350-501 Architecture Practice Test 10 — 15 Questions

Question 1

In IS-IS, which TWO are types of Link State PDUs (LSPs)?

Accepted Answer

Level 2 LSP. In IS-IS, Link State PDUs (LSPs) come in two distinct flooding scopes: Level 1 LSPs, which are flooded only within a Level 1 area, and Level 2 LSPs, which are flooded within the Level 2 backbone. Option B (Level 2 LSP) is correct because it is the LSP type used to distribute Level 2 link-state information (TLVs) across the backbone. Option E (Level 1 LSP) is correct because it is the LSP type used to distribute Level 1 link-state information within a single IS-IS area. Options A (PSNP) and D (CSNP) are not LSPs at all; they are Sequence Numbers PDUs used to acknowledge and synchronize the link-state database, and they exist in both Level 1 and Level 2 forms. Option C (Hello LSP) is not a valid IS-IS PDU type; IS-IS uses IIH (IS-IS Hello) PDUs for neighbor discovery, not a 'Hello LSP'.

Answer

Partial Sequence Numbers PDU (PSNP)

Answer

Hello LSP

Answer

Complete Sequence Numbers PDU (CSNP)

Question 2

A large ISP is designing a multicast architecture to support IPTV, requiring high availability and minimal traffic convergence. Which RP placement design is most appropriate?

Accepted Answer

Anycast-RP with multiple RPs sharing same IP. Anycast-RP with multiple RPs sharing the same IP address is the most appropriate design for a large ISP supporting IPTV because it provides high availability and load sharing without a single point of failure. In the event of an RP failure, traffic automatically converges to the nearest surviving RP using the same anycast address, minimizing disruption. This design also avoids the convergence delays inherent in dynamic RP discovery protocols like Auto-RP or BSR.

Answer

Single static RP placed on the core router

Answer

Auto-RP with one RP mapping agent

Answer

BSR with one candidate RP

Question 3

Which encapsulation technology is commonly used in service provider networks to separate subscriber traffic in an Ethernet aggregation network?

Accepted Answer

Q-in-Q (802.1ad). Q-in-Q (802.1ad) is the correct encapsulation technology because it allows service providers to stack an outer service VLAN tag (S-Tag) on top of a customer's inner VLAN tag (C-Tag), effectively separating subscriber traffic in an Ethernet aggregation network. This double-tagging mechanism preserves the customer's VLAN space while enabling the provider to aggregate multiple subscribers over a single physical port, which is essential for Metro Ethernet and DSLAM aggregation scenarios.

Answer

VXLAN

Answer

802.1Q

Answer

MPLS

Question 4

A service provider wants to implement Segment Routing in its MPLS core to simplify traffic engineering. What is the primary advantage of Segment Routing over traditional RSVP-TE?

Accepted Answer

No per-flow state on transit routers. Segment Routing (SR) eliminates the need for per-flow state on transit routers by encoding the path as a list of segment identifiers (SIDs) directly in the packet header. In contrast, RSVP-TE requires each transit router to maintain soft-state for every LSP, consuming memory and CPU. This state reduction simplifies network operation and scales better in large MPLS cores.

Answer

Improved ECMP load balancing

Answer

Better support for Fast Reroute

Answer

Requires a central controller for path calculation

Question 5

An ISP is deploying EVPN-VXLAN for its data center interconnect. Which statement about control-plane learning is correct?

Accepted Answer

MAC addresses are learned via BGP MP-BGP EVPN address family. In EVPN-VXLAN deployments for data center interconnect, MAC address learning occurs via the control plane using BGP with the MP-BGP EVPN address family (AFI 25 / SAFI 70). This eliminates the need for traditional data-plane flooding and learning, providing better scalability and control. The correct statement is that MAC addresses are learned via BGP MP-BGP EVPN address family.

Answer

MAC addresses are learned via IRB

Answer

MAC addresses are learned via OSPF

Answer

MAC addresses are learned via VXLAN data plane

Question 6

An engineer needs to ensure that a core router can forward MPLS packets without checking the IP header. Which forwarding mechanism should be enabled?

