350-501 Architecture Practice Test 8 — 15 Questions

Question 1

Which THREE of the following are required components for implementing MPLS Layer 3 VPN (L3VPN) in a service provider network? (Choose three.)

Accepted Answer

MP-BGP between PE routers to exchange VPNv4 routes. Option A is correct because MPLS L3VPN requires MP-BGP (multiprotocol BGP) between PE routers to exchange VPNv4 routes carrying the route distinguisher and route target extended communities that identify each customer VPN. Option B is correct because each PE router must have VRFs configured to maintain separate per-customer routing and forwarding tables, isolating customer routes on the shared PE device. Option C is correct because MPLS forwarding must be enabled on all core (P) routers so that labeled packets are switched through the provider backbone using LFIB entries, forming the transport for VPN traffic. Option D is not required because label distribution in the core is handled by LDP (or RSVP-TE/SR), not by IBGP between PE and P routers; IBGP is used between PE routers for VPNv4 routes, not for label distribution to P routers. Option E is not required because P routers only swap outer labels and do not hold customer VRFs; VRF configuration belongs on the PE routers, which perform the VPN-specific routing.

Answer

IBGP between PE and P routers for label distribution

Answer

VRF configuration on P routers

Question 2

A service provider is designing a new MPLS core network and needs to choose a routing protocol that supports traffic engineering and fast convergence. Which protocol should be used?

Accepted Answer

IS-IS. IS-IS is the correct choice because it natively supports MPLS Traffic Engineering (TE) via IS-IS TE extensions (RFC 5305) and offers fast convergence through mechanisms like IS-IS Fast Flooding and LSP throttling. Unlike OSPF, IS-IS operates directly over Layer 2, making it more scalable and robust in large service provider core networks, and it avoids the need for a separate flooding domain for TE.

Answer

RIP

Answer

EIGRP

Answer

OSPF

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 network engineer needs to design a multicast solution for IPTV distribution across a service provider network. Which protocol is best suited for building a shared distribution tree where the RP is dynamically elected?

Accepted Answer

PIM-SM with BSR. PIM-SM with BSR (Bootstrap Router) is the correct choice because it provides a dynamic, automated mechanism for electing an RP (Rendezvous Point) within a PIM-SM domain. BSR uses a distributed election process where candidate BSRs exchange bootstrap messages to elect a single BSR, which then collects candidate-RP advertisements and distributes the RP-set to all routers, enabling shared distribution trees without manual RP configuration.

Answer

PIM-DM

Answer

PIM-SM with Auto-RP

Answer

MSDP

Question 5

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 6

Drag and drop the steps to configure OSPF on a Cisco IOS router into the correct order.

Accepted Answer

Enter global configuration mode, then enable the OSPF process with 'router ospf' command, then advertise networks under the OSPF process using 'network' command.. OSPF configuration requires entering global config mode, enabling the OSPF process, and then advertising networks under the OSPF process.

Answer

Advertise networks using 'network' command, then enter global config mode, then enable OSPF process.

Answer

Enable OSPF process, then advertise networks, then enter global config mode.

Answer

Enter global configuration mode, then advertise networks, then enable OSPF process.

Question 7

Match each MPLS VPN technology to its description.

Accepted Answer

MPLS Layer 3 VPN: Uses BGP to distribute customer routes between PE routers. MPLS provides multiple VPN services: Layer 3 VPNs use BGP for route exchange, Layer 2 VPNs emulate L2 circuits, TE controls traffic paths, and Inter-AS extends connectivity across providers. Common confusions involve swapping the L2 and L3 definitions.

Answer

MPLS Layer 3 VPN: Provides transparent transport of Layer 2 frames

Answer

MPLS Layer 2 VPN: Uses BGP to distribute customer routes between PE routers

Question 8

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 9

A service provider is deploying Segment Routing (SR) with TI-LFA for fast convergence. Which mechanism does TI-LFA use to repair a link failure in a node segment path?

Accepted Answer

Precomputes a backup path using a segment list (label stack) that avoids the failed link. TI-LFA (Topology Independent Loop-Free Alternate) precomputes a backup path using a segment list (label stack) that explicitly avoids the failed link. This is achieved by encoding a repair path as a sequence of adjacency and node segments, ensuring that traffic is steered around the failure without loops, regardless of the network topology. The backup path is installed in the forwarding table before the failure occurs, enabling sub-50ms convergence.

Answer

Uses loop-free alternate (LFA) as defined in IPFRR

Answer

Uses RSVP-TE to signal a protected LSP

Answer

Relies on BFD to trigger a backup path in the forwarding table

Question 10

In an MPLS VPN environment, which address family is used to exchange VPNv4 routes between PE routers?

