As of June 5, 2025, AWS WAF just got a powerful new capability — you can now match incoming traffic based on Autonomous System Numbers (ASNs).

This opens up a new layer of control in your WAF rules, making it easier to block:

• 🚫 Known VPN providers
• 🛑 Malicious bot networks
• 📉 Poor-performing ISPs
• ✅ Or allow traffic from trusted carriers

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🤔 Wait, What’s an ASN?

An ASN (Autonomous System Number) represents a group of IP addresses owned and managed by an organization — usually:

• An ISP
• A VPN provider
• A cloud/data center provider

For example:

Google ASN → 15169

Cloudflare ASN → 13335

A shady VPN provider → 12345

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🔍 Why Is This Update So Useful?

Before:

• You had to manually maintain IP lists to block VPNs
• Couldn’t easily identify traffic by provider
• Blocking was brittle and error-prone

Now:

• Just block by ASN — clean and fast
• Works natively inside AWS WAF
• Combine it with rate limiting, geo match, IP sets, and more

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🎯 Example: Blocking a Known VPN ASN

You notice excessive scraping or login abuse from a VPN provider with ASN 12345.

Here’s how you block it in AWS WAF:

🛠️ In AWS Console:

1. Go to your Web ACL
2. Create a new Rule
3. Choose "Match Rule" > ASN match
4. Enter 12345
5. Set Action to Block
6. Save

✅ Done — all traffic from that ASN will now be blocked.

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📈 Advanced Use: Rate Limit by ASN

Let’s say you want to throttle traffic instead of fully blocking:

“If ASN 12345 sends more than 100 requests in 5 minutes, block it temporarily.”

Use a Rate-based Rule with:

• Condition: ASN match = 12345
• Rate limit: 100 requests / 5 min
• Action: Block

Perfect for mitigating abuse without hurting good traffic.

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🧠 TL;DR

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💬 Final Thoughts

This update gives you ISP-level control over your traffic — perfect for securing web apps against bad actors using anonymous networks.

🔐 Better security
⚡️ Faster decisions
💸 Lower WAF maintenance effort

Are you using ASN-based rules in your WAF yet? Let’s talk in the comments 👇