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CCNA BGP Advanced Questions

37 questions · BGP Advanced · All types, answers revealed

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1
Multi-Selecteasy

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

Select 2 answers
A.COMMUNITIES
B.MULTI_EXIT_DISC
C.AS_PATH
D.LOCAL_PREF
E.NEXT_HOP
AnswersC, E

AS_PATH is a well-known mandatory attribute, so every BGP implementation must recognise it and it must appear in every UPDATE message. It records the sequence of autonomous systems a route traverses, satisfying the stem's requirement for attributes recognised by all implementations and present in all updates.

Why this answer

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.

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2
MCQeasy

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?

A.Setting the MED attribute to zero on all incoming EBGP updates.
B.BGP multipath with the 'as-path-relax' or equivalent multipath options enabled.
C.Configuring static routes with identical preferences for every BGP prefix.
D.Enabling BGP Route Reflection on the local routing engine.
AnswerB

Relaxing strict AS path or IGP cost checks allows multipath load balancing across paths with different metrics.

Why this answer

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.

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3
MCQeasy

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

A.show route protocol bgp extensive
B.show bgp group summary
C.show bgp neighbor extensive
D.show route forwarding-table protocol bgp
AnswerA

`show route protocol bgp extensive` satisfies the requirement to display active BGP routes with their communities. The `extensive` modifier expands each route's detail, including the Communities attribute, whereas the default `show route protocol bgp` output omits community values entirely. This makes it the precise command for viewing both routes and their associated communities together.

Why this answer

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

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4
MCQhard

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?

A.It removes the Originator ID and replaces the Cluster List with its own cluster ID.
B.It increments the Originator ID value by one and clears the Cluster List.
C.It leaves the Originator ID intact and appends its own cluster ID to the Cluster List.
D.It clears both the Originator ID and Cluster List to reset loop detection for the local cluster.
AnswerC

The RR preserves the Originator ID and adds its local cluster ID to the front of the Cluster List.

Why this answer

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

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5
MCQhard

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?

A.BGP Link-State (BGP-LS) topology databases.
B.Multiprotocol Label Switching (MPLS) label imposition without routing table participation.
C.Recursive lookups through the routing table using the active IGP or static route entries.
D.Address Resolution Protocol (ARP) directly against the BGP peer IP address.
AnswerC

Junos resolves an indirect BGP next hop by performing recursive route lookups, walking the routing table until it reaches a directly connected next hop learned via an active IGP or static route, which is the constraint the stem specifies.

Why this answer

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.

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6
MCQmedium

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?

A.MED comparison and router ID tie-breakers
B.AS Path prepending and local preference manipulation
C.TTL security decrement and loose reverse path forwarding
D.Cluster List and Originator ID attributes
AnswerD

The route reflector prepends its cluster ID to the Cluster List and inserts the originating client's router ID into the Originator ID attribute. Receiving peers detect their own cluster or originator in these attributes and discard the route, preventing iBGP loops.

Why this answer

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.

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7
MCQmedium

You are the network architect for a service provider that offers BGP/MPLS IP VPNs to enterprise customers. A customer reports that routes from one of its sites are being leaked into the global Internet table of a remote provider edge (PE) router. You have already verified that the VRF import policy on the remote PE is correct and that the route target (RT) communities are properly assigned. Which Junos configuration on the originating PE router is the most likely cause of the route leak?

A.The PE router has a 'rib-groups' configuration that imports the customer's VPN routes into the inet.0 table, and the export policy to the remote PE allows those routes.
B.The export policy applied under the customer's routing instance uses a 'then accept' term that matches all routes, including the global table, and the instance is configured with 'vrf-table-label'.
C.The customer's CE router is advertising the same prefixes with a different route distinguisher (RD) than the one configured on the PE.
D.The BGP session to the remote PE is configured with 'family inet-vpn unicast' instead of 'family inet unicast'.
AnswerA

A rib-group that imports routes from a VPN routing instance into inet.0 makes them part of the global table. If the BGP export policy then advertises them to the remote PE, they will appear as global Internet routes, causing the leak. This is a common misconfiguration when trying to share routes between instances.

Why this answer

Routes leak into the global table when they are copied from a VPN instance into inet.0, typically via a rib-group import. The export policy then advertises them as global routes. The other options describe features that either are correct for VPNs or do not cause global leakage.

