Unfortunately I had to hear that starting with Core 142 the package check_mk_agent is no longer offered and removed from the system. I was able to monitor the router with this package from my check_mk server and also collect the up- and download rates. Is there a possibility to continue using this package?
You probably mean SNMP but that’s not as charming and as with the check_mk_agent and the traffic analysis is also not really that well implemented.
There are agents everywhere. In my company nsclient++, nagios-nrpe or the check_mk agent (home) and now I have to switch to SNMP by force. This will be a fiddle, if it works out.
I was able to successfully integrate my router into my CheckMK monitoring using NRPE check and Check_MK via SSH.
Maybe this will help you a little bit.