How does routing actually work?

[costo]

All nodes need to share the same modem_settings. Otherwise they do not see each other.

https://meshtastic.org/docs/settings/channel#modem_config

and this:

Encryption / Secondary Channels

Some people seem to misunderstand the working of the LoRa modules used in meshtastic_nodes. These modules are usually built around SemTech chips, like SX1276 . All these chips are single frequency/channel, single spreadfactor and single coding_rate, which in meshtastic is called ‘modem_settings’. This means that the chip/module cannot read,decode or retransmit LoRa-transmissions with a different modem_setting than it has been setup for.