350-501 Practice Test 36 — 15 Questions

Question 1

In SRv6, what is the function of the 'End.DT4' behavior?

Accepted Answer

Decapsulation and IPv4 lookup in a VRF table. End.DT4 is an SRv6 endpoint behavior that decapsulates an IPv4 packet from an SRv6 header and performs an IPv4 lookup in a specified VRF table. It is used for IPv4 VPN services, allowing IPv4 payloads to be forwarded based on the VRF routing table. This behavior is defined in RFC 8986 and is essential for interworking between SRv6 and IPv4 VPNs.

Answer

Decapsulation and IPv6 lookup in a VRF table

Answer

Decapsulation and Ethernet switching

Answer

Encapsulation and forwarding to an IPv6 destination

Question 2

In RSVP-TE, which filter spec style allows multiple senders to share the same reserved resources on a link, as long as their flows do not exceed the reservation?

Accepted Answer

Shared Explicit (SE). The Shared Explicit (SE) filter spec style in RSVP-TE allows multiple senders to share the same reserved resources on a link, as long as their combined flows do not exceed the reservation. This is used for make-before-break and for merging flows from different senders into a single reservation. The SE style explicitly lists the senders that can share the reservation.

Answer

Distinct Explicit (DE)

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Fixed Filter (FF)

Answer

Wildcard Filter (WF)

Question 3

An SP uses NSO with a YANG service model to provision L3VPNs. Which database in NSO stores the configuration and state for all managed devices?

Accepted Answer

Configuration Database (CDB). The Configuration Database (CDB) is correct because NSO stores all service and device configuration in the CDB, which is the central transactional datastore that NSO reads and writes when provisioning L3VPNs via YANG service models. The CDB holds both the intended configuration and, through the operational data store, the state synchronized from managed devices.

Answer

Operational database

Answer

YANG repository

Answer

NED database

Question 4

What is the purpose of the SRGB (Segment Routing Global Block) in SR-MPLS?

Accepted Answer

It defines a contiguous block of labels used for global SIDs such as Node SIDs.. The Segment Routing Global Block (SRGB) is a reserved, contiguous range of MPLS labels (default 16000–23999 on Cisco) from which globally significant SIDs — most notably Node SIDs — are allocated. Because the SRGB is consistent across the SR domain, any node can interpret a global SID in that range to reach the same destination, enabling stateless source routing.

Answer

It defines the range of labels for Adjacency SIDs.

Answer

It is used to reserve labels for RSVP-TE tunnels.

Answer

It is the set of labels allowed for MPLS VPNs.

Question 5

A service provider wants to prevent IP spoofing at the customer edge by verifying that the source IP address of incoming packets is reachable via the interface they arrive on. Which uRPF mode should be used?

Accepted Answer

Strict mode. Strict uRPF checks that the source IP of an incoming packet is reachable via the exact same interface the packet arrived on, using the FIB. If the reverse path points to a different interface, the packet is dropped, which directly prevents spoofed source addresses at the customer edge. This is the intended mode when the SP knows the customer's legitimate prefix is only reachable through that specific link.

Answer

ACL-based filtering

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Reverse path filtering disabled

Answer

Loose mode

Question 6

A service provider is deploying network slicing for 5G services. Which slice type is characterized by low latency and high reliability for applications like autonomous driving?

Accepted Answer

uRLLC. uRLLC (Ultra-Reliable Low-Latency Communication) is the 5G slice type specifically designed for mission-critical applications requiring sub-millisecond to a few-millisecond latency and 99.999% reliability, such as autonomous driving, remote surgery, and industrial automation. It is one of the three canonical 5G service categories defined by ITU-R IMT-2020.

Answer

FMC

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eMBB

Answer

mMTC

Question 7

In a Cisco IOS XR router, which statement best describes process separation?

Accepted Answer

Each protocol runs as a separate process with its own memory space. Cisco IOS XR is built on a microkernel architecture where each routing protocol and key system function runs as an independent process with its own protected memory space. This process separation means that a crash or memory corruption in one protocol (e.g., OSPF) does not affect other protocols or the core system, greatly improving high availability. The correct option directly reflects this design principle, which is a fundamental differentiator of IOS XR compared to classic IOS.

Answer

Processes share memory to improve performance

Answer

All routing protocols run in a single process to reduce memory usage

Answer

Only BGP runs as a separate process; others are monolithic

Question 8

Which BGP address family must be used to exchange VPNv4 routes between PE routers in an MPLS L3VPN?

Accepted Answer

VPNv4 unicast. In an MPLS L3VPN, VPNv4 routes carry both the IPv4 prefix and the Route Distinguisher (RD) to ensure uniqueness across overlapping customer address spaces. The VPNv4 unicast address family (address-family ipv4 vpn) is the mandatory BGP address family used between PE routers to exchange these VPNv4 routes, enabling MPLS-based VPN reachability.

Answer

RT constraint

Answer

IPv4 unicast

Answer

L2VPN VPLS

Question 9

A service provider is deploying Segment Routing in the MPLS core using IS-IS. Which extension is required in IS-IS to advertise the prefix-SID?

