350-501 Networking Practice Test 5 — 15 Questions

Question 1

An engineer is troubleshooting a BGP route reflector setup. Clients are not receiving all routes. The 'show bgp neighbors' output shows a state of 'Active'. What is the most likely cause?

Accepted Answer

Incorrect BGP neighbor statement on the route reflector or client. The 'Active' state in BGP indicates that the router is trying to establish a TCP connection with the neighbor but has not yet succeeded. This is most commonly caused by a misconfiguration in the BGP neighbor statement, such as an incorrect IP address, wrong AS number, or a missing neighbor statement on one side. Since the route reflector is not forming a BGP session, clients cannot receive any routes, which explains the symptom.

Answer

The route reflector does not have a full mesh with clients

Answer

The route reflector is detecting an AS_PATH loop

Answer

Next-hop reachability issue

Question 2

Which MPLS VPN technology allows a service provider to offer overlapping IP addresses to different customers while using a single routing table per VPN?

Accepted Answer

MPLS Layer 3 VPN (BGP/MPLS IP VPN). D is correct because MPLS Layer 3 VPN (BGP/MPLS IP VPN) uses per-VPN routing tables (VRFs) to maintain separate forwarding instances for each customer. This allows overlapping IP addresses across different customers while keeping each VPN's routes isolated. The provider edge routers exchange VPNv4 routes using MP-BGP with route distinguishers (RDs) to make overlapping prefixes unique, and route targets (RTs) control which VRFs import/export those routes.

Answer

Any Transport over MPLS (AToM)

Answer

VPLS

Answer

MPLS Traffic Engineering (TE)

Question 3

A network engineer needs to ensure that a specific customer's traffic is not adversely affected by other customers' traffic in a shared MPLS core. Which technology should be used?

Accepted Answer

QoS policies on PE routers with shaping and policing. QoS policies on PE routers with shaping and policing allow the service provider to enforce traffic contracts per customer, ensuring that one customer's traffic does not consume bandwidth allocated to another. This is achieved by applying ingress policing to limit customer traffic to the Committed Information Rate (CIR) and egress shaping to smooth bursts, preventing congestion in the MPLS core from affecting other customers.

Answer

iBGP route reflectors

Answer

MPLS Traffic Engineering

Answer

802.1Q VLANs

Question 4

Which statement about the use of MTU in an MPLS network is correct?

Accepted Answer

MPLS adds a label stack to packets, reducing the payload MTU.. MPLS adds a label stack (typically 4 bytes per label) between the Layer 2 header and the IP packet. This additional overhead reduces the maximum payload size that can be carried without exceeding the interface MTU, effectively lowering the payload MTU available for the IP packet.

Answer

MPLS does not affect the MTU because labels are part of the header.

Answer

MTU must be increased on all MPLS interfaces.

Answer

MPLS eliminates the need for IP fragmentation.

Question 5

An ISP is designing a new core network using MPLS-TE. They require very fast failure detection for link and node failures to minimize traffic loss. Which two technologies should they combine? (Choose two.)

Accepted Answer

MPLS-TE Fast Reroute (FRR). MPLS-TE Fast Reroute (FRR) provides sub-50 ms protection switching by pre-computing backup paths (bypass tunnels) for link and node failures, ensuring minimal traffic loss. Bidirectional Forwarding Detection (BFD) provides sub-second failure detection by sending rapid, lightweight hello packets independent of routing protocols, enabling faster convergence when combined with FRR.

Answer

OSPF with hello timers set to 1 second

Answer

LSP Ping and Traceroute

Answer

Label Distribution Protocol (LDP)

Question 6

Which LISP feature allows a device to register its location to a mapping system so that another device can find it?

Accepted Answer

ETR. The Egress Tunnel Router (ETR) is the LISP device that registers its location (RLOC) to the mapping system (Map-Server) so that other devices can resolve the endpoint identifier (EID) to that RLOC. This registration process populates the mapping database, enabling remote Ingress Tunnel Routers (ITRs) to find and forward traffic to the ETR. Without ETR registration, the mapping system would have no location information for the EID.

Answer

Map-Resolver (MR)

Answer

Proxy ITR (PITR)

Answer

xTR

Question 7

A service provider is troubleshooting BGP route selection between two eBGP peers. The router receives a prefix from Peer A with local preference 150 and AS path length 3. From Peer B, the same prefix has local preference 100 and AS path length 2. Which route will be preferred?

Accepted Answer

The route from Peer A because local preference is higher.. B is correct because BGP's route selection process evaluates local preference before AS path length. The route from Peer A has a local preference of 150, which is higher than Peer B's 100, so it is preferred regardless of the shorter AS path from Peer B. Local preference is the second BGP attribute in the decision process (after weight) and is used to influence outbound traffic from an AS.

Answer

The route from Peer A because it has a higher weight.

Answer

Both routes are equally preferred and will be used for load balancing.

Answer

The route from Peer B because AS path is shorter.

Question 8

An MPLS-TE tunnel is configured with Fast Reroute using link protection. The primary path traverses links A-B and B-C. If link B-C fails, which action does the head-end router take?

