350-501 Networking Practice Test 2 — 15 Questions

Question 1

A network engineer is troubleshooting a BGP route selection issue on a router that receives the same prefix from two different peers. Which THREE BGP attributes are considered in the route selection process before the 'prefer the route with the lowest metric' step?

Accepted Answer

Highest weight. Weight is a Cisco-proprietary BGP attribute that is locally significant to the router and is checked first in the BGP best-path selection process. A route with a higher weight is preferred over all other attributes, including local preference and AS_PATH length, making it the most influential attribute for inbound traffic engineering on a single router.

Answer

Shortest AS_PATH

Answer

Lowest origin type (IGP < EGP < incomplete)

Question 2

A service provider is deploying MPLS L3VPN to connect multiple customer sites. The PE router receives a route from a CE router via MP-BGP. Which attribute must the PE router add to the route before advertising it to the route reflector?

Accepted Answer

Route distinguisher (RD). When a PE router receives a customer route from a CE router via MP-BGP, it must first make the route unique within the MPLS VPN context by adding a Route Distinguisher (RD). The RD prepended to the IPv4 prefix creates a VPNv4 address (per RFC 4364), which is the format required for advertisement to a route reflector. Without the RD, the route would not be distinguishable from other customers' overlapping IP prefixes in the BGP table.

Answer

MPLS label

Answer

Route target (RT)

Answer

IGP metric

Question 3

A network engineer is troubleshooting MPLS LSP connectivity. The MPLS LDP session is up on both endpoints, but some MPLS labels are missing in the LFIB. Which configuration change would most likely resolve the issue?

Accepted Answer

Enable 'mpls ldp advertise-labels'. Option B is correct because the 'mpls ldp advertise-labels' command ensures that LDP advertises label bindings to its peers. If this is disabled (default is enabled, but can be overridden), LDP sessions may be up but no labels are distributed, resulting in missing labels in the LFIB. Re-enabling it forces LDP to send label mappings for all FECs, resolving the connectivity issue.

Answer

Configure 'label protocol ldp' on all routers

Answer

Configure 'mpls ip' on all interfaces

Answer

Enable 'mpls ldp explicit-null' on the ingress

Question 4

A network administrator is designing an MPLS TE tunnel for a service provider backbone. The goal is to provide bandwidth protection for voice traffic. Which MPLS TE feature should be configured?

Accepted Answer

Fast Reroute (FRR). MPLS TE Fast Reroute (FRR) provides sub-50 ms protection against link or node failures by pre-computing and pre-signaling a backup tunnel that bypasses the protected element. This meets the requirement for bandwidth protection of voice traffic, which is sensitive to packet loss and delay during network convergence.

Answer

Autoroute announce

Answer

Path-option

Answer

Bandwidth protection

Question 5

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.. Option B is correct because 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 6

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 7

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 8

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 9

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 10

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

Question 11

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

Question 12

Match each QoS mechanism to its primary function.

Question 13

Match each service provider architecture term to its description.

Question 14

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 15

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.