The key is that the rib-group makes the customer routes part of the main routing table, and the export policy sends them out.

Exam trap

The trap here is assuming that a permissive VRF export policy alone causes global route leaks, when the real issue is the rib-group that imports VPN routes into inet.0.

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8
Multi-Selecthard

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

Select 3 answers
A.The BGP next-hop IP address is automatically rewritten to the local router loopback address by default for eBGP.
B.The resolved next-hop information along with the egress interface and MAC address are installed into the forwarding table.
C.Junos checks the active routing table (RIB) to find a resolving route for the BGP next-hop IP address.
D.Junos automatically ignores next-hop resolution if multipath is enabled.
E.If the next-hop IP address resolves to a discard or reject route, the BGP route is considered unusable and is hidden.
AnswersB, C, E

Once resolved, the forwarding plane programs the next hop with specific interface and adjacency details.

Why this answer

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.

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9
MCQmedium

An enterprise network uses BGP route reflection. The design team has deployed two route reflectors in the same cluster for redundancy, with all client routers peering to both route reflectors. After a link failure, some clients receive duplicate route advertisements. Which BGP attribute is used to prevent routing loops within a route reflection cluster, and how does it function?

A.ORIGINATOR_ID — it identifies the originating router, and a route reflector discards a route if it sees its own router ID as the originator.
B.AS_PATH — it records the autonomous systems a route has traversed, and a route reflector discards a route if its own AS number appears in the path.
C.CLUSTER_LIST — it records the cluster IDs of route reflectors that a route has traversed, and a route reflector discards a route if its own cluster ID is already present.
D.MULTI_EXIT_DISC (MED) — it carries metric information and is used to prevent loops by comparing metrics across multiple route reflectors.
AnswerC

CLUSTER_LIST is the BGP path attribute specifically designed to prevent loops within a route reflection cluster. When a route reflector reflects a route, it prepends its cluster ID. If a route reflector receives a route whose CLUSTER_LIST already contains its own cluster ID, it discards the route, preventing loops and duplicate advertisements among redundant route reflectors in the same cluster.

Why this answer

The CLUSTER_LIST attribute is the mechanism that prevents routing loops when multiple route reflectors serve the same cluster. Each route reflector prepends its cluster ID to the CLUSTER_LIST when reflecting a route. If a route reflector receives a route that already contains its own cluster ID in the CLUSTER_LIST, it discards the route.

This ensures that a route cannot loop back to a route reflector that has already processed it, even if multiple route reflectors exist in the same cluster.

Exam trap

The trap here is confusing ORIGINATOR_ID with CLUSTER_LIST; while ORIGINATOR_ID prevents a route from being reflected back to its originator, CLUSTER_LIST specifically prevents loops between multiple route reflectors in the same cluster.

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10
MCQeasy

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

A.routing-options autonomous-system
B.interfaces <interface-name> unit 0 family inet bgp
C.protocols bgp group <group-name>
D.policy-options community
AnswerC

The protocols bgp group hierarchy defines a named peer group, letting common BGP parameters and policies be applied once to many neighbours. This satisfies the stem's requirement to simplify neighbour configuration through a single reusable group definition.

Why this answer

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

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11
MCQmedium

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?

A.Yes, all routes received by a route reflector are reflected to all peers regardless of client status.
B.No, route reflectors never reflect routes received from any IBGP peer.
C.No, routes received from a non-client peer are only reflected to client peers, not to other non-client peers.
D.Yes, provided the routes contain the same Cluster ID as the receiving non-client peer.
AnswerC

Route reflection follows client and non-client roles: a route learned from a non-client IBGP peer is reflected only to client peers, never to other non-clients. This prevents the non-client-to-non-client advertisement that full-mesh IBGP would otherwise require.

Why this answer

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.

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12
MCQeasy

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?

A.set routing-options community-list CUSTOM-COMM value 65000:100
B.set protocols bgp group external community CUSTOM-COMM 65000:100
C.set policy-options community CUSTOM-COMM members 65000:100
D.set policy-options policy-statement CUSTOM-COMM community 65000:100
AnswerC

Defining the community under policy-options with the members statement creates a named community object holding the value 65000:100, which policy terms can then match or apply to BGP routes. This satisfies the stem's requirement for a correctly named community using the Junos policy framework.

