JNCIS-ENT BGP Practice Test 4 — 15 Questions

Question 1

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?

Accepted Answer

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

Answer

Nonstop Active Routing (NAR)

Answer

TCP MD5 Signature bypass

Answer

BGP Bidirectional Forwarding Detection (BFD)

Question 2

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?

Accepted Answer

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

Answer

STP (Spanning Tree Protocol)

Answer

LDP (Label Distribution Protocol)

Answer

OSPF

Question 3

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

Accepted Answer

KEEPALIVE. B. KEEPALIVE is correct because BGP peers exchange KEEPALIVE messages periodically (default 60 seconds, hold time 180 seconds) to confirm the session is still alive and to maintain the established state without carrying any NLRI routing information. E. NOTIFICATION is correct because it is sent when an error condition is detected (for example a hold-timer expiry, bad message header, or unsupported capability), causing the session to be torn down; it reports the error and carries no routing information. A. OPEN is not correct here because, although it establishes the session and negotiates capabilities, it is a session-initiation message rather than a state-maintenance or error-reporting message. C. UPDATE is not correct because UPDATE is precisely the message that carries routing information (NLRI and path attributes). D. QUERY is not correct because QUERY is not a BGP message type; the four BGP message types are OPEN, UPDATE, KEEPALIVE, and NOTIFICATION.

Answer

OPEN

Answer

UPDATE

Answer

QUERY

Question 4

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

Accepted Answer

Peers reside in different Autonomous Systems. Option C is correct because eBGP (External BGP) is specifically designed to exchange routing information between routers in different Autonomous Systems, whereas iBGP peers must be within the same AS. Option D is correct because eBGP sessions between directly connected external peers use a default IP TTL of 1 (multihop eBGP requires explicitly raising the TTL with the ebgp-multihop command), while iBGP sessions default to TTL 255. Option A is incorrect because route reflection is an iBGP mechanism (used to avoid the full-mesh requirement) and is not enabled by default on eBGP. Option B is incorrect because residing within the same Autonomous System describes iBGP, not eBGP. Option E is incorrect because the default Local Preference in BGP is 100, not 200, and this value is not a distinguishing eBGP-versus-iBGP characteristic.

Answer

Automatic route reflection enabled by default

Answer

Must reside within the same Autonomous System

Answer

Default Local Preference of 200

Question 5

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?

Accepted Answer

ORIGINATOR_ID and CLUSTER_LIST. When a route reflector reflects a route, it adds the ORIGINATOR_ID (the router ID of the route's originator) and CLUSTER_LIST (a list of cluster IDs the route has traversed) to prevent routing loops. If a route reflector receives a route with its own router ID in ORIGINATOR_ID or its cluster ID in CLUSTER_LIST, it discards the route.

Answer

MED and NEXT_HOP

Answer

AS_PATH and LOCAL_PREF

Answer

COMMUNITY and ATOMIC_AGGREGATE

Question 6

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

Accepted Answer

Communities are optional transitive path attributes.. Option A is correct because BGP communities are carried as an optional transitive path attribute (attribute type code 8), meaning they are not required in every UPDATE but, when present, are propagated to other BGP speakers. Option E is correct because a standard community is a 32-bit value expressed as two 16-bit numbers in the ASN:value format, for example 65000:100, where the first field is typically the autonomous system number and the second is an administrator-defined value. Option B is wrong because communities are an additional attribute and do not replace AS_PATH, which remains the primary loop-prevention and path-selection attribute. Option C is wrong because community matching is a policy action performed during route evaluation, not a tie-breaker after router ID; the router ID tie-breaker applies only when comparing otherwise equal paths. Option D is wrong because communities can be attached and matched on both eBGP and iBGP sessions, and they are not automatically stripped on iBGP.

Answer

Communities replace the AS_PATH attribute entirely.

Answer

Communities are evaluated after the router ID tie-breaker.

Answer

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

Question 7

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

Accepted Answer

Evaluation of the current policy terminates immediately.. Option A is correct because the 'next policy' action terminates evaluation of the current policy immediately, so no further terms within that policy are processed. Option B is correct because, after stopping the current policy, Junos proceeds to evaluate the next independent policy in the chain (the next policy referenced in the import/export chain), allowing subsequent policies to make the final accept/reject decision. Option C is incorrect because 'next policy' does not itself accept or install a route; acceptance requires an explicit 'accept' action or a default policy decision. Option D is incorrect because 'next policy' does not reject or drop the route; rejection is performed by a 'reject' action. Option E is incorrect because jumping to the next term within the same policy block is not what 'next policy' does; that would be the behavior of 'next term'.

