Network Implementation practice questions

Spanning Tree Protocol (STP)

Why wrong: STP prevents loops in redundant switch topologies, but does not segment broadcast domains.

VLAN Trunking Protocol (VTP)

Why wrong: VTP is used to manage VLAN configurations across switches, but it does not itself create broadcast domains.

Access Control List (ACL)

Why wrong: ACLs filter traffic based on rules, but they do not create separate broadcast domains.

Default route (0.0.0.0/0)

Why wrong: The default route is the least specific and only used if no other route matches.

10.0.0.0/8 via 192.168.1.1

Why wrong: Although this route also matches, it is less specific than the /16 route, so it is not chosen.

None; the packet is dropped

Why wrong: There are matching routes, so the packet is not dropped.

Electromagnetic interference

Why wrong: Fiber optic cables are immune to electromagnetic interference because they transmit light, not electrical signals. EMI would not cause signal weakening in fiber.

Incorrect termination

Why wrong: While incorrect termination can cause light loss, the most likely issue over such a long distance is distance-related attenuation. Termination issues are more likely to cause total failure or high loss at the connection points, not gradual weakening along the run.

Crosstalk

Why wrong: Crosstalk occurs in copper cables when signals interfere with each other. Fiber optics do not experience crosstalk in the same way.

The printer is on a different VLAN

Why wrong: In a small office with a simple wireless router, VLANs are rarely configured. Even if VLANs were used, the router would need to route between them, and the printer's IP 192.168.1.50 suggests the same VLAN as the laptop (192.168.1.100).

The default gateway is misconfigured

Why wrong: For local subnet communication (same network), the default gateway is not used. Devices use ARP to find each other directly. A misconfigured gateway on the printer would only affect traffic to other subnets.

The DHCP scope is exhausted

Why wrong: The laptop obtained an IP (192.168.1.100), so the DHCP scope is not exhausted. DHCP scope exhaustion would prevent new devices from getting IP addresses, but the printer has a static IP, so it is not affected by DHCP.

Mismatched encryption algorithms between the two VPN peers

Why wrong: If encryption algorithms were mismatched, the tunnel would not establish. Since the tunnel is up, this is not the issue.

Firewall on the main office server blocking ICMP

Why wrong: While possible, the main office can ping the branch gateway, and if the tunnel is up, firewall rules affecting ICMP are less likely the root cause compared to missing routing.

Incorrect IKE authentication settings

Why wrong: IKE authentication issues would prevent the tunnel from being established; since the tunnel is active, this is not the cause.

VLAN 20 is not allowed on the trunk to the router

Why wrong: This would affect communication to other VLANs, not within the same VLAN. Intra-VLAN communication does not go through the router.

The server does not have a default gateway configured

Why wrong: A default gateway is only required for communication outside the local subnet. It is not needed for devices in the same VLAN.

The port is administratively down

Why wrong: If the port were down, there would be no connectivity at all, but the question implies the server is connected (just unable to communicate).

B) Native VLAN mismatch on the trunk

Why wrong: Incorrect. A native VLAN mismatch can cause issues for untagged frames, but it would not specifically prevent VLAN 10 traffic if both sides allow it.

C) Trunk encapsulation mismatch (ISL vs 802.1Q)

Why wrong: Incorrect. An encapsulation mismatch would likely cause the trunk to not come up or to flap, but the trunk is already operational (up/up).

D) STP is blocking the VLAN 10 traffic on the trunk

Why wrong: Incorrect. STP blocks redundant paths to prevent loops, but on a single trunk link, STP should not block traffic unless there is a topology loop. The trunk is up, so STP is not blocking.

B) Different channels per AP to reduce interference

Why wrong: Incorrect. Using different channels is important for performance but does not directly affect roaming capability.

C) WPA2-Enterprise with RADIUS authentication

Why wrong: Incorrect. WPA2-Enterprise provides strong security but is not specifically required for roaming; roaming works with WPA2-Personal as well if SSID and passphrase are consistent.

D) Mesh topology for AP interconnection

Why wrong: Incorrect. A mesh topology describes how APs backhaul traffic (wirelessly vs wired). It does not directly impact client roaming behavior.

Site-to-site IPsec VPN with static IPs

Why wrong: This requires static public IP addresses on both ends; dynamic IPs would break the tunnel configuration unless using additional technologies like dynamic DNS.

Remote access VPN using SSL

Why wrong: This is typically used for individual client devices connecting to a corporate network, not for connecting entire networks (site-to-site).

Policy-based VPN

Why wrong: Policy-based VPNs often rely on static IPs and specific traffic selectors; they do not inherently handle dynamic IPs.

802.11n

Why wrong: 802.11n can operate in both 2.4 GHz and 5 GHz, but its maximum throughput is lower than 802.11ac.

