350-501 Practice Test 30 — 15 Questions

Question 1

Refer to the exhibit. An engineer monitors the queue depths on a core interface. Which class is experiencing the most congestion?

Accepted Answer

Best-effort class, because its average depth is 580.. The exhibit shows that the best-effort class has an average queue depth of 580 packets, which is significantly higher than the voice class's average depth. This indicates that the best-effort class is experiencing the most congestion, as queue depth is a direct measure of buffered packets waiting for transmission. The voice class, despite having a taildrop threshold, has a much lower average depth, showing it is not as congested.

Answer

The interface is not congested because bandwidth is 1 Gbps.

Answer

Voice class, because it has a taildrop threshold.

Answer

Both classes equally, because they both have taildropping.

Question 2

A service provider is designing a new MPLS core network and wants to simplify traffic engineering without deploying a centralized controller. Which technology should be used to enable source-routed paths with explicit path control?

Accepted Answer

Segment Routing (SR-MPLS). Segment Routing (SR-MPLS) enables source-routed paths with explicit path control by encoding the path as a list of segment identifiers (SIDs) in the packet header, allowing the ingress router to steer traffic along a specific path without a centralized controller. This simplifies traffic engineering in an MPLS core network by eliminating the need for per-flow signaling and state maintenance on intermediate nodes, which is exactly what the question requires.

Answer

BGP-LU

Answer

LDP

Answer

RSVP-TE

Question 3

An engineer is configuring MPLS-TE FRR for link protection. Which of the following options describes a 1:1 protection scheme where a dedicated detour LSP is created for each protected LSP?

Accepted Answer

Detour LSP for each protected LSP. In MPLS-TE Fast Reroute (FRR), a 1:1 protection scheme means a dedicated detour LSP is created for each protected LSP. This provides per-LSP backup, ensuring that if a link fails, traffic is immediately switched to the detour tunnel. Option C correctly describes this exact mechanism, where each protected LSP has its own pre-established detour path.

Answer

Shared mesh protection

Answer

Bypass tunnel protecting multiple LSPs

Answer

Node protection bypass tunnel

Question 4

Which TWO statements about SR-MPLS compared to LDP are correct? (Choose two.)

Accepted Answer

SR-MPLS uses a global label block (SRGB) that is consistent across the domain.. SR-MPLS uses a Segment Routing Global Block (SRGB), which is a reserved label range (e.g., 16000–23999 per RFC 8660) that is configured consistently across all routers in the SR domain. This global consistency allows any router to interpret a label from the SRGB as the same topological or service instruction, eliminating the need for per-hop label negotiation.

Answer

SR-MPLS requires LDP for label distribution.

Answer

SR-MPLS supports only dynamic label allocation.

Answer

SR-MPLS requires RSVP-TE for TE tunnels.

Question 5

Which three are required components for deploying Segment Routing in an MPLS network? (Choose three.)

Accepted Answer

MPLS forwarding capability on routers. B is correct because Segment Routing relies on the existing MPLS forwarding plane; routers must be capable of pushing, swapping, and popping MPLS labels based on the Segment Routing label stack. Without MPLS forwarding hardware or software support, the SR-MPLS data plane cannot function, even if the control plane is configured.

Answer

RSVP-TE signaling protocol

Answer

LDP for label distribution

Question 6

A network operator is configuring RSVP-TE tunnels for traffic engineering in an MPLS core. They want to enforce that the tunnel path strictly follows a predefined set of hops. Which explicit path option should be used?

Accepted Answer

Strict. (Strict) is correct because RSVP-TE explicit paths with the 'strict' keyword require each hop in the path to be directly adjacent (connected) to the previous hop. This enforces that the tunnel path follows exactly the predefined set of hops without any intermediate routers being inserted, which is the requirement in the question.

Answer

Exact

Answer

Loose

Answer

Dynamic

Question 7

Which label distribution protocol is replaced by segment routing in SR-MPLS deployments?

Accepted Answer

LDP. In SR-MPLS deployments, segment routing replaces LDP as the label distribution protocol. LDP traditionally distributes labels for each prefix in the IGP, while segment routing uses the IGP itself to advertise prefix-SIDs and adjacency-SIDs, eliminating the need for a separate label distribution protocol. This simplifies the control plane and removes the dependency on LDP.

Answer

RSVP-TE

Answer

IGP itself

Answer

BGP

Question 8

A service provider is deploying MPLS L2VPN using Virtual Private Wire Service (VPWS). After configuration, the two CEs cannot ping each other. The PE routers show the xconnect interface is up, but no MAC addresses are learned. What is the most likely cause?

