350-401 Hard Questions — 25 Difficult Questions

Question 1

Refer to the exhibit. A network engineer is troubleshooting a routing issue. The route for 10.0.0.0/8 is learned via EIGRP with metric 2560512. Which change would most likely cause the metric to increase?

Accepted Answer

Increase the delay on GigabitEthernet0/0.. The EIGRP metric is calculated using the formula: metric = (K1 * bandwidth + (K2 * bandwidth) / (256 - load) + K3 * delay) * 256, with default K values (K1=1, K3=1, others=0). Increasing the delay on the outgoing interface (GigabitEthernet0/0) directly increases the delay component in the composite metric, causing the overall metric to increase. Option D is correct because delay is a key variable in the EIGRP metric calculation.

Answer

Increase the bandwidth on GigabitEthernet0/0.

Answer

Add a redistribute static command under EIGRP.

Answer

Change the administrative distance to 90.

Question 2

Refer to the exhibit. R1 has two equal-cost OSPF E2 routes to 10.1.1.0/24 via two different next hops. However, when tracing to 10.1.1.1, all traffic uses the path through 10.0.1.2. What is the most likely reason?

Accepted Answer

OSPF E2 routes do not factor interface cost; but the router uses the interface cost as a tie-breaker for equal-cost routes.. OSPF E2 routes do not include the internal cost to the ASBR; the cost shown in the routing table is the external metric only. When two E2 routes have the same external metric, Cisco IOS uses the interface cost as a tie-breaker to select the best next hop. In this scenario, the interface to 10.0.1.2 has a lower cost than the interface to 10.0.2.2, so all traffic is forwarded via 10.0.1.2.

Answer

One route has a higher administrative distance.

Answer

A default route is overriding the specific route.

Answer

The route via 10.0.2.2 is an E1 route.

Question 3

Your company has deployed a Cisco Catalyst 9300 switch stack as the distribution layer for a campus network. The network uses VLANs 10 (data), 20 (voice), and 30 (management). The switch stack is configured with DHCP snooping, Dynamic ARP Inspection (DAI), and IP Source Guard (IPSG) on access ports. Recently, users in VLAN 10 report intermittent connectivity issues. You notice that some users receive duplicate IP addresses from the DHCP server. The DHCP server is connected to a trunk port on the switch stack. After reviewing logs, you see that DHCPACK messages are being dropped on the trunk port. The DHCP snooping binding table shows entries for legitimate clients, but also some entries with MAC addresses from a different vendor. Which action should you take to resolve the issue?

Accepted Answer

Configure the trunk port connecting to the DHCP server as a trusted port for DHCP snooping.. The DHCP snooping feature treats all ports as untrusted by default, which means DHCP server messages (DHCPOFFER, DHCPACK, DHCPNAK) are dropped on untrusted ports. Since the DHCP server is connected to a trunk port and DHCPACK messages are being dropped, that trunk port must be explicitly configured as a trusted port for DHCP snooping using the 'ip dhcp snooping trust' interface command. This allows legitimate DHCP server responses to reach clients, resolving the duplicate IP address issue caused by clients not receiving their assigned addresses.

Answer

Manually shut down the access ports that have unknown MAC addresses in the binding table.

Answer

Disable Dynamic ARP Inspection on VLAN 10.

Answer

Disable IP Source Guard on all access ports in VLAN 10.

Question 4

Which TWO statements are true about RESTCONF and NETCONF in a Cisco IOS XE environment? (Choose two.)

Accepted Answer

RESTCONF uses HTTP methods (GET, POST, PUT, DELETE) and supports JSON and XML encoding.. Option A is correct because RESTCONF is designed to use standard HTTP methods (GET, POST, PUT, DELETE, PATCH) for CRUD operations on YANG-defined data, and it supports both JSON and XML encoding formats. This aligns with its goal of providing a simpler, web-friendly interface compared to NETCONF.

Answer

RESTCONF supports the candidate datastore for editing configurations.

Answer

NETCONF uses HTTP as its transport protocol.

Answer

RESTCONF and NETCONF both support JSON and XML encoding.

