Setting up GRE Tunnels on Debian 🚇

To set up a GRE tunnel on Debian between two endpoints (102.219.109.8 and 102.222.161.20) using tunnel IPs 100.64.0.1/30 and 100.64.0.2/30, follow these steps.

✅ Step-by-Step GRE Tunnel Setup on Debian

🖥️ Assumptions:

Host	Public IP	Tunnel IP
Host A	`102.219.109.8`	`100.64.0.1/30`
Host B	`102.222.161.20`	`100.64.0.2/30`

You’ll need to do the following steps on both hosts, changing local/remote accordingly.

🔧 1. Create the GRE tunnel

On Host A (`102.219.109.8`)

ip tunnel add gre1 mode gre local 102.219.109.8 remote 102.222.161.20 ttl 255
ip addr add 100.64.0.1/30 dev gre1
ip link set gre1 up

On Host B (`102.222.161.20`)

ip tunnel add gre1 mode gre local 102.222.161.20 remote 102.219.109.8 ttl 255
ip addr add 100.64.0.2/30 dev gre1
ip link set gre1 up

🔁 2. Test the Tunnel

From Host A, ping Host B:

ping 100.64.0.2

From Host B, ping Host A:

ping 100.64.0.1

💾 3. Make it Persistent (Optional)

If you want to make the tunnel persistent across reboots, you can:

Option A: Use a systemd unit or init script

(not ideal unless scripted manually)

Option B: Use `/etc/network/interfaces` (legacy method)

Edit /etc/network/interfaces on Host A:

auto gre1
iface gre1 inet static
    address 100.64.0.1
    netmask 255.255.255.252
    pre-up ip tunnel add gre1 mode gre local 102.219.109.8 remote 102.222.161.20 ttl 255
    up ip link set gre1 up
    down ip link set gre1 down
    post-down ip tunnel del gre1

Edit /etc/network/interfaces on Host B:

auto gre1
iface gre1 inet static
    address 100.64.0.2
    netmask 255.255.255.252
    pre-up ip tunnel add gre1 mode gre local 102.222.161.20 remote 102.219.109.8 ttl 255
    up ip link set gre1 up
    down ip link set gre1 down
    post-down ip tunnel del gre1

Then restart networking:

sudo systemctl restart networking

📌 Notes

Ensure GRE (IP protocol 47) is allowed through any firewall (iptables, nftables, cloud firewall, etc.).
No NAT should be applied to the tunnel unless explicitly required.
GRE doesn't encrypt traffic — it's purely encapsulation.

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Setting up GRE Tunnels on Debian 🚇

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✅ Step-by-Step GRE Tunnel Setup on Debian

🖥️ Assumptions:

🔧 1. Create the GRE tunnel

On Host A (`102.219.109.8`)

On Host B (`102.222.161.20`)

🔁 2. Test the Tunnel

💾 3. Make it Persistent (Optional)

Option A: Use a systemd unit or init script

Option B: Use `/etc/network/interfaces` (legacy method)

📌 Notes

Command Palette

Comments

More from this blog

✅ Step-by-Step GRE Tunnel Setup on Debian

🖥️ Assumptions:

🔧 1. Create the GRE tunnel

On Host A (102.219.109.8)

On Host B (102.222.161.20)

🔁 2. Test the Tunnel

💾 3. Make it Persistent (Optional)

Option A: Use a systemd unit or init script

Option B: Use /etc/network/interfaces (legacy method)

📌 Notes

On Host A (`102.219.109.8`)

On Host B (`102.222.161.20`)

Option B: Use `/etc/network/interfaces` (legacy method)