350-501 Practice Test 31 — 15 Questions

Question 1

A service provider is designing its core network to carry both IPv4 and IPv6 traffic. Which BGP approach best minimizes routing table size on core routers while maintaining full reachability?

Accepted Answer

Use iBGP with route reflectors. iBGP with route reflectors minimizes the number of BGP sessions required in the core network, reducing routing table size and control-plane overhead while still maintaining full IPv4 and IPv6 reachability. Route reflectors allow iBGP speakers to advertise routes learned from other iBGP peers without requiring a full mesh, which is essential for scalability in large service provider cores.

Answer

Use eBGP between all core routers

Answer

Use static routing for all prefixes

Answer

Rely on OSPF for external routes

Question 2

An engineer is troubleshooting an MPLS VPN issue where CE1 cannot ping CE2 across the provider network. The PE routers are configured with MP-BGP and LDP. On PE1, 'show ip bgp vpnv4 vrf CUST' shows the route to CE2's loopback as valid, but 'show mpls forwarding-table' does not list a label for that prefix. What is the most likely cause?

Accepted Answer

Route target mismatch between PE1 and PE2. The route is present in the VRF BGP table on PE1 (valid), but no MPLS label is assigned for that prefix in the forwarding table. This indicates that PE1 has learned the route via MP-BGP but cannot install it into the MPLS forwarding table because the route target (RT) import policy on PE1 does not match the RT export policy on PE2. Without a matching RT, PE1 does not consider the VPNv4 route as belonging to the CUST VRF, so it cannot resolve the next hop or assign a label for forwarding.

Answer

MTU mismatch on the MPLS core interfaces

Answer

LDP is not enabled on the core link between PE1 and P

Answer

BGP session between PE1 and PE2 is not established

Question 3

An engineer is configuring QoS on a service provider edge router to prioritize real-time traffic. Which queuing mechanism provides the lowest latency and jitter for voice traffic?

Accepted Answer

LLQ. LLQ (Low Latency Queuing) is the correct choice because it combines a strict priority queue with CBWFQ, ensuring that voice traffic is always served before any other queue. This strict priority scheduling minimizes both latency and jitter for real-time traffic, which is critical for voice quality.

Answer

FIFO

Answer

CBWFQ

Answer

WRED

Question 4

A service provider is implementing EVPN with MPLS data plane. Which encapsulation type is used in MPLS EVPN to carry Ethernet frames across the MPLS network?

Accepted Answer

MPLS label stack with a control word for Ethernet frames. In MPLS EVPN, Ethernet frames are carried across the MPLS network using an MPLS label stack that includes a control word. The control word (4 bytes) is inserted between the MPLS label stack and the Ethernet frame to prevent misordering and to enable proper frame delineation. This encapsulation is defined in RFC 8214 (formerly RFC 7432) and is distinct from older EoMPLS or simple IP/MPLS tunneling.

Answer

Ethernet over MPLS (EoMPLS) with VLAN encapsulation

Answer

EVPN encapsulation defined by IETF RFC 7432

Answer

IP/MPLS tunnel with Ethernet frame inside

Question 5

In BGP route reflection, what is the purpose of the ORIGINATOR_ID attribute?

Accepted Answer

To prevent routing loops by ensuring that a route is not reflected back to its originator. ORIGINATOR_ID is a non-transitive optional attribute that identifies the router that originated the route into the iBGP domain, used to prevent loops.

Answer

To indicate the next-hop IP address

Answer

To identify the route reflector

Answer

To carry the community value

Question 6

A service provider is experiencing suboptimal routing due to BGP route reflection. To improve path selection while maintaining IBGP scalability, which feature should be implemented?

Accepted Answer

BGP optimal route reflection (ORR). BGP optimal route reflection (ORR) improves path selection by allowing the route reflector to calculate the best path based on the IGP metric to the client's location, rather than using its own BGP table. This overcomes the suboptimal routing caused by standard route reflection, where the RR's best path may not be optimal for all clients, while still maintaining IBGP scalability by avoiding a full mesh.

Answer

BGP deterministic med

Answer

BGP next-hop-self

Answer

BGP add-path

Question 7

Which TWO are essential components for deploying EVPN in a service provider network?

Accepted Answer

Overlay tunnel encapsulation such as VXLAN or MPLS. A is correct because EVPN requires an overlay tunnel encapsulation to transport Layer 2 frames across the IP/MPLS underlay. VXLAN (RFC 7348) and MPLS (RFC 7432) are the two primary encapsulations used to carry Ethernet frames over the overlay, enabling MAC address learning and forwarding in the EVPN control plane.

Answer

OSPF as the underlay routing protocol

Answer

PIM-SM for multicast replication

Answer

RSVP-TE for path computation

Question 8

Drag and drop the steps to configure MPLS LDP on a Cisco router into the correct order.

Accepted Answer

Step 1: Enable CEF (ip cef), Step 2: Configure LDP router-id (mpls ldp router-id), Step 3: Enable MPLS on interfaces (mpls ip). MPLS LDP requires CEF, enabling MPLS on interfaces, and setting the LDP router-id.