Question 5

An organization is migrating from a traditional three-tier architecture to a leaf-spine fabric using VXLAN EVPN. The design requires that virtual machines can move between racks without IP address changes. Which technology must be enabled at the leaf switches to support this mobility?

Accepted Answer

VXLAN with EVPN control plane.. VXLAN with EVPN control plane (B) is correct because it provides a Layer 2 overlay network that extends VLANs across the leaf-spine fabric, enabling virtual machine mobility without IP address changes. EVPN uses BGP to distribute MAC and IP address information, allowing the leaf switches to learn and forward traffic to VMs regardless of their physical location, which is essential for seamless VM migration between racks.

Answer

Overlay Transport Virtualization (OTV).

Answer

VRF-Lite with route redistribution.

Answer

MPLS L3VPN with BGP.

Question 6

A global enterprise is transitioning from a traditional three-tier campus architecture to a software-defined access (SD-Access) fabric. Which architectural consideration is most critical for the underlay network?

Accepted Answer

Configure a routed access layer with a link-state routing protocol (IS-IS or OSPF).. In an SD-Access fabric, the underlay network must provide IP connectivity between all fabric devices (edge, control plane, border nodes) using a routed access layer with a link-state routing protocol like IS-IS or OSPF. This ensures fast convergence, loop-free topology, and support for the overlay's VXLAN tunnels. A routed access layer eliminates spanning-tree dependencies and aligns with the fabric's requirement for a simple, scalable IP-based transport.

Answer

Implement PIM-SM for multicast routing in the underlay.

Answer

Preserve existing VLANs across the fabric to minimize changes.

Answer

Deploy VRF-lite on all edge nodes to isolate tenants.

Question 7

A network administrator is deploying a new QoS policy to prioritize voice traffic across a WAN link. The policy must ensure that voice packets are not dropped even during congestion, and that bandwidth is guaranteed for voice. Which queuing mechanism should be used for the voice class?

Accepted Answer

Low Latency Queuing (LLQ). LLQ is the correct choice because it combines strict priority queuing with CBWFQ, ensuring that voice traffic is placed into a strict priority queue that is serviced before any other queues. This guarantees low latency and prevents voice packet drops during congestion by allowing the priority queue to be policed to a configured bandwidth limit, while still providing bandwidth guarantees for the voice class.

Answer

Weighted Random Early Detection (WRED)

Answer

Class-Based Weighted Fair Queuing (CBWFQ)

Answer

First-In, First-Out (FIFO) queuing

Question 8

Which THREE conditions are required for OSPF routers to become fully adjacent? (Choose three.)

Accepted Answer

Same area ID. OSPF routers must share the same area ID to form a full adjacency because the area ID defines the link-state database scope. Routers in different areas cannot exchange Type 1 LSAs directly; they rely on ABRs for inter-area routing. Without matching area IDs, the routers will not even proceed to the 2-Way state.

Answer

Different router IDs

Answer

Same subnet mask

Question 9

Based on the exhibit, which traffic will be permitted outbound on GigabitEthernet0/0?

Accepted Answer

HTTP and HTTPS traffic from 192.168.1.0/24. The exhibit shows an access control list (ACL) applied outbound on GigabitEthernet0/0. The ACL permits TCP traffic from source 192.168.1.0/24 to any destination with a destination port of 80 (HTTP) or 443 (HTTPS). Therefore, only HTTP and HTTPS traffic from the 192.168.1.0/24 network is permitted outbound.

Answer

ICMP traffic from any source

Answer

FTP traffic from 192.168.1.0/24

Answer

SSH traffic from 192.168.1.0/24

Question 10

A network engineer is designing a data center network using Cisco ACI. The design must support multiple tenants with isolated policies. The engineer needs to ensure that traffic between endpoints in different tenants is blocked by default. Which ACI construct provides this isolation?

Accepted Answer

Tenant. In Cisco ACI, a Tenant is the top-level logical container that provides administrative and policy isolation. By default, endpoints in different tenants cannot communicate because each tenant has its own separate policy domain, and no contracts exist between them. This makes the Tenant the correct construct for ensuring traffic between different tenants is blocked by default.

