350-501 Practice Test 29 — 15 Questions

Question 1

A network engineer is troubleshooting an OSPF adjacency failure between two directly connected routers, R1 and R2. Both routers are configured with the same OSPF process ID and area. The engineer verifies that the interfaces are up and IP connectivity exists. Which configuration mismatch is most likely causing the adjacency to fail?

Accepted Answer

OSPF network type mismatch between the interfaces. Option C is correct because OSPF network type mismatch, such as one side configured as point-to-point and the other as broadcast, prevents adjacency formation. Option A is wrong because an MTU mismatch would cause the adjacency to form but show problems during LSA exchange. Option B is wrong because area mismatch would cause a mismatch in area ID. Option D is wrong because a passive interface would allow the neighbor to be seen but not become full.

Answer

MTU mismatch between the interfaces

Answer

Passive interface configuration on one router

Answer

Area ID mismatch on the interfaces

Question 2

Based on the exhibit, what is preventing the BGP session from establishing?

Accepted Answer

The TTL security check is blocking the connection. Option C is correct. The error message indicates the TTL security check is rejecting the connection because the incoming TTL is not 255 (as expected for an eBGP multihop session). The remote AS is shown as 65000, so it is eBGP. The neighbor is reached via a single-hop but the TTL check expects TTL=255, but the router sees a TTL less than that. Option A is wrong because no prefix limit is mentioned. Option B is wrong because no MD5 error is shown. Option D is wrong because the message clearly states TTL security check.

Answer

The BGP MD5 password is mismatched

Answer

The BGP update-source is misconfigured

Answer

The neighbor has reached its maximum prefix limit

Question 3

Given the output, which configuration mismatch would prevent a remote PE in the same VPN from installing this route into its VRF?

Accepted Answer

The remote PE has an import RT that does not include RT:65000:200.. The route carries RT:65000:200. A remote PE must have a VRF with an import RT that matches this RT to install the route. If the remote PE's VRF imports RT:65000:100 instead, the route will not be installed. Option A is incorrect because different RDs do not prevent route installation as long as the RT matches. Option B is incorrect because the next-hop is reachable (10.1.1.2) via the global table. Option D is incorrect because MPLS VPN does not use AS-path filtering by default.

Answer

The remote PE uses a different route distinguisher for its VRF.

Answer

The remote PE filters routes based on BGP AS-path containing AS 65000.

Answer

The next-hop 10.1.1.2 is not reachable in the remote PE's global routing table.

Question 4

Which two statements about MPLS Layer 3 VPN route target (RT) communities are correct?

Accepted Answer

RTs control the import and export of routes between VRFs on PE routers.. Route targets are used to import and export VPN routes between VRFs, and they are encoded as extended community attributes in BGP updates. Option B is incorrect because RTs do not directly determine the next hop; that is done by the BGP next-hop attribute. Option C is incorrect because RTs are not used for loop prevention (that is the role of the route distinguisher and AS-override). Option D is incorrect because RTs are not required to be manually configured if auto-RT is used. Option E is incorrect because RTs are not carried in IP headers; they are part of BGP VPNv4 updates.

Answer

RTs must be manually configured on every PE router for each VRF.

Answer

RTs are used to prevent routing loops within the MPLS VPN network.

Answer

RTs are used to determine the next-hop IP address for VPN prefixes.

Answer

RTs are carried in the IP header to enable per-VPN forwarding.

Question 5

An ISP operates an MPLS Layer 3 VPN backbone. A customer, Corporation X, has four sites (A, B, C, D) each connected to a different PE router (PE-A, PE-B, PE-C, PE-D). They use OSPF as the CE-PE routing protocol. Sites A, B, and C can exchange routes without issue. However, Site D suddenly loses connectivity to Site B, though it can still reach Sites A and C. Show commands on PE-D reveal that the VRF for Corporation X imports RT:100:200, and the route for Site B (prefix 10.10.20.0/24) is present in the BGP VPNv4 table with RT:100:200 and next-hop 10.0.2.2. The OSPF neighbor between PE-D and the CE at Site D is up, and no route filters are configured. ‘ping 10.10.20.0’ from PE-D fails. What is the most likely cause of the issue?

