I wanted to observe the congestion window of a TCP flow so for that I have to nodes (using Linux namespaces) connected to each other through veth pairs and a bridge.
To limit bandwidth to 10mbps I use a htb qdisc in each interface with a queue length of 1000 packets.
Then I set an iperf session between them:
1) You can observe that the bit rate does adapt to the bandwidth the qdisc will shape for us.
2) However checking the pcap file and queues drop counters also see that there are never drops or as an effect retransmissions
If i start a second flow they both get a fair share of 5mbps.
What it is going on here? How is TCP adapting the flow size if there is the congestion control is not getting signals? Am I missing something ?