350-501 Networking Practice Test 4 — 15 Questions

Question 1

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 2

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 3

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 4

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 5

Which TWO statements about BGP route reflectors are true?

Accepted Answer

The cluster ID is used to detect routing loops.. 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 6

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 7

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 8

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.. The most likely cause is a mismatched MTU because OSPF uses the interface MTU to determine whether to form an adjacency. If the MTU on one side is smaller than the size of the Database Description (DBD) packet, the neighbor will reject the packet and remain in the EXSTART state, preventing full adjacency. This is a common issue when connecting interfaces with different MTU values, such as a default 1500 bytes on one side and a lower value on the other.

Answer

Duplicate router IDs.

Answer

Mismatched authentication.

Answer

Mismatched hello interval.

Question 9

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

Accepted Answer

Penultimate hop.. The router is the penultimate hop for prefix 10.0.1.0/24 because it performs a 'Pop tag' operation (implicit null label). In MPLS, the penultimate hop pops the label before forwarding the unlabeled IP packet to the egress LSR. Therefore, this router is not the egress; it is the penultimate Label Switching Router (LSR).

Answer

Transit LSR.

Answer

Egress LSR.

Answer

Ingress LSR.

Question 10

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. The correct command is 'show mpls forwarding-table' because it displays the LFIB (Label Forwarding Information Base) on each P router. Since the ingress PE has a label binding for FEC 10.1.1.0/24 but no LSP is established, the issue likely lies in label propagation or forwarding along the path. Checking the LFIB on P routers reveals whether they have installed the correct outgoing label and interface for that FEC, which is essential for LSP connectivity.

Answer

show mpls interface

Answer

show mpls ldp neighbor

Answer

show ip route 10.1.1.0

Question 11

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

Question 12

Which technology should be used to provide per-flow load balancing across multiple equal-cost paths in an MPLS network while preserving packet order?

Accepted Answer

ECMP with a hash algorithm based on layer 3 and layer 4 headers. ECMP with a hash algorithm based on Layer 3 and Layer 4 headers is the correct choice because it provides per-flow load balancing by computing a hash over source/destination IP addresses and TCP/UDP port numbers, ensuring that all packets belonging to the same flow are forwarded over the same equal-cost path. This preserves packet order while distributing different flows across multiple paths in an MPLS network.

Answer

LAG with default hashing

Answer

Policy-based routing with next-hop per destination

Answer

Per-packet round-robin load balancing

Question 13

An engineer is configuring VPLS on a Cisco ASR 9000. After verifying the pseudowire status, they notice that the 'pw status' shows 'down' for one of the PWs. Which two conditions could cause this? (Choose two.)

Accepted Answer

Mismatched encapsulation type on the pseudowire (e.g., Ethernet vs. VLAN). A mismatched encapsulation type (e.g., Ethernet vs. VLAN) on the pseudowire causes the PW to fail to come up. In VPLS, the encapsulation must match between the local and remote PE for the pseudowire to be operational; otherwise, the PW status will show 'down' due to a negotiation failure.

Answer

VPLS ID mismatch on the same bridge domain

Answer

SNMP MIB not loaded

Answer

LDP session is missing

Question 14

In a VXLAN EVPN deployment, a host sends a broadcast ARP request. Which component in the fabric is responsible for replying on behalf of the target host to reduce flooding?

Accepted Answer

The VTEP that has the target host's MAC address in its local table (ARP suppression). In VXLAN EVPN, ARP suppression is a feature implemented on the ingress VTEP (the VTEP that receives the broadcast ARP request). The ingress VTEP maintains a local ARP/ND cache populated via EVPN Type-2 routes (MAC/IP advertisement routes). When a broadcast ARP request arrives, the ingress VTEP checks its local cache for the target IP; if found, it replies directly on behalf of the target host, suppressing the broadcast and preventing unnecessary flooding across the fabric. Option C correctly identifies this VTEP as the component responsible for the reply.

Answer

The VTEP that receives the broadcast

Answer

The spine switch

Answer

The default gateway (anycast IP)

Question 15

A service provider is running OSPF in their core network. After a link failure, routing convergence is taking longer than expected. The engineer suspects the issue is related to the SPF calculation. Which OSPF feature can reduce the SPF calculation time?

Accepted Answer

Incremental SPF (iSPF). Incremental SPF (iSPF) reduces SPF calculation time by recalculating only the affected portion of the Shortest Path Tree (SPT) after a topology change, rather than recomputing the entire tree. This is especially beneficial in large OSPF networks where full SPF runs are CPU-intensive and slow convergence.

Answer

OSPF database overload protection

Answer

Bidirectional Forwarding Detection (BFD)

Answer

LSA pacing timers (pacing-interval)