On Feb 8, 2022, at 2:49 PM, Stephane Bortzmeyer via Outages <outages@outages.org> wrote:
Replying to ICMP echoes is not part of the service Google Public DNS officially does, so it is possible that they sometimes filter and/or rate-limit ICMP echo. It's not an outage.
If this goes on much further, we should probably move to -discuss, but I digress. :) I can confirm I’ve seen this behavior before with 8.8.8.8 - I’ve had times where ICMP echo indicates 100+ms latency to it (whereas 8.8.4.4 is fine), but both will reply to DNS queries with much, much less latency than ICMP echo was indicating. Definitely seems like they’re rate-limiting or de-prioritizing ICMP echo at least on occasion. One should definitely not use ICMP echo against 8.8.8.8 / 8.8.4.4 in monitoring systems (although I know it happens.) This is a good reminder as to why. :) Jeremy