diff --git a/api/src/handlers/pool_api.rs b/api/src/handlers/pool_api.rs
index 1b0733360..b458787bd 100644
--- a/api/src/handlers/pool_api.rs
+++ b/api/src/handlers/pool_api.rs
@@ -76,7 +76,7 @@ impl PoolPushHandler {
 				})
 				.and_then(move |tx_bin| {
 					// TODO - pass protocol version in via the api call?
-					let version = ProtocolVersion::default();
+					let version = ProtocolVersion::local();
 
 					ser::deserialize(&mut &tx_bin[..], version)
 						.map_err(|e| ErrorKind::RequestError(format!("Bad request: {}", e)).into())
diff --git a/api/src/types.rs b/api/src/types.rs
index 3bb5b28c9..4a384a911 100644
--- a/api/src/types.rs
+++ b/api/src/types.rs
@@ -83,7 +83,7 @@ pub struct Status {
 impl Status {
 	pub fn from_tip_and_peers(current_tip: chain::Tip, connections: u32) -> Status {
 		Status {
-			protocol_version: ser::ProtocolVersion::default().into(),
+			protocol_version: ser::ProtocolVersion::local().into(),
 			user_agent: p2p::msg::USER_AGENT.to_string(),
 			connections: connections,
 			tip: Tip::from_tip(current_tip),
diff --git a/chain/src/chain.rs b/chain/src/chain.rs
index ded052021..bc3294908 100644
--- a/chain/src/chain.rs
+++ b/chain/src/chain.rs
@@ -647,7 +647,8 @@ impl Chain {
 	/// TODO - Write this data to disk and validate the rebuilt kernel MMR.
 	pub fn kernel_data_write(&self, reader: &mut Read) -> Result<(), Error> {
 		let mut count = 0;
-		let mut stream = StreamingReader::new(reader, ProtocolVersion::default(), Duration::from_secs(1));
+		let mut stream =
+			StreamingReader::new(reader, ProtocolVersion::local(), Duration::from_secs(1));
 		while let Ok(_kernel) = TxKernelEntry::read(&mut stream) {
 			count += 1;
 		}
diff --git a/core/src/core/block.rs b/core/src/core/block.rs
index aad9b280f..1270d9bc7 100644
--- a/core/src/core/block.rs
+++ b/core/src/core/block.rs
@@ -359,7 +359,7 @@ impl BlockHeader {
 	pub fn pre_pow(&self) -> Vec<u8> {
 		let mut header_buf = vec![];
 		{
-			let mut writer = ser::BinWriter::new(&mut header_buf);
+			let mut writer = ser::BinWriter::default(&mut header_buf);
 			self.write_pre_pow(&mut writer).unwrap();
 			self.pow.write_pre_pow(&mut writer).unwrap();
 			writer.write_u64(self.pow.nonce).unwrap();
diff --git a/core/src/core/hash.rs b/core/src/core/hash.rs
index e0638762c..b2221e021 100644
--- a/core/src/core/hash.rs
+++ b/core/src/core/hash.rs
@@ -25,7 +25,9 @@ use std::{fmt, ops};
 
 use crate::blake2::blake2b::Blake2b;
 
-use crate::ser::{self, AsFixedBytes, Error, FixedLength, Readable, Reader, Writeable, Writer};
+use crate::ser::{
+	self, AsFixedBytes, Error, FixedLength, ProtocolVersion, Readable, Reader, Writeable, Writer,
+};
 use crate::util;
 
 /// A hash consisting of all zeroes, used as a sentinel. No known preimage.
@@ -219,6 +221,10 @@ impl ser::Writer for HashWriter {
 		self.state.update(b32.as_ref());
 		Ok(())
 	}
+
+	fn protocol_version(&self) -> ProtocolVersion {
+		ProtocolVersion::local()
+	}
 }
 
 /// A trait for types that have a canonical hash
diff --git a/core/src/core/merkle_proof.rs b/core/src/core/merkle_proof.rs
index 747819c2c..a4a21e524 100644
--- a/core/src/core/merkle_proof.rs
+++ b/core/src/core/merkle_proof.rs
@@ -17,7 +17,7 @@
 use crate::core::hash::Hash;
 use crate::core::pmmr;
 use crate::ser;
-use crate::ser::{PMMRIndexHashable, ProtocolVersion, Readable, Reader, Writeable, Writer};
+use crate::ser::{PMMRIndexHashable, Readable, Reader, Writeable, Writer};
 use crate::util;
 
 /// Merkle proof errors.
@@ -78,14 +78,14 @@ impl MerkleProof {
 	/// Serialize the Merkle proof as a hex string (for api json endpoints)
 	pub fn to_hex(&self) -> String {
 		let mut vec = Vec::new();
-		ser::serialize(&mut vec, &self).expect("serialization failed");
+		ser::serialize_default(&mut vec, &self).expect("serialization failed");
 		util::to_hex(vec)
 	}
 
 	/// Convert hex string representation back to a Merkle proof instance
 	pub fn from_hex(hex: &str) -> Result<MerkleProof, String> {
 		let bytes = util::from_hex(hex.to_string()).unwrap();
-		let res = ser::deserialize(&mut &bytes[..], ProtocolVersion::default())
+		let res = ser::deserialize_default(&mut &bytes[..])
 			.map_err(|_| "failed to deserialize a Merkle Proof".to_string())?;
 		Ok(res)
 	}
diff --git a/core/src/core/transaction.rs b/core/src/core/transaction.rs
index 32fa308cb..8fd4172c6 100644
--- a/core/src/core/transaction.rs
+++ b/core/src/core/transaction.rs
@@ -185,13 +185,19 @@ hashable_ord!(TxKernel);
 impl ::std::hash::Hash for TxKernel {
 	fn hash<H: ::std::hash::Hasher>(&self, state: &mut H) {
 		let mut vec = Vec::new();
-		ser::serialize(&mut vec, &self).expect("serialization failed");
+		ser::serialize_default(&mut vec, &self).expect("serialization failed");
 		::std::hash::Hash::hash(&vec, state);
 	}
 }
 
