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Cisco Bug: CSCvt66337 - Shaping rate in x86 platform not working properly for TCP traffic

Last Modified

Sep 04, 2020

Products (2)

  • Cisco vEdge Router
  • Cisco vEdge Router Model

Known Affected Releases

19.2.1 20.1.0

Description (partial)

Symptom:
Version 19.2.1,19.2.2
Platform :  ISR1100-4G

When configuring the shaping-rate on the WAN interface. The traffic got cut into almost half of the shaping-rate value.

We tested by pumping the TCP traffic sending across WAN by FTP, IPERF, SCP. We notice that the Bandwidth got cut to half but when removing shaping rate. The traffic forwarding can go high.  We tested it with purely UDP packets, it seems to work ok.

Tested at 10Mbps, from our observation, we need to have UDP stream coming in to make the TCP throughput goes up beyond 5Mbps. 

Generating flows for multiple sessions (5 Parallel), Still the BW cannot go beyond 5Mbps

Conditions:
suppose one intermittent burst contain 512 pkts, they are all put into port ring then put into QoS queue, while qos only dequeue most 256(maybe less decided by the bandwidth) and leaving 256 more pkts hold in the QoS queue, at the same time, system doesn't have any priority traffic and normal traffic put into the same port, as a result, the 256 more pkts will stuck in the QoS queue.
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