Why this answer

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.

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13
Multi-Selecthard

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

Select 2 answers
A.Sub-AS numbers are included in AS_CONFED_SEQUENCE attributes and are stripped when exiting the confederation.
B.External peers outside the confederation treat the confederation as a single autonomous system.
C.BGP multipath cannot be enabled across different member ASNs within the same confederation.
D.MED values are automatically removed across member AS boundaries regardless of configuration.
E.Local preference is discarded when passing routes between different member ASNs inside the confederation.
AnswersA, B

Confederation member ASNs are encapsulated in AS_CONFED segments and stripped at the outer boundary.

Why this answer

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.

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14
Multi-Selecteasy

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

Select 2 answers
A.Modifying the local preference attribute of incoming IBGP routes.
B.Dynamically altering the BGP session TCP handshake port numbers.
C.Filtering routes based on AS path regular expressions.
D.Adjusting the BGP keepalive timer values dynamically via policy match actions.
E.Manually assigning physical interface MTU sizes for BGP sessions.
AnswersA, C

BGP routing policies can set or modify local preference on incoming IBGP routes, influencing outbound path selection within the local autonomous system. This satisfies the stated action, since local preference is a well-known BGP attribute adjustable via policy.

Why this answer

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.

Exam trap

JNCIP-ENT often tests the confusion between routing policy capabilities and neighbor/interface configuration, tempting candidates to select options about timers, ports, or MTU that are not policy-controlled.

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15
MCQeasy

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?

A.BGP confederation member AS boundaries only
B.Both EBGP and IBGP peers equally
C.External BGP (EBGP) peers only
D.Internal BGP (IBGP) peers only
AnswerD

Local Preference is a well-known discretionary attribute propagated only across IBGP sessions within an autonomous system; it is not advertised to EBGP peers. This satisfies the stem by confirming that IBGP peers alone evaluate and exchange the attribute.

Why this answer

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

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16
MCQmedium

An administrator is configuring BGP multipath on a Junos router. The router has two BGP paths to the same destination: one with a MED of 100 and another with a MED of 200. Both paths are from the same neighboring AS. The administrator wants both paths to be installed in the forwarding table for load balancing. Which configuration is required?

A.Configure 'multipath' under BGP and set the 'med' to 'always-compare'.
B.Configure 'multipath multiple-as' under BGP and set the MED to the same value on both paths.
C.Enable multipath under the BGP group and ensure that the paths have the same MED.
D.Enable multipath under BGP and ensure that the paths have the same MED by using a routing policy to set MED to a common value.
AnswerD

BGP multipath requires that the paths have equal MED values. By using a routing policy to set the MED to the same value on both paths, and enabling multipath under BGP, the router can install both paths for load balancing. This is the correct approach.

Why this answer

For BGP multipath to install multiple paths, the paths must be equal in terms of MED, among other attributes. If MED values differ, they are not eligible for multipath. The solution is to enable multipath and use a routing policy to set the MED to a common value on both paths, making them equal.

This allows the router to load-balance traffic across both paths.

Exam trap

The trap here is assuming that simply enabling multipath will work even with different MED values, but BGP multipath requires equal MED (and other attributes) to consider paths as equal.

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17
MCQeasy

Which BGP attribute is used to prevent routing loops in a BGP confederation?

A.ORIGINATOR_ID
B.AS_PATH
C.CLUSTER_LIST
D.AS_CONFED_SEQUENCE
AnswerD

AS_CONFED_SEQUENCE is a BGP attribute used within a confederation to record the sub-AS numbers that a route has traversed. It functions similarly to AS_PATH but is only used within the confederation. When a route leaves the confederation, the AS_CONFED_SEQUENCE is removed and replaced with the confederation identifier in the AS_PATH. This attribute prevents loops within the confederation by allowing routers to detect if a route has already passed through their sub-AS.

Why this answer

In a BGP confederation, the AS_CONFED_SEQUENCE attribute is used to prevent loops within the confederation. It records the sub-AS numbers that a route has traversed. When a router receives a route with its own sub-AS number in the AS_CONFED_SEQUENCE, it detects a loop and rejects the route.

This attribute is only used internally within the confederation and is stripped when advertising to external peers. The other attributes serve different purposes.

