350-501 Architecture Practice Test 2 — 15 Questions

Question 1

A service provider is redesigning its MPLS core to support both L3VPN and L2VPN services. They want to minimize the number of labels in the forwarding table while maintaining per-VRF label allocation. Which label allocation mode should be used for the L3VPN service?

Accepted Answer

Per-VRF label allocation. Per-VRF label allocation assigns a single MPLS label per VRF, meaning all routes within a VRF share the same label. This minimizes the number of labels in the forwarding table compared to per-prefix allocation, while still maintaining per-VRF isolation for L3VPN services. It is the recommended mode when the goal is to reduce label consumption without sacrificing VPN separation.

Answer

Per-CE label allocation

Answer

Per-prefix label allocation

Answer

Per-instance label allocation

Question 2

A service provider is deploying Segment Routing over IPv6 (SRv6) and needs to ensure that the forwarding plane can support SRv6 encapsulated packets. Which hardware capability is most critical for SRv6 at the line rate?

Accepted Answer

IPv6 extension header processing. SRv6 (Segment Routing over IPv6) encapsulates packets with an IPv6 header containing a Segment Routing Header (SRH), which is a type of IPv6 extension header. For line-rate forwarding, the hardware must natively process IPv6 extension headers in the forwarding plane without punting to the CPU, as software processing would cause performance degradation. Option C is correct because this capability is the most critical for SRv6 at line rate.

Answer

MPLS label swap capability

Answer

VXLAN tunnel termination

Answer

NAT64 translation support

Question 3

A network engineer is troubleshooting an OSPF issue in a service provider network. The network uses OSPFv2 with multiple areas. Routers in area 0 are able to ping each other, but routers in area 1 cannot reach routers in area 2. All routers are OSPF-enabled and have correct network type configurations. What is the most likely cause?

Accepted Answer

Missing or misconfigured ABRs between area 1 and area 0, or area 2 and area 0. In OSPFv2, inter-area communication must traverse area 0 (the backbone). Routers in area 1 and area 2 can only reach each other if Area Border Routers (ABRs) exist between each non-backbone area and area 0, and those ABRs are correctly configured and have full adjacencies. Since area 0 routers can ping each other but area 1 and area 2 cannot, the most likely cause is a missing or misconfigured ABR on either side, preventing the exchange of Type 3 summary LSAs between the areas.

Answer

Mismatched OSPF area IDs on routers in area 1 and area 2

Answer

Lack of BGP peering between ABRs

Answer

OSPF network type mismatch preventing adjacency formation

Question 4

A service provider is implementing MPLS-TE with FRR (Fast Reroute) using one-to-one backup tunnels. After activation, they notice that the number of labels in the forwarding table has increased significantly. What is the most likely reason for this increase?

Accepted Answer

One-to-one backup creates a unique backup tunnel for each protected LSP. One-to-one backup tunnels in MPLS-TE FRR create a dedicated backup LSP for each protected primary LSP. This means every primary LSP gets its own unique set of labels for the backup path, leading to a significant increase in the number of labels in the forwarding table. In contrast, facility backup shares a single bypass tunnel among multiple protected LSPs, which conserves labels.

Answer

RSVP-TE signaling is not properly aggregating labels

Answer

Penultimate Hop Popping (PHP) is disabled

Answer

Facility backup is being used instead of one-to-one

Question 5

A service provider is deploying EVPN-MPLS for L2VPN services. The customer requires that MAC addresses learned from one PE are not advertised to other PEs unless they are active. Which EVPN route type is used for MAC address withdrawal?

Accepted Answer

Route Type 2: MAC/IP Advertisement. Option C is correct because EVPN Route Type 2 (MAC/IP Advertisement) carries both MAC addresses and their associated IP addresses, and it supports a 'sticky' or 'withdraw' mechanism via the BGP Withdraw message. When a MAC address becomes inactive on a PE, the PE sends a BGP Withdraw for the specific Route Type 2 route, effectively removing that MAC from the control plane of other PEs. This ensures that only active MAC addresses are advertised, meeting the customer requirement.

Answer

Route Type 5: IP Prefix

Answer

Route Type 1: Ethernet Auto-Discovery (A-D)

Answer

Route Type 3: Inclusive Multicast Ethernet Tag

Question 6

Which TWO statements about MPLS label operations in a service provider core are correct? (Choose two.)

Accepted Answer

The ingress router pushes a label stack onto the IP packet. Option A is correct because the ingress router (LER) in an MPLS network performs a push operation, adding a label stack (typically one or more labels) onto the incoming IP packet. This label stack is used to direct the packet along a Label Switched Path (LSP) through the core, enabling MPLS forwarding based on labels rather than IP routing.

Answer

The egress router receives an MPLS packet with two labels by default

Answer

The penultimate hop performs label swap for the top label

Answer

The penultimate hop is disabled by default in MPLS networks

Question 7

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 MP-BGP (Multiprotocol BGP) is essential for carrying VPNv4 routes between PE routers. It uses address family VPNv4 to transport customer IPv4 prefixes along with their Route Distinguisher (RD) and Route Target (RT) attributes, enabling the separation and distribution of multiple customer VPNs across the MPLS core.

