JNCIP-ENT BGP Advanced Practice Test 3 — 15 Questions

Question 1

A network engineer has configured BGP multipath on a Junos routing device using the 'multipath' statement under the routing-options bgp hierarchy. However, traffic is still only utilizing a single path. Which condition must be met for BGP multipath to become active for a destination prefix?

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

Accepted Answer

All competing BGP paths must have identical AS path lengths, local preference, origin, and MED.. For BGP multipath to be valid in Junos, the paths must have matching AS path lengths, local preferences, origins, and MEDs, along with valid next-hop resolution through the IGP.

Answer

Multipath requires BGP prefix-independent convergence (PIC) to be explicitly enabled on all routing engines.

Answer

The next hops must be directly connected interfaces without relying on IGP resolution.

Answer

All paths must originate from the exact same autonomous system in the AS path attribute.

Question 2

An administrator applies a policy containing 'as-path-prepend "65001 65001"' to outbound BGP updates sent to an external provider. What is the primary objective of this configuration?

Accepted Answer

To artificially increase the AS path length attribute to make this path less preferred by inbound traffic.. Prepending the local AS number multiple times increases the AS path length attribute, making the path less desirable to external peers and manipulating inbound traffic engineering.

Answer

To force the external peer to drop all updates due to an AS path loop check failure.

Answer

To enable BGP multipath load balancing across multiple external links.

Answer

To establish a confederation sub-AS relationship with the external provider.

Question 3

An enterprise network uses a BGP route reflector (RR) architecture where client routers reflect routes to each other. A non-client router sends a route with an Originator ID and Cluster List to the RR. How does the route reflector handle these attributes when reflecting the route to other clients?

Accepted Answer

It leaves the Originator ID intact and appends its own cluster ID to the Cluster List.. A route reflector leaves the Originator ID untouched and prepends its own Cluster ID to the existing Cluster List to prevent routing loops.

Answer

It removes the Originator ID and replaces the Cluster List with its own cluster ID.

Answer

It increments the Originator ID value by one and clears the Cluster List.

Answer

It clears both the Originator ID and Cluster List to reset loop detection for the local cluster.

Question 4

During BGP route resolution on Junos, an indirect next hop is encountered. What mechanism does Junos use to resolve this indirect next hop to a direct forwarding next hop?

Accepted Answer

Recursive lookups through the routing table using the active IGP or static route entries.. Junos relies on the underlying IGP (OSPF or IS-IS) or static routes to resolve indirect BGP next hops to direct interface and gateway forwarding entries.

Answer

BGP Link-State (BGP-LS) topology databases.

Answer

Multiprotocol Label Switching (MPLS) label imposition without routing table participation.

Answer

Address Resolution Protocol (ARP) directly against the BGP peer IP address.

Question 5

An engineer needs to ensure that a Junos router balances BGP traffic across multiple paths with unequal IGP costs. Which feature must be configured to achieve this?

Accepted Answer

BGP multipath with the 'as-path-relax' or equivalent multipath options enabled.. By default, BGP multipath requires equal cost. To allow paths with different costs, 'as-path-multipath' or variance-based multipath configurations are required depending on specific Junos platform support, but generally standard multipath requires equal IGP cost unless specific multipath relaxation options are set.

Answer

Setting the MED attribute to zero on all incoming EBGP updates.

Answer

Configuring static routes with identical preferences for every BGP prefix.

Answer

Enabling BGP Route Reflection on the local routing engine.

Question 6

A network administrator wants to advertise an aggregate BGP route while suppressing the more specific component routes from being sent to external peers. Which Junos routing-options configuration achieves this?

Accepted Answer

Configure the aggregate route with the 'summary-only' parameter under routing-options bgp.. Using the 'aggregate' statement with the 'summary-only' option generates the aggregate prefix and suppresses all component specific routes.

Answer

Enable BGP dampening on the aggregate route and disable it on the component routes.

Answer

Apply a routing policy that sets the NO_EXPORT community on all component routes.

Answer

Configure an aggregate route with the 'discard' policy and apply an export policy that drops component routes.

Question 7

A network designer needs to implement BGP route reflection where multiple route reflectors are deployed in the same cluster to provide redundancy. What parameter must be identical across all route reflectors in that same cluster to prevent routing loops?

Accepted Answer

Cluster ID. Route reflectors within the same cluster must share the same Cluster ID so they can recognize and ignore routes reflected by their peer route reflector.