Exam trap

The trap here is confusing the loop prevention mechanisms of route reflection (CLUSTER_LIST, ORIGINATOR_ID) with those of BGP confederations (AS_CONFED_SEQUENCE).

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18
MCQmedium

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?

A.show route resolution
B.show bgp summary
C.show bgp group
D.show route advertising-protocol bgp
AnswerA

The 'show route resolution' command displays how the routing table resolves next hops, including unresolved BGP next hops and their underlying IGP or static routes. This directly satisfies the need to troubleshoot why the BGP next hop is not being resolved.

Why this answer

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.

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19
MCQmedium

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?

A.To force the external peer to drop all updates due to an AS path loop check failure.
B.To enable BGP multipath load balancing across multiple external links.
C.To establish a confederation sub-AS relationship with the external provider.
D.To artificially increase the AS path length attribute to make this path less preferred by inbound traffic.
AnswerD

Prepending repeats the local AS number in the AS path, lengthening it so remote BGP speakers applying shortest-path selection deprioritise this route. This satisfies the stated objective of making the path less preferred for inbound traffic from the external provider.

Why this answer

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.

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20
MCQmedium

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

A.They require explicit configuration of every member AS in their own EBGP import filters.
B.They see all member AS numbers prepended individually in the AS path.
C.They see only the top-level confederation AS number in the AS path attribute.
D.They reject all updates originating from a confederation due to AS path validation failures.
AnswerC

External peers receive routes with only the confederation's top-level AS number in the AS path; sub-AS numbers are stripped when advertisements cross the confederation boundary. This satisfies the stem's constraint that outside peers remain unaware of internal sub-AS structure, preserving standard eBGP behaviour without requiring reconfiguration on external routers.

Why this answer

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.

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21
MCQhard

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?

A.as-number:identifier
B.large-community:global_administrator:local_data1:local_data2
C.target:as-number:identifier
D.ipv4-address:identifier
AnswerB

Junos uses the three-part format for defining large communities.

Why this answer

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

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22
MCQeasy

Which BGP community is a well-known transitive community used to prevent a route from being advertised outside of a local autonomous system?

A.no-peer
B.local-as
C.no-export
D.no-advertise
AnswerC

The well-known no-export community prevents a route from being advertised beyond the local autonomous system, including to confederation peers. It is transitive, so it propagates between internal BGP speakers while still blocking external advertisement, matching the stem's constraint.

Why this answer

The NO_EXPORT well-known community instructs a BGP peer not to advertise the affected route to any external BGP peers.

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23
MCQhard

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?

A.Hashing selected packet header fields to compute an index into the set of resolved BGP next hops.
B.Using the lowest MED value among the multipath entries for every packet transmission.
C.Consulting the BGP Route Reflector cluster list to determine the optimal egress port.
D.Round-robin packet scheduling across all available BGP next hops regardless of flow headers.
AnswerA

Junos hashes selected packet header fields, such as source and destination addresses, to produce an index into the set of resolved BGP next hops. This satisfies the equal-cost forwarding requirement by distributing traffic across the multiple paths rather than pinning one interface.

Why this answer

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.

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24
MCQhard

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?

A.The confederation AS number is prepended to the front of the path, removing all member AS numbers.
B.The member AS numbers are completely stripped and replaced by the confederation AS number.
C.The route is dropped by the receiving member AS due to an inter-AS loop prevention violation.
D.The member AS numbers are placed in AS_CONFED_SEQUENCE segments and are not treated as external AS hops.
AnswerD

Within a confederation, routes crossing member AS boundaries carry AS_CONFED_SEQUENCE segments rather than ordinary AS_SEQUENCE entries. Member numbers 65001 and 65002 are recorded there and are not counted as external AS hops, so loop detection and path length treat the confederation as one AS.

Why this answer

Confederation member AS numbers are included in the AS_CONFED_SEQUENCE attribute and are stripped when the route exits the confederation boundary.

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25
MCQmedium

You are the network architect for a large enterprise that uses BGP route reflectors (RRs) in a single cluster. You want to ensure that when an RR receives a route from a client, it reflects that route to other clients but does not reflect it back to the originating client. Which BGP attribute or mechanism prevents the route from being reflected back to the originating client?