Accepted Answer

VPNv4 unicast. In an MPLS VPN environment, VPNv4 routes (which include both the IPv4 prefix and the Route Distinguisher) are exchanged between Provider Edge (PE) routers using the VPNv4 unicast address family under the BGP configuration. This address family allows PE routers to carry customer routes with unique RD values, enabling address overlap across different VPNs.

Answer

Route-target (RT)

Answer

IPv4 unicast

Answer

VPNv6 unicast

Question 11

An SP is deploying Inter-AS MPLS VPN option B. Which design characteristic is unique to Option B compared to Option A?

Accepted Answer

ASBRs exchange VPNv4 routes directly via MP-EBGP. In Option B, ASBRs exchange VPNv4 routes directly via MP-EBGP without requiring a full mesh of MP-IBGP sessions between PEs. This eliminates the need for per-VPN VRF configuration on ASBRs, as they only carry labeled VPNv4 routes and perform label allocation per next-hop, not per VPN.

Answer

Requires a full mesh of MP-IBGP sessions between all PEs

Answer

ASBRs maintain separate VRF for each VPN

Answer

Traffic is forwarded using IP, not MPLS

Question 12

A service provider is designing a core network with IS-IS as the IGP. To support MPLS traffic engineering, which IS-IS extensions are required?

Accepted Answer

IS-IS TE extensions (RFC 5305). IS-IS TE extensions (RFC 5305) are required to carry MPLS Traffic Engineering information, such as link bandwidth, administrative groups, and TE metric, in Type-Length-Value (TLV) fields within IS-IS Link State PDUs. These extensions enable the IGP to flood TE attributes that MPLS TE uses for constraint-based path computation, such as with RSVP-TE or Segment Routing.

Answer

IS-IS multi-topology (MT)

Answer

IS-IS wide metrics

Answer

IS-IS L1/L2 routing

Question 13

In Segment Routing over IPv6 (SRv6), what is the function of the SRH (Segment Routing Header)?

Accepted Answer

It contains the segment list (ordered list of SIDs). The Segment Routing Header (SRH) is a new IPv6 extension header defined in RFC 8754 that carries an ordered list of Segment Identifiers (SIDs). When a packet is forwarded along a segment-routed path, the SRH encodes the explicit path by listing each segment (node or adjacency SID) in sequence, and the active segment is updated as the packet traverses each hop. This allows the source node to steer packets through a specific path without intermediate nodes needing to maintain per-flow state.

Answer

It replaces the IPv6 header to reduce overhead

Answer

It provides OAM capabilities for path monitoring

Answer

It uses the IPv6 flow label to encode the path

Question 14

Which TWO statements about EVPN Route Type 2 (MAC/IP advertisement) are correct?

Accepted Answer

It is used for MAC learning and ARP suppression. Option A is correct because EVPN Route Type 2 (MAC/IP Advertisement) is the route type that carries host MAC addresses (and optionally IP addresses) across the BGP EVPN control plane, enabling remote MAC learning and, when the IP is included, ARP/ND suppression on the ingress PE. Option B is correct because the Type 2 NLRI explicitly encodes both the MAC address and, optionally, the IP address of a host, which is why it is called MAC/IP Advertisement. Option C is incorrect because load balancing via aliasing is a function of Route Type 1 (Ethernet Auto-Discovery) with the aliasing flag, not Type 2. Option D is incorrect because the Ethernet Segment Identifier is carried in Route Type 1 (and Type 4), not in the Type 2 MAC/IP Advertisement route. Option E is incorrect because Type 2 is precisely the route type used to signal host mobility, with MAC Mobility extended community enabling moves between PEs.

Answer

It provides load balancing via aliasing

Answer

It includes the Ethernet Segment Identifier (ESI)

Answer

It is not used for host mobility

Question 15

Which THREE are requirements for deploying MPLS Traffic Engineering with RSVP-TE?

Accepted Answer

Links must have reservable bandwidth advertised. Option C is correct because RSVP-TE path computation relies on the IGP (OSPF or IS-IS) advertising each link's reservable bandwidth via TE extensions, so the tunnel headend knows which links can satisfy the requested bandwidth. Option D is correct because the headend must run CSPF, which prunes links that lack sufficient unreserved bandwidth or violate affinity/administrative constraints before running SPF to compute an explicit path. Option E is correct because RSVP-TE is the signaling protocol that establishes and maintains the label-switched path, carrying the EXPLICIT_ROUTE and LABEL_REQUEST objects to reserve resources hop by hop. Option A is wrong because MPLS TE works with either OSPF or IS-IS as the IGP, and OSPFv3 is not mandatory. Option B is wrong because LDP is not required for RSVP-TE tunnels; RSVP-TE distributes labels for the TE LSPs itself, and LDP may even be disabled on TE-enabled interfaces.

Answer

OSPFv3 must be the IGP

Answer

LDP must be enabled on all routers