CCNA BGP Questions

MCQeasy

An administrator wants to modify the Local Preference attribute for all routes received from a specific external BGP peer. Where must this policy be applied in Junos?

A.Import policy applied to the eBGP neighbor or group

B.Export policy applied to the eBGP group

C.Forwarding plane firewall filter

D.Global system-level static route policy

AnswerA

Import policies applied to eBGP peers can set local-preference since it is an iBGP attribute applied upon entry.

Why this answer

Inbound routing policies on Junos affect attributes like Local Preference before path selection occurs.

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Multi-Selectmedium

Which TWO characteristics describe eBGP compared to iBGP? (Choose two)

Select 2 answers

A.Automatic route reflection enabled by default

B.Must reside within the same Autonomous System

C.Peers reside in different Autonomous Systems

D.Default TTL of 1

E.Default Local Preference of 200

AnswersC, D

eBGP connects different ASes.

Why this answer

eBGP peers are typically in different Autonomous Systems and have a default TTL of 1, whereas iBGP peers are in the same AS and have a default TTL of 255.

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MCQmedium

An administrator is configuring eBGP between two Junos devices and notices the session is stuck in the Active state. The direct connection is up, and ping succeeds. Which Junos configuration parameter is most likely missing to resolve this issue?

A.set protocols bgp group ebgp type internal

B.set protocols bgp group ebgp multihop

C.set protocols bgp group ebgp peer-as 65002 multipath

D.set protocols bgp group ebgp local-address 192.168.1.1

AnswerB

The multihop statement increases the TTL allowing eBGP sessions to establish over non-directly connected interfaces like loopbacks.

Why this answer

When establishing eBGP, Junos defaults to expecting the peer to be directly connected with a TTL of 1. If connecting via loopback interfaces or a multi-hop path, the multihop statement is required.

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MCQhard

A Junos router receives four identical routes via BGP. Reviewing the routing table, path selection picked route 3. Route 1 has a lower MED, Route 2 has a higher Local Preference, Route 4 is from an eBGP peer while Route 3 is iBGP. Assuming standard default path selection, why was Route 3 chosen over Route 4?

A.Route 3 had a lower router ID than Route 4.

B.Route 3 had a lower MED value.

C.Junos prefers iBGP paths over eBGP paths during the tie-breaking steps.

D.Route 3 was received from a peer with a lower peer IP address.

AnswerC

Junos path selection prefers internal paths over external paths if all prior metrics are identical.

Why this answer

In Junos BGP path selection, after comparing local preference, AS path length, origin type, and MED, Junos prefers internal (iBGP) paths over external (eBGP) paths, provided all other tie-breakers are equal.

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Multi-Selecthard

Which THREE statements describe the role and function of the BGP Router ID? (Choose three)

Select 3 answers

A.It automatically replaces the AS_PATH attribute if missing.

B.It is exchanged during the BGP OPEN message negotiation phase.

C.It is used as a final tie-breaker in the BGP path selection algorithm.

D.It must be identical across all routers within the same Autonomous System.

E.It is a 32-bit identifier represented in dotted-quad notation.

AnswersB, C, E

The router ID is communicated in the OPEN message.

Why this answer

The Router ID is a 32-bit identifier chosen during startup, used as a tie-breaker in BGP path selection, and included in OPEN messages.

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MCQmedium

During troubleshooting of a flapping BGP session, you notice BGP Notification messages being sent. Which BGP message type is responsible for tearing down a session due to an error condition?

A.KEEPALIVE

B.UPDATE

C.OPEN

D.NOTIFICATION

AnswerD

NOTIFICATION messages are sent to report errors and immediately tear down the BGP peering session.

Why this answer

The Notification message is sent when an error is detected, causing the BGP connection to close immediately.

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Multi-Selecthard

When troubleshooting a BGP routing loop or unexpected route suppression, which THREE Junos operational commands provide visibility into BGP path attributes and decision processes? (Choose three)

Select 3 answers

A.show ldp database

B.show route extensive

C.show bgp neighbor

D.show route protocol bgp

E.show ospf interface

AnswersB, C, D

Show route extensive reveals detailed path attributes, AS_PATH, MED, and route preference details.

Why this answer

Detailed route inspection and BGP neighbor debugging commands include 'show route extensive', 'show bgp neighbor', and 'show route protocol bgp'.

