diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,10 @@
 # Revision history for net-spider-rpl
 
+## 0.3.1.0  -- 2019-10-04
+
+* Expose an internal module `NetSpider.RPL.IPv6`.
+* Confirm test with `ip-1.5.1`, `ip-1.6.0`, `hashable-1.3.0.0`, `time-1.9.3`.
+
 ## 0.3.0.0  -- 2019-09-30
 
 ### ContikiNG module
diff --git a/net-spider-rpl.cabal b/net-spider-rpl.cabal
--- a/net-spider-rpl.cabal
+++ b/net-spider-rpl.cabal
@@ -1,5 +1,5 @@
 name:                   net-spider-rpl
-version:                0.3.0.0
+version:                0.3.1.0
 author:                 Toshio Ito <debug.ito@gmail.com>
 maintainer:             Toshio Ito <debug.ito@gmail.com>
 license:                BSD3
@@ -30,16 +30,16 @@
                         NetSpider.RPL.DIO,
                         NetSpider.RPL.DAO,
                         NetSpider.RPL.Combined,
-                        NetSpider.RPL.ContikiNG
-  other-modules:        NetSpider.RPL.IPv6
+                        NetSpider.RPL.ContikiNG,
+                        NetSpider.RPL.IPv6
   build-depends:        base >=4.11.1.0 && <4.13,
                         aeson >=1.3.1.1 && <1.5,
                         greskell >=0.2.3.0 && <0.3,
                         net-spider >=0.3.1.0 && <0.4,
                         text >=1.2.3.1 && <1.3,
-                        ip >=1.3.0 && <1.5,
-                        hashable >=1.2.7.0 && <1.3,
-                        time >=1.8.0.2 && <1.9,
+                        ip >=1.3.0 && <1.7,
+                        hashable >=1.2.7.0 && <1.4,
+                        time >=1.8.0.2 && <1.10,
                         conduit-parse >=0.2.1.0 && <0.3,
                         conduit >=1.3.1 && <1.4,
                         mtl >=2.2.2 && <2.3,
@@ -64,8 +64,9 @@
   main-is:              Spec.hs
   -- default-extensions:   
   other-extensions:     OverloadedStrings
-  other-modules:        NetSpider.RPL.ContikiNGSpec
-  build-depends:        base, net-spider-rpl, net-spider, text, monad-logger,
+  other-modules:        NetSpider.RPL.ContikiNGSpec,
+                        NetSpider.RPL.IPv6Spec
+  build-depends:        base, net-spider-rpl, net-spider, text, monad-logger, ip,
                         hspec >=2.5.5,
                         bytestring >=0.10.8.2 && <0.11,
                         fast-logger >=2.4.11 && <2.5
diff --git a/src/NetSpider/RPL/FindingID.hs b/src/NetSpider/RPL/FindingID.hs
--- a/src/NetSpider/RPL/FindingID.hs
+++ b/src/NetSpider/RPL/FindingID.hs
@@ -23,18 +23,22 @@
 
 import Control.Applicative ((<$>), (<*>))
 import Control.Monad.Fail (MonadFail)
+import Data.Bits (shiftL, (.|.))
 import Data.Monoid ((<>))
 import Data.Aeson (FromJSON(..), ToJSON(..))
 import qualified Data.Aeson as Aeson
 import Data.Greskell (FromGraphSON(..))
 import Data.Hashable (Hashable(..))
 import Data.Text (Text)
+import Data.Word (Word64, Word32)
 import qualified Data.Text as T
 import GHC.Generics (Generic)
-import Net.IPv6 (IPv6(..))
+import Net.IPv6 (IPv6)
 import qualified Net.IPv6 as IPv6
 import NetSpider.GraphML.Writer (ToNodeID(..))
 
