350-501 Networking Practice Test 3 — 15 Questions

Question 1

Which TWO statements correctly describe the use of OSPF in a service provider network?

Accepted Answer

OSPF uses different LSA types to advertise different types of routing information.. OSPF uses different LSA types (e.g., Type 1 Router LSA, Type 2 Network LSA, Type 3 Summary LSA, Type 5 AS-External LSA) to advertise different categories of routing information, such as router links, network links, inter-area routes, and external routes. This LSA-type differentiation is fundamental to OSPF's link-state architecture, enabling efficient flooding and route computation within and across areas.

Answer

OSPF uses the Bellman-Ford algorithm to compute routes.

Answer

OSPF is a distance-vector routing protocol.

Answer

OSPF uses TLVs to encode routing information.

Question 2

Refer to the exhibit. An engineer is troubleshooting an MPLS LDP session between two routers. The output shows that the LDP session is operational. However, MPLS labels are not being exchanged. What is the most likely cause?

Accepted Answer

The LDP label advertisement mode is 'downstream on demand'.. The exhibit shows that the LDP session is operational (state = Operational), but no labels are being exchanged. In 'downstream on demand' mode, a router does not advertise labels unless explicitly requested by an upstream neighbor via a Label Request message. Since the session is up but no labels are exchanged, this mismatch in label advertisement mode is the most likely cause.

Answer

The peer's addresses are not bound to the LDP Ident.

Answer

The TCP connection is not using port 646.

Answer

The LDP session is not established.

Question 3

A service provider is deploying a new MPLS core network. The network has four routers: P1, P2, PE1, and PE2. OSPF is used as the IGP. The engineer configures MPLS LDP on all interfaces. After enabling LDP, the engineer notices that the LDP session between P1 and P2 is established, but no labels are exchanged for the loopback0 interfaces of PE1 and PE2. The loopback0 addresses are advertised in OSPF. The engineer verifies that the OSPF routes are present in the routing table of all routers. What is the most likely reason for the missing labels?

Accepted Answer

An access-list is applied under 'mpls ldp advertise-labels' that denies the loopback prefixes.. The most likely reason is that an access-list is applied under 'mpls ldp advertise-labels' that denies the loopback prefixes. LDP by default advertises labels for all prefixes in the routing table, but the 'advertise-labels' command can filter which prefixes receive labels. If the loopback0 prefixes of PE1 and PE2 are denied by such an access-list, no labels will be advertised for them, even though OSPF routes are present.

Answer

LDP is using UDP for label exchange.

Answer

The OSPF cost to the loopbacks is too high.

Answer

The loopback interfaces are not enabled with 'mpls ip'.

Question 4

Which TWO MPLS VPN features are used to provide Layer 3 VPN services in a service provider network?

Accepted Answer

MPLS labels. MP-BGP (Option E) is used to exchange VPNv4 routes between Provider Edge (PE) routers, carrying both the route and its corresponding MPLS label. MPLS labels (Option C) are used to forward packets across the provider core via label-switched paths (LSPs), enabling the separation of customer traffic. Together, MP-BGP and MPLS labels form the foundation of Layer 3 MPLS VPN services.

Answer

LDP

Answer

VRF

Answer

RSVP-TE

Question 5

You are a network engineer at a service provider. Your network uses MPLS L3VPN with OSPF as the IGP and LDP for label distribution. A customer has two sites connected to different PEs (PE1 and PE2) in the same VPN. The customer's CE routers are running eBGP with the PEs. Recently, the customer reports that traffic between the two sites is intermittently dropping. Upon investigation, you find that the BGP session between PE1 and the CE at site A goes down briefly every few minutes. The logs on PE1 show BGP notifications with error code 'Hold Timer Expired'. The CE router at site A is a low-end device with limited CPU. What is the most likely cause and the best course of action?

Accepted Answer

Increase the BGP hold time on PE1 to 180 seconds.. The BGP session drops due to 'Hold Timer Expired' because the low-end CE router's CPU is overloaded, causing it to fail sending BGP keepalives within the default 90-second hold time. Increasing the hold time on PE1 to 180 seconds (option D) gives the CE more time to send keepalives, reducing false timeouts. This directly addresses the root cause—insufficient CPU to maintain timely keepalives—without changing routing protocols or suppressing routes.

Answer

Configure BGP route dampening on PE1 to suppress flapping routes.

Answer

Disable LDP on the link between PE1 and CE1.

Answer

Change the IGP from OSPF to IS-IS to reduce routing updates.

Question 6

Drag and drop the steps to configure a VLAN on a Cisco switch into the correct order.

Accepted Answer

Step 1: Create VLAN, Step 2: Name VLAN, Step 3: Assign ports to VLAN. VLAN configuration involves creating the VLAN, optionally naming it, and then assigning ports to it.

Answer

Step 1: Assign ports to VLAN, Step 2: Create VLAN, Step 3: Name VLAN

Answer

Step 1: Name VLAN, Step 2: Create VLAN, Step 3: Assign ports to VLAN

Answer

Step 1: Create VLAN, Step 2: Assign ports to VLAN, Step 3: Name VLAN

Question 7

Drag and drop the steps to configure a Layer 3 interface on a Cisco switch (SVI) into the correct order.

Accepted Answer

Create the VLAN, then enter interface VLAN mode, then assign IP address, then enable the interface.. SVI configuration requires creating the VLAN, then the interface VLAN, assigning an IP, and enabling it.

Answer

Enter interface VLAN mode, then assign IP address, then enable the interface, then create the VLAN.

