350-501 Services Practice Test 2 — 15 Questions

Question 1

Which THREE of the following L3VPN services require the use of a dedicated control plane per VPN instance?

Accepted Answer

6VPE. 6VPE (IPv6 VPN Provider Edge) requires a dedicated control plane per VPN instance because it uses separate per-VPN routing tables and a distinct BGP session (typically MP-BGP with the IPv6 address family) to exchange IPv6 VPN routes. This ensures that each customer's IPv6 routing information is isolated and processed independently, which is a core requirement for L3VPN services that maintain per-VPN forwarding and control plane separation.

Answer

VPLS

Answer

MDT VPN

Question 2

Refer to the exhibit. CE1 is not receiving the VPNv4 route for the 192.168.1.0/24 subnet. What is the most likely cause?

Accepted Answer

PE1 is missing the neighbor statement under address-family ipv4 vrf CUSTOMER_A. For CE1 to receive the VPNv4 route for 192.168.1.0/24, PE1 must redistribute the route from the VRF into BGP. The neighbor statement under address-family ipv4 vrf CUSTOMER_A is required to establish an eBGP peering with CE1 and exchange IPv4 routes within that VRF. Without it, PE1 will not send any routes to CE1, even if the VRF and route targets are correctly configured.

Answer

PE1 is missing the VRF configuration for CUSTOMER_A

Answer

CE1 is missing the network statement under router bgp 65001

Answer

The neighbor 10.0.0.2 is using an incorrect update-source

Question 3

A service provider is deploying a point-to-point Layer 2 VPN across an MPLS network using Ethernet over MPLS (EoMPLS) with Martini encapsulation. The customer requires transparent transport of VLAN tags (Q-in-Q) between two sites. The provider configures the attachment circuits on the PE routers as VLAN subinterfaces with dot1q encapsulation. After configuration, the customer reports that only untagged frames pass through the pseudowire; double-tagged frames are dropped at the egress PE. Which action resolves the issue?

Accepted Answer

Change the encapsulation on the PE subinterfaces to dot1q second-dot1q and enable the preservation of the outer VLAN tag at the ingress PE. EoMPLS with Martini encapsulation (RFC 4448) supports Q-in-Q transparent transport only when the ingress PE is configured to preserve the outer VLAN tag. Using 'dot1q second-dot1q' encapsulation on the subinterface tells the PE to treat the outer tag as part of the payload and not strip it, allowing both tags to be carried across the pseudowire. Without this, the default dot1q encapsulation strips the outer tag, causing double-tagged frames to be dropped at the egress PE.

Answer

Replace the attachment circuit with a port-mode Layer 2 interface and disable VLAN tagging on the PE

Answer

Configure the pseudowire to use the 'tag-imposition' keyword to allow double tagging

Answer

Configure the PE routers to use VLAN translation to map both tags to a single tag before encapsulation

Question 4

Drag and drop the steps to configure a GRE tunnel on a Cisco router into the correct order.

Accepted Answer

Step 1: Create tunnel interface (interface tunnel0), Step 2: Configure tunnel source (tunnel source source-ip), Step 3: Configure tunnel destination (tunnel destination dest-ip), Step 4: Assign IP address (ip address ip mask). GRE tunnel configuration involves creating the tunnel interface, setting source and destination, and assigning an IP address.

Answer

Step 1: Create tunnel interface, Step 2: Assign IP address, Step 3: Configure tunnel source, Step 4: Configure tunnel destination

Answer

Step 1: Configure tunnel destination, Step 2: Configure tunnel source, Step 3: Create tunnel interface, Step 4: Assign IP address

Answer

Step 1: Assign IP address, Step 2: Create tunnel interface, Step 3: Configure tunnel source, Step 4: Configure tunnel destination

Question 5

Match each Segment Routing component to its function.

Accepted Answer

SID: A unique identifier for a segment in a segment routing network.. In Segment Routing, SID uniquely identifies a segment, SRGB reserves a label range for global SIDs, and Prefix-SID is a global SID for an IGP prefix. Common confusions include mixing SID with SRGB and Prefix-SID with Adjacency-SID.

