JNCIS-ENT BGP Practice Test 3 — 15 Questions

Question 1

A Juniper router is configured with BGP and receives multiple paths to the same destination. The router is configured with the multipath multiple-as statement. Two paths are from different autonomous systems and have identical local preference, AS path length, origin, and MED. However, the router only installs one path in the forwarding table. What is the reason for this behavior?

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

Accepted Answer

The AS path attribute contains different AS numbers, and the router is not configured to accept multiple AS paths.. BGP multipath requires that paths have identical AS path attributes unless the multipath multiple-as statement is configured. Since the paths are from different autonomous systems, their AS paths differ, so the router will not install both paths by default. Enabling multipath multiple-as allows the router to treat paths with different AS paths as equal, enabling load balancing.

Answer

The paths have different next-hop addresses.

Answer

The MED values are not the same.

Answer

The router ID of the two paths is the same.

Question 2

You are configuring BGP on a Juniper router and want to ensure that the router prefers routes learned from a specific eBGP peer. Which BGP attribute should you manipulate, and how, to achieve this?

Accepted Answer

Set a higher local preference for routes from that peer using an import policy.. To prefer routes from a specific eBGP peer for outbound traffic, you should manipulate the local preference attribute. A higher local preference is preferred in BGP's path selection process. This is done using an import policy on the local router, as local preference is only exchanged within an AS.

Answer

Set a lower MED for routes from that peer using an export policy.

Answer

Prepend the AS path with additional AS numbers using an import policy.

Answer

Set a higher origin type for routes from that peer using an import policy.

Question 3

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?

Accepted Answer

Import policy applied to the eBGP neighbor or group. Inbound routing policies on Junos affect attributes like Local Preference before path selection occurs.

Answer

Export policy applied to the eBGP group

Answer

Forwarding plane firewall filter

Answer

Global system-level static route policy

Question 4

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?

Accepted Answer

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

Answer

KEEPALIVE

Answer

UPDATE

Answer

OPEN

Question 5

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?

Accepted Answer

show bgp neighbor 10.1.1.1. The command 'show bgp neighbor 10.1.1.1' displays detailed BGP session information for the specified neighbor, including state, received prefix counts, and other statistics. It is the correct command to inspect a specific neighbor.

Answer

show ospf neighbor

Answer

show route protocol bgp

Answer

show bgp summary

Question 6

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?

Accepted Answer

NEXT_HOP. 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.

Answer

AS_PATH

Answer

ORIGIN

Answer

LOCAL_PREF

Question 7

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?

Accepted Answer

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

Answer

pref

Answer

metric

Answer

community

Question 8

What is the primary function of the BGP OPEN message?

Accepted Answer

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

Answer

To advertise reachability and path attributes for network prefixes.

Answer

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

Answer

To signal fatal errors and immediately terminate the BGP session.

Question 9

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

Accepted Answer

TCP 179. BGP operates over TCP port 179.

Answer

UDP 520

Answer

TCP 80

Answer

TCP 500

Question 10

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

Accepted Answer

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

Answer

Strip the attribute and propagate the route to iBGP peers.

Answer

Send an UPDATE message requesting retransmission.

Answer

Silently ignore the attribute and install the route.

Question 11

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?

Accepted Answer

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

Answer

firewall family inet filter bgp-auth

Answer

system authentication-algorithm md5

Answer

routing-options md5-key

Question 12

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

Accepted Answer

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

Answer

show bgp forwarding

Answer

show route table inet.0

Answer

show route summary

Question 13

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

Accepted Answer

To maintain the session; sent every 30 seconds by default.. BGP KEEPALIVE messages are sent periodically to confirm that the peer session is still alive and to reset the Hold Timer, preventing the session from being torn down. In Junos (and per RFC 4271), the default Keepalive interval is 30 seconds, with a default Hold Time of 90 seconds — exactly three times the Keepalive interval. If three consecutive Keepalives are missed, the Hold Timer expires and the session resets.

Answer

To report session errors; sent immediately upon failure.

Answer

To negotiate capabilities; sent every 60 seconds.

Answer

To update routing tables; sent every 5 seconds.

Question 14

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?

Accepted Answer

The router uses the reserved AS 23456 (AS_TRANS) in place of the 4-byte ASN for legacy peers.. When a BGP speaker with a 4-byte ASN peers with a legacy 2-byte-only router, BGP uses the reserved AS number 23456 (AS_TRANS) in the AS_PATH for the legacy peer. The 4-byte ASN is carried in a separate AS4_PATH attribute, and the legacy router sees AS_TRANS as a placeholder, preserving compatibility.

Answer

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

Answer

The session establishes as iBGP instead of eBGP.

Answer

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

Question 15

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?

Accepted Answer

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

Answer

The route was learned via eBGP from an unknown AS.

Answer

The BGP update packet was corrupted in transit.

Answer

The route is an aggregate route without specific components.