LFCS Networking Practice Question
To permanently disable IPv6 on a network interface, which configuration should be added to /etc/sysctl.conf?
⚠ Common exam trap
Many exam-takers confuse the sysctl parameter name `disable_ipv6` with the simpler `disable` (Option A) or mix up sysctl settings with kernel boot parameters like `ipv6.disable=1` (Option B), while also overlooking that `all` is the correct scope for a permanent, interface-agnostic configuration in `/etc/sysctl.conf`.
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
✓
net.ipv6.conf.all.disable_ipv6 = 1
The sysctl parameter `net.ipv6.conf.all.disable_ipv6 = 1` is the proper kernel interface to globally disable IPv6 on all network interfaces. This setting is applied via the sysctl system, which reads `/etc/sysctl.conf` at boot to configure kernel parameters. The key must use the exact `disable_ipv6` suffix (not `disable`) and the `all` scope ensures the setting applies to every interface, including future ones.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
net.ipv6.conf.all.disable=1
Why it's wrong here
The correct key is 'disable_ipv6', not 'disable'.
- ✗
ipv6.disable=1
Why it's wrong here
This is a kernel command-line parameter, not a sysctl setting.
- ✗
net.ipv6.conf.eth0.disable_ipv6 = 1
Why it's wrong here
This disables IPv6 only on eth0, not necessarily all interfaces.
- ✓
net.ipv6.conf.all.disable_ipv6 = 1
Why this is correct
This disables IPv6 on all interfaces system-wide.
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