Answer

IBGP between PE and P routers for label distribution

Answer

VRF configuration on P routers

Question 8

A customer reports that CE routers attached to PE1 and PE2 in the same VRF cannot ping each other. Based on the exhibit, what is the most likely cause?

Accepted Answer

LDP is not enabled on the core interfaces between PE1 and PE2. B is correct because LDP must be enabled on the core interfaces between PE1 and PE2 to establish LDP sessions, which are required to exchange MPLS labels for the transport LSP. Without LDP, the MPLS forwarding path between the PEs is broken, preventing CE-to-CE ping even if BGP VPNv4 routes are correctly advertised.

Answer

Missing address-family ipv4 for BGP neighbor

Answer

Mismatched route distinguisher (RD) values on PE1 and PE2

Answer

Route target (RT) import/export mismatch

Question 9

Based on the exhibit, which label operation will occur when a packet destined to 10.2.2.1 enters PE1 with label 17?

Accepted Answer

Swap label 17 to label 18. The correct answer is D because the exhibit shows an MPLS VPN scenario where PE1 receives a labeled packet destined for 10.2.2.1. The incoming label 17 corresponds to the VPNv4 route for 10.2.2.1/32, and the LFIB on PE1 indicates a swap operation to label 18, which is the transport label used to forward the packet across the MPLS core toward the next-hop PE.

Answer

Forward with no label (Untagged)

Answer

Pop the label and forward as IP

Answer

Push label 17 onto the packet

Question 10

Refer to the exhibit. The router is configured as a PE router in an MPLS VPN network. Which option correctly identifies a configuration error that would prevent proper operation?

Accepted Answer

The OSPF network statement uses an incorrect wildcard mask. Option C is correct because the OSPF network statement uses a wildcard mask of 0.0.0.0, which matches only the exact IP address 10.1.1.1, but the interface has a /30 prefix (255.255.255.252), so the correct wildcard mask should be 0.0.0.3 to include the entire subnet. This misconfiguration prevents OSPF from advertising the correct network, breaking MPLS VPN CE-to-PE routing.

Answer

The neighbor remote-as should be the same AS number for iBGP

Answer

The interface lacks the 'mpls ip' command

Answer

The BGP network statement does not match the interface prefix

Question 11

A service provider is deploying an MPLS L3VPN solution for a customer with two sites. The PE routers are running OSPF as the IGP and LDP for label distribution. The provider wants to ensure that customer traffic is load-balanced across two equal-cost paths between the PEs. The network team notices that all traffic is taking only one path despite the IGP showing equal-cost routes. The team has verified that the MPLS forwarding table on the P router shows only one label entry for the BGP next-hop. The team suspects a load-balancing issue. Which action best resolves the problem?

Accepted Answer

Enable per-flow load balancing on all routers with 'load-balance per-flow'. Option B is correct because the issue is that MPLS L3VPN traffic is not being load-balanced despite equal-cost IGP paths. This typically occurs when the MPLS forwarding table on the P router has only one label entry for the BGP next-hop, indicating that per-flow load balancing is not enabled. Enabling 'load-balance per-flow' on all routers ensures that the CEF (Cisco Express Forwarding) uses per-flow hashing to distribute traffic across multiple equal-cost LSPs (Label Switched Paths), rather than per-packet or default behavior that may favor a single path.

Answer

Increase the OSPF maximum-paths value to 4

Answer

Enable BGP additional-paths on the PE routers

Answer

Configure LDP to use the 'mpls ldp igp sync' command

Question 12

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 13

An engineer is troubleshooting a BGP route propagation issue. The customer is receiving a default route from upstream provider, but the route is not being installed in the routing table. The BGP table shows the route is valid but not best. What is the most likely cause?

Accepted Answer

A static default route with lower administrative distance exists. Option D is correct because a static default route with a lower administrative distance (e.g., 1) will be preferred over a BGP default route (AD 20 for eBGP). Even though the BGP route is valid in the BGP table, it is not installed in the routing table because the static route is more trustworthy. This is a common scenario where the routing table already has a better path, preventing the BGP route from becoming 'best' and being installed.

Answer

The next-hop is unreachable

Answer

The route is filtered by an inbound route-map

Answer

The BGP session is not established

Question 14

A network engineer is designing a Layer 2 VPN using EVPN with MPLS data plane. The customer requires all-hub multipoint connectivity with optimal multicast replication. Which EVPN route type is used to advertise multicast group membership?

Accepted Answer

Route Type 6 (Selective Multicast Ethernet Tag). Route Type 6 (Selective Multicast Ethernet Tag) is used in EVPN to advertise multicast group membership for selective multicast replication. This allows the provider edge (PE) routers to build optimal multicast trees for specific groups, enabling efficient all-hub multipoint connectivity with EVPN-MPLS data plane.

Answer

Route Type 3 (Inclusive Multicast Ethernet Tag)

Answer

Route Type 2 (MAC/IP Advertisement)

Answer

Route Type 4 (Ethernet Segment)

Question 15

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