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MCQmedium

A network operator needs to peer two routers in different Autonomous Systems that are not directly connected. Security policy mandates that TTL security checks be bypassed. Which command satisfies this requirement for the BGP session?

A.set protocols bgp group ebgp hold-time 180

B.set protocols bgp group ebgp multihop ttl 255

C.set protocols bgp group ebgp passive

D.set protocols bgp group ebgp disable-ttl-drop

AnswerB

Configuring multihop sets an appropriate TTL for non-directly connected eBGP sessions.

Why this answer

TTL security can be bypassed or adjusted using multihop or adjusting the ttl value directly.

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MCQmedium

What is the purpose of the BGP Keepalive message and what is its default interval in Junos?

A.To maintain the session; sent every 30 seconds by default.

B.To report session errors; sent immediately upon failure.

C.To negotiate capabilities; sent every 60 seconds.

D.To update routing tables; sent every 5 seconds.

AnswerA

Keepalives keep the session alive and default to every 30 seconds in Junos (derived from a 90-second hold time).

Why this answer

Keepalive messages are sent periodically to maintain the BGP session when no UPDATE messages are sent. Default hold time is 90 seconds, and keepalive is 30 seconds.

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Multi-Selecthard

When evaluating the BGP path selection algorithm on a Junos device, which THREE attributes are evaluated BEFORE the router considers the IGP metric to the BGP next hop? (Choose three)

Select 3 answers

A.IGP metric to next hop

B.Router ID

C.Multi-Exit Discriminator (MED)

D.AS path length

E.Local Preference

AnswersC, D, E

MED is evaluated after origin type and before iBGP/eBGP preference.

Why this answer

The path selection order in Junos is: 1. Local Preference, 2. AS Path length, 3.

Origin type, 4. MED, 5. iBGP over eBGP, 6. IGP metric to next hop.

Therefore, local preference, AS path length, and MED are evaluated before the IGP metric.

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MCQmedium

An administrator implements an inbound policy to discard BGP routes matching a specific community. Which action statement is required in the policy term?

A.then drop;

B.then reject;

C.then next term;

D.then discard;

AnswerB

The 'reject' action discards the route and stops evaluating subsequent policy terms.

Why this answer

To discard routes in a Junos routing policy, the 'reject' action is used.

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Multi-Selecthard

Which THREE path attributes are classified as 'well-known mandatory'? (Choose three)

Select 3 answers

A.MED

B.NEXT_HOP

C.ORIGIN

D.AS_PATH

E.LOCAL_PREF

AnswersB, C, D

NEXT_HOP is a well-known mandatory attribute.

Why this answer

The well-known mandatory attributes in BGP are ORIGIN, AS_PATH, and NEXT_HOP. Local Preference is well-known discretionary, and MED is optional non-transitive.

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MCQeasy

An administrator configures a BGP policy to reject routes with an AS_PATH containing a specific AS number. Which match condition in a Junos routing policy is used to evaluate the AS_PATH?

A.pref

B.metric

C.as-path

D.community

AnswerC

The as-path match condition references a named as-path object containing regular expressions.

Why this answer

In Junos, the as-path match condition evaluates routes against a defined as-path regular expression.

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Multi-Selectmedium

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

Select 2 answers

A.Accepting or rejecting routes based on AS_PATH regular expressions.

B.Changing the TCP port used for BGP session establishment from 179 to another port.

C.Directly modifying the physical interface speed when BGP flaps.

D.Encrypting BGP payload data using policy-based IPsec keys.

E.Modifying the Local Preference attribute on incoming eBGP routes.

AnswersA, E

Routing policies match AS_PATH and accept or reject routes accordingly.

Why this answer

Routing policies can modify path attributes such as local preference and MED, as well as accept or reject routes.

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MCQhard

Which BGP message type is responsible for negotiating session parameters, including autonomous system numbers, hold times, and BGP identifiers during session establishment?

A.Notification

B.Open

C.Update

D.Keepalive

AnswerB

Correct. The Open message is sent immediately after establishing a TCP connection to initialize the BGP session and negotiate parameters.

Why this answer

The BGP Open message is the first message sent after a TCP connection is established. It contains parameters such as the BGP version, local AS number, hold time, BGP identifier, and optional parameters (capabilities).

