If you’re setting up a router, a VPN gateway, or just need your Debian 12 (Bookworm) machine to forward packets between interfaces, you’ll need to enable IP forwarding.

By default, Debian does not forward packets, but enabling it is straightforward. Let’s dive in! 🏊‍♂️

🛠 Step 1: Temporarily Enable IP Forwarding

If you want to enable IPv4 forwarding for the current session (without making it permanent), run:

sudo sysctl -w net.ipv4.ip_forward=1

🔹 Note: These changes will disappear after a reboot! To make them permanent, proceed to Step 2.

📄 Step 2: Make IP Forwarding Permanent

To ensure IP forwarding is always enabled after reboots, we modify the sysctl configuration file.

🔧 Enable IPv4 Forwarding Permanently

1️⃣ Open the sysctl configuration file:

sudo nano /etc/sysctl.conf

2️⃣ Find this line (or add it if it doesn’t exist):

net.ipv4.ip_forward=1
net.netfilter.nf_conntrack_max=1048576

3️⃣ Save the file (Ctrl + X, then Y, then Enter).

🔄 Step 3: Apply Changes Without Rebooting

Instead of restarting the system, apply the new settings immediately:

sudo sysctl -p

🔥 Step 4: Verify That Forwarding is Enabled

You can check if forwarding is active using:

cat /proc/sys/net/ipv4/ip_forward

It should return 1 if enabled.

🛡 Step 5: Adjust Firewall Rules (If Needed)

If you’re using nftables, ensure your firewall allows forwarding.

For nftables, use something like:

nft add rule ip filter forward accept

✅ Wrap

That’s it! 🎉 Your Debian 12 (Bookworm) machine is now forwarding packets like a pro. 🚀 Whether you’re setting up a router, VPN gateway, or multi-interface server, you’re good to go!

Happy networking! 🌐🔥

🔄 How to Enable IP Forwarding on Debian 12 (Bookworm) 🚀