 impl Writeable for TxKernel {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
+		// We have access to the protocol version here.
+		// This may be a protocol version based on a peer connection
+		// or the version used locally for db storage.
+		// We can handle version specific serialization here.
+		let _version = writer.protocol_version();
+
 		self.features.write(writer)?;
 		ser_multiwrite!(writer, [write_u64, self.fee], [write_u64, self.lock_height]);
 		self.excess.write(writer)?;
@@ -1165,7 +1171,7 @@ hashable_ord!(Input);
 impl ::std::hash::Hash for Input {
 	fn hash<H: ::std::hash::Hasher>(&self, state: &mut H) {
 		let mut vec = Vec::new();
-		ser::serialize(&mut vec, &self).expect("serialization failed");
+		ser::serialize_default(&mut vec, &self).expect("serialization failed");
 		::std::hash::Hash::hash(&vec, state);
 	}
 }
@@ -1276,7 +1282,7 @@ hashable_ord!(Output);
 impl ::std::hash::Hash for Output {
 	fn hash<H: ::std::hash::Hasher>(&self, state: &mut H) {
 		let mut vec = Vec::new();
-		ser::serialize(&mut vec, &self).expect("serialization failed");
+		ser::serialize_default(&mut vec, &self).expect("serialization failed");
 		::std::hash::Hash::hash(&vec, state);
 	}
 }
@@ -1528,7 +1534,7 @@ mod test {
 		};
 
 		let mut vec = vec![];
-		ser::serialize(&mut vec, &kernel).expect("serialized failed");
+		ser::serialize_default(&mut vec, &kernel).expect("serialized failed");
 		let kernel2: TxKernel = ser::deserialize_default(&mut &vec[..]).unwrap();
 		assert_eq!(kernel2.features, KernelFeatures::Plain);
 		assert_eq!(kernel2.lock_height, 0);
@@ -1546,7 +1552,7 @@ mod test {
 		};
 
 		let mut vec = vec![];
-		ser::serialize(&mut vec, &kernel).expect("serialized failed");
+		ser::serialize_default(&mut vec, &kernel).expect("serialized failed");
 		let kernel2: TxKernel = ser::deserialize_default(&mut &vec[..]).unwrap();
 		assert_eq!(kernel2.features, KernelFeatures::HeightLocked);
 		assert_eq!(kernel2.lock_height, 100);
diff --git a/core/src/genesis.rs b/core/src/genesis.rs
index 8dc37797e..be41a48db 100644
--- a/core/src/genesis.rs
+++ b/core/src/genesis.rs
@@ -288,13 +288,13 @@ pub fn genesis_main() -> core::Block {
 mod test {
 	use super::*;
 	use crate::core::hash::Hashed;
-	use crate::ser;
+	use crate::ser::{self, ProtocolVersion};
 
 	#[test]
 	fn floonet_genesis_hash() {
 		let gen_hash = genesis_floo().hash();
 		println!("floonet genesis hash: {}", gen_hash.to_hex());
-		let gen_bin = ser::ser_vec(&genesis_floo()).unwrap();
+		let gen_bin = ser::ser_vec(&genesis_floo(), ProtocolVersion(1)).unwrap();
 		println!("floonet genesis full hash: {}\n", gen_bin.hash().to_hex());
 		assert_eq!(
 			gen_hash.to_hex(),
@@ -310,7 +310,7 @@ mod test {
 	fn mainnet_genesis_hash() {
 		let gen_hash = genesis_main().hash();
 		println!("mainnet genesis hash: {}", gen_hash.to_hex());
-		let gen_bin = ser::ser_vec(&genesis_main()).unwrap();
+		let gen_bin = ser::ser_vec(&genesis_main(), ProtocolVersion(1)).unwrap();
 		println!("mainnet genesis full hash: {}\n", gen_bin.hash().to_hex());
 		assert_eq!(
 			gen_hash.to_hex(),
diff --git a/core/src/global.rs b/core/src/global.rs
index f9bc334c2..719f0a7b6 100644
--- a/core/src/global.rs
+++ b/core/src/global.rs
@@ -33,6 +33,13 @@ use crate::util::RwLock;
 /// Define these here, as they should be developer-set, not really tweakable
 /// by users
 
+/// The default "local" protocol version for this node.
+/// We negotiate compatible versions with each peer via Hand/Shake.
+/// Note: We also use a specific (possible different) protocol version
+/// for both the backend database and MMR data files.
+/// This one is p2p layer specific.
+pub const PROTOCOL_VERSION: u32 = 1;
+
 /// Automated testing edge_bits
 pub const AUTOMATED_TESTING_MIN_EDGE_BITS: u8 = 9;
 
diff --git a/core/src/ser.rs b/core/src/ser.rs
index 035ad7bcd..57a089816 100644
--- a/core/src/ser.rs
+++ b/core/src/ser.rs
@@ -20,6 +20,7 @@
 //! `serialize` or `deserialize` functions on them as appropriate.
 
 use crate::core::hash::{DefaultHashable, Hash, Hashed};
+use crate::global::PROTOCOL_VERSION;
 use crate::keychain::{BlindingFactor, Identifier, IDENTIFIER_SIZE};
 use crate::util::read_write::read_exact;
 use crate::util::secp::constants::{
@@ -135,6 +136,9 @@ pub trait Writer {
 	/// The mode this serializer is writing in
 	fn serialization_mode(&self) -> SerializationMode;
 
