diff --git a/include/qemu/jhash.h b/include/qemu/jhash.h
new file mode 100644
index 0000000..0fcd875
--- /dev/null
+++ b/include/qemu/jhash.h
@@ -0,0 +1,61 @@
+/* jhash.h: Jenkins hash support.
+  *
+  * Copyright (C) 2006. Bob Jenkins (bob_jenkins@burtleburtle.net)
+  *
+  * http://burtleburtle.net/bob/hash/
+  *
+  * These are the credits from Bob's sources:
+  *
+  * lookup3.c, by Bob Jenkins, May 2006, Public Domain.
+  *
+  * These are functions for producing 32-bit hashes for hash table lookup.
+  * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
+  * are externally useful functions.  Routines to test the hash are
+included
+  * if SELF_TEST is defined.  You can use this free for any purpose.
+It's in
+  * the public domain.  It has no warranty.
+  *
+  * Copyright (C) 2009-2010 Jozsef Kadlecsik (kadlec@blackhole.kfki.hu)
+  *
+  * I've modified Bob's hash to be useful in the Linux kernel, and
+  * any bugs present are my fault.
+  * Jozsef
+  */
+
+#ifndef QEMU_JHASH_H__
+#define QEMU_JHASH_H__
+
+#include "qemu/bitops.h"
+
+/*
+ * hashtable relation copy from linux kernel jhash
+ */
+
+/* __jhash_mix -- mix 3 32-bit values reversibly. */
+#define __jhash_mix(a, b, c)                \
+{                                           \
+    a -= c;  a ^= rol32(c, 4);  c += b;     \
+    b -= a;  b ^= rol32(a, 6);  a += c;     \
+    c -= b;  c ^= rol32(b, 8);  b += a;     \
+    a -= c;  a ^= rol32(c, 16); c += b;     \
+    b -= a;  b ^= rol32(a, 19); a += c;     \
+    c -= b;  c ^= rol32(b, 4);  b += a;     \
+}
+
+/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
+#define __jhash_final(a, b, c)  \
+{                               \
+    c ^= b; c -= rol32(b, 14);  \
+    a ^= c; a -= rol32(c, 11);  \
+    b ^= a; b -= rol32(a, 25);  \
+    c ^= b; c -= rol32(b, 16);  \
+    a ^= c; a -= rol32(c, 4);   \
+    b ^= a; b -= rol32(a, 14);  \
+    c ^= b; c -= rol32(b, 24);  \
+}
+
+/* An arbitrary initial parameter */
+#define JHASH_INITVAL           0xdeadbeef
+
+#endif /* QEMU_JHASH_H__ */
diff --git a/net/Makefile.objs b/net/Makefile.objs
index ba92f73..119589f 100644
--- a/net/Makefile.objs
+++ b/net/Makefile.objs
@@ -17,3 +17,4 @@ common-obj-y += filter.o
 common-obj-y += filter-buffer.o
 common-obj-y += filter-mirror.o
 common-obj-y += colo-compare.o
+common-obj-y += colo-base.o
diff --git a/net/colo-base.c b/net/colo-base.c
new file mode 100644
index 0000000..6bb80ca
--- /dev/null
+++ b/net/colo-base.c
@@ -0,0 +1,182 @@
+/*
+ * COarse-grain LOck-stepping Virtual Machines for Non-stop Service (COLO)
+ * (a.k.a. Fault Tolerance or Continuous Replication)
+ *
+ * Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD.
+ * Copyright (c) 2016 FUJITSU LIMITED
+ * Copyright (c) 2016 Intel Corporation
+ *
+ * Author: Zhang Chen <zhangchen.fnst@cn.fujitsu.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * later.  See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/error-report.h"
+#include "net/colo-base.h"
+
+uint32_t connection_key_hash(const void *opaque)
+{
+    const ConnectionKey *key = opaque;
+    uint32_t a, b, c;
+
+    /* Jenkins hash */
+    a = b = c = JHASH_INITVAL + sizeof(*key);
+    a += key->src.s_addr;
+    b += key->dst.s_addr;
+    c += (key->src_port | key->dst_port << 16);
+    __jhash_mix(a, b, c);
+
+    a += key->ip_proto;
+    __jhash_final(a, b, c);
+
+    return c;
+}
+
+int connection_key_equal(const void *key1, const void *key2)
+{
+    return memcmp(key1, key2, sizeof(ConnectionKey)) == 0;
+}
+
+int parse_packet_early(Packet *pkt)
+{
+    int network_length;
+    uint8_t *data = pkt->data;
+    uint16_t l3_proto;
+    ssize_t l2hdr_len = eth_get_l2_hdr_length(data);
+
+    if (pkt->size < ETH_HLEN) {
+        error_report("pkt->size < ETH_HLEN");
+        return 1;
+    }
+    pkt->network_layer = data + ETH_HLEN;
+    l3_proto = eth_get_l3_proto(data, l2hdr_len);
+    if (l3_proto != ETH_P_IP) {
+        return 1;
+    }
+
+    network_length = pkt->ip->ip_hl * 4;
+    if (pkt->size < ETH_HLEN + network_length) {
+        error_report("pkt->size < network_layer + network_length");
+        return 1;
+    }
+    pkt->transport_layer = pkt->network_layer + network_length;
+    if (!pkt->transport_layer) {
+        error_report("pkt->transport_layer is valid");
+        return 1;
+    }
+
+    return 0;
+}
+
+void fill_connection_key(Packet *pkt, ConnectionKey *key)
+{
+    uint32_t tmp_ports;
+
+    key->ip_proto = pkt->ip->ip_p;
+    key->src = pkt->ip->ip_src;
+    key->dst = pkt->ip->ip_dst;
+
+    switch (key->ip_proto) {
+    case IPPROTO_TCP:
+    case IPPROTO_UDP:
+    case IPPROTO_DCCP:
+    case IPPROTO_ESP:
+    case IPPROTO_SCTP:
+    case IPPROTO_UDPLITE:
+        tmp_ports = *(uint32_t *)(pkt->transport_layer);
+        key->src_port = ntohs(tmp_ports & 0xffff);
+        key->dst_port = ntohs(tmp_ports >> 16);
+        break;
+    case IPPROTO_AH:
+        tmp_ports = *(uint32_t *)(pkt->transport_layer + 4);
+        key->src_port = ntohs(tmp_ports & 0xffff);
+        key->dst_port = ntohs(tmp_ports >> 16);
+        break;
+    default:
+        key->src_port = 0;
+        key->dst_port = 0;
+        break;
+    }
+}
+
+Connection *connection_new(ConnectionKey *key)
+{
+    Connection *conn = g_slice_new(Connection);
+
+    qemu_mutex_init(&conn->list_lock);
+    conn->ip_proto = key->ip_proto;
+    conn->processing = false;
+    g_queue_init(&conn->primary_list);