Answer

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

Answer

The route is rejected and dropped.

Answer

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

Question 8

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

Accepted Answer

AS4_PATH. AS4_PATH (A) is an optional transitive attribute defined in RFC 6793 that carries 4-byte AS path information for backward compatibility with 2-byte AS speakers, and it is propagated to other ASes. AGGREGATOR (B) is an optional transitive attribute (type code 7) that records the AS and router ID of the device that performed route aggregation, and it is passed along to BGP peers. COMMUNITY (D) is an optional transitive attribute (type code 8) used to tag routes with community values that are propagated across AS boundaries. MED (C) is an optional nontransitive attribute, so it is not propagated beyond the neighboring AS, and LOCAL_PREF (E) is a well-known discretionary attribute used only within a single AS, so neither qualifies as optional transitive.

Answer

MED

Answer

LOCAL_PREF

Question 9

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

Accepted Answer

It is a well-known mandatory attribute.. Option B is correct because AS_PATH is classified as a well-known mandatory BGP attribute, meaning every BGP UPDATE that carries reachable NLRI must include it, and all BGP-speaking routers must recognize and process it. Option C is correct because when a router advertises a route to an external BGP (eBGP) peer, it prepends its own local AS number to the AS_PATH, which is the core loop-prevention and path-length mechanism of BGP. Option A is wrong because AS_PATH is not stripped at confederation boundaries; confederation sub-AS numbers are carried in a separate AS_CONFED_SEQUENCE/AS_CONFED_SET segment, and the attribute itself is preserved. Option D is wrong because updates sent to internal BGP (iBGP) peers do not modify AS_PATH — the local AS is only prepended on eBGP advertisements. Option E is wrong because AS_PATH is not an optional non-transitive attribute; that description fits attributes like MED, and AS_PATH is well-known mandatory rather than used for internal metrics.

Answer

It is automatically stripped when crossing a confederation boundary.

Answer

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

Answer

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

Question 10

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

Accepted Answer

It is exchanged during the BGP OPEN message negotiation phase.. Option B is correct because the BGP Router ID is carried in the BGP OPEN message as part of session establishment, allowing peers to identify each other during negotiation. Option C is correct because when all other path attributes are equal, BGP uses the lowest Router ID as the final tie-breaker in the best-path selection algorithm. Option E is correct because the Router ID is a 32-bit value written in dotted-quad notation, just like an IPv4 address. Option A is wrong because the AS_PATH attribute is generated and propagated by BGP itself and is never replaced by the Router ID. Option D is wrong because Router IDs must be unique within an Autonomous System, not identical across all routers.

Answer

It automatically replaces the AS_PATH attribute if missing.

Answer

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

Question 11

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?

Accepted Answer

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

Answer

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

Answer

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

Answer

The BGP session is fully operational and exchanging Keepalive messages.

Question 12

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

Accepted Answer

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

Answer

show ospf neighbor

Answer

show bgp summary

Answer

show route advertising-protocol bgp

Question 13

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

Accepted Answer

Open. 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).

Answer

Notification

Answer

Update

Answer

Keepalive

Question 14

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?

Accepted Answer

protocols bgp group neighbor import. To modify Local Preference for routes received from a specific eBGP peer, the routing policy must be applied as an import policy on that neighbor or group under 'protocols bgp group neighbor import '. Import policies are evaluated on inbound updates, which is where Local Preference is typically set for eBGP-learned routes.

Answer

policy-options policy-statement term then export

Answer

routing-options rib inet.0 static

Answer

protocols ospf area

Question 15

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

Accepted Answer

Well-known mandatory attributes must be recognized by all BGP implementations and included in every Update message containing path information.. Option C is correct because well-known mandatory attributes, by definition in BGP (RFC 4271), must be recognized by every BGP implementation and must appear in every UPDATE message that carries reachable NLRI/path information. Option E is correct because AS_PATH is one of the three well-known mandatory attributes (along with NEXT_HOP and ORIGIN), and it is present in every UPDATE advertising a route. Option A is wrong because Local Preference is a well-known discretionary attribute, not one exchanged across eBGP peers — it is typically propagated only within an AS via iBGP. Option B is wrong because MED is an optional non-transitive attribute, not well-known mandatory, and it influences inter-AS route selection only when explicitly configured. Option D is wrong because optional transitive attributes that are unrecognized are still passed along to other peers (with the partial bit set), not discarded.

Answer

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

Answer

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

Answer

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