diff --git a/docs/spec/ibc/ibc2.md b/docs/spec/ibc/ibc2.md
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+# IBC Spec
+
+## MVP2
+
+`IBCUpdate` is added, making it able to prove the header.
+
+### IBC Module
+
+```golang
+type IBCOutMsg struct {
+  IBCTransfer
+}
+
+type IBCInMsg struct {
+  IBCTransfer
+  Proof           merkle.IAVLProof
+  FromChainID     string
+  FromChainHeight uint64
+}
+
+// update sync state of other blockchain
+type IBCUpdateMsg struct {
+  Header tm.Header
+  Commit tm.Commit
+}
+
+type IBCTransfer struct {
+  Destination sdk.Address
+  Coins       sdk.Coins
+}
+```