Answer

VRF

Answer

Bridge Domain

Answer

Contract

Question 11

A network engineer configured VRF TENANT_A and moved the subinterfaces into the VRF. After the change, the CEF table shows the prefixes but the next-hop addresses are unreachable. What is the most likely cause?

Accepted Answer

The next-hop IP addresses are in the global routing table, not in the VRF.. When subinterfaces are moved into a VRF, the CEF table for that VRF will contain the learned prefixes, but the next-hop addresses must also be reachable within the same VRF. If the next-hop IP addresses reside in the global routing table instead of the VRF, the VRF will have no route to those next hops, causing them to be marked as unreachable. This is a common misconfiguration where the next-hop adjacency is not established within the VRF context.

Answer

LISP is not configured to map the virtual network.

Answer

OSPF is not redistributing the routes into the VRF.

Answer

The physical interface is not configured as a trunk.

Question 12

A company is implementing QoS in a campus network. Voice traffic must be prioritized over data traffic, and all traffic should be marked at Layer 2 and Layer 3. Which combination of marking values should be used on access ports to achieve this?

Accepted Answer

CoS 5, DSCP EF. Option C is correct because voice traffic requires strict priority queuing, which is achieved by marking with CoS 5 at Layer 2 and DSCP EF (46) at Layer 3. CoS 5 maps to the priority queue in Cisco switches, and DSCP EF is the standard per-hop behavior for Expedited Forwarding (RFC 3246), ensuring low latency and jitter for voice. Access ports must trust these markings to prioritize voice over data traffic.

Answer

CoS 5, DSCP AF41

Answer

CoS 5, DSCP CS3

Answer

CoS 4, DSCP EF

Question 13

An engineer is troubleshooting a BGP routing issue. The router is not receiving routes from an eBGP neighbor. The neighbor is reachable via ping. The BGP session is established and in the Established state. What is the most likely cause?

Accepted Answer

The next-hop IP address is not reachable.. The BGP session is established, which confirms that the TCP connection and BGP open messages have been successfully exchanged. However, routes are not being received. The most common cause in this scenario is that the next-hop IP address for the advertised routes is not reachable via the router's routing table. eBGP by default sets the next-hop to the IP address of the neighbor's interface, and if that address is not reachable (e.g., missing route, incorrect static route, or interface down), the router will not install the routes into the BGP table or the routing table.

Answer

The AS number is incorrect.

Answer

The BGP session is using an incorrect interface.

Answer

The network is not advertised under BGP.

Question 14

A network administrator is troubleshooting an issue where OSPF routes are not being learned from a neighbor. The administrator checks the OSPF configuration and sees that both routers are in the same area. The neighbor state is stuck in EXSTART. What is the most likely cause?

Accepted Answer

The interface MTU does not match.. When OSPF neighbors are stuck in the EXSTART state, it typically indicates a problem with the Database Description (DBD) packet exchange process. The most common cause is an MTU mismatch between the interfaces, because OSPF will not proceed to the Exchange state if the DBD packet is larger than the interface MTU and gets silently dropped. This prevents the routers from agreeing on the master/slave relationship and exchanging link-state information.

Answer

The router ID is the same on both routers.

Answer

The area ID is different.

Answer

The hello timer is set to 30 seconds on one router.

Question 15

A service provider wants to deploy a virtualized firewall as a VNF in a service chain. The VNF must be inserted transparently into the traffic path without requiring changes to the existing IP addressing. Which service chaining method should the architect choose?

Accepted Answer

Implement policy-based routing (PBR) to redirect traffic to the VNF.. Policy-based routing (PBR) allows the architect to redirect traffic to the VNF based on match criteria such as source/destination IP or protocol, without altering the existing IP addressing scheme. This enables transparent insertion of the VNF into the service chain, as PBR overrides the routing table for selected traffic and forwards it to the virtualized firewall, while the original IP headers remain unchanged.

Answer

Use static routing to point traffic to the VNF.

