Infrastructure — 350-401 Practice Quiz

Question 1

Two Catalyst switches, DSW1 and ASW1, are connected by a manually configured 802.1q trunk. Users in VLAN 1 on ASW1 can reach the network, but the switches log repeated '%CDP-4-NATIVE_VLAN_MISMATCH' messages every 60 seconds. On DSW1 the trunk port shows 'switchport trunk native vlan 99'; on ASW1 the same port shows 'switchport trunk native vlan 1'. Tagged VLANs 10 and 20 pass traffic correctly. What is the effect of this condition, and how should you resolve it?

Accepted Answer

Untagged frames can be leaked between VLAN 99 and VLAN 1, creating a potential VLAN-hopping risk; configure the same native VLAN on both trunk ends.

Answer

The trunk will go down; set both ends to 'switchport mode dynamic auto' so DTP renegotiates the native VLAN automatically.

Answer

Tagged VLANs 10 and 20 will be pruned; enable VTP pruning on both switches to restore connectivity.

Answer

The mismatch only affects CDP and is purely cosmetic; disable CDP on the trunk ports to stop the log messages with no other action needed.

Question 2

A network engineer connects two Catalyst switches with a single link and expects an 802.1Q trunk to form dynamically. On both switches the interface is configured with 'switchport mode dynamic auto' and no other switchport commands. After the link comes up, VLAN traffic from non-native VLANs is not passing between the switches. 'show interfaces switchport' on both sides shows the operational mode as 'static access'. What is the cause of this behavior?

Accepted Answer

Both interfaces are in dynamic auto mode, so neither actively initiates DTP negotiation and the link defaults to access mode.

Answer

DTP frames are being blocked because the native VLAN does not match on the two switches.

Answer

Dynamic auto requires 'switchport nonegotiate' on at least one side before a trunk can form.

Answer

The link formed an access port because dynamic auto always overrides dynamic desirable when both are configured.

Question 3

You are configuring eBGP between two directly connected routers, R1 and R2. R1 uses 'neighbor 10.1.1.2 remote-as 65002' pointing at R2's directly connected interface IP, and R2 uses 'neighbor 10.1.1.1 remote-as 65001'. However, an engineer changed R1 to peer with R2's Loopback0 address (192.168.2.2) instead, using 'neighbor 192.168.2.2 remote-as 65002' with a static route to reach the loopback. The session fails to establish. What is the MOST likely cause, and what corrects it?

Accepted Answer

eBGP packets are sent with a TTL of 1; peering to a loopback adds a hop, so 'neighbor 192.168.2.2 ebgp-multihop 2' (and matching update-source) is required

Answer

eBGP requires both peers to be in the same AS; change R2 to remote-as 65001 to match R1

Answer

eBGP does not support loopback peering under any circumstances; the only fix is to revert to the directly connected interface IPs

Answer

The loopback must be advertised via an IGP first; adding 'network 192.168.2.2' under BGP will restore the adjacency

Question 4

A network engineer manages an eBGP edge router (AS 65010) that advertises the 203.0.113.0/24 prefix to two directly connected upstream ISPs: ISP-A (AS 64500) via GigabitEthernet0/0 and ISP-B (AS 64501) via GigabitEthernet0/1. The company wants ISP-A to be the primary path for all INBOUND traffic to 203.0.113.0/24, using ISP-B only if the ISP-A link fails. The engineer cannot influence the ISPs' local policies. Which action taken on the edge router will best achieve this goal?

Accepted Answer

Apply an outbound route-map to the ISP-B neighbor that prepends the local AS multiple times to the AS-path of 203.0.113.0/24

Answer

Apply an outbound route-map to the ISP-A neighbor that sets a higher local-preference for 203.0.113.0/24

Answer

Apply an inbound route-map to the ISP-A neighbor that sets a higher weight for received routes

Answer

Apply an outbound route-map to the ISP-B neighbor that sets a lower MED for 203.0.113.0/24

Question 5

Two directly connected routers, R1 (AS 65010) and R2 (AS 65020), are configured for eBGP peering using their physical interface IP addresses. The link is up and both routers can ping each other's interface, but the BGP session cycles between Idle and Active and never reaches Established. On R1 you see the neighbor configured with 'neighbor 10.0.0.2 update-source Loopback0'. R1's Loopback0 is 1.1.1.1/32 and R2 is peering to 10.0.0.1 (R1's physical interface). What is the most likely cause of the session failure?

