Configure Rate-Based Firewall Rules on Your VPS with nftables

[johny899]

You may have experienced that situation where your VPS feels slow or unresponsive and you think, "Is someone attacking my server again?" I have been there too. The good news is that rate-based firewall rules address this situation quickly. They will cutoff traffic from bad actors and allow real users back into your site. I am going to walk you through how to do this simply.

How Rate Limits Assist​

I have always said this; don't the bots push your server around. When the bogus requests are hitting your VPS, your CPU is busy for no good reason. Rate limits prevent this by only allowing a certain number of requests per second. Have you ever hosted a database or website or stream without limits? It quickly spirals out of control.

Basic Setup​

Before the rules are added, I remove everything first into a blank ruleset. This helps to keep it simple.

nft flush ruleset

I will first just add a table and a chain.

• nft add table inet filter
• nft add chain inet filter input { type filter hook input priority 0; }

This gives me a clean space to add my rules.

Creating Rate-Based Rules​

Now we come to the good stuff: controlling new connections. I really like how simple it is to create this with nftables, step-by-step:

• nft add rule inet filter input tcp dport 22 ct state new limit rate 5/second accept
• nft add rule inet filter input tcp dport 22 drop

What this does is:

• Allows 5 new SSH connections per second
• Drops all the rest

In one case I watched a bot try over 200 SSH attempts per second. If I hadn’t limited the number of attempts, then the logs would be unnecessarily large.

Creating Rate Limit Rules for Websites (HTTP/HTTPS)​

Do you run a website? You can safely limit incoming connections:

• nft add rule inet filter input tcp dport {80,443} limit rate 200/second accept
• nft add rule inet filter input tcp dport {80,443} drop

With this rate limit you can ensure your website stays fast for users, while limiting flood attempts on the site. I have this rule on nearly every VPS I setup, it just works for this purpose.

Additional Features​

You can fortify your firewall further with:

• Connection tracking rules
• IP sets to protect against repeat attackers
• Logging rules (although use logging lightly)

These tools give you additional controls and more polished protection.