Network

What is IP Address?

An IP address is the numeric identifier a device presents on an IP network so packets can be routed to and from it. IPv4 writes 32 bits as four decimal octets, such as 203.0.113.7. IPv6 writes 128 bits as hexadecimal groups, such as 2001:db8::1. Every request a server logs is tied to one.

An address splits into a network prefix and a host portion, divided by a mask written in CIDR notation. 198.51.100.0/24 describes 256 addresses whose first 24 bits are fixed. Blocks flow down a chain from IANA to the five regional registries, which allocate to ISPs and hosting companies, which assign to customers. Whoever announces a block into global routing does so under an autonomous system number, and that ASN is often the first attribute an anti-fraud system checks, before it looks at the address itself.

The address on your laptop is rarely the one a server records. RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 for private networks, and 100.64.0.0/10 is set aside for carrier-grade NAT. Packets leaving those ranges have their source rewritten by a router. Add a proxy and the rewrite happens a second time at the exit node, so the destination sees the proxy's public address and learns nothing about the machine behind it, unless something in the stack leaks around the tunnel.

A server reads the source address of the TCP connection it accepted. Everything else is hearsay. A transparent proxy adds X-Forwarded-For and Via headers naming the original client, an anonymous one strips them, and an application sitting behind a load balancer should trust X-Forwarded-For only when it comes from its own front end. Code that reads the header without validating the hop chain can be handed any address the caller feels like claiming.

Geolocation is inference rather than a property of the number. Commercial databases combine registry records, reverse DNS, latency measurements and provider feeds, and they lag reassignment by weeks, which is why a freshly transferred block sometimes resolves to the wrong country. Reputation works the same way. Scoring services track spam reports, abuse history and past automation against an address and against the block around it, so an address arrives carrying whatever the previous holder did with it.

Where you meet it

The address a target site logs is the one you have to control, and it is not the one your operating system shows you. Before debugging a block, check where your traffic leaves from at each layer - the proxy, the browser and the tool making the requests can each report something different. A mismatch between them usually explains why a session that works in a browser fails in a script minutes later.

Check your IP

Common questions

Does using a proxy change my IP address?

It changes the address the destination sees. Your own interface keeps its address; the request goes to the proxy, which opens a separate connection to the target and presents its public address there. Anything that bypasses the tunnel - DNS resolution, WebRTC, an IPv6 route - still exits under your real address.

What is the difference between a private and a public IP address?

Private addresses come from ranges reserved for internal networks, such as 192.168.0.0/16, and are not routed across the internet. Public addresses are globally unique and allocated through the regional registries. A router translates between the two, which is how every device in a house shares one public address.

Can two devices have the same IP address?

Yes, and it is normal. Every device behind a home router shares that router's public address, and mobile carriers put many subscribers behind one address using carrier-grade NAT. A site therefore cannot treat an address as a single person, which changes how much weight it can put on the address in fraud scoring.

Related terms

IPv4
IPv4 is version 4 of the Internet Protocol, addressing hosts with 32 bits written as four dot-separated octets, which gives roughly 4.3 billion addresses. The top-level pool ran dry in 2011, pushing providers toward private addressing, carrier-grade NAT and a paid transfer market. Nearly all proxy traffic still runs over IPv4 because that is what target sites accept.
IPv6
IPv6 is version 6 of the Internet Protocol, addressing hosts with 128 bits written as eight hexadecimal groups, such as 2001:db8::1. The space is large enough that carriers assign each subscriber a whole subnet, usually a /64 or wider, so reputation systems score prefixes instead of single addresses. Adoption is broad but far from universal.
Proxy Server
A proxy server is an intermediary that accepts your connection, makes its own request to the destination, and relays the response back. The destination logs the proxy's IP address instead of yours. Proxies are used for anonymity, geographic routing, access control, caching, and spreading a workload across many addresses so no single one is rate limited.
CGNAT
Carrier-grade NAT is address translation performed by an ISP rather than in the customer's router, putting many subscribers behind one public IPv4 address. Mobile networks depend on it. Each customer holds a private or shared-range address, usually from 100.64.0.0/10, and the carrier rewrites the source address and port on every outbound flow.
NAT
Network Address Translation rewrites the address and port fields of packets as they cross a router, letting many private hosts share one public IP. The router keeps a translation table, mapping each outbound flow to a free public port and reversing the rewrite on replies. Home routers do this for a household; carriers do it for whole regions.
ASN
An Autonomous System Number identifies a network that announces its own IP address ranges to the rest of the internet through BGP. Every routable address sits inside a prefix announced by some AS, so the ASN behind an IP tells you who operates it - a mobile carrier, a hosting provider, a home ISP or a corporate network.
DNS
The Domain Name System turns a hostname such as example.com into the IP addresses a client can connect to. A stub resolver on the device asks a recursive resolver, which walks the root, TLD and authoritative name servers, then caches the answer for the record's TTL. Queries travel on port 53, or over TLS or HTTPS when encrypted.
DNS Leak
A DNS leak happens when a client sends its name lookups outside the proxy tunnel, so queries travel over the real ISP connection while the traffic itself exits on the proxy IP. The resolver operator, and any authoritative server it contacts, then sees a lookup tied to your actual network, region and provider.
WebRTC Leak
A WebRTC leak is a browser exposing your real IP address through its peer-to-peer connection API while page traffic goes through a proxy. WebRTC gathers ICE candidates over its own UDP sockets, which ignore the browser's proxy configuration, and any script on the page can read those candidates without asking permission.

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