Accepted Answer

R1 is sourcing BGP packets from Loopback0 (1.1.1.1), but R2 expects the session from 10.0.0.1, so the incoming packets do not match R2's configured neighbor address

Answer

eBGP requires the 'ebgp-multihop 2' command whenever routers are directly connected on the same subnet

Answer

The two routers are in different autonomous systems, which prevents any eBGP session from forming without a route reflector

Answer

BGP synchronization is enabled by default and must be disabled before the neighbor can reach Established

Question 6

An engineer configures eBGP between two directly connected routers, R1 (AS 100) and R2 (AS 200), using the interface IP addresses on the shared 10.1.1.0/30 link. R2 advertises 192.168.50.0/24 to R1. On R1, the BGP table shows the 192.168.50.0/24 prefix as valid but with a status of 'inaccessible' and it is not installed in the routing table. The neighbor is in the Established state and other prefixes are learned fine. What is the MOST likely cause?

Accepted Answer

R1 has no route to reach the BGP next-hop address advertised for 192.168.50.0/24, so the recursive lookup fails

Answer

The eBGP session requires the 'ebgp-multihop' command because the routers are directly connected

Answer

R2 must be configured with 'next-hop-self' for the eBGP session to install the prefix

Answer

The prefix is being filtered by an inbound distribute-list on R1

Question 7

A network engineer notices that a route in the EIGRP topology table shows no feasible successor after the primary path failed. The router sends queries to its neighbors and waits for replies before installing a new path. Which statement best explains why this behavior occurs and its consequence?

Accepted Answer

No neighbor met the feasibility condition, so DUAL places the route into the active state and queries neighbors, risking a stuck-in-active (SIA) condition if replies are delayed.

Answer

The router lost its adjacency, so it must rebuild the neighbor table using hello packets before any route can be reused.

Answer

The successor's reported distance was lower than the feasible distance, which caused DUAL to immediately promote the backup path without querying.

Answer

EIGRP summarization at the boundary removed the backup route, forcing the router to rely on a floating static route instead.

Question 8

A network engineer wants R1 to load-balance traffic across two paths toward 10.20.0.0/24. The successor route has a feasible distance of 3072000, and a feasible successor exists with a reported distance of 2560000 and a feasible distance of 4096000. Currently only the successor path is installed in the routing table. Which action will cause EIGRP to install BOTH paths for unequal-cost load balancing?

Accepted Answer

Configure 'variance 2' under the EIGRP process on R1

Answer

Configure 'maximum-paths 2' under the EIGRP process on R1

Answer

Configure 'variance 1' under the EIGRP process on R1

Answer

Lower the EIGRP hello and hold timers on both interfaces

Question 9

A network engineer is documenting the differences between EIGRP and OSPF for a design review. Both protocols are being evaluated for a campus WAN with links of varying bandwidth. Which statement correctly describes a fundamental difference in how these two protocols select the best path?

Accepted Answer

EIGRP calculates its metric using bandwidth and delay by default, while OSPF uses a cost derived from a reference bandwidth divided by interface bandwidth.

Answer

OSPF uses a composite metric based on bandwidth and delay by default, while EIGRP uses cumulative cost derived only from interface bandwidth.

Answer

Both EIGRP and OSPF use hop count as the primary metric, but EIGRP allows a maximum of 255 hops while OSPF allows unlimited hops.

Answer

OSPF supports unequal-cost load balancing natively with the variance command, while EIGRP only supports equal-cost load balancing.

