LFCS Networking Practice Question
An administrator is configuring network bonding on a RHEL 7 server with two physical NICs (eth0 and eth1) to provide redundancy. The bond interface bond0 is configured with mode 1 (active-backup). The administrator uses the following configuration in /etc/sysconfig/network-scripts/ifcfg-bond0: BONDING_OPTS="miimon=100 mode=1". The slave interfaces are configured with MASTER=bond0 and SLAVE=yes. After restarting the network service, the bond interface comes up with the active link on eth0. To test failover, the administrator disconnects the cable from eth0. The bond interface does not fail over to eth1. The administrator checks /proc/net/bonding/bond0 and sees that both slaves are listed but eth0 is still marked as active even though the cable is disconnected. What is the most likely reason for the failover failure?
⚠ Common exam trap
Watch out — candidates often assume miimon always detects physical disconnection, but the exam tests the understanding that carrier detection can fail, requiring ARP monitoring as a fallback for reliable failover.
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
✓
Add arp_interval=1000 and arp_ip_target=192.168.1.1 to BONDING_OPTS.
In mode 1 (active-backup), the bonding driver uses MII monitoring (miimon) to detect link state changes via the physical carrier signal. However, some switches or NICs do not properly report carrier loss when a cable is disconnected, causing miimon to miss the failure. Adding arp_interval and arp_ip_target forces the bonding driver to use ARP-based monitoring, which actively probes a target IP to verify link availability, thus detecting failures that miimon cannot see.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Add arp_interval=1000 and arp_ip_target=192.168.1.1 to BONDING_OPTS.
Why this is correct
ARP monitoring can detect link failures when MII monitoring fails.
- ✗
Change bonding mode to mode 4 (802.3ad load balancing).
Why it's wrong here
Mode 4 is for load balancing with switch support, not redundancy.
- ✗
Remove one slave and re-add it to force a failover.
Why it's wrong here
Temporary workaround, not a permanent fix.
- ✗
Check /var/log/messages for bonding driver errors.
Why it's wrong here
Diagnostic but does not fix the failover issue.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.