JNCIP-ENT BGP Advanced Practice Test 4 — 15 Questions

Question 1

An administrator configures BGP dampening on a Junos router to mitigate the impact of flapping routes. When a route exceeds the reuse threshold after being suppressed, what happens to its penalty value?

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

Accepted Answer

The penalty value continues to decay exponentially until it drops to zero.. When a dampened route's penalty decays below the reuse threshold, the route becomes eligible again, and its penalty continues to decay exponentially toward zero.

Answer

The penalty value is locked at the reuse threshold value indefinitely.

Answer

The penalty value is doubled to discourage further flapping.

Answer

The penalty value is instantly reset to zero.

Question 2

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

Accepted Answer

Modifying the local preference attribute of incoming IBGP routes.. Option A is correct because Junos routing policies applied as import policies can match incoming IBGP routes and set the BGP local preference attribute (for example with the 'then local-preference' action), which influences outbound path selection within the local AS. Option C is correct because Junos policy-options support AS path regular expressions via the 'as-path' match condition, allowing routes to be filtered or manipulated based on the AS_PATH attribute. Option B is not valid because BGP TCP port 179 is fixed by the protocol and cannot be changed by routing policy; port configuration is not a policy action. Option D is not valid because keepalive and hold timers are configured under the BGP neighbor or group hierarchy, not dynamically modified through policy match/action statements. Option E is not valid because interface MTU is a physical/logical interface property configured under interfaces, not something a BGP routing policy can assign.

Answer

Dynamically altering the BGP session TCP handshake port numbers.

Answer

Adjusting the BGP keepalive timer values dynamically via policy match actions.

Answer

Manually assigning physical interface MTU sizes for BGP sessions.

Question 3

An operator configures BGP attribute value manipulation using a Junos routing policy. Specifically, the policy uses 'as-path-action prepend' combined with community matching. When is this outbound policy evaluated relative to BGP route selection?

Accepted Answer

When advertising routes to a BGP peer, after the best path has been chosen.. Outbound export policies are evaluated when advertising routes to peers, after the best path has been selected locally.

Answer

During the initial import processing from EBGP peers before next-hop resolution.

Answer

Before the best path is selected, affecting the local routing table calculation.

Answer

During the route selection algorithm right after MED comparison.

Question 4

When configuring a BGP confederation, how are external peers outside the confederation affected by the internal sub-AS structure?

Accepted Answer

They see only the top-level confederation AS number in the AS path attribute.. External peers outside the confederation see only the top-level confederation AS number, as internal member AS numbers are stripped when exiting the confederation boundary.

Answer

They require explicit configuration of every member AS in their own EBGP import filters.

Answer

They see all member AS numbers prepended individually in the AS path.

Answer

They reject all updates originating from a confederation due to AS path validation failures.

Question 5

Which THREE parameters are part of the standard Junos BGP route selection algorithm prior to evaluating the router ID? (Choose three)

Accepted Answer

Weight (local to the router). Before router ID, Junos evaluates Weight, Local Preference, AS path length, Origin, MED, and IBGP vs EBGP preference.

Answer

Cluster List length

Answer

Originator ID value

Question 6

When designing a BGP confederation architecture, which TWO rules govern how sub-AS numbers and attributes behave across confederation boundaries? (Choose two)

Accepted Answer

Sub-AS numbers are included in AS_CONFED_SEQUENCE attributes and are stripped when exiting the confederation.. Confederations use AS_CONFED_SEQUENCE and AS_CONFED_SET segments to track internal paths, and strip them when advertising to external peers outside the confederation.

Answer

BGP multipath cannot be enabled across different member ASNs within the same confederation.

Answer

MED values are automatically removed across member AS boundaries regardless of configuration.

Answer

Local preference is discarded when passing routes between different member ASNs inside the confederation.

Question 7

An engineer is configuring BGP route resolution and next-hop tracking in Junos. Which TWO circumstances will cause a BGP next hop to be marked as unresolved or unusable? (Choose two)

Accepted Answer

The resolving route in the IGP routing table points to a discard or reject dead-end route.. BGP next hops become unusable if the resolving route in the IGP table is missing, points to a discard/reject route, or lacks reachability.

Answer

The BGP next-hop IP address matches a directly connected interface subnet on the router.

Answer

The BGP neighbor session is established over a loopback interface using multihop.

Answer

The resolving route has an active loop-free alternate backup path installed.

Question 8

An engineer notices that a Junos device is not installing a BGP route into the forwarding table because the BGP next hop is unresolved. Which tool or command can be used to troubleshoot how the BGP next hop is being resolved in the Junos routing table?

Accepted Answer

show route resolution. To check BGP next-hop resolution, the 'show route resolution' command displays how next hops are resolved via the routing table (RIB-local), showing whether an active IGP or static route covers the BGP next-hop IP address.

