JNCIP-ENT BGP Advanced — Timed 30 Questions

Question 1

An administrator configures a BGP routing policy to match routes with community members using regex matching in Junos. Which statement accurately describes how Junos represents standard BGP communities in policy matching?

30 minute time limit — choose an answer to begin.

Accepted Answer

Communities are defined within policy-options using community members specified in AS:number format and matched via community-list.. In Junos, standard BGP communities are represented as target communities or community sets in the form of autonomous_system:identifier or named community lists.

Answer

Community matching in Junos requires explicit activation under the forwarding-options hierarchy.

Answer

Communities must be converted to extended communities before any regular expression can be applied.

Answer

Communities are matched exclusively using hexadecimal bitmasks in policy match conditions.

Question 2

Which command should an engineer use on a Junos device to verify whether a BGP next hop is successfully resolved via the routing table?

Accepted Answer

show route protocol bgp next-hop. The command `show route protocol bgp next-hop` is specifically designed to display BGP next-hop resolution information. It shows whether each BGP next hop is resolvable via the routing table (e.g., through an IGP or static route) and the associated metric or preference. This directly answers the question of whether the next hop is successfully resolved.

Answer

show bgp neighbor detail

Answer

show route forwarding-table destination

Answer

show bgp summary

Question 3

An administrator is reviewing the BGP route selection process on a Junos device and notices that two paths have identical weights, local preferences, AS path lengths, origins, and MEDs. Which tie-breaking criterion does Junos evaluate next in the BGP route selection algorithm?

Accepted Answer

Preference for internal (IBGP) paths over external (EBGP) paths. After comparing weight, local preference, AS path length, origin, and MED, Junos checks the routing table to prefer routes learned via internal peer (IBGP) over external peer (EBGP) before moving to router ID and IGP cost.

Answer

Preference for the lowest IGP metric to the BGP next hop

Answer

Preference for the oldest route

Answer

Preference for the lowest router ID

Question 4

An enterprise network uses BGP communities to tag routes at regional branch offices. Headquarters needs to strip these specific communities from routes before advertising them to external transit providers. Which Junos routing policy action accomplishes this?

Accepted Answer

community delete target_community. The Junos routing policy action 'community delete target_community' removes the specified BGP community from routes matching the policy term. When applied outbound toward external transit providers, it strips the regional branch communities before advertisement, which is exactly the requirement.

Answer

community set target_community

Answer

as-path-remove target_community

Answer

metric set 0

Question 5

An administrator wants to disable the default behavior where BGP advertises all active routing table paths to peers. Which configuration statement restricts BGP to only advertise the active best path?

Accepted Answer

Configure an export policy that filters out non-active paths.. Junos by default advertises only the active best path, but multipath or specific advertisement behaviors can be adjusted. However, advertising only the best path is standard behavior, and policies control what is exported.

Answer

Enable route dampening on all EBGP peers.

Answer

Set the BGP advertisement-interval to zero.

Answer

Disable routing-options bgp multipath globally.

Question 6

A network engineer is configuring a Junos routing device to use BGP Prefix-Independent Convergence (PIC) edge for faster failover. What is the fundamental mechanism that enables BGP PIC to achieve sub-second convergence upon primary path failure?

Accepted Answer

It pre-installs a backup loop-free alternate (LFA) next hop in the forwarding plane for rapid hardware switching.. BGP PIC pre-computes a backup loop-free alternate next hop and installs it in the forwarding table alongside the primary next hop, allowing hardware-based failover.

Answer

It bypasses the routing table entirely and queries the BGP route reflector directly upon failure.

Answer

It forces the IGP to recalculate shortest paths immediately using fast-reroute without BGP participation.

Answer

It increases the BGP keepalive and hold timers to prevent session tearing during link flaps.

Question 7

A BGP routing policy on a Junos router uses an 'as-path' regular expression '^[0-9]+$' in a match condition. Which routes will this regular expression match?

Accepted Answer

Routes whose AS path contains exactly one AS number ( originated from a directly connected neighboring AS ).. The regex '^[0-9]+$' matches an AS path that consists of exactly one autonomous system number (from the beginning to the end of the path string).

Answer

Routes that contain internal confederation segments.

Answer

Routes whose AS path starts with local AS 65000 and has multiple hops.

Answer

Any route originating from any AS path of any length.

Question 8

Which THREE conditions must be met for a Junos routing device to consider two BGP paths as valid candidates for multipath load balancing when standard multipath is configured? (Choose three)

Accepted Answer

The next hops must be resolvable via active routing table entries.. Standard BGP multipath in Junos requires matching AS path lengths, local preferences, and valid IGP next-hop resolution, among other consistent attributes.

Answer

The router IDs of the advertising peers must be identical.

Answer

The route advertisement intervals must be synchronized across all peers.