+	/// Protocol version for version specific serialization rules.
+	fn protocol_version(&self) -> ProtocolVersion;
+
 	/// Writes a u8 as bytes
 	fn write_u8(&mut self, n: u8) -> Result<(), Error> {
 		self.write_fixed_bytes(&[n])
@@ -286,9 +290,10 @@ where
 #[derive(Clone, Copy, Debug, Deserialize, Eq, Ord, PartialOrd, PartialEq, Serialize)]
 pub struct ProtocolVersion(pub u32);
 
-impl Default for ProtocolVersion {
-	fn default() -> ProtocolVersion {
-		ProtocolVersion(1)
+impl ProtocolVersion {
+	/// Our default "local" protocol version.
+	pub fn local() -> ProtocolVersion {
+		ProtocolVersion(PROTOCOL_VERSION)
 	}
 }
 
@@ -346,27 +351,31 @@ pub fn deserialize<T: Readable>(
 	T::read(&mut reader)
 }
 
-/// Deserialize a Readable based on our local db version protocol.
-pub fn deserialize_db<T: Readable>(source: &mut dyn Read) -> Result<T, Error> {
-	deserialize(source, ProtocolVersion::local_db())
-}
-
-/// Deserialize a Readable based on our local "default" version protocol.
+/// Deserialize a Readable based on our default "local" protocol version.
 pub fn deserialize_default<T: Readable>(source: &mut dyn Read) -> Result<T, Error> {
-	deserialize(source, ProtocolVersion::default())
+	deserialize(source, ProtocolVersion::local())
 }
 
 /// Serializes a Writeable into any std::io::Write implementation.
-pub fn serialize<W: Writeable>(sink: &mut dyn Write, thing: &W) -> Result<(), Error> {
-	let mut writer = BinWriter { sink };
+pub fn serialize<W: Writeable>(
+	sink: &mut dyn Write,
+	version: ProtocolVersion,
+	thing: &W,
+) -> Result<(), Error> {
+	let mut writer = BinWriter::new(sink, version);
 	thing.write(&mut writer)
 }
 
+/// Serialize a Writeable according to our default "local" protocol version.
+pub fn serialize_default<W: Writeable>(sink: &mut dyn Write, thing: &W) -> Result<(), Error> {
+	serialize(sink, ProtocolVersion::local(), thing)
+}
+
 /// Utility function to serialize a writeable directly in memory using a
 /// Vec<u8>.
-pub fn ser_vec<W: Writeable>(thing: &W) -> Result<Vec<u8>, Error> {
+pub fn ser_vec<W: Writeable>(thing: &W, version: ProtocolVersion) -> Result<Vec<u8>, Error> {
 	let mut vec = vec![];
-	serialize(&mut vec, thing)?;
+	serialize(&mut vec, version, thing)?;
 	Ok(vec)
 }
 
@@ -475,32 +484,28 @@ impl<'a> StreamingReader<'a> {
 	}
 }
 
+/// Note: We use read_fixed_bytes() here to ensure our "async" I/O behaves as expected.
 impl<'a> Reader for StreamingReader<'a> {
 	fn read_u8(&mut self) -> Result<u8, Error> {
 		let buf = self.read_fixed_bytes(1)?;
 		Ok(buf[0])
 	}
-
 	fn read_u16(&mut self) -> Result<u16, Error> {
 		let buf = self.read_fixed_bytes(2)?;
 		Ok(BigEndian::read_u16(&buf[..]))
 	}
-
 	fn read_u32(&mut self) -> Result<u32, Error> {
 		let buf = self.read_fixed_bytes(4)?;
 		Ok(BigEndian::read_u32(&buf[..]))
 	}
-
 	fn read_i32(&mut self) -> Result<i32, Error> {
 		let buf = self.read_fixed_bytes(4)?;
 		Ok(BigEndian::read_i32(&buf[..]))
 	}
-
 	fn read_u64(&mut self) -> Result<u64, Error> {
 		let buf = self.read_fixed_bytes(8)?;
 		Ok(BigEndian::read_u64(&buf[..]))
 	}
-
 	fn read_i64(&mut self) -> Result<i64, Error> {
 		let buf = self.read_fixed_bytes(8)?;
 		Ok(BigEndian::read_i64(&buf[..]))
@@ -683,12 +688,18 @@ impl<T: Hashed> VerifySortedAndUnique<T> for Vec<T> {
 /// to write numbers, byte vectors, hashes, etc.
 pub struct BinWriter<'a> {
 	sink: &'a mut dyn Write,
+	version: ProtocolVersion,
 }
 
 impl<'a> BinWriter<'a> {
 	/// Wraps a standard Write in a new BinWriter
-	pub fn new(write: &'a mut dyn Write) -> BinWriter<'a> {
-		BinWriter { sink: write }
+	pub fn new(sink: &'a mut dyn Write, version: ProtocolVersion) -> BinWriter<'a> {
+		BinWriter { sink, version }
+	}
+
+	/// Constructor for BinWriter with default "local" protocol version.
+	pub fn default(sink: &'a mut dyn Write) -> BinWriter<'a> {
+		BinWriter::new(sink, ProtocolVersion::local())
 	}
 }
 
@@ -702,6 +713,10 @@ impl<'a> Writer for BinWriter<'a> {
 		self.sink.write_all(bs)?;
 		Ok(())
 	}
+
+	fn protocol_version(&self) -> ProtocolVersion {
+		self.version
+	}
 }
 
 macro_rules! impl_int {
diff --git a/core/tests/block.rs b/core/tests/block.rs
index f1b142e0f..1e3aa4f95 100644
--- a/core/tests/block.rs
+++ b/core/tests/block.rs
@@ -211,10 +211,10 @@ fn remove_coinbase_kernel_flag() {
 #[test]
 fn serialize_deserialize_header_version() {
 	let mut vec1 = Vec::new();
-	ser::serialize(&mut vec1, &1_u16).expect("serialization failed");
+	ser::serialize_default(&mut vec1, &1_u16).expect("serialization failed");
 
 	let mut vec2 = Vec::new();
-	ser::serialize(&mut vec2, &HeaderVersion::default()).expect("serialization failed");
+	ser::serialize_default(&mut vec2, &HeaderVersion::default()).expect("serialization failed");
 
