Anycast IP location issue
Why Your Google Cloud Global Load Balancer IP Shows Up in the US (and Why It’s Misleading)
Have you ever looked up the location of your Google Cloud’s Global Load Balancer’s IP address using a third-party IP geolocation tool and been surprised to see it listed in the United States, even if your users are spread across the globe? You’re not alone! This is a common observation and arises due to the nature of Google’s Global Load Balancer and the magic of Anycast.
The Misleading Result of IP Geolocation Tools
When you use a typical IP geolocation service, it attempts to map an IP address to a physical location based on databases that associate IP ranges with geographic regions. For standard, unicast IPs, this works reasonably well. However, Google’s Global Load Balancer utilizes Anycast, which throws a wrench into the traditional geolocation process.
Understanding Anycast: A Network Broadcast for the Closest Server
Anycast is a network addressing and routing methodology where multiple servers share the same IP address. Instead of a one-to-one mapping like unicast, Anycast allows a single IP address to be associated with multiple geographically distributed servers.
Here’s how it works:
1. Anycast IP: Google assigns a single Anycast IP address to its Global Load Balancer.
2. Routing Magic: When a user sends a request to this IP, the network routers determine the closest server (in terms of network latency) that is advertising that IP.
3. Local Response: The user’s request is then handled by the nearest server, regardless of where the IP address “originates” from in a traditional sense.
Why the US Location?
Many IP geolocation databases are built on assumptions that don’t hold true for Anycast. They might associate the Anycast IP with a central point in Google’s network, often located in the United States, where Google has a large network presence. Thus, the geolocation tools incorrectly report the IP location as being in the US.
The Right Way: Traceroute for Network Path Insight
To get a more accurate understanding of where your traffic is being routed, you need to look at the actual network path. This can be achieved using the `traceroute` (or `tracert` on Windows) command.
How to Use Traceroute
1. Open your terminal or command prompt
2. Type `traceroute [your-load-balancer-ip]` (or `tracert [your-load-balancer-ip]` on Windows) and press Enter.
3. Analyze the output.
The output of `traceroute` will show you the sequence of network hops your traffic takes to reach the destination. Each hop represents a router along the path. By examining the hostnames and IP addresses of the hops, you can often determine the geographic locations of the servers involved.
Interpreting Traceroute Results
Look for hostnames that include airport codes or city names.
You may see Google’s internal network names, which can provide clues about the data center locations.
If you see a hop that is close to your location, it indicates that your traffic is being routed to a nearby server.
Example:
traceroute 34.111.164.242
The output might show hops that include airport codes like lax (Los Angeles), ams (Amsterdam), or sin (Singapore), indicating that your traffic is being routed through those locations based upon the users location.
Another way
When you enable CDN on the Global Load Balancer, it will allow you to add customer response headers. Add a response header with any name. say x-cache and the value as {cdn_cache_status}. This will result in responses to contain a response header called -x-cache and value will tell you from where the response was served by mentioning 3 character IATA code, eg DEL, or BOM. Now you know easily from where your responses are being served for the IP assigned.
Key Takeaway
Don’t rely solely on IP geolocation tools for Anycast IPs. They can be misleading. Instead, use traceroute to gain a better understanding of the actual network path and where your traffic is being routed. This will give you a much clearer picture of how Google’s Global Load Balancer is distributing your traffic.
Anycast is a powerful technology that enhances performance and availability by routing traffic to the nearest server. Understanding how it works will help you avoid misinterpretations and gain a more accurate view of your network traffic.
