LPIC-1 System Architecture Practice Question
A data center server with two NICs (eth0 and eth1) is configured for network bonding in mode 1 (active-backup). The admin notices that after a cable pull on eth0, the bond interface fails over to eth1 as expected. However, when the cable is reconnected to eth0, the bond remains on eth1 indefinitely. The admin checks /proc/net/bonding/bond0 and sees that eth0 is marked as 'up' but not as 'active'. Which parameter is most likely missing from the bond configuration? Options: A) 'miimon=100' to enable link monitoring, B) 'downdelay=0', C) 'updelay=0', D) 'primary=eth0' to prefer eth0 as the active slave.
⚠ Common exam trap
Test-takers frequently assume 'miimon' alone handles both failover and failback, but in active-backup mode, failback to a preferred slave requires the explicit 'primary' parameter.
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
✓
primary=eth0
The bond is in active-backup mode (mode 1) and eth0 is marked as 'up' but not 'active' after reconnection. Without the 'primary=eth0' parameter, the bond does not automatically switch back to the preferred slave (eth0) once it becomes available; it only fails over to eth1 when eth0 goes down. Setting 'primary=eth0' ensures that eth0 is always preferred as the active slave when it is in 'up' state, triggering a failback.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
updelay=0
Why it's wrong here
updelay controls how long the bond waits before treating a recovered link as usable, delaying reversion only briefly, not indefinitely. It is the right parameter when a link needs settling time after reconnection before carrying traffic.
- ✗
downdelay=0
Why it's wrong here
downdelay governs how long the bond waits before marking a failed slave down, so it affects failover timing away from eth0, not reversion back. Setting it is relevant when links flap and premature failover must be suppressed.
- ✗
miimon=100
Why it's wrong here
miimon already functions, since failover to eth1 occurred on cable pull; the bond simply never reverts. miimon is the correct choice when no link-state monitoring exists at all and failover never triggers, not when reversion to a preferred slave is the issue.
- ✓
primary=eth0
Why this is correct
Active-backup mode does not automatically fail back; without the primary=eth0 parameter, the bond keeps using whichever slave is currently active. Setting primary=eth0 makes the bond prefer eth0 as the active slave once its link returns, restoring the original path.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LPIC-1 practice question is part of Courseiva's free LPI certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the LPIC-1 exam.