JNCIP-ENT BGP Advanced Practice Test 2 — 15 Questions

Question 1

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?

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

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 2

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 3

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 4

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 5

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.

Question 6

A service provider uses BGP confederations to reduce iBGP mesh complexity. An engineer is configuring a Junos router in sub-AS 65001 that peers with a router in sub-AS 65002. The engineer wants to ensure that the AS_PATH attribute behaves correctly across the confederation boundary. Which statement is correct about AS_PATH handling in BGP confederations?

Accepted Answer

When advertising routes to a peer outside the confederation, the confederation ID is prepended to the AS_PATH, and the sub-AS numbers are removed.. In BGP confederations, when a router advertises a route to an external peer outside the confederation, it prepends the confederation ID to the AS_PATH and removes all sub-AS numbers. This makes the confederation appear as a single autonomous system to external peers. Within the confederation, sub-AS numbers are used for loop prevention but are not prepended in the same manner as external AS numbers. This design reduces the iBGP mesh while maintaining proper AS_PATH behavior.

Answer

When advertising routes to a peer in a different sub-AS within the same confederation, the confederation ID is prepended to the AS_PATH.

Answer

When advertising routes to a peer in a different sub-AS within the same confederation, the local sub-AS number is prepended to the AS_PATH.

Answer

When advertising routes to a peer outside the confederation, the sub-AS numbers are retained in the AS_PATH along with the confederation ID.

Question 7

An engineer is configuring a BGP confederation on Junos devices to reduce iBGP mesh complexity. The confederation consists of sub-AS 65001 and 65002, with the confederation ID 100. Which statement correctly describes the behavior of BGP attributes across confederation boundaries?

Accepted Answer

The AS_PATH attribute is modified: sub-AS numbers are removed when advertising to peers outside the confederation, and the confederation ID is prepended.. In a BGP confederation, sub-AS numbers are treated like internal AS numbers. When advertising to external peers outside the confederation, the sub-AS numbers are stripped from the AS_PATH, and the confederation ID is prepended. This allows the confederation to appear as a single AS to the outside world. LOCAL_PREF is propagated within the confederation, and NEXT_HOP is not automatically changed.

Answer

The NEXT_HOP attribute is always changed to the local interface address when crossing sub-AS boundaries.

Answer

The AS_PATH attribute is preserved across confederation boundaries, and the confederation ID is prepended.

Answer

The LOCAL_PREF attribute is not propagated between sub-AS within the confederation.

Question 8

You are configuring a Junos router to advertise a default route to an eBGP peer only if the router has a valid route to 0.0.0.0/0 in its routing table. You want to avoid advertising the default route if the upstream link fails. Which configuration approach accomplishes this?

Accepted Answer

Use a policy with a condition that checks for the existence of a specific route, such as a loopback or a summary route, and then advertise the default route.. Junos policies support route existence conditions. By referencing a route that tracks the upstream link, such as a specific prefix learned via the upstream, you can advertise the default route only when that route is present. This provides conditional advertisement. The other options either advertise unconditionally or affect the wrong direction of routing.

Answer

Create a static route to 0.0.0.0/0 with a next-hop of 'discard' and a policy that advertises it unconditionally.

Answer

Apply an import policy on the eBGP peer that accepts only the default route and rejects all other routes.

Answer

Configure a BGP export policy that matches the default route and set the 'next-hop' to 'self'.

Question 9

You are configuring BGP on a Juniper Networks router and want to ensure that the router does not advertise any BGP routes to a specific EBGP peer until the BGP session is fully established and the peer has sent its initial routes. Which BGP feature should you configure?

Accepted Answer

advertise-bgp. In Junos, the 'advertise-bgp' feature under BGP configuration controls the advertisement of BGP routes. When enabled, it delays the advertisement of BGP routes until the BGP session is established and the peer has sent its initial routes. This prevents the router from advertising routes that the peer may not be ready to handle, avoiding potential blackholing. The other options are unrelated to this timing control.

Answer

damping

Answer

advertise-inactive

Answer

hold-time

Question 10

An administrator is configuring BGP route reflection on a Junos router. The router is a route reflector with several clients. The administrator wants to ensure that the route reflector does not reflect routes back to the client from which they were received. Which BGP attribute or mechanism prevents this behavior?

