We have a switch with two different VLAN's 10 and 99 for management. They are connected to one F/E port on the router. Now we made on the switchport a trunk and on the router side divided the F/E port in 2 subinterfaces. But if on first subinterface we put Encapsulation dot1Q native 10 we don't get any traffic passing anymore but interfaces stay up. What could be the cause?
Currently subinterfaces are configured but only VLAN10 traffic is passed and interface on router has encap dot1Q native 1.
You appear to have native VLAN as 10 on the router and 1 on the switch - drop the native bit. If it insists on you having native somewhere, put it under th interface
int fas 0/0
enc dot1q 1 native