 	// Check that a header_version serializes to a
 	// single u16 value with no extraneous bytes wrapping it.
@@ -235,7 +235,7 @@ fn serialize_deserialize_block_header() {
 	let header1 = b.header;
 
 	let mut vec = Vec::new();
-	ser::serialize(&mut vec, &header1).expect("serialization failed");
+	ser::serialize_default(&mut vec, &header1).expect("serialization failed");
 	let header2: BlockHeader = ser::deserialize_default(&mut &vec[..]).unwrap();
 
 	assert_eq!(header1.hash(), header2.hash());
@@ -252,7 +252,7 @@ fn serialize_deserialize_block() {
 	let b = new_block(vec![&tx1], &keychain, &builder, &prev, &key_id);
 
 	let mut vec = Vec::new();
-	ser::serialize(&mut vec, &b).expect("serialization failed");
+	ser::serialize_default(&mut vec, &b).expect("serialization failed");
 	let b2: Block = ser::deserialize_default(&mut &vec[..]).unwrap();
 
 	assert_eq!(b.hash(), b2.hash());
@@ -270,7 +270,7 @@ fn empty_block_serialized_size() {
 	let key_id = ExtKeychain::derive_key_id(1, 1, 0, 0, 0);
 	let b = new_block(vec![], &keychain, &builder, &prev, &key_id);
 	let mut vec = Vec::new();
-	ser::serialize(&mut vec, &b).expect("serialization failed");
+	ser::serialize_default(&mut vec, &b).expect("serialization failed");
 	let target_len = 1_265;
 	assert_eq!(vec.len(), target_len);
 }
@@ -284,7 +284,7 @@ fn block_single_tx_serialized_size() {
 	let key_id = ExtKeychain::derive_key_id(1, 1, 0, 0, 0);
 	let b = new_block(vec![&tx1], &keychain, &builder, &prev, &key_id);
 	let mut vec = Vec::new();
-	ser::serialize(&mut vec, &b).expect("serialization failed");
+	ser::serialize_default(&mut vec, &b).expect("serialization failed");
 	let target_len = 2_847;
 	assert_eq!(vec.len(), target_len);
 }
@@ -298,7 +298,7 @@ fn empty_compact_block_serialized_size() {
 	let b = new_block(vec![], &keychain, &builder, &prev, &key_id);
 	let cb: CompactBlock = b.into();
 	let mut vec = Vec::new();
-	ser::serialize(&mut vec, &cb).expect("serialization failed");
+	ser::serialize_default(&mut vec, &cb).expect("serialization failed");
 	let target_len = 1_273;
 	assert_eq!(vec.len(), target_len);
 }
@@ -313,7 +313,7 @@ fn compact_block_single_tx_serialized_size() {
 	let b = new_block(vec![&tx1], &keychain, &builder, &prev, &key_id);
 	let cb: CompactBlock = b.into();
 	let mut vec = Vec::new();
-	ser::serialize(&mut vec, &cb).expect("serialization failed");
+	ser::serialize_default(&mut vec, &cb).expect("serialization failed");
 	let target_len = 1_279;
 	assert_eq!(vec.len(), target_len);
 }
@@ -333,7 +333,7 @@ fn block_10_tx_serialized_size() {
 	let key_id = ExtKeychain::derive_key_id(1, 1, 0, 0, 0);
 	let b = new_block(txs.iter().collect(), &keychain, &builder, &prev, &key_id);
 	let mut vec = Vec::new();
-	ser::serialize(&mut vec, &b).expect("serialization failed");
+	ser::serialize_default(&mut vec, &b).expect("serialization failed");
 	let target_len = 17_085;
 	assert_eq!(vec.len(), target_len,);
 }
@@ -353,7 +353,7 @@ fn compact_block_10_tx_serialized_size() {
 	let b = new_block(txs.iter().collect(), &keychain, &builder, &prev, &key_id);
 	let cb: CompactBlock = b.into();
 	let mut vec = Vec::new();
-	ser::serialize(&mut vec, &cb).expect("serialization failed");
+	ser::serialize_default(&mut vec, &cb).expect("serialization failed");
 	let target_len = 1_333;
 	assert_eq!(vec.len(), target_len,);
 }
@@ -439,7 +439,7 @@ fn serialize_deserialize_compact_block() {
 	let mut cb1: CompactBlock = b.into();
 
 	let mut vec = Vec::new();
-	ser::serialize(&mut vec, &cb1).expect("serialization failed");
+	ser::serialize_default(&mut vec, &cb1).expect("serialization failed");
 
 	// After header serialization, timestamp will lose 'nanos' info, that's the designed behavior.
 	// To suppress 'nanos' difference caused assertion fail, we force b.header also lose 'nanos'.
diff --git a/core/tests/core.rs b/core/tests/core.rs
index d0f5dff17..a3da0037a 100644
--- a/core/tests/core.rs
+++ b/core/tests/core.rs
@@ -39,7 +39,7 @@ use std::sync::Arc;
 fn simple_tx_ser() {
 	let tx = tx2i1o();
 	let mut vec = Vec::new();
-	ser::serialize(&mut vec, &tx).expect("serialization failed");
+	ser::serialize_default(&mut vec, &tx).expect("serialization failed");
 	let target_len = 955;
 	assert_eq!(vec.len(), target_len,);
 }
@@ -48,7 +48,7 @@ fn simple_tx_ser() {
 fn simple_tx_ser_deser() {
 	let tx = tx2i1o();
 	let mut vec = Vec::new();
-	ser::serialize(&mut vec, &tx).expect("serialization failed");
+	ser::serialize_default(&mut vec, &tx).expect("serialization failed");
 	let dtx: Transaction = ser::deserialize_default(&mut &vec[..]).unwrap();
 	assert_eq!(dtx.fee(), 2);
 	assert_eq!(dtx.inputs().len(), 2);
@@ -62,11 +62,11 @@ fn tx_double_ser_deser() {
 	let btx = tx2i1o();
 
