docs: def add_interface_to_router(self, segment_id,
                                  router_name, gip, router_ip, mask, server):
          """Adds an interface to existing HW router on Arista HW device.
  
          :param segment_id: VLAN Id associated with interface that is added
          :param router_name: globally unique identifier for router/VRF
          :param gip: Gateway IP associated with the subnet
          :param router_ip: IP address of the router
          :param mask: subnet mask to be used
          :param server: Server endpoint on the Arista switch to be configured
          """
  
          if not segment_id:
              segment_id = DEFAULT_VLAN
          cmds = []
          for c in self._interfaceDict['add']:
              if self._mlag_configured:
                  # In VARP config, use router ID else, use gateway IP address.
                  ip = router_ip
              else:
                  ip = gip + '/' + mask
              cmds.append(c.format(segment_id, router_name, ip))
          if self._mlag_configured:
              for c in self._additionalInterfaceCmdsDict['add']:
                  cmds.append(c.format(gip))
  
          self._run_config_cmds(cmds, server)