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Advanced Networking ConfigurationhardMultiple ChoiceObjective-mapped

LPIC-2 Advanced Networking Configuration Practice Question

Exhibit

Refer to the exhibit.
Contents of /etc/network/interfaces:
auto br0
iface br0 inet static
    address 192.168.1.1
    netmask 255.255.255.0
    bridge_ports eth0 eth1
auto eth0
iface eth0 inet manual
auto eth1
iface eth1 inet manual

After rebooting, the bridge br0 does not forward traffic between eth0 and eth1. Which configuration is most likely missing?

⚠ Common exam trap

Test-takers frequently assume the bridge is down or needs STP enabled, but the real issue is the forward delay timer blocking traffic immediately after boot, which is a subtle but common misconfiguration in Linux bridging.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

bridge_fd 0

The bridge br0 is not forwarding traffic because the default bridge forward delay (bridge_fd) is too long, causing the bridge to remain in a blocking state while waiting for STP convergence. Setting bridge_fd 0 disables the forward delay, allowing the bridge to start forwarding immediately after boot. This is essential when STP is not needed or when the bridge must be operational without delay.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • bridge_stp on

    Why it's wrong here

    STP is on by default, and this would not prevent forwarding; it only adds a delay.

  • bridge_fd 0

    Why this is correct

    Setting the forwarding delay to 0 disables the STP listening/learning phases, allowing immediate forwarding.

  • bridge_maxwait 10

    Why it's wrong here

    This sets the maximum time to wait for ports to come up, but does not affect forwarding delay.

  • up ip link set br0 up

    Why it's wrong here

    The interface is already brought up by the 'auto' directive and static configuration.

Visual reference

SW1 Root Bridge SW2 SW3 BLK DP DP RP RP STP blocks one link to prevent loops DP = Designated Port RP = Root Port BLK = Blocked

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Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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