Question 9

An administrator is troubleshooting BGP route reflector operations in a Junos environment. Which TWO statements regarding route reflection behavior and loop prevention are correct? (Choose two)

Accepted Answer

A route reflector ignores any advertised route that contains its own local Cluster ID in the Cluster List.. Route reflectors use Originator ID to prevent loops from clients and Cluster Lists to prevent loops between cluster route reflectors.

Answer

Route reflectors change the BGP next hop to their own IP address when reflecting routes to clients by default.

Answer

Route reflectors remove the AS_PATH attribute when reflecting routes to internal non-client peers.

Answer

Route reflectors modify the Local Preference attribute to zero for all reflected routes.

Question 10

Which TWO attributes are considered transitive BGP path attributes? (Choose two)

Accepted Answer

COMMUNITY. AS_PATH and COMMUNITY are standard well-known transitive and optional transitive attributes respectively, whereas LOCAL_PREF is well-known discretionary (non-transitive across AS).

Answer

MED (Multi-Exit Discriminator)

Answer

ORIGINATOR_ID

Answer

LOCAL_PREF

Question 11

Which TWO well-known BGP communities are recognized universally to control route propagation? (Choose two)

Accepted Answer

no-export. NO_EXPORT and NO_ADVERTISE are standard well-known communities.

Answer

local-only

Answer

transit-only

Answer

no-peer

Question 12

Which THREE methods can be used on Junos devices to influence inbound BGP traffic selection from external ASNs? (Choose three)

Accepted Answer

AS path prepending outbound to external peers.. Option B is correct because AS path prepending is applied outbound toward external peers, making the advertised path longer so the remote AS prefers a different entry point into your network, which directly influences inbound EBGP traffic selection. Option C is correct because provider-supported BGP communities (for example, well-known or ISP-specific communities) are attached to outbound announcements and signal the upstream provider to apply routing policy changes such as local preference adjustments, thereby steering inbound traffic. Option E is correct because MED (Multi-Exit Discriminator) is sent to external peers to indicate the preferred entry point among multiple links to the same neighboring AS, influencing how that AS routes traffic toward you. Option A is not correct because local preference is a local, iBGP-scoped attribute that affects outbound path selection within your own AS, not inbound traffic from external ASNs. Option D is not correct because weight is a Cisco-proprietary, locally significant attribute on the receiving router and is not advertised to external peers, so it cannot influence inbound EBGP traffic selection from other ASNs.

Answer

Adjusting the local preference attribute on incoming EBGP updates.

Answer

Changing the local router's weight attribute for incoming EBGP routes.

Question 13

Which TWO statements describe characteristics of BGP route reflectors? (Choose two)

Accepted Answer

They eliminate the requirement for a full-mesh IBGP topology within an autonomous system.. Route reflectors reduce IBGP mesh requirements and reflect routes according to strict client/non-client rules.

Answer

They rewrite the AS path length attribute for all reflected client routes.

Answer

They replace the underlying IGP entirely for packet forwarding.

Answer

They operate exclusively at Layer 2 switching boundaries.

Question 14

You are troubleshooting a BGP route selection issue on a Junos device. Two otherwise identical paths are received from external peers. According to the standard BGP route selection algorithm implemented by Junos, which tie-breaking attribute is evaluated immediately AFTER comparing the Router ID (RID) of the advertising routers?

Accepted Answer

Lowest neighbor IP address. In the Junos BGP route selection algorithm, after comparing local preference, AS path length, origin, MED, eBGP over iBGP, IGP metric to next hop, and router ID (lowest router ID), the next step evaluates the neighbor IP address (lowest neighbor IP address).

Answer

AS path length

Answer

Multi-Exit Discriminator (MED)

Answer

Cluster list length

Question 15

Which THREE optional BGP attributes are supported and processed by Junos routing devices? (Choose three)

Accepted Answer

COMMUNITY. The three optional BGP attributes supported and processed by Junos are COMMUNITY (A), ATOMIC_AGGREGATE (C), and MED (E). COMMUNITY (A) is a well-known optional transitive attribute that Junos supports and processes for route tagging and policy matching via community lists. ATOMIC_AGGREGATE (C) is an optional transitive attribute that Junos recognizes and propagates to indicate that a route was aggregated and the original AS path information was lost. MED (E) is an optional non-transitive attribute that Junos supports and processes to influence inbound traffic from neighboring autonomous systems. LOCAL_WEIGHT (B) is not a BGP attribute at all; it is a Junos/Cisco proprietary local parameter used only within the local router and is never transmitted in BGP updates. NEXT_HOP_OVERRIDE (D) is not a BGP path attribute; it is a Junos configuration statement applied under BGP groups or neighbors to rewrite the next-hop address, not an attribute carried in BGP UPDATE messages.

