/ # cat /etc/calico/confd/templates/bird_ipam.cfg.template
# Generated by confd
filter calico_pools {
  loop_allow();
  if ( net ~ 192.168.100.100/32 ) then {
    accept;
  }
  calico_aggr();
{{range ls "/pool"}}{{$data := json (getv (printf "/pool/%s" .))}}
  if ( net ~ {{$data.cidr}} ) then {
    accept;
  }
{{end}}
  reject;
}



generates

/ # cat /etc/calico/confd/config/bird_ipam.cfg
# Generated by confd
filter calico_pools {
  loop_allow();
  if ( net ~ 192.168.100.100/32 ) then {
    accept;
  }
  calico_aggr();

  if ( net ~ 192.168.4.0/22 ) then {
    accept;
  }

  reject;
}


which is the filter applied outbound to the ebgp peer