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I'm trying to limit traffic to test performance of some in-house applications, but I am getting inconsistent results when configuring my home PC and my company testbed.

The goal is to police the rate to 256kbps, which works as expected at home (tested by wget), but when I repeat the same test on the company testbed, the rate drops to 20KBps. I have tested that without TC settings, the testbed runs in excess of 10 mbps.

I wonder if TC mangles packets in some way that is causing the firewall to treat them differently?

My configuration commands:

tc qdisc add dev eth0 handle ffff: ingress 
tc filter add dev eth0 parent ffff: protocol ip prio 50 u32 match ip src 0.0.0.0/0 police rate 256kbps burst 100kb drop flowid :1
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20 kiloBYTE per second is not all that different from 256kiloBIT per second. –  Hennes Jul 6 '12 at 15:53

1 Answer 1

No, tc doesn't alter the packets. It places them in a queue and then pulls them from the queue, putting them onto the wire at the rate specified.

However, the firewall may be aggressive about packet charactaristics or have a very short lifetime for the protocol you're using. You should contact the firewall administrator to see if there's anything they can tell you about what might be happening.

Remember that today's networks are complex. Various technologies that don't often come into contact with each other sometimes have bizarre results.

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