OpenWRT

https://openwrt.org/docs/guide-user/services/snmp/mini_snmpd

# you may add more than the 'default' mini_snmpd instances provided they all bind to different ports/interfaces
# to get around max 4 interface or mountpoint limit constrained by mini_snmpd's mib
config mini_snmpd default
  option enabled 1
  option ipv6 0
  # Verbose flag given to mini_snmpd, extra verbose is only possible with compile time config flags
  option debug 0
  # Turn on community authentication (snmp agent must use community name)
  option auth 0
  option community private
  option contact david@daper.email
  option location home
  # to listen on all interfaces you need to set option listen_interface ''
  option listen_interface wan
  option udp_port 161
  #option tcp_port 161
  #option vendor_oid ''
  option mib_timeout 1
  # enable basic disk usage statistics on specified mountpoint
  list disks '/overlay'
  list disks '/tmp'
  # enable basic network statistics on specified interface
  # 4 interfaces maximum per instance, as named in /etc/config/network and luci
  # not physical device names
  list interfaces wan
  list interfaces tun0
  list interfaces tun1
  list interfaces tun2

https://openwrt.org/docs/guide-user/services/network_monitoring/darkstat