Latest · Networking
CIDR and subnetting without the mental arithmetic
Subnetting is binary arithmetic wearing a disguise, and dotted-decimal notation is the disguise. Take it off and it is straightforward.
8 min read
Blog
Notes on IP geolocation, networking, and the data underneath them. Written for people who have to make this work in production.
Privacy
What your IP address actually reveals about you
Narrower than the scare pieces suggest, broader than most people assume — and not the part of your privacy that matters most.
7 min read
Geolocation
How CDNs and anycast break IP geolocation
An anycast address is in thirty cities at once, so asking where it is has no answer. The fix is on your side, not the database's.
6 min read
Geolocation
Why your IP address shows the wrong city
The most common question any geolocation provider gets, and why the answer is almost never that the database is broken.
6 min read
Engineering
What we found in 134,000 cloud provider IP ranges
We measured how often ASN-based hosting detection misses cloud addresses. Six providers scored under 2.3%. AWS missed 15.3%.
8 min read
Privacy
Detecting VPNs, proxies and datacenter traffic
Four different questions with four very different answer qualities — and why a single "VPN: true" boolean flattens all of them.
8 min read
Engineering
Rate limiting by IP: everything that goes wrong
One address is not one user, one user is not one address, and rotation is cheap. What to count instead.
8 min read
Networking
IPv6 for developers who have been avoiding it
The same address has many valid spellings, one user has trillions of addresses, and blocking ICMP will break you. The short version.
9 min read
Geolocation
How accurate is IP geolocation, really?
Country-level accuracy is above 99%. City-level is a different story, and the number that matters is the one most APIs never return.
7 min read