Accepted Answer

ORIGINATOR_ID — the route reflector checks this attribute and does not advertise a route back to the client whose router ID matches the ORIGINATOR_ID.. The ORIGINATOR_ID attribute is used to prevent a route reflector from reflecting a route back to the client that originated it. When a route is first injected into the iBGP mesh, the route reflector sets the ORIGINATOR_ID to the router ID of the originating client. If the route reflector later receives a route with an ORIGINATOR_ID matching one of its clients, it will not advertise that route back to that client. This prevents routing loops and unnecessary advertisements.

Answer

AS_PATH — the route reflector checks the AS_PATH and does not advertise a route back to a client if the client's AS number is in the path.

Answer

CLUSTER_LIST — the route reflector checks this attribute and does not advertise a route back to any client if the cluster ID is present.

Answer

NEXT_HOP — the route reflector checks the NEXT_HOP attribute and does not advertise a route back to a client if the next hop is the client itself.

Question 11

You are deploying a route reflector (RR) cluster in a large iBGP network. You have two RRs in the same cluster serving multiple clients. Which two statements are true about the operation of BGP route reflection in this scenario? (Choose two.)

Accepted Answer

The originator ID attribute is used to prevent loops when a route is reflected back to the originating client.. In a route reflection cluster, all RRs must use the same cluster ID to prevent loops. The originator ID attribute is used to prevent a route from being reflected back to its originator. These two mechanisms work together to ensure loop-free operation. The other statements are incorrect because they either misstate the reflection rules or suggest configurations that are not required.

Answer

A route reflector will reflect a route to all clients and nonclients, except the one from which it was received.

Answer

Routes reflected from one RR to another RR in the same cluster are allowed and do not require additional loop prevention.

Answer

A route reflector must be configured with a full mesh of iBGP sessions to all clients and nonclients.

Question 12

An operator is configuring BGP route reflection on a Junos router. The router is a route reflector for clients in cluster 1.2.3.4. The operator wants to ensure that routes received from a client are reflected to other clients and non-clients, but not back to the originating client. Which configuration is required?

Accepted Answer

Ensure that the route reflector is configured with the 'cluster' statement and that the originator ID is set automatically.. In Junos, when a route reflector reflects a route received from a client, it automatically adds the originator ID (the router ID of the client). The route reflector will not reflect the route back to that client, preventing loops. The cluster ID must be configured to identify the cluster. No additional policy is needed for this basic behavior.

Answer

Enable the 'no-client-reflect' statement under the BGP group.

Answer

Configure the cluster ID as the router ID.

Answer

Configure a policy to filter routes based on the neighbor address.

Question 13

You are configuring a Junos router to perform BGP multipath load balancing. You have two paths to the same destination: one from an eBGP peer and one from an iBGP peer. The eBGP path has a lower MED than the iBGP path. You have enabled 'multipath' under the BGP configuration. Will both paths be installed in the forwarding table?

Accepted Answer

No, because eBGP paths are always preferred over iBGP paths, and multipath cannot override this preference.. BGP path selection prefers eBGP paths over iBGP paths before considering multipath. Even with multipath enabled, only paths that are equal up to the multipath tie-breaker can be installed. Since one path is eBGP and the other is iBGP, they are not equal, and only the eBGP path is installed. The MED difference is irrelevant because the eBGP preference takes precedence.

Answer

Yes, because the lower MED on the eBGP path makes it equal to the iBGP path for multipath purposes.

Answer

No, because the iBGP path has a higher MED and is therefore not eligible for multipath.

Answer

Yes, because multipath is enabled and both paths are considered equal if they have the same AS path length and origin.

Question 14

A Juniper Networks router is configured with BGP and you want to implement BGP route reflection. You have a cluster with two route reflectors for redundancy. Which two statements are correct regarding the configuration of multiple route reflectors in the same cluster? (Choose two.)

Accepted Answer

Each route reflector in the cluster must have a unique router ID.. When deploying multiple route reflectors in the same cluster, they must share the same cluster ID to ensure consistent loop prevention via the CLUSTER_LIST attribute. Additionally, each route reflector must have a unique router ID because the router ID is used in the ORIGINATOR_ID attribute to prevent loops. These two conditions are essential for correct operation. Full mesh between route reflectors is not required, and the cluster ID can be the same as a router ID, so those options are incorrect.

Answer

All route reflectors in the same cluster must be in the same autonomous system.

Answer

The cluster ID must be different from the router ID of any route reflector in the cluster.

Answer

Route reflectors in the same cluster must be fully meshed with each other.

Question 15

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