Answer

SID: A range of MPLS labels reserved for global segments.

Answer

Prefix-SID: A local SID assigned to a specific adjacency.

Question 6

A service provider is migrating its MPLS core from LDP to Segment Routing with MPLS data plane (SR-MPLS). The network currently uses TE tunnels with RSVP-TE for traffic engineering. Which technology can the provider use to continue performing traffic engineering after the migration without requiring RSVP-TE?

Accepted Answer

SR-TE. C is correct because Segment Routing Traffic Engineering (SR-TE) allows the service provider to perform traffic engineering without RSVP-TE by using segment lists (label stacks) to steer traffic along explicit paths. SR-TE leverages the IGP (OSPF or IS-IS) to distribute segment IDs (SIDs) and uses a centralized controller or headend node to compute and enforce TE policies, eliminating the need for RSVP-TE's per-flow signaling and state maintenance.

Answer

LDP

Answer

MPLS-TE (RSVP-TE)

Answer

BGP-LU

Question 7

A network engineer is configuring QoS on a Cisco ASR 9000 router to support multiple traffic classes. The policy must ensure that real-time traffic (EF) is not starved by high-volume bulk data (AF11). Which queuing strategy should be applied to the EF class to provide low latency and strict priority?

Accepted Answer

Priority Queuing (LLQ). Low Latency Queuing (LLQ) is the correct choice because it combines strict priority queuing with CBWFQ, ensuring that EF (real-time) traffic is always served before other queues. This prevents starvation of delay-sensitive traffic by bulk data (AF11) while still allowing fair treatment of other classes. LLQ is the standard Cisco mechanism for supporting real-time traffic like VoIP with guaranteed low latency.

Answer

Weighted Round Robin (WRR)

Answer

Class-Based Weighted Fair Queuing (CBWFQ)

Answer

First-In-First-Out (FIFO)

Question 8

A service provider is implementing Multicast VPN (MVPN) in an MPLS backbone. They use Rosen GRE (draft-rosen) for multicast transport. What is the primary limitation of Rosen GRE compared to mLDP-based MVPN?

Accepted Answer

All multicast traffic is sent to every PE in the VPN, even if no receiver exists.. In Rosen GRE (draft-rosen) MVPN, a default MDT (Multicast Distribution Tree) is built using a shared PIM-SM group across all PEs in the VPN. All multicast traffic from any source in the VPN is encapsulated in GRE and sent to this default MDT group, meaning every PE receives the traffic regardless of whether it has any local receivers. This is the primary limitation because it wastes bandwidth and processing on PEs that do not need the traffic, unlike mLDP-based MVPN which builds trees only to PEs with receivers.

Answer

It requires full-mesh of GRE tunnels between all PEs.

Answer

It cannot use Source-Specific Multicast (SSM).

Answer

It does not support Protocol Independent Multicast (PIM).

Question 9

An SP is designing a MPLS L3VPN service with BGP as the PE-CE routing protocol. They want to ensure that the CE router does not become a transit router between two sites. Which BGP feature should be configured on the PE to prevent the CE from advertising routes received from one site to another?

Accepted Answer

Site of Origin (SoO). The Site of Origin (SoO) BGP community is the correct feature because it prevents routing loops in MPLS L3VPN environments where the same CE router connects to multiple sites. When configured on the PE, SoO tags routes received from a CE with a unique identifier for that site; if the PE receives a route with the same SoO value from another site, it discards the route, ensuring the CE does not become a transit router between sites.

Answer

allowas-in

Answer

disable-connected-check

Answer

as-override

Question 10

A service provider is deploying LISP (Locator/ID Separation Protocol) to provide mobility and multihoming for customer endpoints. Which LISP component is responsible for maintaining the mapping between Endpoint Identifiers (EIDs) and Routing Locators (RLOCs) and for responding to Map-Request messages from ITRs?

