An internet service provider (ISP) is the company that connects you to the internet: fixed broadband over fibre, cable or DSL, or mobile data. It gives your connection an IP address and carries your traffic into the rest of the internet.
What the provider does
- Access: the line or radio signal from your home into its network.
- Addresses: a public IPv4 address (or a shared one, with CGNAT) and usually an IPv6 prefix.
- Routing: the provider is an autonomous system that announces its addresses with BGP and exchanges traffic with other networks.
- Services: often DNS resolvers, email and a router.
Where the addresses come from
Providers are members of their regional internet registry — RIPE NCC for Norway and the rest of Europe — and receive address blocks from it. IPv4 has run out, so new blocks are bought on a transfer market. Allocations are public: the IP lookup shows the block an address was delegated in, and WHOIS shows the registration.
Why a lookup shows another name
The name in a lookup is often not the brand you pay:
- the AS name is the network that routes the address, such as “Lyse Tele AS” for Altibox customers in Norway;
- the registered holder of the block can be a parent company, a former company or a wholesaler;
- many small providers rent capacity from a wholesaler, whose AS then appears.
What the provider can see
Your provider sees which IP addresses you connect to, when and how much data flows. With HTTPS, which most sites use, it can’t see the content or which pages you read, but it can see which services you use. DNS lookups are often unencrypted, so the provider can also see the names you look up unless you use encrypted DNS (DoH/DoT). See What can a website see about me?.
Switching providers
A new provider means new IP addresses. Anything that depends on your address — a fixed IP, open ports, an allowlist at work — has to be updated.