QoS in input direction question

[Network Digger]

Hello,

I have a question please about QoS. 

What is the point of having a QoS policy applied in the input direction of a WAN interface??

I mean here the traffic is going from the WAN link having small BW into the LAN interface having 1 Gbps BW, I found a policy applied in the input direction but I don’t think it should make any difference. 

Any explanation will be helpful here, thank you. 

[Mark Malone]

Usually the LAN an WAN policy's are different shape police on WAN , mark honour on LAN side , good practice have QOS end to end not just on WAN circuits , you would want your voice call being crushed on LAN by someone sending 20GB file , but if LAN also marks for EF your voice traffic wont break down on LAN and everyone is still happy , call could be only going to cube beside them and never leave for the WAN

Its not a necessity on some networks which are not that busy but some networks its a requirement and its also good practice to follow

obviously bit more important the WAN is not hammered as it can effect everyone but you done want LAN users taking irregular hits on busy networks especially with highly sensitive LAN applications that may speak to each other locally and not cross the WAN

[Joseph W. Doherty]

Well, on ingress, anywhere, you might be jumping a trust boundary, so you might check QoS markings agree with your QoS policy, and if not, remark or drop, and/or you might also want to police some traffic to enforce some bandwidth agreement.