diff --git a/scapy/contrib/rpl_metrics.py b/scapy/contrib/rpl_metrics.py
index 4f8961f6041..d6ed3f02607 100644
--- a/scapy/contrib/rpl_metrics.py
+++ b/scapy/contrib/rpl_metrics.py
@@ -21,7 +21,7 @@
 import struct
 from scapy.packet import Packet
 from scapy.fields import ByteEnumField, ByteField, ShortField, BitField, \
-    BitEnumField, FieldLenField, StrLenField, IntField, PacketListField
+    BitEnumField, StrLenField, IntField, PacketListField
 from scapy.layers.inet6 import _PhantomAutoPadField
 from scapy.contrib.rpl import RPLOPTSSTR, RPLOPTS, _RPLGuessOption
 
@@ -48,28 +48,6 @@ def post_build(self, pkt, pay):
                  8: "Link Color"}
 
 
-class DAGMCObjUnknown(Packet):
-    """
-    Dummy unknown metric/constraint
-    """
-    name = 'Unknown DAGMC Object Option'
-    fields_desc = [ByteEnumField("otype", 3, DAGMC_OBJTYPE),
-                   FieldLenField("olen", None, length_of="odata", fmt="B"),
-                   StrLenField("odata", "",
-                               length_from=lambda pkt: pkt.olen)]
-
-    @classmethod
-    def dispatch_hook(cls, _pkt=None, *_, **kargs):
-        """
-        Dispatch hook for DAGMC sub-fields
-        """
-        if _pkt:
-            opt_type = _pkt[0]  # Option type
-            if opt_type in DAGMC_CLS:
-                return DAGMC_CLS[opt_type]
-        return cls
-
-
 AGG_RTMETRIC = {0: "additive",
                 1: "maximum",
                 2: "minimum",
@@ -107,6 +85,31 @@ def extract_padding(self, s):
         return s[:tmp_len], s[tmp_len:]
 
 
+class DAGMCObjUnknown(DAGMCObj):
+    """
+    Metric/constraint object of a type without its own class: the
+    common header of RFC 6551 - 2.1, then Length octets of body
+    """
+    name = 'Unknown DAGMC Object Option'
+    deprecated_fields = {
+        "olen": ("len", "2.8.1"),
+    }
+    fields_desc = DAGMCObj.fields_desc + [
+        StrLenField("odata", "", length_from=lambda pkt: pkt.len)
+    ]
+
+    @classmethod
+    def dispatch_hook(cls, _pkt=None, *_, **kargs):
+        """
+        Dispatch hook for DAGMC sub-fields
+        """
+        if _pkt:
+            opt_type = _pkt[0]  # Option type
+            if opt_type in DAGMC_CLS:
+                return DAGMC_CLS[opt_type]
+        return cls
+
+
 class RPLDAGMCNSA(DAGMCObj):
     """
     DAG Metric: Node State and Attributes
diff --git a/test/contrib/rpl.uts b/test/contrib/rpl.uts
index f4190981ab2..87bc28d4a91 100644
--- a/test/contrib/rpl.uts
+++ b/test/contrib/rpl.uts
@@ -228,3 +228,29 @@ assert raw(p.options[0].payload) == bytes.fromhex("0241")
 assert p.options[1].HopCount == 4
 p.clear_cache()
 assert raw(p) == raw_mc
+
+= RPL DAG Metric Container with an object of an unassigned type
+# An unknown object has the same 4-octet header as the others (RFC 6551, 2.1)
+
+# Type 9 with a 2-octet body, then Hop Count
+raw_mc = bytes.fromhex("020c09000002abcd" + "030000020003")
+p = RPLOptDAGMC(raw_mc)
+assert [type(o) for o in p.options] == [DAGMCObjUnknown, RPLDAGMCHopCount]
+assert p.options[0].otype == 9
+assert p.options[0].len == 2
+assert p.options[0].odata == b"\xab\xcd"
+assert p.options[0].olen == 2  # deprecated name of len
+assert p.options[1].HopCount == 3
+p.clear_cache()
+assert raw(p) == raw_mc
+
+# Type 9 with an empty body between Hop Count and Link ETX
+raw_mc = bytes.fromhex("0210030000020003" + "09000000" + "070000020100")
+p = RPLOptDAGMC(raw_mc)
+assert [type(o) for o in p.options] == [RPLDAGMCHopCount, DAGMCObjUnknown, RPLDAGMCLinkETX]
+assert p.options[2].ETX == 256
+
+# Building fills in the Length of the body
+assert raw(DAGMCObjUnknown(otype=9, P=1, odata=b"\xab\xcd")) == bytes.fromhex("09040002abcd")
+mc = RPLOptDAGMC(options=[DAGMCObjUnknown(otype=9, odata=b"\xab\xcd"), RPLDAGMCHopCount(HopCount=3)])
+assert raw(mc) == bytes.fromhex("020c09000002abcd030000020003")