Answer

AS Path Prepend count

Answer

Local Preference value

Answer

Router ID

Question 8

An operator configures a BGP routing policy to modify the Local Preference attribute. Under which BGP neighbor relationship type can Local Preference be advertised and evaluated?

Accepted Answer

Internal BGP (IBGP) peers only. Local Preference is an IBGP attribute and is exchanged only between internal BGP peers within the same autonomous system.

Answer

BGP confederation member AS boundaries only

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Both EBGP and IBGP peers equally

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External BGP (EBGP) peers only

Question 9

A Junos router is configured with BGP path selection, and multiple paths arrive with different MED values. Under what specific condition does Junos compare the MED values of paths from different autonomous systems during route selection?

Accepted Answer

Junos compares MEDs from different ASs only when the 'always-compare-med' statement is configured under protocols bgp.. By default, Junos (like standard BGP implementations) only compares MEDs from different ASs if the 'always-compare-med' configuration is explicitly enabled.

Answer

Junos compares MEDs from different ASs when the AS path lengths are completely identical.

Answer

Junos never compares MEDs from different ASs under any circumstance.

Answer

Junos compares MEDs from different ASs automatically if the routes share the same IGP metric.

Question 10

In a BGP confederation setup, two member ASNs (65001 and 65002) belong to a larger confederation AS (65100). When routes are advertised between these two member ASs, how is the AS path attribute handled?

Accepted Answer

The member AS numbers are placed in AS_CONFED_SEQUENCE segments and are not treated as external AS hops.. Confederation member AS numbers are included in the AS_CONFED_SEQUENCE attribute and are stripped when the route exits the confederation boundary.

Answer

The confederation AS number is prepended to the front of the path, removing all member AS numbers.

Answer

The member AS numbers are completely stripped and replaced by the confederation AS number.

Answer

The route is dropped by the receiving member AS due to an inter-AS loop prevention violation.

Question 11

An administrator implements BGP entropy labels and path load balancing on a Junos routing platform. During packet forwarding for a BGP-learned IPv4 prefix with multiple equal-cost paths, how does Junos determine the output interface when hash-based load balancing is active?

Accepted Answer

Hashing selected packet header fields to compute an index into the set of resolved BGP next hops.. Junos hashes packet header fields (such as source/destination IP, ports, and optional hash keys or entropy labels) to select a specific path from the available BGP multipaths.

Answer

Using the lowest MED value among the multipath entries for every packet transmission.

Answer

Consulting the BGP Route Reflector cluster list to determine the optimal egress port.

Answer

Round-robin packet scheduling across all available BGP next hops regardless of flow headers.

Question 12

Which command allows an administrator to view the active BGP routes along with their associated communities on a Junos device?

Accepted Answer

show route protocol bgp extensive. The 'show route protocol bgp' command with the 'extensive' modifier displays detailed path attributes including BGP communities.

Answer

show bgp group summary

Answer

show bgp neighbor extensive

Answer

show route forwarding-table protocol bgp

Question 13

A Junos router receives a BGP route containing multiple extended and large communities. The administrator writes a routing policy to filter routes based on large communities. Which format is used to define a large community in Junos policy-options?

Accepted Answer

large-community:global_administrator:local_data1:local_data2. Large communities in Junos policy-options are defined using the format large-community:global_administrator:local_data1:local_data2.

Answer

as-number:identifier

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target:as-number:identifier

Answer

ipv4-address:identifier

Question 14

An engineer is troubleshooting a BGP route reflection topology where a non-client IBGP peer sends a route to a route reflector. Will the route reflector reflect this route to other non-client IBGP peers?

Accepted Answer

No, routes received from a non-client peer are only reflected to client peers, not to other non-client peers.. A route reflector reflects routes from clients to clients, clients to non-clients, and non-clients to clients, but it does NOT reflect routes received from a non-client to other non-client peers.

Answer

Yes, all routes received by a route reflector are reflected to all peers regardless of client status.

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No, route reflectors never reflect routes received from any IBGP peer.

Answer

Yes, provided the routes contain the same Cluster ID as the receiving non-client peer.

Question 15

Which Junos configuration hierarchy is used to define a BGP peer group to simplify neighbor configurations?

Accepted Answer

protocols bgp group <group-name>. BGP peer groups and neighbor settings are configured under the 'protocols bgp group' hierarchy in Junos.

Answer

routing-options autonomous-system

Answer

interfaces <interface-name> unit 0 family inet bgp

Answer

policy-options community