I address that. Old hosts and networks only know about the first part of the address and the rest of the address resides in the data section so a new application can run on an old host even. When you cross from an old to a new network, the router can hand packets to a side box that runs CGNAT. This allows for new hosts and networks to talk to old without having to include their full address in the data payload.
Think of it like the mail service. For the majority of the journey your letter is only routed based on the first 3 digits of the zip code. When it reaches the last mile sorting facilities is when the full address becomes relevant.
Think of it like the mail service. For the majority of the journey your letter is only routed based on the first 3 digits of the zip code. When it reaches the last mile sorting facilities is when the full address becomes relevant.