Member Avatar for camelNotation

Do ISP's have a database that lists the names and phone numbers of all of its users by their private IP addresses?

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Short answer: no — not in the way the question suggests. Private RFC1918 addresses (for example 192.168.x.x, 10.x.x.x) are local to a home/office LAN and are reused by every router; an ISP normally cannot and does not maintain a global phonebook keyed by those private addresses. See the private-address rules in RFC 1918.

What ISPs do record is the address the customer’s gateway uses on the ISP side (the public IP, or the ISP-side private address when carrier-grade NAT is used), plus identifiers such as the CPE MAC, account ID, and timestamps. When providers use shared address space / CGNAT they keep additional mapping or port-allocation records so they can tie an Internet connection back to a subscriber — see RFC 6598. How long those logs are kept depends on the provider and local law.

Practical steps and context: to match an event to a subscriber you need the public IP (or shared-space IP) and the exact timestamp (with timezone/UTC). Consumers who want to know what their ISP logs should read the provider’s privacy/retention policy or ask support; law-enforcement access normally requires legal process. Retention and disclosure rules vary by country (for example, the UK’s Investigatory Powers Act is one statutory framework) — check local law for specifics: Investigatory Powers Act 2016.

To tie back to earlier replies: was right to flag MAC-based mapping on some networks, and is right that ISPs have kept assignment logs for a long time — the crucial distinction is whether you mean a customer’s internal (private) LAN address, which ISPs generally do not use for identity, or the address the ISP actually assigns/observes on the WAN side, which they do log.

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Member Avatar for jbennet

Possibly.

Most ISPs assign public IPs to consumers via DHCP. This can be totally random (and unlikely to be any logs although not impossible) and is generally the case with dial-up and ADSL. Alternatively, they can assign IPs via DHCP based on the MAC address of the modem (common with cable broadband) . If so, they are probably quite likely to keep records.

Member Avatar for Stylish

ISPs record who received what IP and when (if DHCP). They have been for years. (in the US anyway) Even as far back as dial-up..

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