+    g_queue_init(&conn->secondary_list);
+
+    return conn;
+}
+
+void connection_destroy(void *opaque)
+{
+    Connection *conn = opaque;
+
+    qemu_mutex_lock(&conn->list_lock);
+    g_queue_foreach(&conn->primary_list, packet_destroy, NULL);
+    g_queue_free(&conn->primary_list);
+    g_queue_foreach(&conn->secondary_list, packet_destroy, NULL);
+    g_queue_free(&conn->secondary_list);
+    qemu_mutex_unlock(&conn->list_lock);
+    qemu_mutex_destroy(&conn->list_lock);
+    g_slice_free(Connection, conn);
+}
+
+Packet *packet_new(const void *data, int size)
+{
+    Packet *pkt = g_slice_new(Packet);
+
+    pkt->data = g_memdup(data, size);
+    pkt->size = size;
+
+    return pkt;
+}
+
+void packet_destroy(void *opaque, void *user_data)
+{
+    Packet *pkt = opaque;
+
+    g_free(pkt->data);
+    g_slice_free(Packet, pkt);
+}
+
+/*
+ * Clear hashtable, stop this hash growing really huge
+ */
+void connection_hashtable_reset(GHashTable *connection_track_table)
+{
+    g_hash_table_remove_all(connection_track_table);
+}
+
+/* if not found, create a new connection and add to hash table */
+Connection *connection_get(GHashTable *connection_track_table,
+                           ConnectionKey *key,
+                           uint32_t *hashtable_size)
+{
+    /* FIXME: protect connection_track_table */
+    Connection *conn = g_hash_table_lookup(connection_track_table, key);
+
+    if (conn == NULL) {
+        ConnectionKey *new_key = g_memdup(key, sizeof(*key));
+
+        conn = connection_new(key);
+
+        *hashtable_size += 1;
+        if (*hashtable_size > HASHTABLE_MAX_SIZE) {
+            error_report("colo proxy connection hashtable full, clear it");
+            connection_hashtable_reset(connection_track_table);
+            *hashtable_size = 0;
+            /* TODO:clear conn_list */
+        }
+
+        g_hash_table_insert(connection_track_table, new_key, conn);
+    }
+
+    return conn;
+}
diff --git a/net/colo-base.h b/net/colo-base.h
new file mode 100644
index 0000000..5d72302
--- /dev/null
+++ b/net/colo-base.h
@@ -0,0 +1,89 @@
+/*
+ * COarse-grain LOck-stepping Virtual Machines for Non-stop Service (COLO)
+ * (a.k.a. Fault Tolerance or Continuous Replication)
+ *
+ * Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD.
+ * Copyright (c) 2016 FUJITSU LIMITED
+ * Copyright (c) 2016 Intel Corporation
+ *
+ * Author: Zhang Chen <zhangchen.fnst@cn.fujitsu.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * later.  See the COPYING file in the top-level directory.
+ */
+
+#ifndef QEMU_COLO_BASE_H
+#define QEMU_COLO_BASE_H
+
+#include "slirp/slirp.h"
+#include "qemu/jhash.h"
+#include "qemu/rcu.h"
+
+#define HASHTABLE_MAX_SIZE 16384
+
+typedef enum colo_conn_state {
+     COLO_CONN_IDLE,
+
+    /* States on the primary: For incoming connection */
+     COLO_CONN_PRI_IN_SYN,   /* Received Syn */
+     COLO_CONN_PRI_IN_PSYNACK, /* Received syn/ack from primary, but not
+                                yet from secondary */
+     COLO_CONN_PRI_IN_SSYNACK, /* Received syn/ack from secondary, but
+                                  not yet from primary */
+     COLO_CONN_PRI_IN_SYNACK,  /* Received syn/ack from both */
+     COLO_CONN_PRI_IN_ESTABLISHED, /* Got the ACK */
+
+    /* States on the secondary: For incoming connection */
+     COLO_CONN_SEC_IN_SYNACK,      /* We sent a syn/ack */
+     COLO_CONN_SEC_IN_ACK,         /* Saw the ack but didn't yet see our syn/ack */
+     COLO_CONN_SEC_IN_ESTABLISHED, /* Got the ACK from the outside */
+} colo_conn_state;
+
+typedef struct Packet {
+    void *data;
+    union {
+        uint8_t *network_layer;
+        struct ip *ip;
+    };
+    uint8_t *transport_layer;
+    int size;
+} Packet;
+
+typedef struct ConnectionKey {
+    /* (src, dst) must be grouped, in the same way than in IP header */
+    struct in_addr src;
+    struct in_addr dst;
+    uint16_t src_port;
+    uint16_t dst_port;
+    uint8_t ip_proto;
+} QEMU_PACKED ConnectionKey;
+
+typedef struct Connection {
+    QemuMutex list_lock;
+    /* connection primary send queue: element type: Packet */
+    GQueue primary_list;
+    /* connection secondary send queue: element type: Packet */
+    GQueue secondary_list;
+    /* flag to enqueue unprocessed_connections */
+    bool processing;
+    uint8_t ip_proto;
+    /* be used by filter-rewriter */
+    colo_conn_state state;
+    tcp_seq  primary_seq;
+    tcp_seq  secondary_seq;
+} Connection;
+
+uint32_t connection_key_hash(const void *opaque);
+int connection_key_equal(const void *opaque1, const void *opaque2);
+int parse_packet_early(Packet *pkt);
+void fill_connection_key(Packet *pkt, ConnectionKey *key);
+Connection *connection_new(ConnectionKey *key);
+void connection_destroy(void *opaque);
+Connection *connection_get(GHashTable *connection_track_table,
+                           ConnectionKey *key,
+                           uint32_t *hashtable_size);
+void connection_hashtable_reset(GHashTable *connection_track_table);
+Packet *packet_new(const void *data, int size);
+void packet_destroy(void *opaque, void *user_data);
+
+#endif /* QEMU_COLO_BASE_H */
diff --git a/net/colo-compare.c b/net/colo-compare.c
index 9768ed8..309d341 100644
--- a/net/colo-compare.c
+++ b/net/colo-compare.c
@@ -28,6 +28,7 @@
 #include "qemu/sockets.h"
 #include "qapi-visit.h"
 #include "trace.h"
+#include "net/colo-base.h"
 