Answer

Deploy the VNF in inline mode with proxy ARP.

Answer

Use VRF-lite to separate traffic and route through the VNF.

Question 16

A network administrator is troubleshooting a DHCP snooping issue on a Cisco switch. The switch is configured with DHCP snooping globally and on VLAN 10. The trusted interface is GigabitEthernet0/1 connected to the DHCP server. However, clients on VLAN 10 are not receiving IP addresses from the DHCP server. What is the most likely cause?

Accepted Answer

The interface GigabitEthernet0/1 is not configured as a trusted port for DHCP snooping.. Option B is correct because the scenario states that DHCP snooping is configured globally and on VLAN 10, and that GigabitEthernet0/1 is connected to the DHCP server. However, for DHCP snooping to allow DHCP server messages (OFFER, ACK) to be forwarded, the interface connected to the legitimate DHCP server must be explicitly configured as a trusted port using the 'ip dhcp snooping trust' interface command. Without this, the switch treats all DHCP server responses as untrusted and drops them, preventing clients from receiving IP addresses.

Answer

The switch has IP Source Guard enabled, blocking valid DHCP traffic.

Answer

The DHCP server is on a different subnet and the switch lacks an IP helper address.

Answer

The DHCP server is sending offers too quickly, exceeding the rate-limit on the switch.

Question 17

Drag and drop the steps of OSPF route redistribution into a different autonomous system into the correct order, from first to last.

Accepted Answer

Configure OSPF process on the ASBR. Redistribution requires first configuring the routing process that will receive the routes, then defining the source protocol and metric, optionally setting route tags for loop prevention, applying a route map for filtering, and finally verifying the redistributed routes appear in the OSPF database.

Question 18

Drag and drop the steps of BGP best path selection process into the correct order, from first to last.

Accepted Answer

Prefer highest weight. BGP best path selection follows a strict order: first, prefer the path with the highest weight (Cisco proprietary). If equal, prefer highest local preference. Next, prefer locally originated routes (network/aggregate). Then, prefer the shortest AS_PATH. Finally, prefer the lowest MED (if same AS).

Question 19

A network engineer is configuring EIGRP on a router that connects to a service provider network. The engineer wants to advertise a default route to internal routers. The engineer configures 'ip default-network 0.0.0.0' and redistributes a static default route into EIGRP. However, internal routers are not receiving the default route. The engineer checks the EIGRP topology table and sees the default route with a metric of 1. What is the most likely reason?

Accepted Answer

The engineer used 'ip default-network' which is not supported in EIGRP; instead, 'default-information originate' should be used.. Option A is correct because EIGRP does not support the 'ip default-network' command to originate a default route; this command is used with IGRP. To advertise a default route in EIGRP, the engineer must use the 'default-information originate' command under the EIGRP process, which redistributes a static default route (0.0.0.0/0) into EIGRP. The presence of the default route in the topology table with a metric of 1 indicates it was redistributed, but without 'default-information originate', EIGRP will not advertise it to neighbors.

Answer

The static default route is not configured correctly; the engineer should use 'ip route 0.0.0.0 0.0.0.0 <next-hop>'.

Answer

The internal routers have a route to the default network with a better metric from another source.

Answer

The engineer needs to configure 'eigrp stub' on the router to allow default route advertisement.

Question 20

Which TWO statements about NETCONF and YANG are true?

Accepted Answer

YANG is a data modeling language used to define the structure of configuration and state data. Option D is correct because YANG (RFC 7950) is a data modeling language specifically designed to define the structure of configuration and state data, as well as notifications and RPCs, for network devices. It provides a hierarchical, schema-based representation of data that can be serialized into XML or JSON, making it the standard for modeling NETCONF and RESTCONF datastores.

Answer

NETCONF sessions are stateless

Answer

YANG defines both the data model and the RPC operations for network devices

Answer

NETCONF uses TLS as the mandatory transport protocol

350-401 Hard Questions — 25 Difficult Questions

Exhibit

350-401 Hard Questions — 25 Difficult Questions

Exhibit