 	let mut vec = Vec::new();
-	assert!(ser::serialize(&mut vec, &btx).is_ok());
+	assert!(ser::serialize_default(&mut vec, &btx).is_ok());
 	let dtx: Transaction = ser::deserialize_default(&mut &vec[..]).unwrap();
 
 	let mut vec2 = Vec::new();
-	assert!(ser::serialize(&mut vec2, &btx).is_ok());
+	assert!(ser::serialize_default(&mut vec2, &btx).is_ok());
 	let dtx2: Transaction = ser::deserialize_default(&mut &vec2[..]).unwrap();
 
 	assert_eq!(btx.hash(), dtx.hash());
diff --git a/core/tests/merkle_proof.rs b/core/tests/merkle_proof.rs
index 56b945c6c..f25497398 100644
--- a/core/tests/merkle_proof.rs
+++ b/core/tests/merkle_proof.rs
@@ -37,7 +37,7 @@ fn merkle_proof_ser_deser() {
 	let proof = pmmr.merkle_proof(9).unwrap();
 
 	let mut vec = Vec::new();
-	ser::serialize(&mut vec, &proof).expect("serialization failed");
+	ser::serialize_default(&mut vec, &proof).expect("serialization failed");
 	let proof_2: MerkleProof = ser::deserialize_default(&mut &vec[..]).unwrap();
 
 	assert_eq!(proof, proof_2);
diff --git a/core/tests/transaction.rs b/core/tests/transaction.rs
index 3e9548b49..65b7ff6f8 100644
--- a/core/tests/transaction.rs
+++ b/core/tests/transaction.rs
@@ -39,7 +39,7 @@ fn test_output_ser_deser() {
 	};
 
 	let mut vec = vec![];
-	ser::serialize(&mut vec, &out).expect("serialized failed");
+	ser::serialize_default(&mut vec, &out).expect("serialized failed");
 	let dout: Output = ser::deserialize_default(&mut &vec[..]).unwrap();
 
 	assert_eq!(dout.features, OutputFeatures::Plain);
diff --git a/p2p/src/conn.rs b/p2p/src/conn.rs
index ad6fb7c8b..e916669b8 100644
--- a/p2p/src/conn.rs
+++ b/p2p/src/conn.rs
@@ -123,6 +123,7 @@ impl<'a> Message<'a> {
 pub struct Response<'a> {
 	resp_type: Type,
 	body: Vec<u8>,
+	version: ProtocolVersion,
 	stream: &'a mut dyn Write,
 	attachment: Option<File>,
 }
@@ -130,20 +131,25 @@ pub struct Response<'a> {
 impl<'a> Response<'a> {
 	pub fn new<T: ser::Writeable>(
 		resp_type: Type,
+		version: ProtocolVersion,
 		body: T,
 		stream: &'a mut dyn Write,
 	) -> Result<Response<'a>, Error> {
-		let body = ser::ser_vec(&body)?;
+		let body = ser::ser_vec(&body, version)?;
 		Ok(Response {
 			resp_type,
 			body,
+			version,
 			stream,
 			attachment: None,
 		})
 	}
 
 	fn write(mut self, tracker: Arc<Tracker>) -> Result<(), Error> {
-		let mut msg = ser::ser_vec(&MsgHeader::new(self.resp_type, self.body.len() as u64))?;
+		let mut msg = ser::ser_vec(
+			&MsgHeader::new(self.resp_type, self.body.len() as u64),
+			self.version,
+		)?;
 		msg.append(&mut self.body);
 		write_all(&mut self.stream, &msg[..], time::Duration::from_secs(10))?;
 		tracker.inc_sent(msg.len() as u64);
@@ -213,11 +219,11 @@ pub struct ConnHandle {
 }
 
 impl ConnHandle {
-	pub fn send<T>(&self, body: T, msg_type: Type) -> Result<u64, Error>
+	pub fn send<T>(&self, body: T, msg_type: Type, version: ProtocolVersion) -> Result<u64, Error>
 	where
 		T: ser::Writeable,
 	{
-		let buf = write_to_buf(body, msg_type)?;
+		let buf = write_to_buf(body, msg_type, version)?;
 		let buf_len = buf.len();
 		self.send_channel.try_send(buf)?;
 		Ok(buf_len as u64)
diff --git a/p2p/src/handshake.rs b/p2p/src/handshake.rs
index 94f5305f0..504ddb242 100644
--- a/p2p/src/handshake.rs
+++ b/p2p/src/handshake.rs
@@ -73,8 +73,8 @@ impl Handshake {
 			Err(e) => return Err(Error::Connection(e)),
 		};
 
-		// Using our default version here.
-		let version = ProtocolVersion::default();
+		// Using our default "local" protocol version.
+		let version = ProtocolVersion::local();
 
 		let hand = Hand {
 			version,
@@ -88,7 +88,7 @@ impl Handshake {
 		};
 
 		// write and read the handshake response
-		write_message(conn, hand, Type::Hand)?;
+		write_message(conn, hand, Type::Hand, version)?;
 
 		// Note: We have to read the Shake message *before* we know which protocol
 		// version our peer supports (it is in the shake message itself).
@@ -132,8 +132,9 @@ impl Handshake {
 		conn: &mut TcpStream,
 	) -> Result<PeerInfo, Error> {
 		// Note: We read the Hand message *before* we know which protocol version
-		// is supported by our peer (it is in the Hand message).
-		let version = ProtocolVersion::default();
+		// is supported by our peer (in the Hand message).
+		let version = ProtocolVersion::local();
+
 		let hand: Hand = read_message(conn, version, Type::Hand)?;
 
