350-501 Networking Practice Test 3 — 15 Questions

Question 1

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.. Option B is correct because 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 2

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 3

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 4

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.

Question 5

A service provider router receives a route with a higher specific prefix length than the same prefix in the routing table. Which route will be preferred?

Accepted Answer

The more specific prefix.. C is correct because a router always prefers the most specific prefix (longest prefix length) when forwarding packets, regardless of administrative distance or metric. This is a fundamental rule of IP routing: the route with the longest subnet mask match is chosen first, as it represents the most precise path to the destination.

Answer

The route with higher administrative distance.

Answer

The route with lower metric.

Answer

The less specific prefix.

Question 6

In an MPLS network, a PE router receives a VPNv4 route from a route reflector. The route is not being installed in the VRF table. Which condition could cause this?

Accepted Answer

The route target does not match the VRF import map.. A VPNv4 route is installed into a VRF table only if its Route Target (RT) matches an import statement in the VRF's route-target import list or import map. If the RT does not match, the PE router will not import the route into the VRF, even though the route is valid in the BGP VPNv4 table. This is the most common cause for a VPNv4 route being present in BGP but missing from the VRF.

Answer

The MPLS label is missing.

Answer

The route distinguisher is incorrect.

Answer

The next-hop is unreachable.

Question 7

A service provider uses MP-BGP with IPv6 address family. They notice that routes redistributed from OSPFv3 are not being advertised to iBGP peers. The OSPF routes are internal. What is a likely reason?

Accepted Answer

The next-hop is not resolved for IPv6.. In MP-BGP for IPv6, the next-hop address for iBGP peers must be reachable via an IPv6 route in the global routing table or the appropriate VRF. When OSPFv3 redistributes internal routes into BGP, the next-hop is often set to the OSPFv3 router's own IPv6 address; if that address is not reachable (e.g., because the interface is not in the IPv6 unicast routing table or the next-hop is link-local), iBGP peers will not install the routes. This is a common cause of routes being learned but not advertised to iBGP peers.

Answer

The network command is missing under IPv6 address family.

Answer

The bgp default ipv4-unicast command is disabled.

Answer

The routes are not in the IPv6 unicast table.

Question 8

Which TWO queuing mechanisms best meet the requirements for voice traffic (low latency and jitter) in a service provider network?

Accepted Answer

LLQ (Low Latency Queuing). LLQ is correct because it combines a strict priority queue with CBWFQ, ensuring voice traffic (which is delay-sensitive) is always serviced first, thereby minimizing latency and jitter. The priority queue is policed to prevent starvation of other traffic, making it ideal for real-time applications like VoIP in service provider networks.

Answer

WRED (Weighted Random Early Detection)

Answer

CBWFQ without LLQ

Answer

FIFO (First In First Out)

Question 9

Which TWO statements about BGP route reflectors are true?

Accepted Answer

The cluster ID is used to detect routing loops.. Option A is correct because BGP route reflectors use the cluster ID to detect and prevent routing loops. When a route reflector receives an update containing its own cluster ID in the cluster-list attribute, it discards the route, breaking the loop. This mechanism is defined in RFC 4456 and is essential for loop-free route propagation in non-full-mesh iBGP topologies.

Answer

Route reflectors modify the AS_PATH attribute.

Answer

Route reflectors must be fully meshed.

Answer

A route reflector passes routes from non-client to non-client.

Question 10

Which THREE actions can help mitigate the impact of BGP prefix flapping in a service provider network?

Accepted Answer

Use route summarization.. Route summarization (A) reduces the number of BGP prefixes advertised, which inherently limits the impact of flapping because a single summary prefix represents many more-specific prefixes. If a specific subprefix flaps, the aggregate remains stable, preventing the flapping from propagating to BGP peers. This is a proactive approach to minimize the control-plane churn caused by unstable routes.

Answer

Use BGP peer groups.

Answer

Apply BGP graceful restart.

Question 11

Refer to the exhibit. The VRF CUSTOMER is configured with route-target import 100:1. Why is this route not installed in the VRF table?

Accepted Answer

Route target mismatch.. B is correct because the VRF CUSTOMER is configured with route-target import 100:1, but the route in question carries a different route-target value (e.g., 100:2). For a route to be installed into a VRF table, the route-target extended community attached to the route must match at least one of the import route-targets configured on the VRF. A mismatch prevents the route from being imported, even if other conditions are satisfied.

Answer

VRF not properly configured.

Answer

Route distinguisher missing.

Answer

Next-hop unreachable.

Question 12

Refer to the exhibit. The router cannot form a full OSPF adjacency with 10.0.0.2. Which is the most likely cause?

Accepted Answer

Mismatched MTU.. Option A is correct because a mismatched MTU commonly causes OSPF to get stuck in EXSTART state. Option B (hello interval) would prevent INIT. Option C (duplicate router ID) might cause other issues. Option D (authentication) would cause failure earlier.

Answer

Duplicate router IDs.

Answer

Mismatched authentication.

Answer

Mismatched hello interval.

Question 13

Refer to the exhibit. What is the role of this router for prefix 10.0.1.0/24?

Accepted Answer

Egress LSR.. Option C is correct because the outgoing tag is 'Pop tag', indicating that the router removes the MPLS label before forwarding. This is the egress LSR. Option A (ingress) would have 'No label' as local tag. Option B (transit) would have a non-pop outgoing label. Option D (penultimate hop) would have 'Untagged' or a specific label.

Answer

Transit LSR.

Answer

Penultimate hop.

Answer

Ingress LSR.

Question 14

An engineer is troubleshooting MPLS LSP connectivity. The ingress PE router has the label binding for the FEC 10.1.1.0/24, but no LSP is established. Which command should be checked on the P routers to verify the LSP path?

Accepted Answer

show mpls forwarding-table. Option B is correct because 'show mpls forwarding-table' displays the label forwarding entries and can identify missing or incorrect label assignments along the path. Option A is not specific to MPLS forwarding; option C shows LDP neighbors only; option D shows MPLS interfaces but not forwarding details.

Answer

show mpls interface

Answer

show mpls ldp neighbor

Answer

show ip route 10.1.1.0

Question 15

A service provider is deploying segment routing in their MPLS core. They want to use an IGP as the control plane for label distribution without running LDP or RSVP-TE. Which IGP is best suited for this purpose?

Accepted Answer

IS-IS. IS-IS is the best-suited IGP for segment routing in an MPLS core because it natively supports the Segment Routing (SR) extensions defined in RFC 8667. These extensions allow IS-IS to advertise Prefix-SIDs and Adjacency-SIDs directly within the link-state database, enabling label distribution without requiring LDP or RSVP-TE. This makes IS-IS a natural fit for service providers deploying SR-MPLS.

Answer

BGP

Answer

EIGRP

Answer

RIP