 #define TYPE_COLO_COMPARE "colo-compare"
 #define COLO_COMPARE(obj) \
@@ -38,6 +39,28 @@
 static QTAILQ_HEAD(, CompareState) net_compares =
        QTAILQ_HEAD_INITIALIZER(net_compares);
 
+/*
+  + CompareState ++
+  |               |
+  +---------------+   +---------------+         +---------------+
+  |conn list      +--->conn           +--------->conn           |
+  +---------------+   +---------------+         +---------------+
+  |               |     |           |             |          |
+  +---------------+ +---v----+  +---v----+    +---v----+ +---v----+
+                    |primary |  |secondary    |primary | |secondary
+                    |packet  |  |packet  +    |packet  | |packet  +
+                    +--------+  +--------+    +--------+ +--------+
+                        |           |             |          |
+                    +---v----+  +---v----+    +---v----+ +---v----+
+                    |primary |  |secondary    |primary | |secondary
+                    |packet  |  |packet  +    |packet  | |packet  +
+                    +--------+  +--------+    +--------+ +--------+
+                        |           |             |          |
+                    +---v----+  +---v----+    +---v----+ +---v----+
+                    |primary |  |secondary    |primary | |secondary
+                    |packet  |  |packet  +    |packet  | |packet  +
+                    +--------+  +--------+    +--------+ +--------+
+*/
 typedef struct CompareState {
     Object parent;
 