 		// all the reasons we could refuse this connection for
@@ -177,17 +178,16 @@ impl Handshake {
 
 		// send our reply with our info
 		let shake = Shake {
-			version: ProtocolVersion::default(),
+			version,
 			capabilities: capab,
 			genesis: self.genesis,
 			total_difficulty: total_difficulty,
 			user_agent: USER_AGENT.to_string(),
 		};
 
-		write_message(conn, shake, Type::Shake)?;
+		write_message(conn, shake, Type::Shake, version)?;
 		trace!("Success handshake with {}.", peer_info.addr);
 
-		// when more than one protocol version is supported, choosing should go here
 		Ok(peer_info)
 	}
 
diff --git a/p2p/src/msg.rs b/p2p/src/msg.rs
index 1ee0f37e4..67338d3c0 100644
--- a/p2p/src/msg.rs
+++ b/p2p/src/msg.rs
@@ -191,15 +191,19 @@ pub fn read_message<T: Readable>(
 	}
 }
 
-pub fn write_to_buf<T: Writeable>(msg: T, msg_type: Type) -> Result<Vec<u8>, Error> {
+pub fn write_to_buf<T: Writeable>(
+	msg: T,
+	msg_type: Type,
+	version: ProtocolVersion,
+) -> Result<Vec<u8>, Error> {
 	// prepare the body first so we know its serialized length
 	let mut body_buf = vec![];
-	ser::serialize(&mut body_buf, &msg)?;
+	ser::serialize(&mut body_buf, version, &msg)?;
 
 	// build and serialize the header using the body size
 	let mut msg_buf = vec![];
 	let blen = body_buf.len() as u64;
-	ser::serialize(&mut msg_buf, &MsgHeader::new(msg_type, blen))?;
+	ser::serialize(&mut msg_buf, version, &MsgHeader::new(msg_type, blen))?;
 	msg_buf.append(&mut body_buf);
 
 	Ok(msg_buf)
@@ -209,8 +213,9 @@ pub fn write_message<T: Writeable>(
 	stream: &mut dyn Write,
 	msg: T,
 	msg_type: Type,
+	version: ProtocolVersion,
 ) -> Result<(), Error> {
-	let buf = write_to_buf(msg, msg_type)?;
+	let buf = write_to_buf(msg, msg_type, version)?;
 	stream.write_all(&buf[..])?;
 	Ok(())
 }
diff --git a/p2p/src/peer.rs b/p2p/src/peer.rs
index 88ae1b436..89b4e2b01 100644
--- a/p2p/src/peer.rs
+++ b/p2p/src/peer.rs
@@ -224,7 +224,10 @@ impl Peer {
 
 	/// Send a msg with given msg_type to our peer via the connection.
 	fn send<T: Writeable>(&self, msg: T, msg_type: Type) -> Result<(), Error> {
-		let bytes = self.send_handle.lock().send(msg, msg_type)?;
+		let bytes = self
+			.send_handle
+			.lock()
+			.send(msg, msg_type, self.info.version)?;
 		self.tracker.inc_sent(bytes);
 		Ok(())
 	}
diff --git a/p2p/src/protocol.rs b/p2p/src/protocol.rs
index 721c56848..33eeea479 100644
--- a/p2p/src/protocol.rs
+++ b/p2p/src/protocol.rs
@@ -66,6 +66,7 @@ impl MessageHandler for Protocol {
 
 				Ok(Some(Response::new(
 					Type::Pong,
+					self.peer_info.version,
 					Pong {
 						total_difficulty: adapter.total_difficulty()?,
 						height: adapter.total_height()?,
@@ -104,7 +105,12 @@ impl MessageHandler for Protocol {
 				);
 				let tx = adapter.get_transaction(h);
 				if let Some(tx) = tx {
-					Ok(Some(Response::new(Type::Transaction, tx, writer)?))
+					Ok(Some(Response::new(
+						Type::Transaction,
+						self.peer_info.version,
+						tx,
+						writer,
+					)?))
 				} else {
 					Ok(None)
 				}
@@ -140,7 +146,12 @@ impl MessageHandler for Protocol {
 
 				let bo = adapter.get_block(h);
 				if let Some(b) = bo {
-					return Ok(Some(Response::new(Type::Block, b, writer)?));
+					return Ok(Some(Response::new(
+						Type::Block,
+						self.peer_info.version,
+						b,
+						writer,
+					)?));
 				}
 				Ok(None)
 			}
@@ -162,7 +173,12 @@ impl MessageHandler for Protocol {
 				let h: Hash = msg.body()?;
 				if let Some(b) = adapter.get_block(h) {
 					let cb: CompactBlock = b.into();
-					Ok(Some(Response::new(Type::CompactBlock, cb, writer)?))
+					Ok(Some(Response::new(
+						Type::CompactBlock,
+						self.peer_info.version,
+						cb,
+						writer,
+					)?))
 				} else {
 					Ok(None)
 				}
@@ -187,6 +203,7 @@ impl MessageHandler for Protocol {
 				// serialize and send all the headers over
 				Ok(Some(Response::new(
 					Type::Headers,
+					self.peer_info.version,
 					Headers { headers },
 					writer,
 				)?))
@@ -232,6 +249,7 @@ impl MessageHandler for Protocol {
 				let peers = adapter.find_peer_addrs(get_peers.capabilities);
 				Ok(Some(Response::new(
 					Type::PeerAddrs,
+					self.peer_info.version,
 					PeerAddrs { peers },
 					writer,
 				)?))
@@ -248,8 +266,12 @@ impl MessageHandler for Protocol {
 				let kernel_data = self.adapter.kernel_data_read()?;
 				let bytes = kernel_data.metadata()?.len();
 				let kernel_data_response = KernelDataResponse { bytes };
-				let mut response =
-					Response::new(Type::KernelDataResponse, &kernel_data_response, writer)?;
+				let mut response = Response::new(
+					Type::KernelDataResponse,
+					self.peer_info.version,
+					&kernel_data_response,
+					writer,
+				)?;
 				response.add_attachment(kernel_data);
 				Ok(Some(response))
 			}
@@ -304,6 +326,7 @@ impl MessageHandler for Protocol {
 					let file_sz = txhashset.reader.metadata()?.len();
 					let mut resp = Response::new(
 						Type::TxHashSetArchive,
+						self.peer_info.version,
 						&TxHashSetArchive {
 							height: sm_req.height as u64,
 							hash: sm_req.hash,
diff --git a/servers/src/grin/server.rs b/servers/src/grin/server.rs
index a3d9fb4b5..9eecad746 100644
--- a/servers/src/grin/server.rs
+++ b/servers/src/grin/server.rs
@@ -417,7 +417,7 @@ impl Server {
 