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MCQmedium

You need to ensure that an iBGP-learned route is properly advertised to other eBGP peers without triggering routing loops. Which mechanism does BGP use automatically to prevent routing loops within an Autonomous System?

A.MED attribute comparison

B.Local Preference check

C.AS-path loop prevention on eBGP export

D.Cluster list checking

AnswerC

When advertising routes to eBGP peers, the local AS is prepended. If an AS sees its own ASN in the AS_PATH, it drops the update.

Why this answer

iBGP split horizon rule specifies that routes learned from an iBGP peer are not advertised to other iBGP peers, but it requires full mesh, route reflectors, or confederations. For eBGP advertising, AS path is used.

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Multi-Selecthard

An administrator is troubleshooting a BGP peering session that is stuck in the Connect or Active state. Which THREE common causes could explain this issue? (Choose three)

Select 3 answers

A.Route reflection client parameters are misconfigured.

B.TCP port 179 is blocked by a firewall filter.

C.Incorrect neighbor IP address configured under protocols bgp.

D.Incorrect peer AS number configured in the OPEN message parameters.

E.Missing multihop configuration for a non-directly connected eBGP peer.

AnswersB, C, E

Firewalls blocking port 179 prevent TCP connection establishment.

Why this answer

A session stuck in Active/Connect means the TCP session cannot be established. Causes include incorrect peer IP/AS, firewall blocking port 179, or missing multihop/TTL settings.

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MCQhard

An MX Series router is configured with BGP Multipath. Two paths have identical Local Preference, AS path length, origin, and MED. Which additional configuration statement is required under protocols bgp to enable multipath load balancing across these iBGP paths?

A.set protocols bgp group internal type external

B.set protocols bgp multipath relaxation

C.set routing-options forwarding-table export load-balance

D.set protocols bgp group internal multihop

AnswerB

The relaxation statement allows iBGP multipath even if the AS path lengths differ slightly, or enables it for iBGP.

Why this answer

By default, multipath is only for eBGP. To enable iBGP multipath, the 'as-path-multipath relaxation' or 'ibgp multipath' statement must be used.

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Multi-Selectmedium

Which TWO BGP message types are responsible for maintaining session state or reporting errors without carrying routing information? (Choose two)

Select 2 answers

A.OPEN

B.KEEPALIVE

C.UPDATE

D.QUERY

E.NOTIFICATION

AnswersB, E

KEEPALIVE confirms session liveness periodically.

Why this answer

KEEPALIVE maintains the session state, and NOTIFICATION reports fatal errors and tears down the session. UPDATE carries routing information, and OPEN establishes the session.

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MCQhard

While examining a BGP routing table, you notice a route with an ORIGIN attribute set to 'Incomplete'. What does this indicate about the origin of the route?

A.The route was learned via eBGP from an unknown AS.

B.The BGP update packet was corrupted in transit.

C.The route is an aggregate route without specific components.

D.The route was injected into BGP via redistribution (e.g., from static or IGP).

AnswerD

Incomplete origin is typically assigned when routes are redistributed into BGP.

Why this answer

BGP origin types are IGP (0), EGP (1), and Incomplete (2). Incomplete means the route origin is unknown, typically redistributed from an IGP or static route.

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MCQeasy

An engineer is troubleshooting a BGP session between two routers and notices that the connection is stuck in the Active state. What does the Active state indicate about the BGP finite state machine?

A.The TCP connection attempt is ongoing or has failed, and the router is actively trying to establish a TCP session with the peer.

B.The local router has successfully completed the TCP handshake and is waiting for an Open message.

C.BGP has exchanged Open messages and is currently negotiating capability parameters.

D.The BGP session is fully operational and exchanging Keepalive messages.

AnswerA

Correct. In the Active state, the router attempts to initiate a TCP connection to the remote BGP speaker.

Why this answer

In the Active state, the local router has initiated a TCP connection to the peer, but the TCP handshake has not yet completed successfully or has failed. This usually points to routing, firewall, or port 179 issues.

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MCQhard

A Junos router is configured as a BGP route reflector. It learns a route from a client and reflects it to a non-client and another client. Which attribute does the route reflector modify or add to prevent routing loops?

