diff --git a/src/sync/chain.rs b/src/sync/chain.rs
index 276b1993c..95505ff81 100644
--- a/src/sync/chain.rs
+++ b/src/sync/chain.rs
@@ -13,20 +13,11 @@
 /// 4. Maintain sync by handling NewBlocks/NewHashes messages
 ///
 
-use std::collections::{HashSet, HashMap};
-use std::cmp::{min, max};
+use util::*;
 use std::mem::{replace};
-use util::network::{PeerId, PacketId};
-use util::hash::{H256, FixedHash};
-use util::bytes::{Bytes};
-use util::uint::{U256};
-use util::rlp::{Rlp, UntrustedRlp, RlpStream, self};
-use util::rlp::rlptraits::{Stream, View};
-use util::rlp::rlperrors::DecoderError;
-use util::sha3::Hashable;
-use client::{BlockNumber, BlockChainClient, BlockStatus, QueueStatus, ImportResult};
 use views::{HeaderView};
 use header::{Header as BlockHeader};
+use client::{BlockNumber, BlockChainClient, BlockStatus, QueueStatus, ImportResult};
 use sync::range_collection::{RangeCollection, ToUsize, FromUsize};
 use sync::io::SyncIo;
 
@@ -66,6 +57,8 @@ const NODE_DATA_PACKET: u8 = 0x0e;
 const GET_RECEIPTS_PACKET: u8 = 0x0f;
 const RECEIPTS_PACKET: u8 = 0x10;
 
+const NETWORK_ID: U256 = ONE_U256; //TODO: get this from parent
+
 struct Header {
 	/// Header data
 	data: Bytes,
@@ -241,7 +234,19 @@ impl ChainSync {
 			asking_blocks: Vec::new(),
 		};
 
-		trace!(target: "sync", "New peer (protocol: {}, network: {:?}, difficulty: {:?}, latest:{}, genesis:{})", peer.protocol_version, peer.network_id, peer.difficulty, peer.latest, peer.genesis);
+		trace!(target: "sync", "New peer {} (protocol: {}, network: {:?}, difficulty: {:?}, latest:{}, genesis:{})", peer_id, peer.protocol_version, peer.network_id, peer.difficulty, peer.latest, peer.genesis);
+		
+		let chain_info = io.chain().chain_info();
+		if peer.genesis != chain_info.genesis_hash {
+			io.disable_peer(peer_id);
+			trace!(target: "sync", "Peer {} genesis hash not matched", peer_id);
+			return Ok(());
+		}
+		if peer.network_id != NETWORK_ID {
+			io.disable_peer(peer_id);
+			trace!(target: "sync", "Peer {} network id not matched", peer_id);
+			return Ok(());
+		}
 
 		let old = self.peers.insert(peer_id.clone(), peer);
 		if old.is_some() {
@@ -449,8 +454,10 @@ impl ChainSync {
 	/// Called by peer when it is disconnecting
 	pub fn on_peer_aborting(&mut self, io: &mut SyncIo, peer: &PeerId) {
 		trace!(target: "sync", "== Disconnected {}", peer);
-		self.clear_peer_download(peer);
-		self.continue_sync(io);
+		if self.peers.contains_key(&peer) {
+			self.clear_peer_download(peer);
+			self.continue_sync(io);
+		}
 	}
 
 	/// Called when a new peer is connected
@@ -769,7 +776,7 @@ impl ChainSync {
 		let mut packet = RlpStream::new_list(5);
 		let chain = io.chain().chain_info();
 		packet.append(&(PROTOCOL_VERSION as u32));
-		packet.append(&0u32); //TODO: network id
+		packet.append(&NETWORK_ID); //TODO: network id
 		packet.append(&chain.total_difficulty);
 		packet.append(&chain.best_block_hash);
 		packet.append(&chain.genesis_hash);