Carrier network
How a phone or modem reaches the internet through a mobile operator, and why that path shapes the IP address a website sees.
CGNAT (carrier-grade NAT)
CGNAT is address translation run by the carrier, which lets many subscribers share one public IPv4 address. Devices get a private address, often from the 100.64.0.0/10 shared range defined in RFC 6598, and the carrier maps their connections to a public address at its gateway.
On a mobile line
The public IPv4 behind a mobile proxy is usually shared with ordinary phone users on the same gateway. A website that blocks it risks blocking those users too, which is the main reason mobile ranges are treated more carefully than datacenter ranges.
Check it: Compare the address your device reports for its cellular interface with the one a website sees. A 100.64.x.x or 10.x.x.x interface address with a different public address means you are behind CGNAT.
APN (Access Point Name)
An APN is the name a device sends when it opens a mobile data session, telling the carrier which packet gateway and network settings to use. Carriers run separate APNs for consumer internet, MMS, business plans and IoT SIMs.
On a mobile line
The APN decides which gateway, and therefore which pool of public addresses, a line exits from. Two SIMs on the same carrier can show different address ranges or IPv6 behaviour if they use different APNs.
Check it: On Android, open the access point settings for the SIM; on a modem, read the APN from its admin page or with the AT+CGDCONT? command.
Data session (PDP context)
A data session, called a PDP context in 3G and a PDN connection or bearer in 4G and 5G, is the link between a device and the carrier's packet gateway that carries its internet traffic. The gateway assigns the session its address when it opens.
On a mobile line
Closing and reopening the session is how a mobile line gets a new IP. The carrier, not the device, chooses the next address, so a reconnect can occasionally return a recently used one.
Check it: Note the public IP, toggle airplane mode for a few seconds, then check again. A different address means a new session was assigned one.
MCC and MNC
The Mobile Country Code (MCC) and Mobile Network Code (MNC) together identify a mobile operator, for example 310 to 316 for the United States and 234 or 235 for the United Kingdom. They are stored on the SIM and broadcast by the network.
On a mobile line
Apps can read the SIM and network operator codes on the device itself, which is separate from the IP a proxy changes. A proxy changes the network path of your traffic, not the SIM identity of the phone you hold.
Check it: On Android, a network info app shows the registered MCC and MNC; on a modem, AT+COPS? returns the operator code.
ASN (Autonomous System Number)
An ASN identifies a network that announces its own IP ranges in internet routing. Major carriers run dedicated mobile ASNs, such as AS21928 for T-Mobile USA, AS6167 for Verizon Wireless and AS20057 for AT&T Mobility.
On a mobile line
Detection services classify an IP partly by the ASN that announces it. An address announced by a carrier's mobile ASN reads as a mobile connection; the same carrier's fixed-line or hosting ASN does not.
Check it: Look up the address in an ASN lookup and confirm the announcing network is the carrier's mobile network.
MVNO
A mobile virtual network operator sells mobile service under its own brand while using another operator's radio network. Many MVNOs also use the host operator's packet gateways and IP ranges.
On a mobile line
An MVNO SIM often exits through the host carrier's ASN, so websites see the host network, not the MVNO brand. Some MVNOs run their own gateways and show their own ranges instead.
Check it: Run an ASN lookup on the public IP of the MVNO line and see which network announces it.
IPv6-only mobile network
Some carriers give phones only an IPv6 address and reach the IPv4 internet through translation at the carrier edge. T-Mobile in the United States is a well-known example.
On a mobile line
On these networks a site may see a native IPv6 address for some requests and a translated IPv4 address for others. A proxy setup should decide which family your tools use, so one session does not appear from two addresses.
Check it: Visit an IP check page over IPv4 and over IPv6 and compare the two results.
464XLAT
464XLAT (RFC 6877) lets IPv4-only apps work on an IPv6-only mobile network: the device translates IPv4 packets to IPv6, and the carrier translates them back to IPv4 at its edge.
On a mobile line
IPv4 traffic from such a line still leaves through a carrier IPv4 address, usually from a shared CGNAT pool, so it keeps the mobile trust profile.
NAT64 and DNS64
NAT64 (RFC 6146) translates IPv6 connections to IPv4 servers, and DNS64 creates the synthetic IPv6 addresses that point at those servers. Together they let IPv6-only devices reach IPv4-only websites.
On a mobile line
DNS answers on such a line can contain synthetic 64:ff9b:: addresses. Tools that resolve DNS locally rather than through the proxy can behave differently from the phone itself.
5G NSA and SA
5G Non-Standalone (NSA) adds 5G radio to a 4G LTE core network, while 5G Standalone (SA) runs on a 5G core. Most early 5G service was NSA.
On a mobile line
The public IP and its ASN come from the carrier's core and gateways, not from the radio, so a 5G line usually exits from the same kind of address range as a 4G line on that carrier. 5G changes speed and latency far more than how a website classifies the IP.
