JNCIS-ENT Hard Questions — 25 Difficult Questions

Question 1

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?

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

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 2

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 3

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 4

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 5

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 6

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 7

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.

Question 8

While reviewing BGP updates, you notice an attribute type code of 3 with a value representing an IP address. Which well-known mandatory path attribute is this?

Accepted Answer

NEXT_HOP. Attribute type code 3 corresponds to NEXT_HOP, which is a well-known mandatory attribute indicating the IP address of the router used to reach the destination.

Answer

AS_PATH

Answer

ORIGIN

Answer

LOCAL_PREF

Question 9

Which THREE statements accurately describe the behavior and configuration of VRRP tracking on Junos devices? (Choose three)

Accepted Answer

If the decremented priority falls below the backup router's priority, mastership transitions to the backup router.. VRRP tracking lowers priority when interfaces fail, can monitor multiple interfaces, and allows backup routers to take over.

Answer

Tracking forces the tracked interface to shut down permanently when a failure occurs.

Answer

Tracking automatically disables GRES on the routing engine.

Question 10

Which THREE attributes are optional transitive BGP path attributes? (Choose three)

Accepted Answer

AS4_PATH. Optional transitive attributes include COMMUNITY, AGGREGATOR, and AS4_PATH. MED is optional non-transitive. Local Pref and AS_PATH are well-known.

Answer

MED

Answer

LOCAL_PREF

Question 11

Which THREE statements describe the role and function of the BGP Router ID? (Choose three)

Accepted Answer

It is exchanged during the BGP OPEN message negotiation phase.. The Router ID is a 32-bit identifier chosen during startup, used as a tie-breaker in BGP path selection, and included in OPEN messages.

Answer

It automatically replaces the AS_PATH attribute if missing.

Answer

It must be identical across all routers within the same Autonomous System.

Question 12

Which THREE statements regarding Juniper Virtual Chassis architecture and master election are correct? (Choose three)

Accepted Answer

Pre-provisioning member serial numbers ensures consistent member ID assignments regardless of boot order.. Virtual Chassis mastership is determined by priority, preemption can cause takeovers, and pre-provisioning serial numbers ensures stable member IDs.

Answer

Split-brain detection automatically shuts down all core routing protocols without administrator intervention.

Answer

Virtual Chassis ports (VCPs) require LACP active mode configuration on every stacking cable.

Question 13

While examining a BGP routing table, you notice a route with an ORIGIN attribute set to 'Incomplete'. What does this indicate about the origin of the route?

Accepted Answer

The route was injected into BGP via redistribution (e.g., from static or IGP).. BGP origin types are IGP (0), EGP (1), and Incomplete (2). Incomplete means the route origin is unknown, typically redistributed from an IGP or static route.

Answer

The route was learned via eBGP from an unknown AS.

Answer

The BGP update packet was corrupted in transit.

Answer

The route is an aggregate route without specific components.

Question 14

An administrator is troubleshooting a BGP peering session that is stuck in the Connect or Active state. Which THREE common causes could explain this issue? (Choose three)

Accepted Answer

TCP port 179 is blocked by a firewall filter.. A session stuck in Active/Connect means the TCP session cannot be established. Causes include incorrect peer IP/AS, firewall blocking port 179, or missing multihop/TTL settings.

Answer

Route reflection client parameters are misconfigured.

Answer

Incorrect peer AS number configured in the OPEN message parameters.

Question 15

Which THREE path attributes are classified as 'well-known mandatory'? (Choose three)

Accepted Answer

NEXT_HOP. The well-known mandatory attributes in BGP are ORIGIN, AS_PATH, and NEXT_HOP. Local Preference is well-known discretionary, and MED is optional non-transitive.

Answer

MED

Answer

LOCAL_PREF

Question 16

A BGP speaker receives an UPDATE message containing a malformed attribute. According to BGP specifications, which action does the receiving router take?

Accepted Answer

Send a NOTIFICATION message and terminate the BGP session.. A malformed attribute or critical error triggers a NOTIFICATION message with an appropriate error code, followed by session teardown.

Answer

Strip the attribute and propagate the route to iBGP peers.

Answer

Send an UPDATE message requesting retransmission.

Answer

Silently ignore the attribute and install the route.

Question 17

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 18

When troubleshooting a BGP routing loop or unexpected route suppression, which THREE Junos operational commands provide visibility into BGP path attributes and decision processes? (Choose three)

Accepted Answer

show route extensive. Detailed route inspection and BGP neighbor debugging commands include 'show route extensive', 'show bgp neighbor', and 'show route protocol bgp'.

Answer

show ldp database

Answer

show ospf interface

Question 19

Which BGP message type is responsible for negotiating session parameters, including autonomous system numbers, hold times, and BGP identifiers during session establishment?

Accepted Answer

Open. The BGP Open message is the first message sent after a TCP connection is established. It contains parameters such as the BGP version, local AS number, hold time, BGP identifier, and optional parameters (capabilities).

Answer

Notification

Answer

Update

Answer

Keepalive

Question 20

During an audit of a Juniper EX4300 Virtual Chassis, you notice that member 1 and member 2 are connected via mixed 1G and 10G uplink ports. How does Junos handle mixed-speed Virtual Chassis port configurations?

Accepted Answer

Virtual Chassis ports (VCPs) must be explicitly configured to match supported transceiver speeds, and mixing unsupported interface types will result in port initialization failure.. Junos EX series virtual chassis ports can be configured for specific speeds, but mismatched or unsupported port combinations will cause initialization failures or link errors depending on the platform.

Answer

Mixed speed links automatically drop to 1G to maintain backward compatibility without administrative intervention.

Answer

Junos automatically load-balances stacking traffic across 1G and 10G links using weighted round-robin.

Answer

Only the 10G ports will carry control plane traffic while 1G ports are restricted to data transit.