You have an LTE or 5G modem, the SIM is in its holder, the antennas are attached, and there is no connection. No address on lte1, no default route, and the lights are not doing what you expect.
This chapter is about a modem that gets no session. If the connection works but is slow or erratic, that is almost always the signal rather than the configuration. If it works and you still cannot reach it from outside, see Two routers behind each other: mobile connections sit behind carrier-grade NAT almost without exception.
The quick checks, in order
- Does the interface exist?
/interface lte print. A good answer is one line forlte1. Nothing at all means the modem itself is not recognised: for a USB stick check/system resource usb print, and check that the right package and firmware are present. - Is the modem registered on the network?
/interface lte monitor lte1 once. A good answer isstatus: connected,registration-status: registered (home), acurrent-operatorand a readablersrporrssi. Anrsrpbetter than -100 dBm is usable, towards -120 dBm it gets difficult. - Does the SIM ask for a PIN?
/interface lte at-chat lte1 input="AT+CPIN?". A good answer is+CPIN: READY. If it saysSIM PIN, that is your entire problem. - Is the APN profile right?
/interface lte apn print. A good answer is a profile with exactly the APN your provider prescribes, and/interface lte print detailshowingapn-profilespointing at it. - Is there an address?
/ip address print. A good answer is an address onlte1, usually from a private range or from 100.64.0.0/10. - Is there a default route?
/ip route print. A good answer is an active0.0.0.0/0vialte1. - What does the log say?
/log print where topics~"lte".
The usual causes, most common first
The SIM has a PIN on it
A SIM with an active PIN never gets past SIM PIN. In RouterOS you set it with /interface lte set lte1 pin=1234. The configurator has no field for the PIN, so that line is yours to write, or you take the PIN off the SIM with a phone first. The second option is usually nicer: a PIN in the configuration is forgotten after a reset.
The APN is wrong
The tool fills in internet, which works on many providers but far from all. Business SIMs, M2M SIMs and MVNOs often have their own APN, sometimes with a username and password and PAP or CHAP on top. Ask, and fill it in exactly.
Roaming is off
The script writes allow-roaming=no. For a fixed installation that is the right choice, but a foreign SIM, an MVNO riding on another network or a spot near a border will not get through because of it. Turn it on by hand then: /interface lte set lte1 allow-roaming=yes. The tool offers no toggle for this.
No signal, or not enough
Antennas not screwed down, the wrong connectors used, or the device sitting in a concrete meter cupboard. In a fixed installation an outdoor antenna is often the difference between unusable and fine. Look at rsrp and sinr, not at the number of bars.
The SIM is in the wrong holder
Some models have two SIM slots and start on the other one. /system routerboard modem print shows which is active.
Data used up, or the wrong PDP type
An exhausted bundle gives you exactly the same picture as a wrong APN: registered, no address. A few providers also insist on IPv4v6 explicitly.
What the configurator does about it
In the WAN and internet section you set an uplink's type to LTE / 5G modem. That type appears as soon as the interface is called lte1 or the catalogue knows the model has a modem. The fields: APN, APN user, APN password, APN authentication (none, PAP or CHAP), IPv6 over LTE, route distance, gateway check, use ISP DNS and add default route. There is no MTU field for LTE.
The script turns that into an /interface lte apn profile named apn-<your apn>, including add-default-route and the distance, and attaches it with /interface lte set lte1 apn-profiles=... allow-roaming=no.
That is the complete list. The tool sets no PIN, picks no band, does not enable roaming, does not lock to an operator, and cannot see whether your SIM is active or your bundle is spent. It also does not know whether you get a public address; on most mobile subscriptions you do not, and then port forwarding will never work no matter how you set it up.
As a second uplink next to a fixed line, LTE does work well: with several uplinks you pick a failover method, give the LTE line a higher distance, and the router falls back as soon as the gateway check fails. See Several WANs and Recipe: LTE as backup.
When it is not your router
The SIM, the bundle, the coverage and the antenna. The fastest way to tell them apart is to put the SIM in a phone: if it works there without a PIN and with the same APN, the router is at fault; if it does not work there either, you are done in RouterOS. For the models with a built-in modem the details are in Chateau and LtAP.
Read on: WAN and internet, Several WANs and RouterOS packages.