just happened again with 6.21.1 on RB433AH
/ip route cache print
cache-size: 16384
max-cache-size: 16384
no ppp, one IPSEC tunnel and one VRRP instance
Solved this issue finally! (tested on version 6.32.1)
I had these problems since upgrade from 6.25 to newest version (last incident it was 6.30.2) on RB1100AHx2 - after few days, the router stopped to respond - still running, reacts to cable connect/disconnect but no response on ethernet ports.
I was able to connect to connect using serial port and found everything running as expected, but just no response to network traffic. When attempted to ping local addresses or even 127.0.0.1 I got the error message “No buffer space available” - later I found that an issue with the same symptoms existed in the past and was claimed to be already fixed (route cache overflow).
Interesting thing is, that we have two RB1100AHx2 routers with the same configuration (just few different IP addresses), but the second one is just backup with a little traffic and deactivated IPsec tunnels - that one works without any issue.
(Months with daily reboots passed)
Yesterday, I finally managed to resolve this issue on router with ~20 IPsec tunnels.
tl;dr version: Guess what… it was solved by turning the ip cache feature back on.
This settings had no effect in version 6.30.2. - when I opened the ticket back then, I got the advice from MT support : “turn the IP cache feature off”, but it has no effect and the setting stayed there.
But turning on the route cache ( /ip settings set route-cache=yes) in 6.32.1 (I did not test the next versions yet) actually force the cache to work as it should. However if you change it on running system, this change affect the cache records from that point only - cache entries created prior to the point you turn the route cache feature on, stays there forever, until the router is restarted.
It almost looks like IPsec tunnels use router cache regardless the cache on/off settings, but if the case is turned off in IP settings, no one cares about the records in cache any more, so it will overflow in the end, causing all IPv4 traffic to stop. Turning on the cache feature forces all records to be managed by regular cache algorithm, so it works as it should.
I can confirm, that enabling /ip settings route-cache works on RB750GL, RB951G-2HnD both on Rel. 6.34rc34 