 	/// The p2p layer protocol version for this node.
 	pub fn protocol_version() -> ProtocolVersion {
-		ProtocolVersion::default()
+		ProtocolVersion::local()
 	}
 
 	/// Returns a set of stats about this server. This and the ServerStats
diff --git a/servers/src/mining/stratumserver.rs b/servers/src/mining/stratumserver.rs
index 6c8a0c1a7..fd5658ace 100644
--- a/servers/src/mining/stratumserver.rs
+++ b/servers/src/mining/stratumserver.rs
@@ -331,7 +331,7 @@ impl Handler {
 		// Serialize the block header into pre and post nonce strings
 		let mut header_buf = vec![];
 		{
-			let mut writer = ser::BinWriter::new(&mut header_buf);
+			let mut writer = ser::BinWriter::default(&mut header_buf);
 			bh.write_pre_pow(&mut writer).unwrap();
 			bh.pow.write_pre_pow(&mut writer).unwrap();
 		}
diff --git a/store/src/lmdb.rs b/store/src/lmdb.rs
index e7f52b090..62c6aca23 100644
--- a/store/src/lmdb.rs
+++ b/store/src/lmdb.rs
@@ -22,7 +22,7 @@ use lmdb_zero as lmdb;
 use lmdb_zero::traits::CreateCursor;
 use lmdb_zero::LmdbResultExt;
 
-use crate::core::ser;
+use crate::core::ser::{self, ProtocolVersion};
 use crate::util::{RwLock, RwLockReadGuard};
 
 /// number of bytes to grow the database by when needed
@@ -68,6 +68,7 @@ pub struct Store {
 	env: Arc<lmdb::Environment>,
 	db: RwLock<Option<Arc<lmdb::Database<'static>>>>,
 	name: String,
+	version: ProtocolVersion,
 }
 
 impl Store {
@@ -111,6 +112,7 @@ impl Store {
 			env: Arc::new(env),
 			db: RwLock::new(None),
 			name: db_name,
+			version: ProtocolVersion(1),
 		};
 
 		{
@@ -230,7 +232,7 @@ impl Store {
 	) -> Result<Option<T>, Error> {
 		let res: lmdb::error::Result<&[u8]> = access.get(&db.as_ref().unwrap(), key);
 		match res.to_opt() {
-			Ok(Some(mut res)) => match ser::deserialize_db(&mut res) {
+			Ok(Some(mut res)) => match ser::deserialize(&mut res, self.version) {
 				Ok(res) => Ok(Some(res)),
 				Err(e) => Err(Error::SerErr(format!("{}", e))),
 			},
@@ -259,6 +261,7 @@ impl Store {
 			cursor,
 			seek: false,
 			prefix: from.to_vec(),
+			version: self.version,
 			_marker: marker::PhantomData,
 		})
 	}
@@ -296,7 +299,7 @@ impl<'a> Batch<'a> {
 	/// Writes a single key and its `Writeable` value to the db. Encapsulates
 	/// serialization.
 	pub fn put_ser<W: ser::Writeable>(&self, key: &[u8], value: &W) -> Result<(), Error> {
-		let ser_value = ser::ser_vec(value);
+		let ser_value = ser::ser_vec(value, self.store.version);
 		match ser_value {
 			Ok(data) => self.put(key, &data),
 			Err(err) => Err(Error::SerErr(format!("{}", err))),
@@ -360,6 +363,7 @@ where
 	cursor: Arc<lmdb::Cursor<'static, 'static>>,
 	seek: bool,
 	prefix: Vec<u8>,
+	version: ProtocolVersion,
 	_marker: marker::PhantomData<T>,
 }
 
@@ -393,7 +397,7 @@ where
 	fn deser_if_prefix_match(&self, key: &[u8], value: &[u8]) -> Option<(Vec<u8>, T)> {
 		let plen = self.prefix.len();
 		if plen == 0 || key[0..plen] == self.prefix[..] {
-			if let Ok(value) = ser::deserialize_db(&mut &value[..]) {
+			if let Ok(value) = ser::deserialize(&mut &value[..], self.version) {
 				Some((key.to_vec(), value))
 			} else {
 				None
diff --git a/store/src/pmmr.rs b/store/src/pmmr.rs
index ee01f2157..ceed2ef0d 100644
--- a/store/src/pmmr.rs
+++ b/store/src/pmmr.rs
@@ -19,7 +19,7 @@ use std::{io, time};
 use crate::core::core::hash::{Hash, Hashed};
 use crate::core::core::pmmr::{self, family, Backend};
 use crate::core::core::BlockHeader;
-use crate::core::ser::{FixedLength, PMMRable};
+use crate::core::ser::{FixedLength, PMMRable, ProtocolVersion};
 use crate::leaf_set::LeafSet;
 use crate::prune_list::PruneList;
 use crate::types::{AppendOnlyFile, DataFile, SizeEntry, SizeInfo};
@@ -206,6 +206,11 @@ impl<T: PMMRable> PMMRBackend<T> {
 		fixed_size: bool,
 		header: Option<&BlockHeader>,
 	) -> io::Result<PMMRBackend<T>> {
+		// Note: Explicit protocol version here.
+		// Regardless of our "default" protocol version we have existing MMR files
+		// and we need to be able to support these across upgrades.
+		let version = ProtocolVersion(1);
+
 		let data_dir = data_dir.as_ref();
 