A.MED and NEXT_HOP

B.AS_PATH and LOCAL_PREF

C.COMMUNITY and ATOMIC_AGGREGATE

D.ORIGINATOR_ID and CLUSTER_LIST

AnswerD

ORIGINATOR_ID and CLUSTER_LIST are added during reflection to detect and prevent loops.

Why this answer

Route reflectors add the ORIGINATOR_ID (to prevent loops back to the originator) and the CLUSTER_LIST (to prevent loops between reflectors).

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MCQmedium

Which BGP attribute is classified as 'well-known discretionary'?

A.AS_PATH

B.ORIGIN

C.MED

D.LOCAL_PREF

AnswerD

LOCAL_PREF is well-known discretionary.

Why this answer

Local Preference is a well-known discretionary attribute, meaning all BGP implementations must recognize it, but it does not have to be included in every update.

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MCQeasy

Which TCP port is used by BGP to establish communication between peers?

A.UDP 520

B.TCP 179

C.TCP 80

D.TCP 500

AnswerB

BGP uses TCP port 179 for session establishment and communication.

Why this answer

BGP operates over TCP port 179.

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MCQmedium

A network administrator needs to modify the Local Preference path attribute for all routes received from a specific external BGP peer using a routing policy on Junos. Under which configuration hierarchy should the routing policy be applied?

A.policy-options policy-statement term then export

B.protocols bgp group neighbor import

C.routing-options rib inet.0 static

D.protocols ospf area

AnswerB

Correct. An import policy applied to a BGP neighbor or group modifies incoming path attributes like Local Preference.

Why this answer

To affect routes received from a specific BGP peer, an import policy must be applied directly to that neighbor or group under 'protocols bgp group <group-name> neighbor <ip> import <policy-name>' or at the group level.

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MCQmedium

What is the primary function of the BGP OPEN message?

A.To advertise reachability and path attributes for network prefixes.

B.To maintain the connection state and verify liveliness at regular intervals.

C.To signal fatal errors and immediately terminate the BGP session.

D.To establish a peering session and negotiate capabilities such as ASNs and timers.

AnswerD

The OPEN message negotiates session parameters between peers.

Why this answer

The OPEN message is the first message sent after a TCP connection is established, used to negotiate BGP parameters such as ASN, hold time, and router ID.

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MCQhard

A network engineer configures BGP confederations to scale an enterprise network. Which BGP path attribute is stripped or modified when an update leaves a sub-AS within the confederation and enters another sub-AS?

A.AS_PATH

B.CONFED_SEQUENCE

C.LOCAL_PREF

D.MED

AnswerB

CONFED_path segments are removed or converted when crossing the boundary out of the confederation.

Why this answer

CONFED_SEQUENCE and CONFED_SET attributes are used within a confederation and are stripped when the update leaves the confederation boundary to a normal eBGP peer.

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MCQeasy

When a Junos router establishes an eBGP session, what is the default value of the Local Preference attribute assigned to incoming routes if not modified by a policy?

A.100

B.Not set / Null

C.0

D.200

AnswerA

Default local preference is 100.

Why this answer

The default Local Preference in Junos and standard BGP implementations is 100.

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Multi-Selecthard

Which THREE actions occur when a BGP speaker receives a Notification message from a peer? (Choose three.)

Select 3 answers

A.A Keepalive message is immediately sent in response to acknowledge the error.

B.The peer router automatically re-establishes the connection without applying the connect retry timer.

C.The TCP connection associated with the BGP session is closed.

D.The BGP session transitions to the Idle state.

E.All routes learned from that specific peer are removed from the BGP routing table.

AnswersC, D, E

Correct. The underlying TCP session is torn down upon receiving a Notification message.

Why this answer

When a BGP Notification message is received, it indicates an error condition. The receiving router moves the session to Idle, closes the TCP connection, and clears all routes learned from that peer.

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MCQhard

You are running BGP between two routers. One router has a 4-byte ASN (e.g., ASN 65536). The remote router only supports 2-byte ASNs. How does BGP handle this compatibility issue?

A.The session fails to open because 4-byte ASNs are strictly incompatible with 2-byte peers.

B.The router uses the reserved AS 23456 (AS_TRANS) in place of the 4-byte ASN for legacy peers.

C.The session establishes as iBGP instead of eBGP.

