new_contents: from exabgp.bgp.message.update.attribute.community.extended import ExtendedCommunity
  from exabgp.bgp.message.update.attribute.community.extended import rt
  
  import logging
  log = logging.getLogger(__name__)
  
  # draft-fm-bess-service-chaining
  
  
  class RTRecord(rt.RouteTarget):
      COMMUNITY_SUBTYPE = 0x13
  
      DESC = "rtrecord"
  
      @classmethod
      def from_rt(cls, rt):
          packed = rt.pack()
          return cls.unpack(packed[0] + chr(cls.COMMUNITY_SUBTYPE) + packed[2:])
  
  
  @ExtendedCommunity.register
  class RTRecordASN2Number(RTRecord, rt.RouteTargetASN2Number):
      pass
  
  
  @ExtendedCommunity.register
  class RTRecordIPNumber(RTRecord, rt.RouteTargetIPNumber):
      pass
  
  
  @ExtendedCommunity.register
  class RTRecordASN4Number(RTRecord, rt.RouteTargetASN4Number):
      pass
  
subject: Add RTRecord extended community