Question 10

A network engineer is evaluating whether to deploy EIGRP or OSPF in an enterprise campus. A key requirement is the fastest possible reconvergence after a primary path failure WITHOUT any recomputation delay, provided a precomputed loop-free backup path already exists in the topology. Which statement correctly compares how each protocol meets this requirement?

Accepted Answer

EIGRP can install a feasible successor immediately from its topology table, avoiding recomputation, whereas OSPF must run the SPF algorithm to recalculate the shortest-path tree.

Answer

OSPF installs a precomputed backup automatically from its link-state database, while EIGRP must rerun the DUAL algorithm for every failure.

Answer

Both protocols use precomputed backup paths identically, so convergence behavior is the same regardless of which is chosen.

Answer

EIGRP must flood a full topology update and rerun DUAL on all routers before installing any backup, making OSPF's SPF faster in this case.

Question 11

A network engineer is documenting the differences between EIGRP and OSPF for a design review. A senior architect asks how each protocol determines the best path and reacts to topology changes. Which statement accurately compares the two protocols?

Accepted Answer

EIGRP uses a composite metric (bandwidth and delay by default) and can use feasible successors for immediate failover, while OSPF calculates a cost based on interface bandwidth and runs the SPF algorithm to build its tree.

Answer

Both EIGRP and OSPF use the Dijkstra SPF algorithm, but EIGRP applies a composite metric while OSPF uses hop count as its metric.

Answer

OSPF maintains feasible successors as precomputed backup routes, whereas EIGRP must recompute the entire topology on every link failure.

Answer

EIGRP requires a hierarchical area design with a backbone area, while OSPF is a flat distance-vector protocol with no area concept.

Question 12

A network engineer is comparing routing protocol behavior on two identical routers. On Router-A running EIGRP and Router-B running OSPF, both connect the campus to remote branch networks. The engineer needs route summarization applied close to the source networks to minimize routing table size. Which statement correctly describes a fundamental difference between where these two protocols allow summarization to be configured?

Accepted Answer

EIGRP supports summarization on any interface of any router, while OSPF only supports summarization on ABRs (inter-area) and ASBRs (external routes).

Answer

OSPF supports summarization on any interface of any router, while EIGRP only allows summarization at area boundaries.

Answer

Both protocols only allow summarization on backbone-connected routers and cannot summarize on access-layer interfaces.

Answer

EIGRP can only summarize on the router originating the network, while OSPF summarizes automatically on every router by default.

Question 13

Two switches, SW1 and SW2, are cabled together on ports Gi1/0/1 and Gi1/0/2 to form a Layer 2 EtherChannel. On both switches, the channel-group is configured with 'channel-group 1 mode passive'. After the configuration, the port-channel interface never comes up and 'show etherchannel summary' shows the ports in an independent (I) state. What is the cause and the correct fix?

Accepted Answer

Both sides are using LACP passive mode, so neither initiates negotiation; change at least one side to 'mode active'.

Answer

PAgP and LACP are being mixed; change both sides to 'mode desirable'.

Answer

The ports must be configured as trunks first; add 'switchport mode trunk' to bring the channel up.

Answer

Passive mode requires 'mode on' on the peer; change SW2 to 'mode on' to force the bundle.

Question 14

Two distribution switches run HSRP for VLAN 20. SW1 is configured with priority 150 and preempt; SW2 uses the default priority and preempt. SW1 is the active router. The network team wants SW1 to give up the active role automatically if its WAN uplink (GigabitEthernet0/1) goes down, so traffic fails over to SW2 which has an independent WAN path. Which configuration on SW1 accomplishes this?

Accepted Answer

standby 20 track GigabitEthernet0/1 decrement 60

Answer

standby 20 priority 90 preempt delay minimum 60

Answer

standby 20 timers 1 3 on GigabitEthernet0/1

Answer

standby 20 authentication md5 key-string TRACK60

Question 15

Two distribution switches, DSW1 and DSW2, share HSRP group 10 for VLAN 20's default gateway. DSW1 is configured with priority 150 and DSW2 with the default priority. During maintenance, DSW1 was reloaded; when it came back online, users noticed DSW2 remained the active router even though DSW1 has the higher priority. What must be configured on DSW1 to make it reclaim the active role automatically when it recovers?

