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TOPIC: Traffic Priority Help!!!!

Traffic Priority Help!!!! 13 years 1 month ago #15198

Please help me. Thanks. I had 3 *3560 catalsyt switch and on all three switches i configure port 1-3 as vlan2. I use cross cable to connect port 3 (Switch 1 ) to port 1 (switch2) and connect port 3 (switch2) to port 1 (switch3). At switch 1, i had pc 1 ( connected to port1 and pc 2( connected to port 2. At switch 2 i had pc3 ( connected to port 2 and at switch3 i had pc 4( connected to port 2. The idea is to configure the switch such that traffic from pc 1 ( is to be treated with highest priority and traffic from pc 2 and 3 are to be treated as noise. PC 4 is the destination with sniffer software to ensure traffic from pc 1 is reaching it in a higer priority than the others. Please advise me on what could be configure in the cisco switches to make this possible. Thanks.

Traffic 13 years 1 month ago #15199

Hello xtrenejl
If you just want to capture/analyse the traffic going to/from PC1 at PC4 then the easiest way might be to set up a SPAN port. This replicates all the traffic to/from the chosen device to another port on the stack. For more information have a look at

Re: Traffic Priority Help!!!! 13 years 1 month ago #15216


Kind a strange , but you really can do it.

start setting up marking all traffic entering switchport where endpoing (the high priority one) once all ip tarffic is entering the switch it is marked by to dscp5 (high priority).

so at each trunk you must cofiugre 2 queues, one for fro strict priority queueing, (reserved for data traffic) and another default queue for everythign else (for other host ip address).

so once, traffic is entering the switch trunk port (the uplink one), it is treated diferently as stric prioritywhile traversing the uplink).

Dont know what type of dasta traffic is crossing the uplinks or originated in the endpoint, but keep in mind that maybe during periods of congestion maybe all other endpoints data traffic will start dropping more agressively than data traffic.

Re: Traffic Priority Help!!!! 13 years 1 month ago #15218

hi havohej and TheBishop,

Thanks for the reply. Is there any configuration commands that you can advise. I am new to networking so will really appreciate if you guys can help me out. Thanks.

Re: Traffic Priority Help!!!! 13 years 1 month ago #15220

Sure we can.
Which approach sounds most like the one that best meets your needs?

Re: Traffic Priority Help!!!! 13 years 1 month ago #15240

of course we can.

As I mentioned you must first differentiate the data traffic inmediatelly it is entering the switch, so how you differentiate the high priority data traffic for a best treatment over the other data traffic?? by marking it in the dscp filed of the ip packet (as close as posible as it enters the network).

so here is the link for how you first classify by access list traffic belonging to the high priority device and also once it is classified, it is marked

once the traffic is differentiated by dscp from the "other traffic" , the next step is to aply policies for queueing and shàping at the uplinks for intra switch communication or at the interface close to the default gateway for external communication maintaining the same policies.

heres is the lingk for establishing queueing and assing one of the queues as stric priority for better handling.
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