Answer

Create the VLAN, then assign IP address, then enter interface VLAN mode, then enable the interface.

Answer

Create the VLAN, then enable the interface, then enter interface VLAN mode, then assign IP address.

Question 8

Match each QoS mechanism to its primary function.

Accepted Answer

Classification: Identifies traffic based on specific criteria.. In QoS, Classification identifies traffic, Marking sets priority, Policing drops/excess, Shaping buffers, and WRED drops probabilistically. Queuing handles packet scheduling, not rate enforcement.

Answer

Queuing: Drops packets that exceed a configured rate.

Question 9

Match each service provider architecture term to its description.

Accepted Answer

Provider Edge (PE) router: Connects to customer edge routers and provides MPLS VPN services.. The correct matches are: PE connects to customer edge, P is MPLS core, ASBR connects to other ASes. Common confusions: mistaking P for CE or confusing Route Reflector with ASBR.

Answer

Customer Edge (CE) router: Core router that forwards packets based on MPLS labels without customer awareness.

Answer

Route Reflector: Router that exchanges routing information with another autonomous system.

Question 10

A service provider is experiencing high CPU usage on a router running BGP. Which action should be taken first to mitigate the issue without disrupting traffic?

Accepted Answer

Apply inbound route filtering using prefix lists.. High CPU usage on a BGP-speaking router is often caused by processing a large number of BGP updates. Applying inbound route filtering using prefix lists (option C) reduces the number of routes the router must process and store, directly lowering CPU load without disrupting existing traffic flows. This is a non-disruptive, targeted mitigation that addresses the root cause of excessive route processing.

Answer

Disable BGP on the router.

Answer

Increase the BGP keepalive timer.

Answer

Implement BGP route dampening.

Question 11

An engineer is designing an MPLS L3VPN for a customer with multiple sites. The customer requires overlapping IP addresses between sites. Which method allows the provider to support overlapping customer addresses?

Accepted Answer

Use separate VRF per site with route distinguisher.. B is correct because a separate VRF per site with a unique route distinguisher (RD) allows the provider to maintain isolated routing tables for each customer site. This isolation enables overlapping IP addresses between sites, as each VRF treats its prefixes as unique within the MPLS L3VPN backbone, regardless of address duplication.

Answer

Implement VPLS instead of L3VPN.

Answer

Use BGP communities to control route distribution.

Answer

Use the same VRF for all sites with different route targets.

Question 12

During a network migration from EIGRP to OSPF, you notice that some routes are being redistributed incorrectly, causing routing loops. The OSPF domain uses area 0 and area 1. The EIGRP domain uses AS 100. Which configuration change would best prevent loops during the migration?

Accepted Answer

Use route-maps to tag EIGRP routes and filter them on OSPF routers.. Route-maps allow you to tag redistributed EIGRP routes with a specific tag value (e.g., 'tag 100') and then filter those tagged routes on OSPF routers using a distribute-list in or prefix-list combined with the route-map. This prevents the redistributed routes from being re-injected back into EIGRP, breaking the redistribution loop. Without such tagging and filtering, mutual redistribution between EIGRP and OSPF can cause routing loops due to the two-way redistribution of routes.

Answer

Implement OSPF stub areas to limit external routes.

Answer

Use distribute-list in EIGRP to block OSPF routes.

Answer

Set a high administrative distance on redistributed routes in OSPF.

Question 13

A client reports intermittent connectivity issues when accessing a server across a provider MPLS network. The issue occurs only during peak hours. Which component should be checked first?

Accepted Answer

Interface errors and discards on the CE router.. Intermittent connectivity during peak hours strongly suggests a bandwidth or queuing issue at the edge of the MPLS network. Interface errors (e.g., CRC, runts) and discards on the CE router indicate congestion or Layer 1/2 problems, which are the most common cause of such time-dependent symptoms. Checking this first aligns with the standard troubleshooting methodology of verifying the physical and data-link layers before moving to higher-layer protocols.

Answer

BGP peering status between CE and PE.

Answer

CPU utilization of the server.

Answer

MPLS labels in the core.

Question 14

An ISP is implementing BGP communities to influence routing behavior for their customers. They want to ensure that a customer's routes are not advertised to a specific transit provider. Which BGP community should be used?

Accepted Answer

NO_EXPORT. The NO_EXPORT community (RFC 1997) tells a router to advertise the route to iBGP peers within the same AS but not to any eBGP peers. In this scenario, the ISP wants to prevent a customer's routes from being advertised to a specific transit provider, which is an eBGP neighbor. Applying the NO_EXPORT community to those routes ensures they stay within the ISP's AS and are not sent to any external transit provider.

Answer

LOCAL_AS

Answer

NO_PEER

Answer

NO_ADVERTISE

Question 15

A network engineer is troubleshooting an OSPF adjacency issue between two routers connected via a serial link. The routers are configured with point-to-point network type. The adjacency stays in EXSTART state. What is the most likely cause?

Accepted Answer

Mismatched MTU.. On a point-to-point OSPF link, the EXSTART state indicates that the routers have formed a bidirectional communication (2WAY) and are now negotiating the master/slave relationship for database description (DBD) packet exchange. A mismatched MTU between the two interfaces causes the DBD packets to be dropped or rejected, preventing the adjacency from progressing beyond EXSTART. This is a common issue on serial links where one side may have a different MTU configured.

Answer

Mismatched OSPF area ID.

Answer

Mismatched hello/dead intervals.

Answer

Duplicate router IDs.