350-501 Practice Test 33 — 15 Questions

Question 1

Which THREE protocols are used for label distribution in an MPLS network?

Accepted Answer

LDP. LDP (Label Distribution Protocol) is a standardized protocol (RFC 5036) specifically designed for label distribution in MPLS networks. It operates by discovering LDP peers and exchanging label mappings for each FEC (Forwarding Equivalence Class), enabling label-switched path (LSP) establishment without requiring a routing protocol to carry label information.

Answer

OSPF

Answer

IS-IS

Question 2

Which THREE characteristics apply to the BGP-LS (BGP Link State) protocol?

Accepted Answer

It uses a separate address family from VPNv4.. BGP-LS uses a separate address family (AFI 16388 / SAFI 71) from VPNv4 (AFI 1 / SAFI 128) to carry link-state information. This separation allows BGP-LS to operate independently from VPNv4 routes, enabling the collection and distribution of IGP topology data without interfering with MPLS VPN signaling.

Answer

It supports only IS-IS, not OSPF.

Answer

It carries traffic-engineering parameters in the NLRI.

Question 3

A service provider is deploying EVPN-VXLAN in its data center to provide Layer 2 and Layer 3 overlay services. The underlay uses an eBGP-based CLOS fabric with spine and leaf switches. The leaf switches act as VTEPs and run EVPN for MAC/VXLAN advertisement. One of the tenants, a financial customer, requires that their traffic between two leaf-connected servers is always forwarded through a firewall for inspection, even when the servers are on the same leaf. The firewall is connected to a service leaf. The architect proposes using EVPN integrated routing and bridging (IRB) with asymmetric IRB. However, traffic between two VMs on the same leaf is bypassing the firewall. Which architectural change ensures that all inter-VM traffic within the same leaf goes through the firewall?

Accepted Answer

Implement a VXLAN tunnel from each leaf to the firewall and use policy-based forwarding (PBF) on the leaf to redirect inter-VM traffic to the firewall via the tunnel.. Implement a VXLAN tunnel from each leaf to the firewall and use policy-based forwarding (PBF) on the leaf to redirect inter-VM traffic to the firewall via the tunnel. This forces traffic to the firewall even for local traffic. Split-horizon prevents loops, not service insertion; static routes are not scalable; symmetric IRB still allows local bridging.

Answer

Configure a gateway on the firewall and use static routes on the leaf to forward traffic to the firewall.

Answer

Use EVPN symmetric IRB and ensure the firewall is attached as a Layer 2 extension.

Answer

Enable 'split-horizon' on the leaf switches to prevent direct forwarding.

Question 4

Match each MPLS protection mechanism to its description.

Accepted Answer

MPLS Fast Reroute (FRR): Protects against link or node failures by pre-computing a backup path for each LSP.. The correct matches are: A (MPLS FRR), B (MPLS TE FRR), C (MPLS PW Redundancy), D (MPLS LSP Protection). Distractors E and F swap definitions or use incorrect descriptions.

Answer

MPLS Fast Reroute (FRR): Protects against failures by using a globally reserved bandwidth pool for all backup LSPs.

Answer

MPLS Traffic Engineering Fast Reroute (TE FRR): Protects against failures by relying on IP routing convergence of the IGP.

Question 5

A service provider uses BGP communities to influence routing policies. An administrator wants to prevent a specific prefix from being advertised to any external AS. Which BGP community should be applied?

Accepted Answer

NO_EXPORT. The NO_EXPORT community (well-known community 0xFFFFFF01) tells the router not to advertise the prefix to any external BGP peer (eBGP), but allows it to be advertised within the same AS (iBGP). This matches the requirement to prevent the prefix from being advertised to any external AS, as NO_EXPORT is specifically designed to keep routes confined to the local autonomous system.

Answer

NO_ADVERTISE

Answer

INTERNET

Answer

LOCAL_AS

Answer

NONE

Question 6

A service provider is deploying segment routing in its MPLS core. Which label allocation method is used by segment routing to distribute prefix SIDs?

Accepted Answer

IGP (IS-IS or OSPF). Segment routing uses the IGP (IS-IS or OSPF) to distribute prefix SIDs. The IGP extensions for segment routing (RFC 8665 for OSPF, RFC 8667 for IS-IS) carry the prefix SID sub-TLV within the prefix reachability information, allowing each router to allocate and advertise the SID associated with a prefix. This is the native label allocation method for segment routing, as it leverages the existing IGP database without requiring a separate label distribution protocol.

Answer

LDP

Answer

BGP

Answer

RSVP-TE

Question 7

A network engineer is troubleshooting an OSPF issue in a service provider network. The network uses OSPFv2 with multiple areas. Routers in area 0 are able to ping each other, but routers in area 1 cannot reach routers in area 2. All routers are OSPF-enabled and have correct network type configurations. What is the most likely cause?

