I came across https://unix.stackexchange.com/questions/210367/changing-the-tcp-rto-value-in-linux which pretty much does exactly what I want, but I need to do it with an IPv6 tunnel.
$ sudo ip -6 route aaaa::/64 dev tun0 proto kernel metric 256 fe80::/64 dev eth0 proto kernel metric 256 fe80::/64 dev wlan0 proto kernel metric 256 fe80::/64 dev tun0 proto kernel metric 256
Then, if I look at my active connections we see:
$ ss -i tcp ESTAB 0 0 aaaa::1:51692 cubic rto:360 rtt:157.424/6.438 ato:40 mss:64 cwnd:10 send 32.5Kbps pacing_rate 65.0Kbps rcv_space:28800
It currently has an rto of 360. This device only deals withs super low bandwidth, high latency, lossy networks (i.e. 6LoWPaN) so I want to increase the min_rto to at least several seconds.
I have disabled frto:
$ sudo cat /proc/sys/net/ipv4/tcp_frto 0
Now I want to set min_rto, as shown in the linked question.
$ sudo ip -6 route change aaaa:: dev tun0 rto_min 2000 RTNETLINK answers: No such file or directory
Why do I get this error and how can I fix it?
It’s worth noting that if I do 2000ms (or 5ms, as in the linked answer), it tells me it’s an invalid value, hence why I dropped off the ms part. In case it matters, my Linux info is below:
Linux 4.4.13-v7+ #894 SMP Mon Jun 13 13:13:27 BST 2016 armv7l GNU/Linux
tcp_* settings listed under IPv4 also apply to IPv6, according to the documentation.
IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also apply to IPv6 [XXX?].
Given the question in the documentation there, it would be wise to verify this applies to your specific (older) kernel before proceeding.
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