Accepted Answer

Sub-TLV 3 (Prefix-SID). In IS-IS, the Prefix-SID is advertised using Sub-TLV 3, which is carried within TLV 135 (Extended IP Reachability). This sub-TLV contains the SID value and flags, enabling Segment Routing in the MPLS core. Without Sub-TLV 3, the prefix-SID cannot be signaled, making it the required extension.

Answer

TLV 22 (Extended IS Reachability)

Answer

TLV 242 (Router Capability)

Answer

TLV 135 (Extended IP Reachability)

Question 10

A service provider is deploying uRPF on customer-facing interfaces to prevent IP spoofing. The network has asymmetric routing due to multiple upstream connections. Which uRPF mode should be used?

Accepted Answer

Loose mode. Strict mode requires the source address to be reachable via the incoming interface, which fails with asymmetric routing. Loose mode only checks that the source address exists in the routing table, making it suitable for asymmetric paths.

Answer

Strict mode

Answer

uRPF with allow-default

Answer

uRPF is not recommended for asymmetric routing

Question 11

A service provider is using Cisco Peakflow for DDoS detection. Peakflow identifies anomalies based on network traffic telemetry. Which data collection method does Peakflow primarily use?

Accepted Answer

NetFlow/IPFIX. Cisco Peakflow (formerly Arbor Networks) is a NetFlow/IPFIX-based DDoS detection platform. It collects flow telemetry exported by routers and switches, then applies behavioral analysis and anomaly detection to identify volumetric and application-layer attacks. NetFlow/IPFIX provides the per-flow metadata (src/dst IP, ports, protocol, byte/packet counts) that Peakflow's algorithms require.

Answer

Syslog

Answer

SNMP polling

Answer

Packet capture

Question 12

A service provider is designing an MPLS L3VPN network to provide Layer 3 VPN services to multiple customers. Which two statements correctly describe the roles of the Provider Edge (PE) and Customer Edge (CE) routers in this architecture?

Accepted Answer

PE routers advertise customer routes via MP-BGP with route distinguishers and route targets.. Option C is correct because in an MPLS L3VPN, PE routers use MP-BGP (multiprotocol BGP, specifically the VPNv4/VPNv6 address families) to advertise customer routes across the provider backbone, and each route is tagged with a Route Distinguisher (RD) to make the prefix unique and Route Targets (RTs) to control import/export into the correct VRFs. Option E is correct because each PE router maintains separate VRF (Virtual Routing and Forwarding) tables per customer VPN, isolating customer routing information and allowing overlapping address spaces between different customers. Option A is incorrect because P (provider core) routers only forward labeled packets and do not store customer VPN routes; they typically hold only the provider's global/IGP routes and label bindings. Option B is incorrect because CE routers are customer-owned devices that do not run MPLS label switching between PEs; label imposition/disposition and VPN label switching occur on the PE routers. Option D is incorrect because CE routers do not participate in the service provider's IGP; the PE-CE routing exchange uses a separate routing protocol or static routes within the VRF, not the provider's core IGP.

Answer

P routers store all customer VPN routes in their global routing table.

Answer

CE routers perform MPLS label switching between PE routers.

Answer

CE routers participate in the service provider's IGP to exchange loopback addresses.

Question 13

A service provider wants to offer a point-to-point Ethernet service between two customer sites with a defined bandwidth and performance guarantee, according to MEF standards. Which Carrier Ethernet service type is appropriate?

Accepted Answer

E-Line. MEF defines E-Line as a point-to-point Ethernet service connecting exactly two customer sites (UNIs) with a committed bandwidth and performance guarantee — matching the requirement for a dedicated point-to-point service with defined bandwidth. E-Line is the Carrier Ethernet equivalent of a leased line or EPL (Ethernet Private Line).

Answer

E-LAN

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E-Access

Answer

E-Tree

Question 14

An SP is deploying SR-TE policies using PCEP. What is the role of the SR-PCE in this architecture?

Accepted Answer

It computes explicit paths and sends them to routers via PCEP. The SR-PCE (Segment Routing Path Computation Element) computes explicit paths for SR-TE policies and sends them to routers via PCEP (Path Computation Element Communication Protocol). It acts as a centralized controller that has a full view of the network topology and can calculate optimal paths based on constraints, then distributes those paths to the head-end routers.

Answer

It forwards MPLS packets based on labels

Answer

It stores all routing tables in the network

Answer

It replaces the IGP for routing

Question 15

A junior automation engineer is writing a Python script to configure OSPF on a Cisco IOS-XE router using RESTCONF. The script sends a PUT request to update the OSPF configuration but receives a 401 Unauthorized response. The engineer has configured a local user with privilege 15 on the router and enabled restconf. The engineer verified that the router's RESTCONF API is running on port 443. What is the most likely missing element in the script?

Accepted Answer

The script must use HTTP basic authentication with the correct username and password.. A 401 Unauthorized response from RESTCONF indicates that the request lacks valid authentication credentials. Even though the engineer configured a privilege-15 local user and enabled RESTCONF on port 443, the Python script must actually send those credentials using HTTP Basic Authentication (or another supported method). Without the Authorization header containing the username and password, the router rejects the request with 401.

Answer

The script must include an Accept header.

Answer

The script must include a Content-Type header set to application/yang-data+json.

Answer

The script must use HTTPS with a valid certificate.