JNCIP-ENT BGP Advanced — 10 Questions

Question 1

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 2

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

Accepted Answer

no-export. The NO_EXPORT well-known community instructs a BGP peer not to advertise the affected route to any external BGP peers.

Answer

no-peer

Answer

local-as

Answer

no-advertise

Question 3

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?

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 4

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?

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 5

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 6

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 'show route protocol bgp next-hop' command displays all BGP next hops and indicates whether they are resolved in the routing table.

Answer

show bgp neighbor detail

Answer

show route forwarding-table destination

Answer

show bgp summary

Question 7

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 8

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 9

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 10

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.