LFCS Networking Practice Question
A server with two network interfaces needs to forward IP packets between them. Which two steps are required to enable IP forwarding? (Choose two.)
⚠ Common exam trap
It's easy for candidates to confuse enabling IP forwarding with adding routes or restarting network services, but the core requirement is a kernel parameter change, not a routing table or service restart.
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
✓
Run sysctl -p
`sysctl -p` reloads kernel parameters from `/etc/sysctl.conf`, making the `net.ipv4.ip_forward=1` setting active without a reboot. Option C is correct because setting `net.ipv4.ip_forward=1` in `/etc/sysctl.conf` enables IP forwarding persistently across reboots. Together, these two steps ensure the kernel forwards IP packets between network interfaces.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Run systemctl restart network
Why it's wrong here
Restarting the network service is not required for enabling IP forwarding; it only affects interface configuration. Kernel parameter changes take effect immediately via sysctl.
- ✓
Run sysctl -p
Why this is correct
Running sysctl -p reloads kernel parameters from /etc/sysctl.conf, making the net.ipv4.ip_forward=1 setting active without rebooting. This is one of the two required steps.
- ✓
Set net.ipv4.ip_forward=1 in /etc/sysctl.conf
Why this is correct
Setting net.ipv4.ip_forward=1 in /etc/sysctl.conf makes the change persistent across reboots. Together with sysctl -p, this enables IP forwarding.
- ✗
Add a route to the second interface
Why it's wrong here
Adding a route is unrelated to enabling IP forwarding. Forwarding must be enabled at the kernel level before routes can be used to forward packets between interfaces.
- ✗
Set net.ipv4.conf.all.forwarding=1
Why it's wrong here
Setting net.ipv4.conf.all.forwarding=1 also enables forwarding, but it is not one of the required steps because the question asks for the combination of persistent configuration and immediate activation. This parameter alone is not persistent and would require sysctl -p or a reboot to take effect if not already loaded.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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