Mar 19

Should I trust COS or DSCP?

To prevent your markings from being stripped by an access port or an Untrusted port, always mark and trust DSCP, COS values could be stripped.

Set your Trunk ports to Trust DSCP. You also need to configure your COS-DSCP mappings for your switches to correctly priorities traffic through the switch.

Mar 14

How to tell if your policy-map is dropping packets?

Run the following command on the interface that you have the policy. The below example is applied outbound and has given classes of traffic a set amount of bandwidth, other classes simply match the DCSP markings to validate packets with those markings are leaving the router

show policy-map interface serial 0/0/0

Service-policy output: WAN-Outbound

queue stats for all priority classes:
Queueing
queue limit 64 packets
     (queue depth/total drops/no-buffer drops) 0/141160/0
(pkts output/bytes output) 178961385/27251094493

Class-map: Seven (match-all)
0 packets, 0 bytes
30 second offered rate 0 bps
Match:  precedence 7

Class-map: Six (match-all)
2049895 packets, 365732733 bytes
30 second offered rate 3000 bps
Match:  precedence 6

Class-map: Five (match-all)
179102552 packets, 27386337382 bytes
30 second offered rate 130000 bps, drop rate 0 bps
Match:  precedence 5
Priority: 12% (184 kbps), burst bytes 4600, b/w exceed drops: 141160

Class-map: Four (match-all)
8258473 packets, 503922161 bytes
30 second offered rate 3000 bps, drop rate 0 bps
Match:  precedence 4
Queueing
queue limit 64 packets
(queue depth/total drops/no-buffer drops/flowdrops) 0/153/0/153
(pkts output/bytes output) 8258320/503701910
bandwidth 9% (138 kbps)
Fair-queue: per-flow queue limit 16

Class-map: Three (match-all)
12140601 packets, 2266058800 bytes
30 second offered rate 10000 bps, drop rate 0 bps
Match:  precedence 3
Queueing
queue limit 64 packets
(queue depth/total drops/no-buffer drops/flowdrops) 0/2869/0/2869
(pkts output/bytes output) 12137732/2229606633
bandwidth 55% (844 kbps)
Fair-queue: per-flow queue limit 16

Class-map: class-default (match-any)
78037660 packets, 16987734544 bytes
30 second offered rate 143000 bps, drop rate 0 bps
Match: any
Queueing
queue limit 64 packets
(queue depth/total drops/no-buffer drops/flowdrops) 0/89674/0/89674
(pkts output/bytes output) 183823669/37946247183
Fair-queue: per-flow queue limit 16

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