D.The 4-byte ASN is truncated to 2 bytes by dropping the most significant bits.

AnswerB

AS 23456 is used as a transition AS for legacy 2-byte AS routers.

Why this answer

BGP uses the TRANSIT_AS or AS4_PATH / AS4_AGGREGATOR capabilities negotiated during the OPEN message phase to support 4-byte ASNs across 2-byte peers using a reserved ASN (AS 23456).

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Multi-Selectmedium

Which TWO statements describe characteristics of BGP path attributes? (Choose two.)

Select 2 answers

A.Local Preference is a well-known discretionary attribute that is exchanged across eBGP peers.

B.MED is a well-known mandatory attribute used for inter-AS route selection.

C.Well-known mandatory attributes must be recognized by all BGP implementations and included in every Update message containing path information.

D.Optional transitive attributes are ignored by BGP speakers that do not recognize them and are never passed along to other peers.

E.AS_PATH is a well-known mandatory attribute.

AnswersC, E

Correct. Well-known mandatory attributes (such as AS_PATH, NEXT_HOP, ORIGIN) must be present in every update message with path data.

Why this answer

BGP path attributes are categorized into well-known (mandatory or discretionary) and optional (transitive or non-transitive). Well-known mandatory attributes must be recognized by all BGP implementations.

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MCQmedium

You notice that an iBGP peer is not advertising routes it learned from an eBGP peer to other iBGP peers. What architectural rule explains this behavior?

A.eBGP TTL security check

B.MED restriction across AS boundaries

C.AS_PATH loop detection

D.iBGP split-horizon rule

AnswerD

iBGP split horizon prevents iBGP-learned routes from being propagated to other iBGP peers.

Why this answer

The iBGP split-horizon rule states that routes learned via iBGP cannot be advertised to other iBGP peers to prevent routing loops.

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MCQmedium

You need to ensure that BGP sessions fail over within sub-second intervals if a link degrades or goes down. Which protocol should you integrate with BGP on your Junos router?

A.BFD (Bidirectional Forwarding Detection)

B.STP (Spanning Tree Protocol)

C.LDP (Label Distribution Protocol)

D.OSPF

AnswerA

BFD integrates with BGP to provide rapid failure detection and fast convergence.

Why this answer

BFD (Bidirectional Forwarding Detection) provides fast failure detection that can trigger BGP session teardown within milliseconds.

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MCQmedium

You need to configure an explicit export policy in Junos so that your eBGP router only advertises locally originated routes and refuses to transit third-party routes. Which AS_PATH regular expression accomplishes this?

A.as-path LOCAL-ONLY ".*";

B.as-path LOCAL-ONLY "[0-9]+";

C.as-path LOCAL-ONLY "^65001$";

D.as-path LOCAL-ONLY "^$";

AnswerD

An empty AS_PATH '^$' matches only routes generated locally by the router.

Why this answer

Locally originated routes have an empty AS_PATH (represented as '^$'), meaning no ASNs have been prepended yet.

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MCQeasy

An engineer must inspect the BGP state and verify the received prefix counts from a specific neighbor on an MX Series router. Which operational command should be used?

A.show bgp neighbor 10.1.1.1

B.show ospf neighbor

C.show route protocol bgp

D.show bgp summary

AnswerA

Show bgp neighbor with a specific IP provides comprehensive session stats, state, and prefix counts for that peer.

Why this answer

The 'show bgp neighbor' command provides detailed information about BGP peer states, prefix counts, and timers.

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MCQmedium

An engineer configures iBGP peering between two routers in the same AS. Route reflection is not used. The engineer notices that routes learned from an eBGP peer by Router A are not being advertised by Router A to Router B (its iBGP peer). Why is this happening?

A.BGP split-horizon prevents a router from advertising routes learned from one iBGP peer to another iBGP peer.

B.External routes cannot be carried over iBGP without encapsulation.

C.The Local Preference attribute defaults to 0 for iBGP routes, causing them to be suppressed.

D.iBGP peers require the 'multipath' statement to be configured before any route exchange can occur.

AnswerA

Correct. This rule prevents loops within an AS, requiring a full mesh of iBGP sessions or a route reflector.