Accepted Answer

The BGP next-hop (10.0.2.2) for Site B's route is not reachable in PE-D's global routing table.. The route is in the VPNv4 table with the correct RT, so import is working. The next-hop is 10.0.2.2. If that next-hop is not reachable in the global routing table of PE-D, the VPNv4 route will not be installed in the VRF. Checking ‘show ip route 10.0.2.2’ on PE-D would confirm. Option A is plausible but incorrect because an RT mismatch would prevent the route from even appearing in the VPNv4 table. Option C is incorrect because OSPF is redistributed, and the route type does not affect reachability. Option D is incorrect because label allocation is not the issue; the prefix is present with labels.

Answer

OSPF route redistribution from PE-B into BGP is set to external type 2, while PE-D expects type 1.

Answer

The route target for Site B is misconfigured on PE-D, not matching the export RT from PE-B.

Answer

PE-D is not assigning an MPLS label for the route to Site B, causing packets to be dropped.

Question 6

Which TWO features are used to improve BGP convergence in an MPLS VPN environment?

Accepted Answer

Bidirectional Forwarding Detection (BFD). Bidirectional Forwarding Detection (BFD) provides sub-second failure detection for BGP sessions, reducing the time to detect a link or neighbor failure from seconds (default BGP keepalive/hold timers) to milliseconds. BGP Prefix Independent Convergence (PIC) pre-installs backup paths in the forwarding table, allowing traffic to be rerouted immediately upon failure without waiting for BGP to reconverge. Together, these features drastically improve BGP convergence in an MPLS VPN environment.

Answer

Route redistribution

Answer

Next-hop-self

Answer

BGP multipath

Question 7

Which TWO statements about QoS policy propagation via BGP (QPPB) are correct?

Accepted Answer

QPPB can be applied on inbound direction only.. Option A is correct because QPPB can be applied on inbound direction only. QPPB uses BGP policy to classify traffic based on IP precedence or QoS group, and the classification is performed on incoming traffic before any routing decision. The outbound direction is not supported for QPPB classification.

Answer

QPPB is an IETF standard.

Answer

It uses MPLS EXP bits to propagate QoS.

Answer

It dynamically adjusts BGP attributes based on QoS policy.

Question 8

A service provider wants to ensure that customer traffic is not impacted during a planned maintenance on a core LSR in an MPLS network. Which MPLS feature should be used?

Accepted Answer

MPLS TE Fast Reroute. MPLS TE Fast Reroute (FRR) is the correct feature because it provides local protection against link or node failures by pre-computing backup paths (bypass tunnels) that are activated within 50 milliseconds of a failure. This ensures that customer traffic is not impacted during planned maintenance on a core LSR, as the backup path is already in place and can be triggered by a manual administrative action (e.g., shutting down the interface) to seamlessly redirect traffic before the maintenance begins.

Answer

MPLS TTL propagation

Answer

MPLS LDP synchronization

Answer

MPLS OAM

Question 9

Refer to the exhibit. Which statement about this BGP configuration is true?

Accepted Answer

The next-hop-self command ensures that the PE sets itself as the next-hop for routes advertised to the route reflector.. Option B is correct because the `next-hop-self` command under the VRF address-family instructs the PE router to set its own IP address as the next-hop for routes advertised to the route reflector. This is necessary in MPLS L3VPN environments to ensure that the route reflector (and other PEs) can reach the customer prefix via the advertising PE, avoiding reachability issues when the original next-hop is not directly connected across the MPLS core.

Answer

The no synchronization command is invalid under address-family ipv4 vrf.

Answer

The send-community extended command is only needed for IPv4 unicast address family.

Answer

The redistribute ospf command will import OSPF routes into the VRF but not into BGP.