Accepted Answer

The router at node B switches traffic to a pre-computed backup tunnel around link B-C.. MPLS-TE Fast Reroute (FRR) with link protection pre-computes a backup tunnel that bypasses the protected link. When link B-C fails, the router at node B (the Point of Local Repair, or PLR) immediately switches traffic to this pre-established backup tunnel, ensuring sub-50ms failover without involving the head-end router.

Answer

The head-end router immediately switches to a secondary explicit path.

Answer

RSVP-TE signals a new LSP from the head-end after detecting the failure.

Answer

Traffic is dropped until the IGP converges on the new topology.

Question 9

Which OSPF neighbor state indicates that a router has received a hello packet from a neighbor but the neighbor's Router ID is not yet seen in its own hello packet?

Accepted Answer

Init. The Init state is the first step in OSPF neighbor formation after the Down state. A router enters Init when it receives a Hello packet from a neighbor but does not yet see its own Router ID in the neighbor's Hello packet, indicating that bidirectional communication is not yet confirmed.

Answer

Down

Answer

Two-way

Answer

ExStart

Question 10

In a Layer 3 MPLS VPN, a CE router is dual-homed to two different PE routers. The PE routers advertise the same prefix to the route reflector with different route targets. What ensures that only the best path is installed in the VRF?

Accepted Answer

Each PE router independently selects the best path based on BGP attributes.. BGP path selection applies within the VRF. The route with higher local preference or shorter IGP metric to the next-hop determines the best path. Route targets are used for import/export only.

Answer

The route reflector discards duplicate prefixes.

Answer

MPLS labels ensure that only one path is used.

Answer

The CE router must advertise the same route to only one PE.

Question 11

During multicast troubleshooting, the command 'show ip mroute' shows that the RPF neighbor for a particular (S,G) entry is incorrect. What is the most likely cause?

Accepted Answer

The unicast routing table does not have a route back to the source.. The RPF (Reverse Path Forwarding) neighbor for an (S,G) entry is determined by the unicast routing table: the router expects to reach the source S via the interface and next-hop that the unicast route provides. If the unicast routing table does not have a route back to the source, the router cannot determine the correct RPF interface and neighbor, leading to an incorrect RPF neighbor in the 'show ip mroute' output. This is the most common cause of RPF failures in multicast troubleshooting.

Answer

The multicast routing protocol is not enabled globally.

Answer

TTL threshold is set too high on the incoming interface.

Answer

IGMP snooping is disabled on the switch.

Question 12

Which QoS mechanism marks packets at the edge of the network to classify traffic into different service classes?

Accepted Answer

Marking. Marking is the QoS mechanism that sets the Differentiated Services Code Point (DSCP) or IP Precedence bits in the packet header at the ingress edge of the network. This classification allows downstream devices to apply per-hop behaviors (PHBs) based on the marked value, as defined in RFC 2474 and RFC 2597. Unlike queuing, shaping, or policing, marking does not delay or drop packets; it only modifies the packet header to indicate the desired service class.

Answer

Queuing

Answer

Shaping

Answer

Policing

Question 13

Segment Routing with TI-LFA (Topology Independent Loop-Free Alternate) provides fast convergence. Which statement accurately describes TI-LFA?

Accepted Answer

TI-LFA computes a backup path that is guaranteed to be loop-free and topology independent.. TI-LFA (Topology Independent Loop-Free Alternate) computes a backup path that is guaranteed to be loop-free regardless of the network topology, using segment lists (label stacks) to steer traffic around a failure. It does not rely on the presence of a natural loop-free alternate in the IGP topology, making it topology independent. This ensures fast convergence (typically sub-50ms) without requiring signaling protocols like RSVP-TE.

Answer

TI-LFA only protects against link failures, not node failures.

Answer

TI-LFA uses a pre-computed backup tunnel signaled via RSVP-TE.

Answer

TI-LFA requires BFD to detect failures.

Question 14

A service provider wants to influence inbound traffic from a customer AS. The customer AS is multi-homed to two provider ASes. Which BGP community is most effective to make the customer prefer a specific entry point?

Accepted Answer

Set community 'no-export' on routes from the undesired entry point.. Setting the BGP 'no-export' community on routes from the undesired entry point prevents those routes from being advertised to the customer AS. Since the customer only learns routes from the desired entry point, they will prefer that entry point for inbound traffic. This is a standard technique for influencing inbound traffic without requiring customer-side configuration.

Answer

Set community 'prepend 3' on routes from the desired entry point.

Answer

Set community 'local-preference 200' on routes from the desired entry point.

Answer

Set community 'no-advertise' on routes from the undesired entry point.

Question 15

Which routing protocol is used between CE and PE routers in a typical MPLS L3VPN deployment?

Accepted Answer

BGP. While BGP is a common choice for routing between CE and PE in MPLS L3VPN deployments due to its scalability, policy control, and support for multi-homing, it is not the only protocol. Other dynamic routing protocols such as OSPF, EIGRP, RIP, and static routing are also valid. In a typical deployment, CE and PE can exchange routes using any routing protocol; the PE then redistributes those routes into MP‑BGP for VPN‑v4 advertisement between PEs. The question’s correct answer is BGP because it is the most common and recommended protocol for many scenarios, but candidates should know that the CE‑PE routing protocol is not limited to BGP.

Answer

RIP

Answer

EIGRP

Answer

IS-IS