Accepted Answer

CEF switching. Cisco Express Forwarding (CEF) is the required switching mechanism for MPLS forwarding. When MPLS is enabled on a router, CEF uses the Label Forwarding Information Base (LFIB) to forward packets based solely on the top label, without inspecting the IP header. This allows core routers (P routers) to perform label switching without IP lookups. Penultimate Hop Popping (PHP) is an optimization that occurs at the penultimate router, but it is not the mechanism that enables label-based forwarding; it relies on CEF. Therefore, enabling CEF switching is necessary for a core router to forward MPLS packets without checking the IP header.

Answer

Link Fragmentation and Interleaving (LFI)

Answer

Per-packet load balancing

Answer

Penultimate Hop Popping (PHP)

Question 7

A service provider is implementing IPv6 transition in its core. Which transition mechanism is recommended for carrying IPv6 over an existing MPLS/IPv4 backbone without dual-stacking all routers?

Accepted Answer

6PE (IPv6 Provider Edge). 6PE (IPv6 Provider Edge) is the correct answer because it allows IPv6 traffic to be carried over an existing MPLS/IPv4 backbone without requiring dual-stack on all core routers. In 6PE, only the Provider Edge (PE) routers need to be dual-stack; they encapsulate IPv6 packets in MPLS labels and transport them across the IPv4 MPLS core, which remains IPv4-only. This meets the requirement of not dual-stacking all routers while leveraging the existing MPLS infrastructure.

Answer

ISATAP

Answer

NAT64

Answer

6to4 tunneling

Question 8

Which TWO are characteristics of Segment Routing?

Accepted Answer

Source routing capability. Segment Routing is fundamentally a source-routing architecture (option B): the ingress node encodes the entire path as an ordered list of segments (SIDs) in the packet header, so intermediate nodes simply execute the instructions rather than compute paths. It also eliminates per-flow state on transit routers (option D), because forwarding is driven solely by the SID stack in each packet, so core routers need no signaling sessions or flow-state tables. Option A is wrong because SR supports both an MPLS data plane (SR-MPLS) and an IPv6 data plane (SRv6), not IPv6 only. Option C is wrong because SR deliberately avoids RSVP-TE-style signaling, relying on IGP extensions (IS-IS/OSPF) or BGP to distribute SIDs. Option E is wrong because SR can be deployed without any centralized SDN controller; distributed IGP-based SID advertisement is sufficient.

Answer

Uses only IPv6 data plane

Answer

Requires RSVP-like signaling for path setup

Answer

Requires a centralized SDN controller

Question 9

Which THREE are benefits of implementing MPLS-TE in a service provider core?

Accepted Answer

Ability to guarantee bandwidth for specific traffic flows. Option B is correct because MPLS-TE uses RSVP-TE to reserve explicit bandwidth along a Label Switched Path (LSP), allowing the provider to guarantee bandwidth for specific traffic flows via resource reservation and admission control. Option C is correct because MPLS-TE supports explicit path computation and unequal-cost multipath forwarding, enabling traffic to be distributed across multiple paths rather than being limited to IGP shortest-path load sharing. Option D is correct because MPLS-TE integrates Fast Reroute (FRR), which pre-computes and pre-signals backup LSPs (facility or one-to-one backup) so that traffic can be redirected within tens of milliseconds upon a link or node failure. Option A is not a benefit of MPLS-TE, since TE operates on the transport/LSP layer and does not reduce the BGP routing table size; BGP table growth is addressed by other mechanisms such as route reflectors, aggregation, or address-family filtering. Option E is not a benefit of MPLS-TE, because MPLS-TE itself is unicast-oriented and does not natively support multicast; multicast in MPLS networks requires separate solutions such as mLDP or PIM over MPLS.

Answer

Reduction in BGP routing table size

Answer

Native support for multicast

Question 10

Which TWO are essential components for deploying EVPN in a service provider network?

