hardMultiple Choice
XK0-006 Practice Question: An administrator is configuring a server to act…
An administrator is configuring a server to act as a router and needs to enable IP forwarding persistently across reboots. Which file should be modified?
⚠ Common exam trap
It's easy for candidates to confuse the runtime procfs file (/proc/sys/net/ipv4/ip_forward) with a persistent configuration file, leading them to choose D, which only changes the value temporarily until the next reboot.
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
✓
/etc/sysctl.conf
/etc/sysctl.conf is the system-wide configuration file for kernel parameters managed by sysctl. Setting net.ipv4.ip_forward = 1 in this file ensures IP forwarding is enabled persistently across reboots, as sysctl applies these settings during boot.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
/etc/network/interfaces
Why it's wrong here
/etc/network/interfaces configures interface addressing and options such as up/down commands, but it is not the canonical persistent store for kernel sysctl parameters, so forwarding may not be set reliably across reboots. It is tempting because interface stanzas can run commands, and would suit defining static addresses or interface-specific directives.
- ✓
/etc/sysctl.conf
Why this is correct
Writing `net.ipv4.ip_forward = 1` into `/etc/sysctl.conf` makes the kernel apply the setting at every boot, satisfying the persistence requirement. The `sysctl -w` command only changes the running kernel, so it would be lost on reboot.
- ✗
/etc/rc.local
Why it's wrong here
Editing /etc/rc.local runs sysctl commands only at boot, so the setting is not applied when interfaces restart or the service reloads, and rc.local is deprecated on many systemd distributions. It is tempting as a general boot-time hook, and would suit arbitrary one-off startup commands rather than kernel parameter persistence.
- ✗
/proc/sys/net/ipv4/ip_forward
Why it's wrong here
Writing to /proc/sys/net/ipv4/ip_forward changes the running kernel only; the procfs entry is volatile and reverts on reboot, so persistence fails. It is tempting because it is the exact runtime switch for forwarding, and would be correct for temporarily enabling forwarding during testing without surviving a restart.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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