There are multiple options for each of the possibilities that you ask about:
- L3 and L2 switch could be connected as
-- access port on L3 to access port on L2. You should be careful that the access ports are in the same vlan. But the connection would still work if the vlans did not match (vlan 3 on L3 connected to vlan 2 on L2 would work - and the result would be a single broadcast domain that included both vlan 2 and vlan 3)
-- trunk port on L3 to trunk port on L2. You should be careful that the same vlans are carried on both trunk ports and that both trunks use the same native vlan.
- L3 and router could be connected as
-- access port in some vlan on L3 to router physical interface. The L3 switch might or might not have an SVI in that vlan. The router typically would function as the gateway for the devices connected in that vlan on the switch.
-- routed port (no switchport) on L3 to router physical interface. The IP of the routed port on L3 would be in same subnet as the physical interface on router. This would typically function as a transit subnet between the L3 and the router. The L3 would provide inter vlan routing for the other vlans on the switch and would forward traffic from those vlans to remote destinations to the router. The router would have routing information that would allow it to forward traffic from remote destinations to the vlans on the L3.
-- trunk port on L3 to router interface configured with subinterfaces. This would function as router on a stick (ROAS) where the router provides inter vlan routing for the subnets on the L3 and access to remote destinations. (effectively the L3 switch is functioning as a L2 switch)
Remember that very few switches are capable of L2 only or capable of L3 only. Most of our switches are capable of both and the distinction is mostly about whether the switch is configured to forward traffic using only L2 logic only (forwarding based on mac address) of is configured to forward traffic using both L2 and L3 logic.
HTH
Rick
