code: @ConditionalOnClass({Inet4Address.class, PcapIf.class})
      //ConditionalOnBean({PcapIf.class})
      @Bean(NETMASK_BEAN_NAME)
      public Inet4Address netmask(@Qualifier(PCAP_IF_BEAN_NAME) PcapIf pcapIf) {
          Iterator<PcapAddr> iterator = pcapIf.getAddresses().iterator();
          while (iterator.hasNext()) {
              PcapAddr pcapAddr = iterator.next();
              if (pcapAddr.getNetmask() != null
                      && pcapAddr.getNetmask().getSaFamily() == SockAddr.Family.AF_INET
                      && pcapAddr.getNetmask().getData() != null) {
                  Inet4Address netmask = Inet4Address.valueOf(pcapAddr.getNetmask().getData());
                  if (LOGGER.isDebugEnabled()) {
                      LOGGER.debug("Default netmask: {}.", netmask);
                  }
                  return netmask;
              }
          }
          throw new UnknownNetmaskException();
      }
docs: Default netmask.
  @param pcapIf default {@link PcapIf} object.
  @return returns default netmask specified by {@link PcapIf} object.