Traffic Policing On 3750 Switch

By Author: Lili router
Total Articles: 4
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We have a Cisco 3750 WS-C3750V2-48TS-S WS-C3750V2-48TS-S
switch and an ASA. The ASA has 100Mbps bandwidth from ISP and it has two ports connected to the switch (inside and outside). 100 users are behind this ASA to access internet. What we want to achieve is to throttle the download rate for these 100 users to 70Mbps and retain the rest of the 30Mbps for other services.

Ideally I should do the traffic shaping/policing on the switch for the outside interface outbound direction. But according to Cisco article, 3750 series only allows to do the traffic shaping/policing on the inbound traffic not outbound. My question is:

If I do the traffic shaping/polcing on the switch for inside interface ingress direction, will it also work?

Litterally it shouldn't work because it only restrict the rate between users (LAN) and the ASA inside interface. However, does TCP protocol know how to adjust the rate to avoid too much packets being dropped before it goes to the inside interface? So the rate between ISP and the ASA outside can also ...
... be shaped? It's something related to TCP congestion theory I think. Anyone ever tested this in your environment or do you have other suggestions?

My configs:

access-list 101 permit ip any any

class-map match-any RSP_ASA_Class
match access-group 101

policy-map RSP_ASA
class RSP_ASA_Class
police 70000000 1000000 exceed-action drop

interface GigabitEthernet2/0/11
description ASA-INSIDE
service-policy input RSP_ASA

The policy will throttle the traffic by dropping packets that violate it. TCP is designed to account for packet loss though, so it will retransmit. The combination effectively limits speeds when shaping isn't an option. It's standard practice when dealing with incoming traffic.

Shaping is better than policing, but can only be done outbound. It gives the device the option of queuing packets rather than just dropping them like policing does. The ASA can do it, but not selectively.

It doesn't look like shaping WS-C3750V2-24TS-S WS-C3750V2-24TS-S is going to be an option here, so falling back on policing and relying on TCP's retransmission mechanism will work well.