[Bug 238741] RACK tcpip stack causes connections to hang

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Fri Jun 28 13:44:46 UTC 2019


https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=238741

--- Comment #1 from adrik at salesmanager.nl ---
I think the problem might be related to the selected TCP Congestion Control
algorithm.
If I select Cdg as the TCP Congestion Control algorithm:

# kldload cc_cdg
# sysctl net.inet.tcp.cc.algorithm=cdg

Tcp connections will sometimes hang and finally timeout.
When this happens, the socket Send-Q is not empty and will never drain, so some
or all data is never sent.

# netstat -6n
Active Internet connections
Proto Recv-Q Send-Q Local Address          Foreign Address        (state)
tcp6       0    383 2a02:xxxx:yyy:18.56748 2a04:4e42:9::729.443   ESTABLISHED

The same happens with IPv4 and IPv6 connections.
If I change the TCP Congestion Control to any other algorithm, the problem
doesn't exist anymore.
I did a quick test with NewReno, Cubic, HTcp and Chd as the selected TCP
Congestion Control algorithm and all work.

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