Accepted Answer

Overlay tunnel encapsulation such as VXLAN or MPLS. Option A is correct because EVPN is an overlay control-plane technology that requires a data-plane encapsulation to carry tenant MAC/IP reachability across the provider backbone, typically VXLAN in data-center contexts or MPLS (e.g., EVPN-MPLS with BGP MPLS-based Ethernet VPN per RFC 7432) in service provider networks. Option C is correct because EVPN uses BGP as its control plane, specifically MP-BGP with the EVPN address family (AFI 25 / SAFI 70) to advertise MAC/IP Advertisement routes, Inclusive Multicast Ethernet Tag routes, and Ethernet Auto-Discovery routes, enabling MAC learning and multihoming. OSPF (Option B) is not essential because the underlay can be any IGP (IS-IS, OSPF, or even eBGP) or a static routing design; it is a design choice, not a required EVPN component. PIM-SM (Option D) is not required because EVPN natively handles BUM traffic via ingress replication or assisted replication using the Inclusive Multicast Ethernet Tag route, without needing PIM in the underlay. RSVP-TE (Option E) is not essential because EVPN does not mandate traffic-engineered LSPs; it only needs transport reachability between PE routers, which can be provided by plain IGP-based forwarding or SR/SR-MPLS.

Answer

OSPF as the underlay routing protocol

Answer

PIM-SM for multicast replication

Answer

RSVP-TE for path computation

Question 11

A service provider is implementing MPLS L3VPN for a customer. The customer requires that routes from two different VPNs be imported into a single VRF. Which feature should be used?

Accepted Answer

Route Target (RT) import/export. Route Target (RT) import/export is the correct feature because it controls which routes from which VPNs are imported into a given VRF. By configuring multiple RT import statements on a single VRF, the provider can selectively import routes from two different VPNs, enabling inter-VPN route sharing without merging the VPNs themselves.

Answer

Route Reflector

Answer

Route Distinguisher (RD)

Answer

BGP extended community

Question 12

A large SP network uses Segment Routing (SR) with MPLS data plane. They want to enforce a strict path for certain traffic flows across the core while using shortest-path for others. Which technique should be used?

Accepted Answer

SR-TE with explicit path using segment list. SR-TE with an explicit path using a segment list allows the operator to define a strict, ordered list of MPLS labels (segments) that the traffic must follow, overriding the default IGP shortest-path behavior. This is the correct technique for enforcing a strict path across the core while leaving other traffic to use shortest-path forwarding.

Answer

Using TI-LFA

Answer

Configuring bandwidth reservation on all links

Answer

Using SR policies with color extended community based on BGP

Question 13

A service provider wants to prioritize voice traffic over data traffic on a PE-CE link. Which QoS mechanism should be applied at the PE ingress to classify packets?

Accepted Answer

Class-based marking based on NBAR. Class-based marking using NBAR (Network-Based Application Recognition) is the correct mechanism because it can inspect packets at the application layer to distinguish voice traffic (e.g., RTP, SIP) from data traffic. On a PE-CE link, marking at ingress allows the service provider to set the appropriate DSCP or IP precedence value, which downstream QoS policies can then trust and act upon. This classification step is essential before any policing, shaping, or queuing can be applied.

Answer

Policer

Answer

WRED

Answer

Shaper

Question 14

In a multicast environment, a PE router is not receiving multicast traffic from a source behind a CE. The PIM neighbors are established. The RP is reachable. What is the most likely issue?

Accepted Answer

The PE does not have the multicast VRF enabled. The most likely issue is that the PE router does not have the multicast VRF enabled. In a multicast VPN (MVPN) environment, even if PIM neighbors are established and the RP is reachable, the PE must have multicast routing explicitly enabled within the VRF using the 'ip multicast-routing vrf <name>' command. Without this, the PE will not process multicast traffic for that VRF, causing it to drop or ignore multicast packets from the source behind the CE.

Answer

The CE is not sending IGMP joins

Answer

The source address is not in the VRF

Answer

The RP is not configured in the VRF

Question 15

An SP is deploying EVPN with VXLAN encapsulation in a data center interconnect. The design requires that the control plane for MAC/VTEP learning is based on BGP. Which BGP address family must be configured?

Accepted Answer

l2vpn evpn. EVPN with VXLAN encapsulation requires the BGP L2VPN address family (l2vpn evpn) to exchange MAC/VTEP reachability information. This address family carries EVPN routes (type-2 for MAC/IP, type-3 for IMET) that populate the control plane for VXLAN tunnel endpoints, enabling MAC learning without flooding.

Answer

l2vpn vpls-vpws

Answer

vpnv4

Answer

ipv4 unicast