 		// Are we dealing with "fixed size" data elements or "variable size" data elements
@@ -216,14 +221,15 @@ impl<T: PMMRable> PMMRBackend<T> {
 			SizeInfo::VariableSize(Box::new(AppendOnlyFile::open(
 				data_dir.join(PMMR_SIZE_FILE),
 				SizeInfo::FixedSize(SizeEntry::LEN as u16),
+				version,
 			)?))
 		};
 
 		// Hash file is always "fixed size" and we use 32 bytes per hash.
 		let hash_size_info = SizeInfo::FixedSize(Hash::LEN as u16);
 
-		let hash_file = DataFile::open(&data_dir.join(PMMR_HASH_FILE), hash_size_info)?;
-		let data_file = DataFile::open(&data_dir.join(PMMR_DATA_FILE), size_info)?;
+		let hash_file = DataFile::open(&data_dir.join(PMMR_HASH_FILE), hash_size_info, version)?;
+		let data_file = DataFile::open(&data_dir.join(PMMR_DATA_FILE), size_info, version)?;
 
 		let leaf_set_path = data_dir.join(PMMR_LEAF_FILE);
 
diff --git a/store/src/types.rs b/store/src/types.rs
index 2f46f7621..2d4de2870 100644
--- a/store/src/types.rs
+++ b/store/src/types.rs
@@ -78,12 +78,16 @@ where
 	T: Readable + Writeable + Debug,
 {
 	/// Open (or create) a file at the provided path on disk.
-	pub fn open<P>(path: P, size_info: SizeInfo) -> io::Result<DataFile<T>>
+	pub fn open<P>(
+		path: P,
+		size_info: SizeInfo,
+		version: ProtocolVersion,
+	) -> io::Result<DataFile<T>>
 	where
 		P: AsRef<Path> + Debug,
 	{
 		Ok(DataFile {
-			file: AppendOnlyFile::open(path, size_info)?,
+			file: AppendOnlyFile::open(path, size_info, version)?,
 		})
 	}
 
@@ -177,6 +181,7 @@ pub struct AppendOnlyFile<T> {
 	path: PathBuf,
 	file: Option<File>,
 	size_info: SizeInfo,
+	version: ProtocolVersion,
 	mmap: Option<memmap::Mmap>,
 
 	// Buffer of unsync'd bytes. These bytes will be appended to the file when flushed.
@@ -191,7 +196,11 @@ where
 	T: Debug + Readable + Writeable,
 {
 	/// Open a file (existing or not) as append-only, backed by a mmap.
-	pub fn open<P>(path: P, size_info: SizeInfo) -> io::Result<AppendOnlyFile<T>>
+	pub fn open<P>(
+		path: P,
+		size_info: SizeInfo,
+		version: ProtocolVersion,
+	) -> io::Result<AppendOnlyFile<T>>
 	where
 		P: AsRef<Path> + Debug,
 	{
@@ -199,6 +208,7 @@ where
 			file: None,
 			path: path.as_ref().to_path_buf(),
 			size_info,
+			version,
 			mmap: None,
 			buffer: vec![],
 			buffer_start_pos: 0,
@@ -268,7 +278,8 @@ where
 
 	/// Append element to append-only file by serializing it to bytes and appending the bytes.
 	fn append_elmt(&mut self, data: &T) -> io::Result<()> {
-		let mut bytes = ser::ser_vec(data).map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;
+		let mut bytes = ser::ser_vec(data, self.version)
+			.map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;
 		self.append(&mut bytes)?;
 		Ok(())
 	}
@@ -415,7 +426,8 @@ where
 
 	fn read_as_elmt(&self, pos: u64) -> io::Result<T> {
 		let data = self.read(pos)?;
-		ser::deserialize_db(&mut &data[..]).map_err(|e| io::Error::new(io::ErrorKind::Other, e))
+		ser::deserialize(&mut &data[..], self.version)
+			.map_err(|e| io::Error::new(io::ErrorKind::Other, e))
 	}
 
 	// Read length bytes starting at offset from the buffer.
@@ -471,10 +483,10 @@ where
 			let reader = File::open(&self.path)?;
 			let mut buf_reader = BufReader::new(reader);
 			let mut streaming_reader =
-				StreamingReader::new(&mut buf_reader, ProtocolVersion::local_db(), time::Duration::from_secs(1));
+				StreamingReader::new(&mut buf_reader, self.version, time::Duration::from_secs(1));
 
 			let mut buf_writer = BufWriter::new(File::create(&tmp_path)?);
-			let mut bin_writer = BinWriter::new(&mut buf_writer);
+			let mut bin_writer = BinWriter::new(&mut buf_writer, self.version);
 
 			let mut current_pos = 0;
 			let mut prune_pos = prune_pos;
@@ -517,11 +529,14 @@ where
 			{
 				let reader = File::open(&self.path)?;
 				let mut buf_reader = BufReader::new(reader);
-				let mut streaming_reader =
-					StreamingReader::new(&mut buf_reader, ProtocolVersion::local_db(), time::Duration::from_secs(1));
+				let mut streaming_reader = StreamingReader::new(
+					&mut buf_reader,
+					self.version,
+					time::Duration::from_secs(1),
+				);
 
 				let mut buf_writer = BufWriter::new(File::create(&tmp_path)?);
-				let mut bin_writer = BinWriter::new(&mut buf_writer);
+				let mut bin_writer = BinWriter::new(&mut buf_writer, self.version);
 
 				let mut current_offset = 0;
 				while let Ok(_) = T::read(&mut streaming_reader) {