iBGP without encapsulation.

Answer

The Local Preference attribute defaults to 0 for iBGP routes, causing them to be suppressed.

Answer

iBGP peers require the 'multipath' statement to be configured before any route exchange can occur.

Question 20

An engineer is preparing to perform an In-Service Software Upgrade (ISSU) on a pair of dual-RE MX240 routers. Which condition must be met to ensure the ISSU succeeds without dropping traffic?

Accepted Answer

Graceful Route Engine Switchover (GRES) and Nonstop Active Routing (NSR) must be enabled and functioning.. ISSU requires specific hardware compatibility (matching RE models, line card types), GRES and NSR configured and operating, and a supported Junos image path.

Answer

The backup Routing Engine must be physically removed from the chassis during the upgrade.

Answer

All physical interfaces must be manually disabled prior to issuing the request system software in-service command.

Answer

All routing protocols must be migrated from OSPF to IS-IS before starting ISSU.