Crap Speedtest but good after reboot

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rockyd
Posts: 136
Joined: Tue Oct 22, 2019 5:49 am

Crap Speedtest but good after reboot

Post by rockyd »

Did a speedtest yesterday for the first time in a while, and got 50Mb/s on my 750Mb/s service. I repeated it a few times with different servers same 50Mb/s. Rebooted my router and it came good.
So my question is what would cause that to happen.

pythonic
Posts: 283
Joined: Mon Mar 11, 2019 5:47 am
Location: Australia

Re: Crap Speedtest but good after reboot

Post by pythonic »

Can't suggest any likely cause as my Gargoyle devices have never exhibited this sort of behaviour even when left running continuously for as long as 6 months, but actions you could take which might help diagnose a possible cause if/when it happens include:
- check system state for exhausted memory and/or unusually high load averages (i.e. greater than about 80% of the total number of CPU cores)
- check system log for error messages
- run top to check for unusual process activity

ispyisail
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Posts: 5232
Joined: Mon Apr 06, 2009 3:15 am
Location: New Zealand

Re: Crap Speedtest but good after reboot

Post by ispyisail »

Most likely cause: conntrack table exhaustion. On a 750 Mb/s link you churn through TCP connections fast. The netfilter connection tracking table has a fixed size (nf_conntrack_max), and once it's full the kernel starts dropping or
refusing new connections. Speed tanks, reboot clears the table, everything's fine again. Classic symptom pattern.

To confirm: cat /proc/sys/net/netfilter/nf_conntrack_count vs cat /proc/sys/net/netfilter/nf_conntrack_max — if they're close, that's the answer.

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