I would like to understand traffic flow in a router. In what direction do i need to apply a policy-map in order to affect traffic? Especially regading tunnel interfaces, as traffic both comes and goes to other virtual interfaces.

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    Dec 17 '20 at 18:45

So i did some labbing and got to the results myself. This is a schematic of a Cisco 892FSP router.

Router schematics

It has a built in switch, so we have to work with vlan interfaces. If we assume traffic flowing from the LAN port (Gi0) going thru a typical VPN out on the WAN (Gi9). I tested service-policies on all interfaces in both directions to see, where exactly the service-policy is being applied to. I marked the corresponding "sides" with blue arrows. So the two interfaces Vlan10 and Dialer1 are pretty straight forward in its funcitonality and are pretty much bound to their respective physical interfaces. A tunnel interface on the other hand is bound to the dialer. If you apply a policy-map at an incoming direction, it affects traffic that comes from your "central office" via VPN going to your LAN port. A policy-map at an outgoing direction affects traffic from your LAN to the "central office".

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