Strange BQM Monitor

I've been trying out a FrtizBox router - ex Zen 7530 off eBay which is running the latest 8.02 firmware.

I set up a TBB Monitor: https://ln5.sync.com/4.0/dl/7d8647240#8vejaee7-gk7au...

The solid red of dropped packets is what I would expect since the box is set to stealth mode and doesn't respond to echo requests. However, the strange behaviour is in the gap where it appears to be accepting ping requests for around an hour yesterday. During this time it was unattended and I can find nothing in the logs to suggest it self rebooted or that there was any work being done by Openreach.

Any body have any ideas as to the cause?

Is the FritzBoz in full stealth mode (ie completely ignoring pings) or just its usual overkill anti-DDOS mode (ie ignoring them if they arrive more often than 1 per second)?

If the first then I've no idea, if the second then theoretically it could happen (but even I would prefer another explanation!) if the clock frequencies of your FritzBox and/or ttb's FireBrick drifted just enough (temperature maybe?) to seem to put the pings outside the one/sec repetition rate...

Edited by billford (Wed 18-Jun-25 08:51:08)

I set it to stealth mode although I think it does ignore pings as default.

Might be worth contacting AVM support. They've been very helpful so far.

I contacted AVM and got the following reply:

......in Stealth Mode ("Internet > Filter > Lists") the packet filter of the FRITZ!Box discards all unsolicited incoming requests from the internet for which no port forwarding (port sharing) rules have been configured instead of replying with ICMP control messages,, such as. "Destination Unreachable".
So, with Stealth Mode enabled, the behaviour of the FRITZ!Box is as follows:

The FRITZ!Box discards all incoming requests to ports for which no port sharing rules exits in the FRITZ!Box (DROP),
The FRITZ!Box continues to reply to ICMP echo requests.
The FRITZ!Box continues to reply to IDENT requests to port 113 with "TCP-Closed" (as otherwise certain Internet applications, e.g. FTP may not work).

On that basis I would anticpate the TBB monitor would show solid red for dropped packets. Why it should suddenly stop doing that as in my initial post remains a mystery.

I've let AVM have more information so we'll see what transpires. I know there are some Fritzbox users on here - mostly I imagine with Zen who supplied a Fritz to new customers.

In practice the 7530 has been rock solid so I've no complaints on that score.