An up hook for openvpn clients to configure routing for private DNS domains. #openvpn #resolvectl

resolvectl-add-routing-domain.bash

#!/bin/bash
set -u -e

# On systems with `systemd-resolved.service`, this script can be used as an "up" hook in client ovpn file. 
# For example:
# ... 
#    script-security 2
#    up /etc/openvpn/add-routing-domain.bash
# ...

function _add_routing_domain() {
  declare -l -r domain=${1}
  resolvectl domain ${dev} ${domain}
  
  declare -l dns_server
  declare var_name=""
  declare -i i=0
  while true; do
    let i=i+1
    var_name="foreign_option_${i}"
    v=${!var_name:-}
    [[ -n "$v" ]] || break;
    dns_server=$(grep -Po -e 'dhcp-option\s+DNS\s+\K(.+)' <<<"${v}")
    if [[ -n "${dns_server}" ]]; then
      resolvectl dns ${dev} ${dns_server}
      break;
    fi
  done
} 

if [[ -n "${OPENVPN_internal_domain:-}" ]]; then
  _add_routing_domain ${OPENVPN_internal_domain}
fi