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rolfschneider
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Joined: Thu Apr 25, 2024 11:17 pm

Long NXDOMAIN list causes looping DNS cache refresh with CPU usage spikes

Thu Apr 25, 2024 11:27 pm

I am filtering about 5000 domain entries (adservers) by returning NXDOMAIN via
/ip dns static
add type=NXDOMAIN name="023hysj.com"
add type=NXDOMAIN name="101com.com"
add type=NXDOMAIN name="101order.com"
.
.
.
on routeros 7.14.3 (mipsbe).

Everything works as expected, but I observe that the DNS cache list (size is 4 MB) is refreshed every four seconds, with a spike in CPU usage. The TTL starts at 24 h and counts back to 23:59:56 before the cycle repeats.

My questions are:

1.) Is this normal?
2.) Can I improve this behaviour (less CPU usage) without affecting the functionality?

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