[c-nsp] Cisco 3550 counters and QoS

[Anthony D Cennami]

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Have you factored in the packet overhead for your dot1q trunk?


Marco Matarazzo wrote:
| Hi all,
|
| usual question about counters... ;)
|
| I've setup a 3550-48 SMI in a lab, one port is a layer3 port, the
other one
| a layer2 trunk to the rest of the network.
| I've applied an inbound and an outbound policy to the layer3 port, to
police
| the traffic at 1Mbps. This is the relevant part of the configuration:
|
| IOS (tm) C3550 Software (C3550-I9Q3L2-M), Version 12.1(22)EA1, RELEASE
| SOFTWARE (fc1)
|
| mls qos
|
| class-map match-any all_traffic
|   match ip dscp 0
|
| policy-map 1MbpsIN
|   class all_traffic
|     police 1024000 192000 exceed-action drop
| policy-map 1MbpsOUT
|   class all_traffic
|     police 1024000 192000 exceed-action drop
|
| interface FastEthernet0/2
|  description CustomerPort
|  no switchport
|  ip address x.x.x.x 255.255.255.0
|  service-policy input 1MbpsIN
|  service-policy output 1MbpsOUT
|  no cdp enable
|
| interface FastEthernet0/48
|  description TrunkCust3Gig1
|  switchport trunk encapsulation dot1q
|  switchport trunk allowed vlan 1,6,1002-1005
|  switchport mode trunk
|
| Now the weird part:
|
| If I download anything on the customer machine, traffic gets policed at
| 1Mbps (5 minute average, I'm using the usual mrtg), and I can see on the
| graphs a nice almost flat line on egress on the layer3 interface, and
a nice
| almost flat line on ingress on the trunk. All fine.
|
| If I upload anything from the customer machine, the traffic gets
policed at
| 1Mbps, but on the graphs, I see on the ingress of the layer3 interface
| 1.20Mbps, and on the egress of the trunk the nice flat line at 1Mbps.
| Checking the ftp client, I can see it's uploading at 125KBps (that's
| 1Mbps!), checking the "sh int":
|
|   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
|   Queueing strategy: fifo
|   Output queue: 0/40 (size/max)
|   5 minute input rate 1270000 bits/sec, 107 packets/sec << Should be
lower!
|   5 minute output rate 39000 bits/sec, 68 packets/sec
|
| Now, it wouldn't be a big problem (traffic gets policed correctly anyway),
| but billing on the layer3 counters becomes impossible, as there's a 20%
| difference on real traffic used! It there something wrong I'm doing? Any
| ideas?
|
| Thanks!
| ]\/[arco
|
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- --
: Anthony D Cennami
: Managing Partner
: NeuPATH, LLC
: acennami at neupath.com
: [PGP KeyID] 0x51cdd6bd

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