Case Study: Identifying a BGP Route Leak Using WHOIS and IP Geolocation

The Day the Packets Took a Detour

On a Tuesday afternoon last month, our monitoring systems lit up. Traffic to our primary US-East data center hadn't dropped, but latency for our European users had suddenly spiked from a respectable 85ms to a staggering 400ms.

This wasn't a DDoS attack. Bandwidth utilization was normal. CPU on our load balancers was resting at 15%. This was a routing issue. Specifically, it looked like a classic BGP Route Leak.

Here is the exact diagnostic workflow I used to identify the responsible Autonomous System (AS) and force a resolution.

Step 1: The Traceroute Anomaly

Standard ping tests confirmed the high latency, but didn't tell us where the delay was happening. I ran an mtr (My Traceroute) from a test server in London targeting our US-East IP address.

Normally, traffic from London to New York hops onto a trans-Atlantic undersea cable (like TAT-14), hitting a Tier-1 provider (like GTT or Level3), and arrives in New York in about 75ms.

Instead, the traceroute showed the packets leaving London, hitting a router in Frankfurt, and then... inexplicably routing to an IP address in Singapore before eventually crawling back to New York.

Step 2: IP Geolocation and ASN Lookup

The offending hop in the traceroute was the IP address 203.0.113.45. Why was European traffic destined for New York being routed through this IP?

I used our IP Lookup Tool to analyze 203.0.113.45. The tool returned two critical pieces of information:

1. Geolocation: Singapore (SG).
2. ASN (Autonomous System Number): AS64496.

This confirmed my suspicion. The traffic was physically detouring through Southeast Asia.

Step 3: WHOIS to Identify the Culprit

Who owned AS64496? I took that ASN and dropped it into our WHOIS Lookup Tool.

The WHOIS database revealed that AS64496 belonged to a mid-sized regional ISP in Southeast Asia. This ISP is what we call a "stub network"—they purchase internet transit from larger providers to give their local customers internet access. They should never act as a transit provider for global traffic.

The Mechanics of the Route Leak

Here is exactly what happened:

1. The regional ISP in Singapore (AS64496) connects to two upstream Tier-1 providers for redundancy.
2. An engineer at AS64496 made a typo in their BGP configuration. Instead of just announcing their own IP addresses to the world, they accidentally announced to Tier-1 Provider A that they had a "great, fast route" to reach Tier-1 Provider B.
3. Provider A believed them (because BGP inherently lacks strict security without RPKI enforcement).
4. Suddenly, global traffic meant for Provider B was being sucked into the tiny Singapore ISP's network, severely congesting their routers and causing massive latency before eventually being pushed back out.

The Resolution

You cannot fix a BGP route leak on your own server. You have to contact the network operators.

Because we used WHOIS to identify the exact ASN and the company name, we were able to find their NOC (Network Operations Center) contact email. I emailed them the traceroute logs proving their AS was leaking routes. Within 45 minutes, they corrected their BGP filters, the route withdrew, and our European latency dropped back to 85ms.

Takeaway: Never blindly trust that "the internet is just slow today." Use IP Lookups, WHOIS, and traceroutes to find exactly which router is dropping your packets, and hold them accountable.