A while back [1], I posted a question asking about timeout issues using
Openup (or any transfers really) to work through a Websense proxy.
Later, I had problems with Smokeping on OpenBSD showing ~50% packet loss
going through the proxy. After far too long staring at debug logs and
packet traces, it turned out that the proxy OS (CentOS) simply wasn't
passing the traffic through to the proxy.
I found a description of a similar problem on Server Fault [2]. It
turned out OpenBSD was sending two SYN packets with timestamps (which
were dropped by CentOS), then sending a SYN without a timestamp (which
was successful). Setting sysctl net.ipv4.tcp_timestamps=0 on the CentOS
proxy worked around the problem.
So, what went wrong here? Was the OpenBSD timestamp "too random" for
CentOS 6.7? Or is there some other issue, and I'm just masking it by
disabling timestamps?
Thanks.
[1] https://marc.info/?m=144625218420037
[2] https://serverfault.com/questions/235965
