How does BGP hijacking occur, and how can you prevent it?

BGP hijacking is a serious network security threat where an attacker injects false BGP routes into the global routing system, diverting traffic to malicious destinations, blackholing it, or enabling man-in-the-middle (MITM) attacks.

🚨 How BGP Hijacking Occurs

BGP (Border Gateway Protocol) works on trust — any Autonomous System (AS) can announce prefixes without built-in validation. BGP hijacking exploits this:

🔧 Common Types of BGP Hijacks:

Prefix Hijack
- An AS announces a prefix it doesn’t own (e.g., AS64500 advertises 192.0.2.0/24).
- If upstream providers accept and propagate this, traffic destined to the real owner is rerouted to the hijacker.
Subprefix Hijack
- Hijacker announces a more specific prefix (e.g., 192.0.2.0/25 instead of 192.0.2.0/24).
- Since BGP prefers longer matches, this overrides the legitimate route.
AS Path Manipulation
- Hijacker spoofs an AS path to appear as a legitimate route.
- Can be used to hide the origin or manipulate routing decisions.
Man-in-the-Middle (MITM)
- Traffic is rerouted through the attacker, observed or modified, then forwarded to the correct destination.

🛡️ How to Prevent BGP Hijacking

✅ 1. Use RPKI (Resource Public Key Infrastructure)

Validates that an AS is authorized to originate specific prefixes.
Uses ROAs (Route Origin Authorizations) to cryptographically bind IP prefixes to AS numbers.
Routers can be configured to drop "invalid" routes.

RPKI is the most effective tool to prevent prefix hijacking today.

✅ 2. Prefix Filtering (by ISPs and peers)

Only allow customers to announce prefixes they own.
Maintain prefix-lists or use IRR databases (e.g., RADb) to validate announcements.

ISPs must implement filtering for their customers to avoid propagating hijacks.

✅ 3. Max Prefix Limits

Prevents a peer or customer from announcing an unexpected number of routes (helps detect hijacks or leaks).

✅ 4. BGP Session Security

Use MD5 authentication to secure BGP sessions (prevents session hijacking).
Deploy TTL Security Hack (GTSM) to protect against spoofed BGP packets.

✅ 5. BGP Monitoring and Detection

Use tools and services like:
- BGPMon
- RIPE RIS
- ARIN's Route Origin Validation
- Cloudflare's BGPStream
Set up alerting for unexpected changes in your prefix announcements.

✅ 6. Route Dampening and Filtering

Apply route dampening to suppress unstable prefixes.
Filter bogon IP space and suspicious AS paths.

🌐 Global Coordination

Work with Regional Internet Registries (RIRs) and participate in MANRS (Mutually Agreed Norms for Routing Security).
Join RPKI validator communities and route collector projects.

✅ Summary Table

Prevention Method	Benefit
RPKI	Validates prefix origins
Prefix Filtering	Stops invalid announcements
Max Prefix Limits	Limits large leaks or attacks
BGP MD5/TTL Security	Protects session integrity
Monitoring Tools	Detects and alerts on hijacks
Routing Policies	Enforce route control

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