What an APN is
APN stands for Access Point Name. It is the setting that tells the mobile network which gateway your data session should use to reach the internet, and it may also carry a username, a password and an authentication type.
Phones almost always configure this automatically, because operators ship the correct values in the phone's carrier settings or push them to the device when the SIM is inserted. Routers frequently do not receive that treatment, which is why the same SIM that works perfectly in a phone can register on the network in a router and still carry no data.
The symptom is distinctive and worth recognising: the router shows good signal and reports that it is registered, but nothing loads. That combination points at the APN far more often than at the hardware.
Where to find the correct value
The operator is the authoritative source. Their support line, customer care app or official website will give the correct APN for the specific plan you are on, and it is worth asking explicitly whether the plan is intended for router use, since some bundles are phone-only.
If the SIM already works in a phone, you can read the value from the phone's settings. On Android it is under mobile network settings, access point names; on iPhone it is under cellular data network, where the field may be greyed out but is still readable.
Be careful with APN lists found on forums. They are often out of date, mix up plan types, or belong to a different country entirely. A wrong APN will fail silently and cost you an hour.
- APN name — the gateway identifier, the essential field.
- Username and password — often blank; only fill them if the operator provides them.
- Authentication type — usually None, PAP or CHAP. Leave on the operator's stated value.
- PDP or IP type — IPv4, IPv6 or IPv4/IPv6. Start with the operator's recommendation.
Entering it in a router
Log in to the router's admin page and find the mobile network, WAN or dial-up settings section. Look for an APN or profile list, then create a new profile rather than editing an existing one, so you can fall back if the new settings do not work.
Type the APN exactly as given, in lower case, with no leading or trailing spaces. A stray space copied from a web page is a genuinely common cause of failure and is invisible in the input field. Leave username and password blank unless the operator has supplied them.
Save, then set the new profile as the active one and allow the router a minute or two to re-establish its data session. Many routers need a full restart before a new APN profile takes effect, so restart before concluding that it has not worked.
Technician’s tip
If the router has an automatic APN option, try it first. It succeeds more often than people expect and saves you from typing errors entirely.
When the APN is not the problem
If a correct APN still yields no data, check the obvious things in order: whether the SIM has an active data bundle, whether the SIM PIN is blocking the session, whether the plan permits use in a router, and whether the account has been suspended for any reason.
It is also worth testing the same SIM in a phone at the same location. If the phone has data and the router does not, the difference is configuration rather than coverage or account status, and you are back to the APN, the band support or the SIM size and seating.