A.ORIGINATOR_ID
B.NEXT_HOP
C.CLUSTER_LIST
D.AS_PATH
AnswerA

ORIGINATOR_ID is set by the first route reflector to the router ID of the iBGP speaker that injected the route into the AS. When the route is reflected back to that originating client, the client sees its own router ID in the ORIGINATOR_ID attribute and rejects the route, preventing a loop. This is the standard BGP route reflection loop-prevention mechanism defined in RFC 4456.

Why this answer

In BGP route reflection, the ORIGINATOR_ID attribute is set by the first route reflector to the router ID of the iBGP speaker that originated the route. When a route reflector reflects a route, it includes the ORIGINATOR_ID. If the route is reflected back to the originating client, that client recognizes its own router ID and discards the route, preventing a loop.

CLUSTER_LIST prevents loops between clusters, not back to the originating client.

Exam trap

The trap here is confusing the roles of ORIGINATOR_ID and CLUSTER_LIST, assuming that CLUSTER_LIST prevents reflection back to the originating client.

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26
MCQmedium

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?

A.The peer IP addresses must reside on the exact same subnet.
B.The IGP metric to the BGP next hop must be identical for all participating paths.
C.The advertising router IDs must be identical.
D.The cluster lists must be completely empty.
AnswerB

Junos BGP multipath requires equal IGP metrics to each BGP next hop; differing interior costs make paths ineligible as candidates. This condition ensures traffic is distributed across next hops reachable at equivalent cost, satisfying the stem's multipath requirement.

Why this answer

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).

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27
MCQhard

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?

A.During the initial import processing from EBGP peers before next-hop resolution.
B.When advertising routes to a BGP peer, after the best path has been chosen.
C.Before the best path is selected, affecting the local routing table calculation.
D.During the route selection algorithm right after MED comparison.
AnswerB

Junos applies export policy after the route selection process has installed the best path in the routing table, so as-path prepend and community matching only affect what is advertised to the peer, never the local decision.

Why this answer

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

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28
Multi-Selecthard

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)

Select 2 answers
A.The BGP next-hop IP address matches a directly connected interface subnet on the router.
B.The BGP neighbor session is established over a loopback interface using multihop.
C.The resolving route has an active loop-free alternate backup path installed.
D.The resolving route in the IGP routing table points to a discard or reject dead-end route.
E.No active route exists in the routing table to reach the BGP next-hop address.
AnswersD, E

Discard or reject resolving routes invalidate BGP next-hop resolution.

Why this answer

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

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29
Multi-Selectmedium

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

Select 3 answers
A.A route reflector must never reflect routes received from a non-client peer back to other non-client peers.
B.Clients of a route reflector must be configured in a full iBGP mesh with each other.
C.Route reflectors automatically modify the AS_PATH attribute of all reflected routes.
D.The Originator ID attribute is added by the route reflector to prevent routing loops from client peers.
E.Redundant route reflectors within the same cluster must be configured with the same cluster ID.
AnswersA, D, E

Standard iBGP full-mesh rules apply between non-client peers; a route reflector reflects routes from clients to all clients and non-clients, and from non-clients to clients only.

Why this answer

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.

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30
MCQhard

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?

A.Junos compares MEDs from different ASs when the AS path lengths are completely identical.
B.Junos compares MEDs from different ASs only when the 'always-compare-med' statement is configured under protocols bgp.
C.Junos never compares MEDs from different ASs under any circumstance.
D.Junos compares MEDs from different ASs automatically if the routes share the same IGP metric.
AnswerB

By default Junos only compares MED between paths from the same neighbouring AS, so MEDs from different autonomous systems are ignored. Configuring always-compare-med under protocols bgp forces Junos to evaluate MED across all paths regardless of originating AS, satisfying the scenario's cross-AS comparison requirement.

Why this answer

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

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31
MCQhard

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?

A.It accepts the update and appends its own router ID to the ORIGINATOR_ID attribute.
B.It rejects the update because the ORIGINATOR_ID matches its own router ID.
C.It rejects the update because the CLUSTER_LIST already contains its own cluster ID.
D.It accepts the update because the CLUSTER_LIST does not contain its own cluster ID.
AnswerC

Both route reflectors are configured with the same cluster ID (10.0.0.1), so when the client reflects the route, the CLUSTER_LIST contains 10.0.0.1. When 10.0.0.2 receives the update, it detects its own cluster ID in the CLUSTER_LIST and discards the route, preventing a routing loop within the cluster. This is the standard BGP route reflection loop-prevention mechanism.