Answer

LOCAL_WEIGHT

Answer

NEXT_HOP_OVERRIDE

Question 16

An administrator needs to ensure that a Junos routing device performs unequal-cost multi-path (UCMP) load balancing across multiple BGP paths with different local preferences or path attributes. Which BGP feature must be enabled to allow multipath load balancing across paths with different AS path lengths?

Accepted Answer

set protocols bgp multipath as-path-ignore. By default, Junos multipath requires multiple attributes (such as AS path length) to match. To allow BGP multipath even when AS path lengths differ (as long as they have the same length numerically, or using 'as-path-ignore'), the 'as-path-ignore' statement under protocols bgp multipath must be configured.

Answer

set protocols bgp family inet unicast multipath relax

Answer

set routing-options rib inet.0 multipath

Answer

set protocols bgp load-balance per-packet

Question 17

An enterprise is designing a BGP confederation to reduce iBGP mesh complexity across multiple data centers. Which statement is correct regarding how confederation members interact with BGP attributes?

Accepted Answer

Sub-AS numbers are preserved in AS_CONFED_SEQUENCE segments inside the confederation but are replaced by the confederation identifier when advertising to external peers.. Within a BGP confederation, sub-AS numbers are stripped as routes leave the confederation and are replaced by the confederation identifier. However, within the confederation, sub-AS numbers are kept in the AS_CONFED_SEQUENCE and AS_CONFED_SET path segments to prevent loops, and MED/Local Preference are preserved across member sub-AS boundaries.

Answer

Confederations eliminate the need for any internal iBGP peering within the member sub-ASes.

Answer

The next-hop IP address is always modified when routes are passed between member sub-ASes within the confederation.

Answer

Local Preference is automatically reset to zero whenever a route crosses a sub-AS boundary inside a confederation.

Question 18

A Juniper Networks router is configured with BGP multipath load balancing. An engineer wants to ensure that BGP can install multiple paths to the same destination into the forwarding table. Which two conditions must be met for BGP multipath to be active on a Junos device? (Choose two.)

Accepted Answer

The multiple paths must have the same ORIGIN attribute.. For BGP multipath to be active, the candidate paths must be considered equal by the BGP path selection algorithm up to the point where multipath is evaluated. This requires that they have the same AS_PATH length, the same ORIGIN, the same MED, and the same local preference, among other attributes. The IGP metric to the next hop does not need to be identical; multipath can balance across paths with different IGP metrics if configured. The paths must come from different peers to be useful.

Answer

The multiple paths must be received from the same BGP peer.

Answer

The multiple paths must have the same next-hop IGP metric.

Answer

The multiple paths must have the same CLUSTER_LIST length.

Question 19

An engineer is configuring a JN0-650 BGP route reflector cluster with two route reflectors (RR1 and RR2) that use the cluster ID 10.10.10.10. A route received from a client is reflected by RR1 to non-clients. RR2 also reflects the same route. The engineer observes that non-client routers are receiving duplicate route updates. What is the primary cause of this behavior?

Accepted Answer

The route reflectors are not configured with a unique originator ID, and they are reflecting routes from each other.. Duplicate route updates in a route reflection cluster often occur when route reflectors do not properly use the originator ID to prevent loops. When two route reflectors in the same cluster reflect the same route to non-clients, they should suppress duplicates based on the originator ID. If the originator ID is not consistent or if the route reflectors reflect routes received from each other, non-clients may receive multiple copies. Ensuring proper originator ID handling and cluster ID configuration prevents this.

Answer

The cluster ID is configured as a loopback address instead of a physical interface address.

Answer

The route reflectors are not configured with the same cluster ID.

Answer

The route reflectors are not configured to use the same cluster ID, causing them to reflect routes independently.

Question 20

A Juniper Networks router is configured with BGP and you want to influence outbound traffic for a specific prefix by prepending the AS path. You apply an export policy to an EBGP peer that prepends the AS number 65001 three times. However, you notice that the peer is still receiving the prefix with the original AS path length. What is the most likely reason?

Accepted Answer

The export policy does not include a 'from' clause, so it matches no routes.. In Junos, a routing policy must have a 'from' clause to match specific routes before applying actions like AS path prepending. Without a 'from' clause, the policy may match all routes, but if the policy is intended for a specific prefix and lacks matching criteria, it may not apply as expected. The scenario indicates the policy is applied to an EBGP peer but the peer still sees the original AS path, suggesting the policy did not match the prefix. Adding a 'from' clause to match the prefix would ensure the prepend action is applied.

Answer

The AS path prepend action requires the 'as-path-expand' command instead.

Answer

The AS path prepend action is only applied to iBGP peers by default.

Answer

The peer is configured with 'remove-private' which strips the prepended AS numbers.