Accepted Answer

Map-Server (MS). The Map-Server (MS) is the central control-plane component in LISP that maintains the authoritative mapping database of EID-to-RLOC entries. When an Ingress Tunnel Router (ITR) sends a Map-Request for an unknown EID, the Map-Server receives it, looks up the mapping, and either responds directly or forwards the request to the appropriate Egress Tunnel Router (ETR) for a reply. This makes the MS the correct answer for maintaining mappings and responding to Map-Requests.

Answer

Ingress Tunnel Router (ITR)

Answer

Map-Resolver (MR)

Answer

Egress Tunnel Router (ETR)

Question 11

A service provider is implementing QoS policies on an access aggregation router. They want to shape traffic to a downstream DSLAM to 10 Mbps, but they do not want to exceed the shaping rate even if the line rate is higher. Which QoS tool should be used on the interface facing the DSLAM?

Accepted Answer

Shaping. Shaping is the correct tool because it buffers excess traffic and smooths the output rate to a configured target (10 Mbps) without exceeding it, even if the physical line rate is higher. Unlike policing, shaping does not drop or re-mark packets when the rate is exceeded, ensuring the downstream DSLAM receives traffic at or below the shaped rate.

Answer

Queuing

Answer

Marking

Answer

Policing

Question 12

An SP is troubleshooting an MPLS L2VPN VPLS network where MAC flapping is occurring between two PEs. Which mechanism in VPLS prevents loops and ensures that a broadcast frame from one PE is not reflected back to the originating PE?

Accepted Answer

Split horizon. In a VPLS environment, split horizon is the mechanism that prevents loops by ensuring that a broadcast, multicast, or unknown unicast frame received from a pseudowire (PW) is never forwarded back to any other PW on the same PE. This rule, defined in RFC 4761 and RFC 4762, stops the originating PE from receiving its own reflected frames, thus eliminating the MAC flapping that would occur if the frame were looped through the MPLS core.

Answer

Spanning Tree Protocol (STP)

Answer

Rapid Spanning Tree Protocol (RSTP)

Answer

MAC address aging

Question 13

Which TWO of the following are characteristics of Segment Routing (SR-MPLS) compared to traditional LDP-based MPLS? (Select two.)

Accepted Answer

SR-MPLS does not require LDP or RSVP-TE for label distribution.. Segment Routing (SR-MPLS) eliminates the need for label distribution protocols like LDP or RSVP-TE. Instead, SR-MPLS encodes label information directly in the packet header as a segment list, and routers use the IGP (e.g., OSPF or IS-IS) to advertise segment identifiers (SIDs). This simplifies the control plane and removes protocol dependencies.

Answer

SR-MPLS requires a dedicated label range from 16 to 99.

Answer

SR-MPLS does not support traffic engineering.

Answer

SR-MPLS cannot provide fast reroute protection.

Question 14

Which THREE of the following are correct statements about EVPN-VXLAN in a data center fabric? (Select three.)

Accepted Answer

EVPN route type 3 is used for BUM traffic forwarding.. EVPN route type 3 (Inclusive Multicast Ethernet Tag Route) is used to advertise the VTEP addresses that participate in a given broadcast domain (EVI). This enables the underlay to forward BUM (Broadcast, Unknown unicast, Multicast) traffic by building a head-end replication list or by signaling multicast group membership, ensuring that BUM frames are delivered to all remote VTEPs in the same VXLAN segment.

Answer

VXLAN is a Layer 3 overlay that requires an IGP in the overlay.

Answer

VXLAN always requires IP multicast in the underlay for BUM traffic.

Question 15

Which TWO of the following are services that can be offered using MPLS Layer 3 VPN (L3VPN) technology? (Select two.)

Accepted Answer

IP transit services. MPLS Layer 3 VPN (L3VPN) uses a peer-to-peer model where the provider edge (PE) router participates in the customer's routing via MP-BGP (RFC 4364). This allows the provider to offer IP transit services by carrying customer IP routes across the MPLS backbone, and Internet access by connecting the customer VRF to an Internet-facing VRF or global routing table. Both services rely on the L3VPN architecture's ability to separate and forward IP traffic based on VRFs and route targets.

Answer

Layer 2 bridging between sites

Answer

Transport of Ethernet frames over MPLS

Answer

Native multicast support without tunnels