Question 10

A service provider is implementing MPLS L3VPN and needs to ensure that BGP route advertisement uses a specific next-hop. Which technique ensures BGP advertises the PE-CE next-hop instead of the PE-PE loopback?

Accepted Answer

next-hop-self. In MPLS L3VPN, the PE-CE next-hop (the PE interface facing the CE) must be advertised to the remote PE so that the remote PE knows to forward traffic directly to the local PE's CE-facing interface. The `next-hop-self` command on the PE forces BGP to set the next-hop to the PE's own IP address (typically the loopback or the interface used for BGP peering), which overrides the default behavior of preserving the original next-hop. This ensures that the remote PE uses the correct next-hop for VPN traffic.

Answer

Route-map with set next-hop

Answer

next-hop-unchanged

Answer

Disable next-hop-check

Question 11

Which TWO BGP path attributes are considered before AS-path length in the default best-path selection process?

Accepted Answer

Weight. Weight (D) is a Cisco-proprietary attribute that is checked first in the BGP best-path selection process, before AS-path length. Local Preference (E) is the second attribute evaluated, also preceding AS-path length. Both are considered before the AS-path length comparison in the default BGP decision process.

Answer

Origin code

Answer

Community

Answer

MED

Question 12

An SP's core router experiences excessive packet drops on a congested link. The QoS policy uses CBWFQ with 4 queues. The drops occur only in the queue for a premium business class. Which is the most likely cause?

Accepted Answer

The premium class is configured with a police action that drops traffic when it exceeds the committed information rate.. The premium business class queue is experiencing excessive packet drops because a police action configured with a 'drop' exceed-action is discarding traffic that exceeds the committed information rate (CIR). Unlike congestion management (queuing), policing is a congestion avoidance mechanism that drops packets immediately when the traffic rate surpasses the configured CIR, regardless of the queue depth or available bandwidth. This explains why drops occur only in the premium class queue, as the policer is explicitly dropping excess packets before they even enter the CBWFQ scheduler.

Answer

The 'bandwidth remaining' command is missing from the policy-map.

Answer

The interface is using MLP with interleaving.

Answer

The queue is using tail-drop without WRED.

Question 13

Refer to the exhibit. Which prerequisite for MPLS L3VPN is missing on PE1?

Accepted Answer

VRF is not defined. Option C is correct because the exhibit shows that PE1 has an interface configured with an IP address and MPLS enabled, but no VRF definition is present. For MPLS L3VPN, a VRF must be defined on the PE router to separate customer routing tables and to associate the customer-facing interface with that VRF. Without the VRF, the PE cannot import/export VPN routes or maintain per-VPN routing instances, which is a fundamental prerequisite for L3VPN operation.

Answer

MPLS is not enabled on the interface

Answer

LDP is not enabled globally

Answer

OSPF is not redistributed into BGP

Question 14

In a Segment Routing network with TI-LFA enabled, which mechanism prevents micro-loops during a link failure?

Accepted Answer

Explicit path with segment list and delay timer. In Segment Routing with TI-LFA, micro-loops are prevented by using an explicit path with a segment list and a delay timer. When a link fails, the protecting router installs a backup path with a segment list that steers traffic around the failure, and a delay timer ensures that the backup path is not activated until the network has converged, preventing transient loops.

Answer

Constraint Shortest Path First computation

Answer

Loop-Free Alternate precomputed backup paths

Answer

Prefix Independent Convergence with fast reroute

Question 15

A service provider is implementing QoS on a PE router for customer traffic. Which tool should be used to classify traffic based on application layer information?

Accepted Answer

MQC with NBAR. NBAR (Network-Based Application Recognition) is a deep packet inspection (DPI) engine within the Modular QoS CLI (MQC) that can identify applications by inspecting payloads up to Layer 7. This allows classification of traffic based on application-layer information such as HTTP, DNS, or proprietary protocols, which is exactly what the question requires.

Answer

Access-list

Answer

Shaping

Answer

Policy-map with police