What is a BGP Looking Glass?
A BGP Looking Glass is a tool that lets you view the internet's routing table from an external vantage point. It shows you the BGP routes that networks are advertising, the AS paths traffic would follow, and which autonomous system is responsible for a given IP address range.
Why Use a Looking Glass?
Looking glasses are essential tools for network engineers and anyone who needs to understand how traffic flows on the internet. Common use cases include:
- Troubleshooting reachability issues — If a server is unreachable, a looking glass can show whether its IP prefix is being announced in BGP at all, or if there is a routing problem.
- Verifying BGP announcements — After making changes to your network's BGP configuration, you can use a looking glass to confirm that your prefixes are visible to the rest of the internet and that the AS path looks correct.
- Detecting BGP hijacks — If someone else is announcing your IP space, a looking glass will show the conflicting routes with a different origin AS.
- Understanding routing paths — You can see exactly which networks traffic would traverse to reach a given destination.
- Checking RPKI validation — Modern looking glasses show whether a route's origin is cryptographically validated.
How a Looking Glass Works
A BGP looking glass collects routing information from BGP route collectors — routers that peer with many networks and store the routes they receive. These collectors don't forward traffic themselves; they simply observe and record the BGP announcements flowing across the internet.
Major route collection projects include:
- RIPE RIS (Routing Information Service) — Operated by RIPE NCC, with collectors at major Internet Exchange Points worldwide.
- RouteViews — An academic project at the University of Oregon that has been collecting BGP data since 1995.
- CAIDA — The Center for Applied Internet Data Analysis, which processes and archives routing data.
When you query a looking glass, it searches this collected data to find all BGP routes matching your query — whether that's an IP address, a prefix, or an ASN.
What You Can Look Up
A looking glass typically supports several types of queries:
- IP address — Find the BGP route covering a specific IP. For example, looking up 8.8.8.8 shows you that it belongs to the prefix 8.8.8.0/24, originated by Google (AS15169).
- ASN — See all prefixes announced by a specific autonomous system. Looking up AS13335 shows all of Cloudflare's announced IP space.
- Domain name — Resolve a hostname to its IP address and then look up the BGP route. Try looking up google.com to see where Google's web servers are routed.
Reading Looking Glass Results
When you look up an IP address, the results typically include:
- Prefix — The IP address block (e.g., 8.8.8.0/24) that covers the queried IP.
- Origin AS — The autonomous system that originated the route — the network that claims to own this IP space.
- AS Path — The sequence of autonomous systems traffic would traverse. Read left to right: the leftmost AS is closest to the collector, the rightmost is the origin. Learn more in our AS paths guide.
- Next Hop — The IP address of the next router in the path.
- Age — How long this route has been stable.
Try It Now
This site is a BGP looking glass powered by real-time data from RIPE RIS and CAIDA RouteViews. Try these lookups:
- 1.1.1.1 — Cloudflare's DNS resolver
- 9.9.9.9 — Quad9 DNS
- AS32934 — Facebook's network
- github.com — GitHub's web servers