Why this answer

BGP split-horizon rule dictates that routes learned from an iBGP peer cannot be advertised to another iBGP peer to prevent routing loops. (Note: standard iBGP to iBGP split horizon applies; to share routes, full mesh, route reflectors, or confederations must be used).

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MCQeasy

An engineer needs to verify which BGP routes are currently installed in the forwarding table (FIB). Which command should be used?

A.show route forwarding-table protocol bgp

B.show bgp forwarding

C.show route table inet.0

D.show route summary

AnswerA

This displays the active BGP routes installed in the forwarding table.

Why this answer

The forwarding table is viewed using 'show route forwarding-table'.

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MCQhard

A BGP speaker receives an UPDATE message containing a malformed attribute. According to BGP specifications, which action does the receiving router take?

A.Strip the attribute and propagate the route to iBGP peers.

B.Send an UPDATE message requesting retransmission.

C.Send a NOTIFICATION message and terminate the BGP session.

D.Silently ignore the attribute and install the route.

AnswerC

Malformed attributes result in a BGP NOTIFICATION and session teardown.

Why this answer

A malformed attribute or critical error triggers a NOTIFICATION message with an appropriate error code, followed by session teardown.

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MCQhard

An enterprise customer connects to two different service providers via eBGP. They want to preferentially use Service Provider A, but fail over to Service Provider B if Provider A fails. How can they influence the inbound traffic from the providers?

A.Use AS-PATH prepending in an outbound policy toward Provider B

B.Modify Local Preference in an inbound policy

C.Change the MED value in an inbound policy

D.Configure a lower router ID

AnswerA

Prepending the local ASN multiple times to Provider B makes its path look longer, causing providers to prefer Provider A.

Why this answer

Inbound traffic (traffic entering the AS from providers) is influenced by advertising path attributes to the providers, primarily AS-PATH prepending.

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Multi-Selectmedium

Which TWO statements are true regarding BGP communities in Junos? (Choose two)

Select 2 answers

A.Communities are optional transitive path attributes.

B.Communities replace the AS_PATH attribute entirely.

C.Communities are evaluated after the router ID tie-breaker.

D.Communities can only be applied to eBGP sessions and are stripped on iBGP.

E.Standard communities are formatted as two 16-bit values separated by a colon (ASN:value).

AnswersA, E

BGP communities are transmitted across autonomous systems if transit is enabled.

Why this answer

Communities can be standard (32-bit values represented as AS:value) or extended, and they are used to group routes for policy enforcement.

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Multi-Selectmedium

Which TWO actions occur when a Junos BGP routing policy includes the 'next policy' action? (Choose two)

Select 2 answers

A.Evaluation of the current policy terminates immediately.

B.Evaluation proceeds to the next independent policy defined in the chain.

C.The route is immediately accepted and installed in the routing table.

D.The route is rejected and dropped.

E.Evaluation jumps to the next term within the same policy block.

AnswersA, B

'next policy' stops checking further terms in the current policy.

Why this answer

'next policy' evaluates the remaining policies in the policy chain, bypassing subsequent terms within the current policy.

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Multi-Selecthard

An administrator configures BGP multipath on a Junos router. Which THREE conditions must be met for BGP paths to be considered equal and installed as multipaths? (Choose three)

Select 3 answers

A.The paths must have the same Local Preference value.

B.The MED values must match (unless remove-private-as is set).

C.The paths must originate from different Autonomous Systems entirely.

D.The paths must have identical AS path lengths (unless AS path relaxation is enabled).

E.The router IDs of the advertising routers must be identical.

AnswersA, B, D

Local Preference must match for multipath consideration.

Why this answer

For BGP multipath, paths must typically have matching AS path lengths (unless relaxation is on), matching local preference, matching MED, and matching origin, and the next-hop router must resolve via the same IGP metric cost.

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MCQmedium

A network engineer configures an eBGP session on a Junos device and notices that routes learned from the external peer are not being installed in the routing table or advertised to other peers. What is the default behavior regarding eBGP route propagation and next-hop resolution on Junos OS?

A.Junos automatically drops all eBGP routes unless an explicit import policy is applied allowing them.

B.eBGP routes require the 'as-override' statement to be active in the forwarding table.

C.The local router does not set the next-hop to itself for eBGP peers, but for iBGP peers the next-hop must be resolvable via an IGP.

