A network with 2 switches, each switch has 2 vlan, one called vlan 10 and another vlan 20. A port-channel with 2 uplinks (trunk). Why in a layer 2 scenario I don't need to configure the trunks with the command 'switchport trunk encapsulation dot1q'? and Why when that trunk goes to a router Do I have to encapsulate with dot1q?
I know this is done on the router to have routing between vlans, but would it have any relation with my router sending the encapsulated packet to another network?