Autonomous System (AS)
Definition
A collection of IP networks operated under a single routing policy and identified by a unique Autonomous System Number (ASN). ISPs, large enterprises, and cloud providers each operate one or more ASes. Identifying the AS behind a suspect IP is the first step in determining which ISP or hosting provider to contact.
- Identifier
- Autonomous System Number (ASN)
- Typical operators
- ISPs, enterprises, cloud providers
- Investigative use
- Identifies which provider to contact
Common questions
Why does identifying the AS matter before sending a legal request for subscriber information?+
It tells the investigator which ISP or hosting provider actually controls the IP address block in question and therefore holds the account records that a subpoena or legal process should be directed to.
Can a single Autonomous System cover networks in multiple physical locations?+
Yes. One ASN can announce many separate IP blocks across different data centers or regions, so the AS alone does not pin down a physical location without further lookup.
Related terms
- BGP (Border Gateway Protocol)
- The routing protocol that autonomous systems use to advertise the IP address ranges they control to one another. BGP is the mechanism...
- CIDR (Classless Inter-Domain Routing)
- A compact notation for IP address ranges that appends a prefix length to the address, such as 192.168.1.0/24. The prefix length states...
- IPv6 Privacy Extensions (RFC 8981)
- A mechanism defined in RFC 8981 (formerly RFC 4941) by which IPv6 hosts generate temporary randomised addresses for outbound connections, rotating them...
- NAT (Network Address Translation)
- A mechanism by which a router replaces private source IP addresses with a single public IP address before forwarding packets to the...
- RIR (Regional Internet Registry)
- One of five organisations that allocate IP address blocks by region: ARIN (Americas), RIPE NCC (Europe, Middle East, Central Asia), APNIC (Asia-Pacific),...