Answer

show bgp summary

Answer

show bgp group

Answer

show route advertising-protocol bgp

Question 9

You are configuring a BGP Route Reflector (RR) in a Junos environment. To prevent routing loops within the iBGP cluster, what mechanism does the route reflector use to track the path of reflected routes?

Accepted Answer

Cluster List and Originator ID attributes. Route reflectors use the 'Originator ID' (a 4-byte attribute containing the router ID of the route originator) and the 'Cluster List' (a sequence of cluster IDs through which the route has passed) to prevent routing loops.

Answer

MED comparison and router ID tie-breakers

Answer

AS Path prepending and local preference manipulation

Answer

TTL security decrement and loose reverse path forwarding

Question 10

You want to tag specific BGP routes with a community value using a Junos policy framework. Which configuration snippet correctly defines a community named 'CUSTOM-COMM' with value 65000:100?

Accepted Answer

set policy-options community CUSTOM-COMM members 65000:100. In Junos, BGP communities are defined under 'policy-options community' with a name and the community value specified in format AS:number or target:AS:number.

Answer

set routing-options community-list CUSTOM-COMM value 65000:100

Answer

set protocols bgp group external community CUSTOM-COMM 65000:100

Answer

set policy-options policy-statement CUSTOM-COMM community 65000:100

Question 11

Which TWO BGP attributes are classified as well-known mandatory attributes that must be recognized by all BGP implementations? (Choose TWO)

Accepted Answer

AS_PATH. The well-known mandatory BGP attributes are AS_Path, NEXT_HOP, and ORIGIN. Among the choices, AS_PATH and NEXT_HOP are well-known mandatory attributes.

Answer

COMMUNITIES

Answer

MULTI_EXIT_DISC

Answer

LOCAL_PREF

Question 12

An engineer needs to ensure that routes received from an external BGP peer are evaluated using multipath load balancing across different next hops. By default, Junos requires several conditions to be met for multipath. Which condition is mandatory for BGP multipath to consider two paths as valid candidates?

Accepted Answer

The IGP metric to the BGP next hop must be identical for all participating paths.. To qualify for BGP multipath in Junos, multiple attributes must match by default, including AS path length, local preference, origin, MED, and the IGP metric to the respective next hops must be equal (or within an acceptable variance if configured).

Answer

The peer IP addresses must reside on the exact same subnet.

Answer

The advertising router IDs must be identical.

Answer

The cluster lists must be completely empty.

Question 13

When configuring a BGP route reflector cluster in Junos, which THREE guidelines or operational behaviors should an engineer keep in mind? (Choose THREE)

Accepted Answer

A route reflector must never reflect routes received from a non-client peer back to other non-client peers.. Route reflectors reflect routes between clients and non-clients. Loop prevention uses Originator ID and Cluster List. Redundant RRs in the same cluster must share the same cluster ID to prevent routing loops and oscillation.

Answer

Clients of a route reflector must be configured in a full iBGP mesh with each other.

Answer

Route reflectors automatically modify the AS_PATH attribute of all reflected routes.

Question 14

Which THREE actions occur during the BGP next-hop resolution process on a Junos device when evaluating an eBGP-learned route? (Choose THREE)

Accepted Answer

The resolved next-hop information along with the egress interface and MAC address are installed into the forwarding table.. When eBGP routes are learned, the next hop is typically the IP address of the external peer. Junos must resolve this next-hop IP in the routing table (RIB-local) via an active IGP or static route, verify that the resolving route is valid and active, and program the forwarding table (FIB) with the resolved next hop.

Answer

The BGP next-hop IP address is automatically rewritten to the local router loopback address by default for eBGP.

Answer

Junos automatically ignores next-hop resolution if multipath is enabled.

Question 15

An enterprise runs a Junos BGP routing domain where a route reflector (RR) in cluster 10.0.0.1 reflects an eBGP-learned route to its iBGP clients. A client router receives the reflected route and notices the ORIGINATOR_ID attribute is set to 10.0.0.1, while the CLUSTER_LIST attribute contains 10.0.0.1. The client also has a second route reflector in the same cluster (10.0.0.2) as a peer. When the client advertises this route to the second route reflector, what does the second route reflector do with the update?

Accepted Answer

It rejects the update because the CLUSTER_LIST already contains its own cluster ID.. In a route reflection cluster, all route reflectors share the same cluster ID. When a route is reflected, the cluster ID is added to the CLUSTER_LIST. A route reflector that receives an update containing its own cluster ID in the CLUSTER_LIST discards the route to prevent loops. Since both route reflectors in the same cluster use the same cluster ID, the second route reflector rejects the update even though its router ID differs from the first route reflector's.

Answer

It accepts the update and appends its own router ID to the ORIGINATOR_ID attribute.

Answer

It rejects the update because the ORIGINATOR_ID matches its own router ID.

Answer

It accepts the update because the CLUSTER_LIST does not contain its own cluster ID.