Why this answer

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.

Exam trap

The trap here is assuming that the CLUSTER_LIST check compares router IDs, when it actually compares the configured cluster ID, which is shared by all route reflectors in the same cluster.

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32
MCQmedium

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?

A.Multipath requires BGP prefix-independent convergence (PIC) to be explicitly enabled on all routing engines.
B.The next hops must be directly connected interfaces without relying on IGP resolution.
C.All paths must originate from the exact same autonomous system in the AS path attribute.
D.All competing BGP paths must have identical AS path lengths, local preference, origin, and MED.
AnswerD

Junos installs multiple BGP paths for a prefix only when they are equal-cost: identical AS path length, local preference, origin and MED. If any of these attributes differ, path selection picks a single best route and multipath remains inactive despite the configuration.

Why this answer

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.

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33
MCQmedium

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?

A.Configure the aggregate route with the 'summary-only' parameter under routing-options bgp.
B.Enable BGP dampening on the aggregate route and disable it on the component routes.
C.Apply a routing policy that sets the NO_EXPORT community on all component routes.
D.Configure an aggregate route with the 'discard' policy and apply an export policy that drops component routes.
AnswerA

The 'summary-only' parameter suppresses specific component routes when advertising the aggregate prefix.

Why this answer

Using the 'aggregate' statement with the 'summary-only' option generates the aggregate prefix and suppresses all component specific routes.

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34
MCQhard

You are troubleshooting a Junos router that is not selecting the expected BGP path for a prefix. The router receives the prefix from two eBGP peers. Peer A sends the route with a MED of 50 and an AS path length of 3. Peer B sends the same prefix with a MED of 100 and an AS path length of 2. Both peers are in the same neighboring AS. The router is configured with 'multipath multiple-as' and 'bgp multipath' under the global BGP hierarchy. Which path will be selected as best, and why?

A.The path from Peer A, because MED is always compared before AS path length when the peers are in the same neighboring AS.
B.The path from Peer A, because MED is compared before AS path length in the BGP path selection algorithm.
C.Both paths are installed in the forwarding table because multipath is enabled, and traffic is load-balanced.
D.The path from Peer B, because AS path length is compared before MED, and the shorter AS path wins.
AnswerD

In Junos BGP path selection, the AS path length is compared before MED. Peer B has an AS path length of 2, which is shorter than Peer A's length of 3. Therefore, Peer B's path is preferred, and MED is not considered. This is the correct order unless additional configuration changes the default behavior.

Why this answer

Junos BGP path selection compares AS path length before MED. Since Peer B advertises a shorter AS path, its path is selected as best. Multipath is not used because the paths are not equal.

The MED value is irrelevant in this comparison because the AS path lengths differ. This order is consistent with the BGP specification and Junos implementation.

Exam trap

The trap here is believing that MED is compared before AS path length when peers are in the same AS, but the AS path length always takes precedence.

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35
Multi-Selectmedium

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

Select 3 answers
A.Cluster List length
B.Weight (local to the router)
C.Local Preference
D.MED (Multi-Exit Discriminator)
E.Originator ID value
AnswersB, C, D

Weight is evaluated first in Junos BGP path selection.

Why this answer

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

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36
MCQmedium

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?

A.AS Path Prepend count
B.Local Preference value
C.Cluster ID
D.Router ID
AnswerC

The cluster ID identifies the route-reflection cluster, and every route reflector within it must share the same value. When a route reflector receives an update carrying its own cluster ID in the CLUSTER_LIST attribute, it discards that route, preventing loops between redundant reflectors. Differing cluster IDs would defeat this loop detection.

Why this answer

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.

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37
MCQmedium

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?

A.The penalty value is locked at the reuse threshold value indefinitely.
B.The penalty value is doubled to discourage further flapping.
C.The penalty value is instantly reset to zero.
D.The penalty value continues to decay exponentially until it drops to zero.
AnswerD

Exceeding the reuse threshold triggers route re-advertisement, but the penalty keeps decaying exponentially toward zero rather than resetting. The stem's constraint concerns post-reuse behaviour, and Junos applies the same exponential half-life decay throughout suppression and after unsuppression, so the penalty only reaches zero once sufficient time elapses.

Why this answer

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.

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