My CRS125-24G-1S exhibits that OID: gapinski@nuc7i7bnh:~$ snmpwalk -On -c public -v 1 192.168.1.200|grep 1.3.6.1.2.1.1.3.0 .1.3.6.1.2.1.1.3.0 = Timeticks: (20990300) 2 days, 10:18:23.00 gapinski@nuc7i7bnh:~$ EDIT: forgot to mention that the firmware version is 6.44beta61. EDIT2: …and that SNMP is en...

I'm unsure why any/all UDP is allowed in.

As idlemind mentioned, ICMPv6 could be a bit more discrete. https://tools.ietf.org/html/rfc4890 has details.