350-501 Practice Test 2 — 10 Questions

Question 1

Refer to the exhibit. The router has three LDP neighbors established. A network administrator notices that MPLS labels for the prefix 10.4.4.0/24 are not being advertised from this router to its neighbors, although the prefix is present in the routing table. Which is the most likely cause?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

The route to 10.4.4.0/24 is not the best path in the routing table.. LDP only advertises labels for prefixes that are the best path in the routing table (unless label advertisement is configured for all routes). If 10.4.4.0/24 is present but not the best path (e.g., a backup route or a route with a higher administrative distance), LDP will not allocate and advertise a label for it. This matches the symptom of the prefix being in the table but no label being advertised.

Answer

The LDP session to 10.3.3.3 is down.

Answer

The 'mpls ldp' command has not been applied globally.

Answer

The multicast routing table is empty for the prefix.

Question 2

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

Accepted Answer

1. Enter global configuration mode (configure terminal)
2. Configure the static route using the ip route command with destination network, subnet mask, and next-hop address or exit interface
3. Verify the configuration (e.g., show ip route)
4. Exit configuration mode (end or exit). Static routes require global config mode and must specify the destination network, subnet mask, and next-hop address or exit interface.

Answer

1. Enter global configuration mode (configure terminal)
2. Verify the configuration (e.g., show ip route)
3. Configure the static route using the ip route command
4. Exit configuration mode (end or exit)

Answer

1. Configure the static route using the ip route command
2. Enter global configuration mode (configure terminal)
3. Verify the configuration (e.g., show ip route)
4. Exit configuration mode (end or exit)

Answer

1. Exit configuration mode (end or exit)
2. Enter global configuration mode (configure terminal)
3. Configure the static route using the ip route command
4. Verify the configuration (e.g., show ip route)

Question 3

An SP deploys EVPN to provide L2VPN services with multi-homing. The customer CE is dual-homed to two different PE routers. Which EVPN mechanism ensures that only one PE forwards traffic to the CE for a given Ethernet segment, preventing loops?

Accepted Answer

Designated Forwarder election based on ESI. Ethernet Segment Identifier (ESI) and designated forwarder (DF) election in EVPN ensure that only one PE forwards traffic to the CE for a given Ethernet segment, preventing loops.

Answer

BGP Route Reflector

Answer

MAC learning via data plane

Answer

Split horizon groups

Question 4

A service provider is implementing EVPN for its VPLS replacement. They have configured BGP EVPN on all PEs and have set up an EVPN instance for a customer requiring broadcast, unknown unicast, and multicast (BUM) traffic. The customer reports that broadcast traffic from one site is not being received at another site. The engineer checks the EVPN configuration and finds that the EVI is configured correctly, the route-target matches, and the BGP sessions are established. The engineer also checks the MAC address table on the receiving PE and sees that the source MAC of the broadcast frame is learned on the local interface, but not from the remote VTEP. The engineer suspects an issue with the IMET (Inclusive Multicast Ethernet Tag) route. Which action should the engineer take to verify the IMET route?

Accepted Answer

Check the BGP EVPN route table for IMET (route-type 3) routes using 'show bgp l2vpn evpn route-type 3'.. In BGP EVPN, the IMET (Inclusive Multicast Ethernet Tag) route is a Type-3 route used to build the multicast tunnel for BUM (broadcast, unknown unicast, multicast) traffic. If BUM traffic from one site is not reaching another, and the MAC table shows the source MAC learned locally but not from the remote VTEP, the IMET route is likely missing or not being advertised/received. The correct verification is to inspect the BGP EVPN route table specifically for Type-3 routes using 'show bgp l2vpn evpn route-type 3'.

Answer

Use 'show evpn instance detail' to check the EVI configuration.

Answer

Use 'show bgp l2vpn evpn route-type 2' to verify MAC/IP routes.

Answer

Use 'show l2vpn vfi' to verify the VPLS forwarding instance.

Question 5

An automation engineer uses RESTCONF to configure a Cisco ASR 9000 router. When sending a PATCH request to update an interface description, the API returns 404 Not Found. What is the most probable issue?

