#/etc/bird/community_filters.conf
function update_latency(int link_latency) {
  bgp_community.add((64511, link_latency));
       if (64511, 9) ~ bgp_community then { bgp_community.delete([(64511, 1..8)]); return 9; }
  else if (64511, 8) ~ bgp_community then { bgp_community.delete([(64511, 1..7)]); return 8; }
  else if (64511, 7) ~ bgp_community then { bgp_community.delete([(64511, 1..6)]); return 7; }
  else if (64511, 6) ~ bgp_community then { bgp_community.delete([(64511, 1..5)]); return 6; }
  else if (64511, 5) ~ bgp_community then { bgp_community.delete([(64511, 1..4)]); return 5; }
  else if (64511, 4) ~ bgp_community then { bgp_community.delete([(64511, 1..3)]); return 4; }
  else if (64511, 3) ~ bgp_community then { bgp_community.delete([(64511, 1..2)]); return 3; }
  else if (64511, 2) ~ bgp_community then { bgp_community.delete([(64511, 1..1)]); return 2; }
  else return 1;
}

function update_bandwidth(int link_bandwidth) {
  bgp_community.add((64511, link_bandwidth));
       if (64511, 21) ~ bgp_community then { bgp_community.delete([(64511, 22..29)]); return 21; }
  else if (64511, 22) ~ bgp_community then { bgp_community.delete([(64511, 23..29)]); return 22; }
  else if (64511, 23) ~ bgp_community then { bgp_community.delete([(64511, 24..29)]); return 23; }
  else if (64511, 24) ~ bgp_community then { bgp_community.delete([(64511, 25..29)]); return 24; }
  else if (64511, 25) ~ bgp_community then { bgp_community.delete([(64511, 26..29)]); return 25; }
  else if (64511, 26) ~ bgp_community then { bgp_community.delete([(64511, 27..29)]); return 26; }
  else if (64511, 27) ~ bgp_community then { bgp_community.delete([(64511, 28..29)]); return 27; }
  else if (64511, 28) ~ bgp_community then { bgp_community.delete([(64511, 29..29)]); return 28; }
  else return 29;
}

function update_crypto(int link_crypto) {
  bgp_community.add((64511, link_crypto));
       if (64511, 31) ~ bgp_community then { bgp_community.delete([(64511, 32..34)]); return 31; }
  else if (64511, 32) ~ bgp_community then { bgp_community.delete([(64511, 33..34)]); return 32; }
  else if (64511, 33) ~ bgp_community then { bgp_community.delete([(64511, 34..34)]); return 33; }
  else return 34;
}
	
function update_flags(int link_latency; int link_bandwidth; int link_crypto)
int dn42_latency;
int dn42_bandwidth;
int dn42_crypto;
{
  dn42_latency = update_latency(link_latency);
  dn42_bandwidth = update_bandwidth(link_bandwidth) - 20;
  dn42_crypto = update_crypto(link_crypto) - 30;
  # replace 4 with your calculated bandwidth value
  if dn42_bandwidth > 4 then dn42_bandwidth = 4;

  bgp_local_pref = 10000+100*dn42_bandwidth + 50*(10-dn42_latency)-200*bgp_path.len+100*dn42_crypto; #(as suggested by tombii)
  bgp_local_pref = 1000*dn42_bandwidth - 10*dn42_latency; if dn42_crypto < 2 then bgp_local_pref = 0; #(as suggested by Jplitza)
  bgp_local_pref = 10000+100*dn42_bandwidth + 50*(10-dn42_latency)-400*(bgp_path.len-1)+100*dn42_crypto; #(as suggested by Mic92 - prefer direct tunnel)

  return true;
}

# Combines filter from local4.conf/local6.conf and filter4.conf/filter6.conf,
# which means, these must included before this file

function dn42_import_filter(int link_latency; int link_bandwidth; int link_crypto) {
  if (roa_check(dn42_roa, net, bgp_path.last) = ROA_INVALID) then {
    print "[dn42] ROA check failed for ", net, " ASN ", bgp_path.last;
    reject;
  }

  if is_valid_network() && !is_self_net() then {
    update_flags(link_latency, link_bandwidth, link_crypto);
    accept;
  }
  reject;
}

function dn42_export_filter(int link_latency; int link_bandwith; int link_crypto) {
  if is_valid_network() then {
    if source = RTS_STATIC then bgp_community.add((64511, DN42_REGION));
    update_flags(link_latency, link_bandwith, link_crypto);
    accept;
  }
  reject;
}