D.eBGP automatically changes the next-hop to the local router interface for all advertised routes.

AnswerC

Correct. When advertising to an eBGP peer, the next-hop is the interface of the advertising router. For iBGP, the next-hop is preserved, requiring IGP resolution.

Why this answer

By default, eBGP does not change the next-hop address when advertising routes to external peers, but when advertising to iBGP peers, it preserves the next-hop unless 'next-hop-self' is configured. However, for routes to be active, the next-hop must be resolvable in the routing table.

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MCQhard

An operator troubleshooting BGP path selection notices two routes have identical Local Preference, AS path length, origin, MED, and both are eBGP routes. Which attribute does the BGP path selection algorithm evaluate next?

A.Lowest Router ID

B.Oldest route

C.Lowest peer IP address

D.Lowest IGP cost to the BGP next hop

AnswerD

IGP cost to next hop is evaluated to prefer the closest exit point when comparing eBGP routes or prior ties.

Why this answer

According to the BGP best path selection algorithm, after comparing local pref, AS path, origin, MED, and iBGP vs eBGP, the router prefers the path with the lowest IGP metric to the BGP next hop.

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MCQhard

While reviewing BGP updates, you notice an attribute type code of 3 with a value representing an IP address. Which well-known mandatory path attribute is this?

A.AS_PATH

B.ORIGIN

C.NEXT_HOP

D.LOCAL_PREF

AnswerC

NEXT_HOP has type code 3.

Why this answer

Attribute type code 3 corresponds to NEXT_HOP, which is a well-known mandatory attribute indicating the IP address of the router used to reach the destination.

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Multi-Selectmedium

Which TWO statements accurately describe the behavior of the BGP AS_PATH attribute? (Choose two)

Select 2 answers

A.It is automatically stripped when crossing a confederation boundary.

B.It is a well-known mandatory attribute.

C.It is prepended with the local AS number when sent to an eBGP peer.

D.It is modified when an update is sent to an iBGP peer.

E.It is an optional non-transitive attribute used for internal metrics.

AnswersB, C

AS_PATH is classified as well-known mandatory.

Why this answer

AS_PATH is well-known mandatory and gets prepended with the local AS number every time an update leaves an Autonomous System via eBGP.

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MCQeasy

Which command allows an administrator to view real-time BGP routing updates being sent and received on a Junos device?

A.monitor traffic protocol bgp

B.traceroute bgp

C.show log bgp-log

D.show bgp updates

AnswerA

Monitor traffic protocol bgp captures and displays live BGP packets on the wire.

Why this answer

Tracing options and packet/update monitoring can be performed using 'monitor traffic' or BGP tracing, but for dynamic operational logging of updates, tracing is enabled. For quick viewing of summary updates, monitor traffic protocol bgp is used.

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MCQmedium

You need to configure authentication for a BGP peering session on a Junos device to prevent spoofing attacks. Where is the MD5 authentication key configured?

A.firewall family inet filter bgp-auth

B.system authentication-algorithm md5

C.protocols bgp group name authentication-key

D.routing-options md5-key

AnswerC

Authentication keys are configured directly under the BGP group or neighbor hierarchy.

Why this answer

BGP MD5 authentication keys are configured under the specific neighbor or group definition using the authentication-key statement.

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MCQeasy

An administrator needs to verify the exact BGP timers negotiated with an eBGP peer on a Junos device. Which operational command should be used?

A.show ospf neighbor

B.show bgp summary

C.show route advertising-protocol bgp

D.show bgp neighbor

AnswerD

Correct. 'show bgp neighbor' displays session state, negotiated timers, and capability information.

Why this answer

The 'show bgp neighbor' command provides detailed information about a BGP neighbor session, including negotiated hold time, keepalive interval, state, and message statistics.

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MCQmedium

An engineer configures a BGP policy to set the MED attribute on routes advertised to an eBGP peer. What is the primary purpose of the MED (Multi-Exit Discriminator) attribute?

A.To dictate the preferred path for traffic leaving the local AS.

B.To prevent routing loops across multiple autonomous systems.

C.To indicate to an external AS which entry point is preferred for traffic entering the local AS.

D.To assign a priority score for internal route selection within the same AS.

AnswerC

MED acts as a hint to neighboring ASes regarding ingress path preference.

