Hello
If I downgrade from a plain RB750 6.18 (just NAT and some firewall rules) to 5.26, after about 30sec from boottime, the CPU goes 100% and IPSEC is using 100% CPU (according to profiler tool).

I need to unistall or disable "security" package.

re-upgrading to 6.18 with security enabled doesnt show this issue.

It's already knowed problem.

The downgrade between so "distant" version prospect everytime problems...

Ciao.

Same here. Best option I found was to export the config in 6.18, downgrade to 5.26, then nuke the config (/system reset) and re-apply from the export. Works fine from then onwards.

Rich

On this case, system reset do not solve anything, because there is not "actual removable configuration" problem, but is like some system file are preserved between versions and use full cpu...

The best is use netinstall everytime, but obviously when is not easy use netinstall, downgrading is a risk...

i had the same problem on a box (RB532) up a mountain - disabled security and advanced tools then cpu was normal...

I have left the 5.26 without security package... and I have resolved. I enabled telnet access since I will access it from GUI and then from my backbone... so a secure network.

I had the same problem with an old RB192 model. I upgraded to the latest 6.18 or 19 i don't know exactly, but not worked.
Downgraded to 5.24 and CPU has all time 100%.
Now I disabled the "security" package is OK.