write rules of a configuration file for nftables to block incomming connections to the port 22

To create a configuration file for `nftables` that blocks incoming connections to port 22 (which is typically used for SSH), you can follow the steps outlined below. A configuration file for `nftables` defines how packets are processed by the firewall.

Here’s an example of a simple `nftables` configuration file (`nftables.conf`):

```nft
# Flush existing rules
flush ruleset

# Define the tables and chains
table inet filter {
    chain input {
        type filter hook input priority 0; policy accept;

        # Allow established and related connections
        ct state established,related accept

        # Allow loopback interface
        iif lo accept

        # Log dropped packets (optional)
        log prefix "DROP: " level info

        # Block incoming connections to port 22 (SSH)
        tcp dport 22 drop

        # Drop all other incoming connections by default
        drop
    }
}
```

### Explanation of the Configuration:

1. **Flush existing rules**: The `flush ruleset` command removes all currently configured rules to prevent conflicts.

2. **Table and Chain Definition**: The `table inet filter` creates a new table named `filter`. The `chain input` further defines a chain for incoming traffic.

3. **Type and Priority**: The `type filter hook input priority 0;` specifies that this chain will filter incoming packets.

4. **Policy**: The `policy accept;` sets the default policy to accept. Each rule can override this as necessary.

5. **Stateful Rule**: The rule `ct state established,related accept` allows packets that are part of established connections or related to established connections.

6. **Loopback Interface**: The `iif lo accept` rule allows all traffic on the loopback interface (local system communication).

7. **Logging**: The `log` command can be used to log dropped packets for debugging or monitoring (this is optional).

8. **Blocking Port 22**: The `tcp dport 22 drop` rule specifically blocks all incoming TCP connections to port 22.

9. **Default Drop**: Finally, the `drop` command at the end of the chain means that if a packet does not match any of the above rules, it will be dropped by default.

### Applying the Configuration:

To apply the configuration, you would typically use a command like the following:

```bash
sudo nft -f /path/to/nftables.conf
```

Make sure to replace `/path/to/nftables.conf` with the actual path to your configuration file.

### Saving the Configuration:

After applying the configuration, you may want to save it to ensure it persists across reboots. The way to save the configuration may depend on your specific Linux distribution. On many systems, you can do:

```bash
sudo nft list ruleset > /etc/nftables.conf
```

And then configure your system to load this file on boot. For more specific details on persistence, you may refer to your distribution’s documentation.