Accepted Answer

standby 10 preempt

Answer

standby 10 priority 150 on DSW2 as well

Answer

standby 10 timers 1 3

Answer

standby version 2

Question 16

A network engineer is documenting the first-hop redundancy design for a distribution layer. The two distribution switches must present a single default-gateway IP to hosts. The design mandates the use of an open-standard protocol (not Cisco-proprietary) and must support a preemption behavior that is enabled by default so the highest-priority router automatically becomes the forwarding router when it recovers. Which protocol meets both requirements?

Accepted Answer

VRRP

Answer

HSRP version 2

Answer

GLBP

Answer

HSRP version 1

Question 17

A financial trading floor uses a Layer 2 switch to distribute a market-data multicast stream to a few subscribed servers. Network engineers notice that the multicast traffic is flooding to every port in the VLAN, including hosts that never joined the group, saturating uninvolved links. Routing and PIM are operating correctly on the upstream router. Which action on the access switch will restrict the multicast frames to only the ports with interested receivers?

Accepted Answer

Enable IGMP snooping on the VLAN so the switch learns which ports have receivers from their IGMP membership reports

Answer

Configure PIM sparse-mode on the switch's SVI to build a shared tree toward the receivers

Answer

Enable an IGMP querier only on the upstream router and remove the switch from the multicast path

Answer

Apply storm control on the receiver ports to police the multicast rate below the link capacity

Question 18

Two switches, SW1 and SW2, are connected by an 802.1Q trunk and both are configured for MST. All VLANs are allowed on the trunk, but you notice that SW1 treats SW2 as a boundary and runs a separate MST instance toward it rather than forming a single common MST region. You confirm both switches have 'spanning-tree mode mst' and identical instance-to-VLAN mappings. Which additional configuration mismatch most likely prevents them from being in the same MST region?

Accepted Answer

The MST region names or revision numbers differ between SW1 and SW2

Answer

The switches use different bridge priorities for instance 0

Answer

Root guard is enabled on SW1's trunk interface

Answer

The trunk is using dynamic (DTP) negotiation instead of a static trunk

Question 19

A network engineer configures PAT on a router named EDGE so that all hosts on the inside LAN (192.168.10.0/24) can reach the Internet using the single public IP assigned to interface GigabitEthernet0/1 (203.0.113.5). Internal users report they cannot browse the Internet. The engineer runs 'show ip nat translations' and sees no entries. The current configuration is:

interface GigabitEthernet0/0
 ip address 192.168.10.1 255.255.255.0
 ip nat inside
interface GigabitEthernet0/1
 ip address 203.0.113.5 255.255.255.248

ip access-list standard NAT_HOSTS
 permit 192.168.10.0 0.0.0.255
ip nat inside source list NAT_HOSTS interface GigabitEthernet0/1 overload

Which action will fix the problem?

Accepted Answer

Add the 'ip nat outside' command to interface GigabitEthernet0/1

Answer

Change the ACL to an extended access list matching TCP and UDP traffic

Answer

Remove the 'overload' keyword because it prevents dynamic translations

Answer

Add a static NAT entry mapping 192.168.10.0 to 203.0.113.5

Question 20

An ASBR redistributes static routes into OSPF using the default configuration. A remote router several hops away receives two paths to the same redistributed prefix through two different ABRs, but it always selects the same next hop regardless of the internal cost to reach each ABR. A network engineer wants the remote router to instead prefer the path with the lowest total cost, accounting for the internal OSPF cost to reach the ASBR. Which action achieves this?

Accepted Answer

Redistribute the routes as OSPF External Type 1 (E1) by adding the metric-type 1 keyword

Answer

Increase the OSPF reference bandwidth on the remote router

Answer

Configure the routes as OSPF External Type 2 (E2) with a higher seed metric

Answer

Enable OSPF summarization on both ABRs with the area range command

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