Why this answer

MED is an optional non-transitive attribute used to inform external peers about the preferred entry point into an AS.

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MCQmedium

You are troubleshooting a route leak between two eBGP peers. You notice that an incoming route contains your own ASN in the AS_PATH attribute, yet the route was installed. Which Junos feature allowed this behavior, and where is it configured?

A.as-override

B.allow-as-in

C.as-path-prepend

D.loop-detect disable

AnswerB

allow-as-in permits the acceptance of routes with the local ASN in the AS_PATH up to a specified count.

Why this answer

The 'allow-as-in' command under BGP configuration allows a router to accept BGP updates that contain its own ASN in the AS_PATH, typically used in VPN or hub-and-spoke scenarios.

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Multi-Selecthard

Which THREE attributes are optional transitive BGP path attributes? (Choose three)

Select 3 answers

A.AS4_PATH

B.AGGREGATOR

C.MED

D.COMMUNITY

E.LOCAL_PREF

AnswersA, B, D

AS4_PATH is an optional transitive attribute.

Why this answer

Optional transitive attributes include COMMUNITY, AGGREGATOR, and AS4_PATH. MED is optional non-transitive. Local Pref and AS_PATH are well-known.

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MCQeasy

An administrator wants to gracefully restart a BGP routing daemon without dropping the underlying TCP session or causing traffic loss. Which Junos feature should be enabled?

A.Nonstop Active Routing (NAR)

B.TCP MD5 Signature bypass

C.BGP Bidirectional Forwarding Detection (BFD)

D.BGP Graceful Restart

AnswerD

Graceful Restart enables helper mode and restart capabilities to maintain forwarding during control plane reboots.

Why this answer

Graceful Restart allows a BGP speaker to express its ability to preserve forwarding state while restarting the control plane.

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Multi-Selectmedium

Which TWO statements correctly differentiate eBGP from iBGP? (Choose two.)

Select 2 answers

A.iBGP routes have a default administrative distance (preference in Junos) of 20.

B.eBGP routers prepend their own AS number to the AS_PATH attribute when advertising routes.

C.eBGP peers must be directly connected by default, as the IP TTL for eBGP packets is set to 1.

D.The default TTL for iBGP packets is 1, requiring explicit multihop configurations for non-directly connected peers.

E.iBGP routers modify the next-hop attribute to their own interface address by default when advertising routes to iBGP peers.

AnswersB, C

Correct. eBGP adds its own AS number to the AS_PATH, whereas iBGP does not.

Why this answer

eBGP sessions are typically established between routers in different autonomous systems and have a default TTL of 1, whereas iBGP sessions are between routers in the same AS and have a default TTL of 255.

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Multi-Selectmedium

Which TWO BGP attributes are strictly internal to an Autonomous System and are never advertised to external eBGP peers? (Choose two)

Select 2 answers

A.NEXT_HOP

B.ORIGIN

C.ORIGINATOR_ID

D.AS_PATH

E.LOCAL_PREF

AnswersC, E

Originator ID and Cluster List are internal route reflector attributes not sent to eBGP peers.

Why this answer

Local Preference and MED (by default, unless propagated) or internal-only attributes like cluster list are restricted. Specifically, Local Preference is never sent to eBGP peers.

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MCQhard

During BGP path selection on a Junos device, two paths are received for the same destination prefix. Path A has a MED of 50 received from a peer in AS 65001, and Path B has a MED of 10. Both AS paths have a length of 2. The router is not configured with 'always-compare-med'. Which path will be preferred by default?

A.Path B, because it has a lower MED value of 10 compared to Path A's MED of 50.

B.Path A, because lower MED is only preferred if 'compare-router-id' is enabled.

C.MED will be ignored during path selection because the paths originate from different autonomous systems, and the selection will proceed to subsequent tie-breakers.

D.Path A will be preferred because Junos always favors higher MED values for eBGP paths.

AnswerC

Correct. MED comparison is restricted to routes from the same AS unless 'always-compare-med' is set.

Why this answer

By default, BGP only compares MED (Multi-Exit Discriminator) values for paths originating from the *same* neighboring Autonomous System unless 'always-compare-med' is configured. Since Path A and Path B come from different ASNs, MED is skipped, and the selection process moves to the next criteria.

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