Answer

Step 1: Enable MPLS on interfaces (mpls ip), Step 2: Enable CEF (ip cef), Step 3: Configure LDP router-id (mpls ldp router-id)

Answer

Step 1: Configure LDP router-id (mpls ldp router-id), Step 2: Enable CEF (ip cef), Step 3: Enable MPLS on interfaces (mpls ip)

Answer

Step 1: Enable CEF (ip cef), Step 2: Enable MPLS on interfaces (mpls ip), Step 3: Configure LDP router-id (mpls ldp router-id)

Question 9

A service provider is deploying a new automation framework using Ansible to configure MPLS VPNs. They need to ensure that the Ansible playbook can handle configuration rollback in case of failure. Which Ansible feature should be used?

Accepted Answer

Use the 'backup' option in the ios_config module. The 'backup' option in the ios_config module instructs Ansible to save a copy of the running configuration to a local file before making any changes. If the playbook fails or produces an undesired state, the operator can restore the device to the previous configuration using that backup file. This provides a straightforward rollback mechanism for MPLS VPN deployments without requiring external version control or manual snapshots.

Answer

Use 'tags' to selectively apply tasks

Answer

Use 'check_mode' to validate changes before applying

Answer

Set 'ignore_errors' to true

Question 10

Which protocol is used by NSO to communicate with network devices for configuration management?

Accepted Answer

NETCONF. NSO (Network Services Orchestrator) uses NETCONF as its primary protocol for configuration management because NETCONF provides a standardized, transaction-based mechanism for editing device configurations using YANG data models. This allows NSO to perform atomic, rollback-capable configuration changes across multiple network devices, which is essential for service orchestration.

Answer

gRPC

Answer

SNMP

Answer

HTTP

Question 11

A service provider is experiencing high CPU usage on a router running BGP. Which action should be taken first to mitigate the issue without disrupting traffic?

Accepted Answer

Apply inbound route filtering using prefix lists.. High CPU usage on a BGP-speaking router is often caused by processing a large number of BGP updates. Applying inbound route filtering using prefix lists (option C) reduces the number of routes the router must process and store, directly lowering CPU load without disrupting existing traffic flows. This is a non-disruptive, targeted mitigation that addresses the root cause of excessive route processing.

Answer

Disable BGP on the router.

Answer

Increase the BGP keepalive timer.

Answer

Implement BGP route dampening.

Question 12

A network engineer needs to automate configuration of multiple Cisco routers and wants to use a protocol that supports both datastore operations and selective retrieval of configuration. Which protocol should be used?

Accepted Answer

NETCONF. NETCONF (RFC 6241) is the correct choice because it is designed specifically for network configuration management, supporting full datastore operations (e.g., , , ) and selective retrieval of configuration data using subtree or XPath filtering. This aligns directly with the engineer's requirement for both datastore operations and selective retrieval.

Answer

SNMPv3

Answer

gRPC

Answer

OpenFlow

Answer

RESTCONF

Question 13

A large enterprise recently implemented centralized QoS policies using Cisco DNA Center. The policies are pushed via RESTCONF to the branch routers. After the deployment, the branch office reports that critical business applications (like ERP) are being delayed. The network team verifies that the QoS policy is applied correctly on the WAN interface (Serial0/0/0) with a shape of 10 Mbps. The policy-map has a class for 'critical-data' with bandwidth 5 Mbps and another class for 'transactional-data' with bandwidth 3 Mbps. The remaining traffic is in class-default with fair-queue. The branch router's CPU utilization is normal. The interface output shows that the queue for critical-data is rarely full, but packets are experiencing high latency. The engineer pings from the branch server to the central site and sees 200 ms RTT normally, but up to 500 ms during peak hours. What is the most likely cause of the high latency for critical-data?

Accepted Answer

The shape rate is too low; increase it to match the access link speed (e.g., 20 Mbps).. The shape rate of 10 Mbps is the bottleneck. Even though the critical-data class has a bandwidth guarantee of 5 Mbps, the overall interface is shaped to 10 Mbps. During peak hours, when the sum of all traffic (critical, transactional, and default) exceeds 10 Mbps, packets are queued at the shaper. This queueing introduces additional delay (up to 500 ms) for all classes, including critical-data, because the shaper enforces a single token bucket for the entire interface. Increasing the shape rate to match the actual access link speed (e.g., 20 Mbps) would reduce the queuing delay by allowing more traffic to be transmitted immediately.

Answer

The critical-data class needs a priority command to reduce latency.

Answer

The queue-limit for critical-data is too high; reduce it to force early drops.

Answer

The bandwidth command in critical-data should be increased above 5 Mbps.

Question 14

Which TWO are characteristics of SR-MPLS when compared to LDP-based MPLS? (Choose two.)

Accepted Answer

Labels are distributed via IGP extensions.. SR-MPLS eliminates LDP and RSVP state, using IGP for label distribution (e.g., via IS-IS TLVs).

Answer

SR-MPLS uses IPv6 SIDs only.

Answer

Labels are distributed using LDP.

Answer

SR-MPLS requires RSVP-TE for traffic engineering.

Question 15

In an MPLS network, which field in the MPLS label header is used to carry QoS information between LSRs?

Accepted Answer

EXP bits. In MPLS, the EXP (Experimental) bits, also known as the Traffic Class (TC) field per RFC 5462, are 3 bits in the MPLS label header used to carry Quality of Service (QoS) information between Label Switch Routers (LSRs). These bits allow LSRs to apply per-hop behaviors (PHBs) such as queuing and scheduling based on the packet's QoS class, enabling differentiated services across the MPLS network.

Answer

ToS

Answer

IP Precedence

Answer

DSCP