802.11g

Why wrong: 802.11g operates only in the 2.4 GHz band with maximum throughput of 54 Mbps.

802.11b

Why wrong: 802.11b operates only in the 2.4 GHz band with maximum throughput of 11 Mbps.

A) 802.11b

Why wrong: 802.11b operates only in the 2.4 GHz band and has a maximum throughput of 11 Mbps.

B) 802.11g

Why wrong: 802.11g operates only in the 2.4 GHz band, though it is backward compatible with 802.11b.

D) 802.11ac

Why wrong: 802.11ac operates exclusively in the 5 GHz band and is not backward compatible with 2.4 GHz devices.

A) That the DNS server addresses are correctly configured

Why wrong: DNS is not directly related to VPN traffic forwarding; the issue is about routing, not name resolution.

C) That the MTU size is set to 1500 on both ends

Why wrong: MTU mismatch can cause packet fragmentation issues but is not the primary cause when the tunnel is up but no traffic passes.

D) That the SSID is correctly configured on the access points

Why wrong: SSID is a wireless network identifier and has no bearing on VPN routing.

The trunk port is in an err-disabled state.

Why wrong: The trunk status is up/up, so it is not err-disabled. An err-disabled port would show as down.

The switchport mode is not set to trunk on one side.

Why wrong: If the trunk link is up/up, both sides are likely configured as trunk ports. The question states the trunk is configured, so this is not the issue.

The spanning-tree protocol is blocking VLAN 10 on the trunk.

Why wrong: Spanning tree can block specific VLANs if there is a loop, but for a simple two-switch topology this is unlikely. Moreover, the symptom is that hosts on the same VLAN cannot communicate, which is more indicative of a native VLAN issue.

Check the IPsec security associations for encryption algorithm mismatch.

Why wrong: If the tunnel is active and both sides can ping tunnel IPs, the IPsec parameters are correctly negotiated. An algorithm mismatch would prevent the tunnel from establishing.

Disable the firewall on the internal interfaces temporarily.

Why wrong: The firewall rules already permit traffic. Disabling firewalls is not a best practice and would not resolve a routing issue.

Regenerate the pre-shared key on both sides.

Why wrong: Regenerating the PSK is unnecessary because the tunnel is already established. The PSK is only used during initial authentication.

Spanning Tree Protocol (STP)

Why wrong: STP prevents loops in redundant topologies but does not combine links to increase bandwidth. It may block redundant links.

VLAN trunking (802.1Q)

Why wrong: Trunking allows multiple VLANs to traverse a single link but does not aggregate bandwidth or provide redundancy by itself.

Power over Ethernet (PoE)

Why wrong: PoE delivers power over Ethernet cables and has no effect on bandwidth aggregation or link redundancy.

RIP

Why wrong: RIP uses hop count as its metric and is classful by default; it does not support VLSM well and converges slowly.

OSPF

Why wrong: OSPF supports VLSM and converges quickly, but its metric is cost (based on bandwidth), not a combination of bandwidth and delay.

BGP

Why wrong: BGP is designed for routing between autonomous systems, not for internal routing within a single organization. It uses path attributes rather than bandwidth/delay.

Mesh network

Why wrong: Mesh networks are designed for extending coverage via wireless backhaul, not primarily for automatic RF coordination and roaming management.

Controller-based wireless

Why wrong: Controller-based wireless requires a dedicated on-premises controller, which the IT manager wants to avoid.

Standalone APs

Why wrong: Standalone APs must be configured individually and cannot automatically coordinate RF settings or roaming.

Cat5e

Why wrong: Cat5e supports 1 Gbps but only up to 100 meters; the distance exceeds that.

Cat6

Why wrong: Cat6 also supports 1 Gbps but is limited to 100 meters.

Coaxial cable

Why wrong: Coaxial cable is typically used for cable internet and TV, not for modern 1 Gbps Ethernet networks over that distance.

The VTP domain name matches on both switches.

Why wrong: VTP is not required for trunking, and mismatched VTP domains do not prevent trunk traffic.

The speed and duplex settings are identical.

Why wrong: Speed/duplex mismatches can cause issues, but they would affect all traffic, not just specific VLANs.

The spanning tree protocol is disabled.

Why wrong: Spanning tree should be enabled to prevent loops; disabling it could cause issues but not selective VLAN blockage.

OFDM (Orthogonal Frequency Division Multiplexing)

Why wrong: OFDM is a modulation technique that divides a channel into subcarriers, but it does not inherently use multiple spatial streams.

DSSS (Direct Sequence Spread Spectrum)

Why wrong: DSSS is an older physical layer technology used in 802.11b.

CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)

Why wrong: CSMA/CA is a Medium Access Control method, not a throughput-enhancing technology.