Accepted Answer

Missing or misconfigured ABRs between area 1 and area 0, or area 2 and area 0. In OSPFv2, inter-area communication must traverse area 0 (the backbone). Routers in area 1 and area 2 can only reach each other if Area Border Routers (ABRs) exist between each non-backbone area and area 0, and those ABRs are correctly configured and have full adjacencies. Since area 0 routers can ping each other but area 1 and area 2 cannot, the most likely cause is a missing or misconfigured ABR on either side, preventing the exchange of Type 3 summary LSAs between the areas.

Answer

Mismatched OSPF area IDs on routers in area 1 and area 2

Answer

Lack of BGP peering between ABRs

Answer

OSPF network type mismatch preventing adjacency formation

Question 8

An engineer is troubleshooting a BGP peering issue between two routers. The peering is established, but routes are not being exchanged. On router R1, 'show bgp neighbors 192.0.2.2' shows the neighbor state as 'Established' but the 'Prefixes received' counter is zero. What is most likely the cause?

Accepted Answer

An outbound route-map on the neighbor is filtering all routes.. The neighbor state is 'Established', confirming that the TCP session and BGP open messages have been successfully exchanged. However, zero prefixes received indicates that R1 is not receiving any routes from the neighbor. An outbound route-map applied on the neighbor (the router sending routes to R1) can filter all prefixes before they are advertised, resulting in zero received prefixes while the session remains up.

Answer

The 'maximum-prefix' limit is exceeded, causing the session to reset.

Answer

The BGP session is in the Idle state due to a misconfigured update-source.

Answer

The 'next-hop-self' command is missing on R1.

Question 9

An OSPF network uses point-to-point links. The engineer notices that LSAs are being flooded every 30 minutes even when no topology changes occur. What is the most likely reason?

Accepted Answer

The LSA refresh interval has expired.. In OSPF, LSAs have a default refresh interval of 30 minutes (1800 seconds). When this timer expires, the router that originated the LSA re-floods it to maintain database synchronization, even if no topology changes have occurred. This is normal OSPF behavior defined in RFC 2328, and it explains why LSAs are flooded every 30 minutes.

Answer

The routers are using LSU packets incorrectly.

Answer

There is a flapping interface on the network.

Answer

The dead timer is set too low.

Question 10

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 11

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 12

An engineer is troubleshooting BGP convergence. The router has multiple paths for a prefix, but it selects a path with a lower local preference over a path with a higher local preference. The higher local preference path is from an EBGP peer. What could cause this?

Accepted Answer

The path with lower local preference has a higher weight.. B is correct because BGP selects the path with the highest weight first, before considering local preference. Weight is a Cisco-proprietary attribute that is local to the router and takes precedence over all other BGP attributes. Therefore, a path with a lower local preference but a higher weight will be preferred over a path with a higher local preference but a lower weight, even if the higher local preference path comes from an EBGP peer.

Answer

The router is configured with 'bgp deterministic-med'.

Answer

The path with lower local preference has a higher router ID.

Answer

The path with lower local preference has a lower MED.

Question 13

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 14

Refer to the exhibit. Which statement is correct about the LDP bindings for prefix 10.0.0.0/24?

Accepted Answer

There are two remote label bindings for this prefix from different LSRs.. The exhibit shows two remote label bindings for prefix 10.0.0.0/24, one with an incoming label of 18 from LSR 192.168.1.2 and another with an incoming label of 19 from LSR 192.168.1.3. This indicates that two different LSRs have advertised label bindings for the same prefix, which is typical in an MPLS network with multiple paths. Therefore, option A is correct.

Answer

Both remote bindings are from the same LSR.

Answer

The local label for this prefix is 18.

Answer

The router is performing PHP for this prefix.

Question 15

An SP is using NETCONF with YANG to automate VRF provisioning. The engineer notices that the NETCONF session is established but configuration changes are not applied. Which issue is most likely?

Accepted Answer

The NETCONF capability :candidate is not advertised. NETCONF uses datastores to manage configuration. The `:candidate` capability allows changes to be made to a candidate configuration before committing them. If this capability is not advertised, the device defaults to the `:writable-running` capability, which requires changes to be applied directly to the running datastore. Since the engineer is likely using a candidate-based workflow (e.g., `edit-config` with target `candidate`), the session establishes but changes are silently ignored or rejected because the device does not support a separate candidate datastore.

Answer

The YANG model does not support the target configuration datastore

Answer

The device does not support :url capability

Answer

The user does not have write access to the candidate datastore