Accepted Answer

The VC ID mismatch between the two PEs. In MPLS L2VPN VPWS, the VC ID (Virtual Circuit ID) must match on both PE routers to establish the pseudowire between them. A mismatch prevents the pseudowire from coming up, so even though the local xconnect interface shows as up (because the attachment circuit is operational), no MAC learning can occur because the pseudowire control plane (e.g., LDP or BGP signaled) fails to bind the two endpoints. This directly explains why the CEs cannot ping and no MAC addresses are learned.

Answer

The MTU on the core links is less than 1500

Answer

The control word is enabled on one PE but not the other

Answer

The encapsulation type on the AC is different on the two PEs

Question 9

An engineer is troubleshooting a BGP route reflector setup. Clients are not receiving all routes. The 'show bgp neighbors' output shows a state of 'Active'. What is the most likely cause?

Accepted Answer

Incorrect BGP neighbor statement on the route reflector or client. The 'Active' state in BGP indicates that the router is trying to establish a TCP connection with the neighbor but has not yet succeeded. This is most commonly caused by a misconfiguration in the BGP neighbor statement, such as an incorrect IP address, wrong AS number, or a missing neighbor statement on one side. Since the route reflector is not forming a BGP session, clients cannot receive any routes, which explains the symptom.

Answer

The route reflector does not have a full mesh with clients

Answer

The route reflector is detecting an AS_PATH loop

Answer

Next-hop reachability issue

Question 10

In an EVPN-VPWS (Virtual Private Wire Service) deployment, which identifier is used to uniquely identify an Ethernet Segment for multi-homing?

Accepted Answer

Ethernet Segment Identifier (ESI). In EVPN-VPWS, the Ethernet Segment Identifier (ESI) uniquely identifies an Ethernet Segment across all multi-homed Provider Edge (PE) nodes. This 10-byte value is used in Designated Forwarder (DF) election and split-horizon filtering to prevent loops when a Customer Edge (CE) is multi-homed to multiple PEs. The ESI is carried in EVPN routes (Type 1 and Type 4) to signal multi-homing membership.

Answer

Ethernet Tag ID

Answer

MAC address of the CE

Answer

Route Distinguisher (RD)

Question 11

A network engineer is configuring Segment Routing on an IOS-XR router. They want to use the preferred algorithm for automatically computing paths based on IGP metrics. Which algorithm should be configured under the SR segment list?

Accepted Answer

preferred. The 'preferred' algorithm is the correct choice because it instructs the router to automatically select the best algorithm for path computation based on IGP metrics. In Segment Routing, the 'preferred' algorithm uses the default SPF (Shortest Path First) algorithm, which computes paths based solely on IGP link metrics, ensuring optimal routing without additional constraints.

Answer

strict-spf

Answer

delay

Answer

te

Question 12

A service provider is deploying MPLS in its core network. The core routers are all configured with LDP. Which label operation does an ingress PE perform on the first packet of a new flow?

Accepted Answer

Push a new label onto the packet. The ingress PE (Provider Edge) router is the first router in the MPLS domain to receive an unlabeled IP packet. For the first packet of a new flow, the ingress PE must perform a label push operation, which adds an MPLS label (or a stack of labels) to the packet. This label is used by subsequent LSRs to forward the packet based on the label rather than the IP header, enabling MPLS forwarding.

Answer

Remove the label stack entirely

Answer

Pop the label (PHP)

Answer

Swap the incoming label for an outgoing label

Question 13

Which TWO are functions of the MPLS data plane?

Accepted Answer

Label push at ingress LSR. The MPLS data plane is responsible for the actual forwarding of packets based on labels. At the ingress LSR, the data plane performs a label push operation, which involves inserting a new MPLS label (or a stack of labels) onto the incoming IP packet before forwarding it into the MPLS domain. This action is a fundamental data-plane function, as it directly manipulates the packet header to enable label switching.

Answer

Label distribution via LDP

Answer

Metric calculation for routing

Answer

Route exchange via BGP

Question 14

In SP automation, which protocol is used by NSO to communicate with network devices for configuration management?

Accepted Answer

NETCONF. NSO uses NETCONF as the southbound protocol to communicate with devices. NETCONF provides transactional configuration operations like edit-config and get-config.

Answer

RESTCONF

Answer

SNMP

Answer

CLI

Question 15

To secure NTP in a service provider network, which feature should be enabled on IOS XR routers to prevent time synchronization with unauthorized NTP servers?

Accepted Answer

NTP authentication with MD5 keys. NTP authentication ensures that the router only synchronizes with trusted servers that have the correct key. Access lists can also limit, but authentication provides cryptographic verification. NTP broadcast mode is less secure; symmetric mode is for peer-to-peer.

Answer

NTP symmetric active mode

Answer

NTP broadcast client mode

Answer

NTP access group with read-only community