+import NetSpider.RPL.IPv6 (getPrefix, getInterfaceID)
+
 -- | Type of local finding.
 data FindingType = FindingDIO
                    -- ^ Local finding about DIO (Upward) routes.
@@ -116,7 +120,7 @@
 
 instance Hashable IPv6ID where
   hashWithSalt s (IPv6ID a) =
-    s `hashWithSalt` (ipv6A a) `hashWithSalt` (ipv6B a)
+    s `hashWithSalt` getPrefix a `hashWithSalt` getInterfaceID a
 
 ipv6ToText :: IPv6ID -> Text
 ipv6ToText (IPv6ID a) = IPv6.encode a
diff --git a/src/NetSpider/RPL/IPv6.hs b/src/NetSpider/RPL/IPv6.hs
--- a/src/NetSpider/RPL/IPv6.hs
+++ b/src/NetSpider/RPL/IPv6.hs
@@ -1,20 +1,23 @@
 -- |
 -- Module: NetSpider.RPL.IPv6
--- Description: 
+-- Description: (INTERNAL) Basic routines for IPv6 type
 -- Maintainer: Toshio Ito <debug.ito@gmail.com>
 --
 -- __This module is for internal use.__
+--
+-- @since 0.3.1.0
 module NetSpider.RPL.IPv6
   ( Prefix,
     InterfaceID,
     isLinkLocal,
     getPrefix,
-    setPrefix
+    setPrefix,
+    getInterfaceID
   ) where
 
-import Data.Bits ((.&.), shift)
-import Data.Word (Word64)
-import Net.IPv6 (IPv6(..), toWord16s)
+import Data.Bits ((.&.), shift, shiftL, (.|.), shiftR)
+import Data.Word (Word64, Word32)
+import Net.IPv6 (IPv6, toWord16s, toWord32s, fromWord32s)
 
 type Prefix = Word64
 
@@ -27,7 +30,22 @@
     bit_mask = (2 ^ (10 :: Int) - 1) `shift` 6
 
 getPrefix :: IPv6 -> Prefix
-getPrefix = ipv6A
+getPrefix addr = to64 u l
+  where
+    (u, l, _, _) = toWord32s addr
 
 setPrefix :: Prefix -> IPv6 -> IPv6
-setPrefix p orig = orig { ipv6A = p }
+setPrefix p orig = fromWord32s u1 u2 l1 l2
+  where
+    (_, _, l1, l2) = toWord32s orig
+    u1 = fromIntegral ((p `shiftR` 32) .&. 0xFFFFFFFF)
+    u2 = fromIntegral (p .&. 0xFFFFFFFF)
+
+getInterfaceID :: IPv6 -> InterfaceID
+getInterfaceID addr = to64 u l
+  where
+    (_, _, u, l) = toWord32s addr
+
+to64 :: Word32 -> Word32 -> Word64
+to64 u l = (fromIntegral u `shiftL` 32) .|. fromIntegral l
+
diff --git a/test/NetSpider/RPL/IPv6Spec.hs b/test/NetSpider/RPL/IPv6Spec.hs
new file mode 100644
--- /dev/null
+++ b/test/NetSpider/RPL/IPv6Spec.hs
@@ -0,0 +1,19 @@
+module NetSpider.RPL.IPv6Spec (main,spec) where
+
+import Net.IPv6 (ipv6)
+import Test.Hspec
+
+import NetSpider.RPL.IPv6 (getPrefix, setPrefix)
+
+main :: IO ()
+main = hspec spec
+
+spec :: Spec
+spec = describe "prefix" $ do
+  let input = ipv6 0xfe00 0x0012 0x4310 0x0020 0xaa9d 0xd393 0xaa00 0x49be
+  specify "getPrefix" $ do
+    getPrefix input `shouldBe` 0xfe00001243100020
+  specify "setPrefix" $ do
+    let prefix = 0xf055aa0d00329391
+        expected = ipv6 0xf055 0xaa0d 0x0032 0x9391 0xaa9d 0xd393 0xaa00 0x49be
+    setPrefix prefix input `shouldBe` expected