Accepted Answer

The interface does not exist on the device.. A 404 Not Found response to a RESTCONF PATCH request targeting a specific interface indicates that the resource (the interface) does not exist at the given URI. RESTCONF uses the URI path to identify the exact YANG data node; if the interface name in the URI does not match any configured interface on the Cisco ASR 9000, the server returns 404. This is consistent with RFC 8040, where 404 is used when the target resource cannot be found.

Answer

HTTP authentication is required.

Answer

The YANG module is not supported.

Answer

The RESTCONF username/password is incorrect.

Question 6

An engineer is configuring IS-IS fast convergence. Which mechanism provides sub-second failure detection independently of the routing protocol?

Accepted Answer

BFD. BFD (Bidirectional Forwarding Detection) provides fast failure detection at the link layer, triggering routing protocol convergence.

Answer

LSP fast flooding

Answer

PRC (Partial Route Computation)

Answer

iSPF (incremental SPF)

Question 7

A service provider needs to prioritize voice traffic over best-effort data in an MPLS VPN. The PE router uses a QoS policy applied to the ingress interface. Which action ensures that voice packets are marked with the correct DSCP value before entering the MPLS core?

Accepted Answer

Apply a policy-map that matches voice traffic using a class-map and the 'set dscp ef' action.. The question specifies that the PE router must mark voice packets with the correct DSCP value before they enter the MPLS core. The 'set dscp ef' action in a policy-map applied to the ingress interface explicitly sets the DSCP field to EF (46) for voice traffic matched by a class-map, ensuring proper classification and treatment across the MPLS network. This is the standard method for marking IP packets at the edge before MPLS encapsulation.

Answer

Configure the ingress interface with 'mls qos trust dscp' to preserve the customer marking.

Answer

Use a policy-map with the 'set mpls experimental 5' command.

Answer

Apply a police action to drop traffic exceeding the voice bandwidth.

Question 8

An ISP is implementing 6PE to provide IPv6 connectivity over an MPLS network that only supports IPv4 in the core. In 6PE, how are IPv6 prefixes carried across the MPLS backbone?

Accepted Answer

IPv6 prefixes are carried as IPv6 prefixes in MP-BGP with an IPv4 next-hop. 6PE uses MP-BGP to carry IPv6 prefixes (using the IPv6 unicast address family, AFI=2 SAFI=1) with an IPv4 next-hop address (the loopback of the peer 6PE router). The BGP session is over IPv4, but the NLRI carries IPv6 prefixes. MPLS labels are used to forward traffic across the IPv4-only core. It is important to note that 6PE does not use the VPNv6 address family (AFI=1 SAFI=128) — that is used for MPLS L3VPN.

Answer

IPv6 prefixes are transported over an IPv6 MPLS core using LDPv6

Answer

IPv6 prefixes are encapsulated in IPv4 tunnels with GRE

Answer

IPv6 prefixes are converted to IPv4 using NAT64 before MPLS forwarding

Question 9

During a maintenance window, an automation script pushed a QoS policy that inadvertently changed the marking for all inbound traffic on a core interface. The change was rolled back, but performance reports show that some traffic is still being marked incorrectly. What is the most logical explanation?

Accepted Answer

The rolled back policy was applied inbound, but the outbound policy that also applies marking was not rolled back. QoS policies can be applied independently in the inbound and outbound directions on an interface. If the original automation script modified the inbound marking policy, and the rollback only reverted that inbound policy, any outbound policy that also performs marking would remain unchanged and continue to incorrectly mark traffic. This explains why some traffic still shows incorrect marking after the rollback.

Answer

The automation script used RESTCONF which requires a commit to finalize

Answer

The device requires a reload to clear the old marking

Answer

The rollback script only applied to the outbound direction

Question 10

In MPLS-TE Fast Reroute (FRR), what is a 'detour'?

Accepted Answer

A backup LSP that protects a single primary LSP. In MPLS-TE Fast Reroute (FRR), a detour is a pre-established backup Label Switched Path (LSP) that protects a single primary LSP. It is created by the Point of Local Repair (PLR) and merges back into the primary LSP downstream of the protected link or node. Detours are 1:1 protection, meaning each primary LSP has its own dedicated detour, which allows for sub-50ms recovery upon failure.

Answer

A secondary path for load balancing

Answer

A bypass tunnel that protects multiple LSPs

Answer

A mechanism to reroute traffic after failure detection