@@ -50,12 +73,78 @@ typedef struct CompareState {
     QTAILQ_ENTRY(CompareState) next;
     SocketReadState pri_rs;
     SocketReadState sec_rs;
+
+    /* connection list: the connections belonged to this NIC could be found
+     * in this list.
+     * element type: Connection
+     */
+    GQueue conn_list;
+    QemuMutex conn_list_lock; /* to protect conn_list */
+    /* hashtable to save connection */
+    GHashTable *connection_track_table;
+    /* to save unprocessed_connections */
+    GQueue unprocessed_connections;
+    /* proxy current hash size */
+    uint32_t hashtable_size;
 } CompareState;
 
 typedef struct CompareClass {
     ObjectClass parent_class;
 } CompareClass;
 
+enum {
+    PRIMARY_IN = 0,
+    SECONDARY_IN,
+};
+
+static int compare_chr_send(CharDriverState *out,
+                            const uint8_t *buf,
+                            uint32_t size);
+
+/*
+ * Return 0 on success, if return -1 means the pkt
+ * is unsupported(arp and ipv6) and will be sent later
+ */
+static int packet_enqueue(CompareState *s, int mode)
+{
+    ConnectionKey key = {{ 0 } };
+    Packet *pkt = NULL;
+    Connection *conn;
+
+    if (mode == PRIMARY_IN) {
+        pkt = packet_new(s->pri_rs.buf, s->pri_rs.packet_len);
+    } else {
+        pkt = packet_new(s->sec_rs.buf, s->sec_rs.packet_len);
+    }
+
+    if (parse_packet_early(pkt)) {
+        packet_destroy(pkt, NULL);
+        pkt = NULL;
+        return -1;
+    }
+    fill_connection_key(pkt, &key);
+
+    conn = connection_get(s->connection_track_table,
+                          &key,
+                          &s->hashtable_size);
+    if (!conn->processing) {
+        qemu_mutex_lock(&s->conn_list_lock);
+        g_queue_push_tail(&s->conn_list, conn);
+        qemu_mutex_unlock(&s->conn_list_lock);
+        conn->processing = true;
+    }
+
+    qemu_mutex_lock(&conn->list_lock);
+    if (mode == PRIMARY_IN) {
+        g_queue_push_tail(&conn->primary_list, pkt);
+    } else {
+        g_queue_push_tail(&conn->secondary_list, pkt);
+    }
+    qemu_mutex_unlock(&conn->list_lock);
+
+    return 0;
+}
+
 static int compare_chr_send(CharDriverState *out,
                             const uint8_t *buf,
                             uint32_t size)
@@ -167,12 +256,21 @@ static void compare_set_outdev(Object *obj, const char *value, Error **errp)
 
 static void compare_pri_rs_finalize(SocketReadState *pri_rs)
 {
-    /* if packet_enqueue pri pkt failed we will send unsupported packet */
+    CompareState *s = container_of(pri_rs, CompareState, pri_rs);
+
+    if (packet_enqueue(s, PRIMARY_IN)) {
+        trace_colo_compare_main("primary: unsupported packet in");
+        compare_chr_send(s->chr_out, pri_rs->buf, pri_rs->packet_len);
+    }
 }
 
 static void compare_sec_rs_finalize(SocketReadState *sec_rs)
 {
-    /* if packet_enqueue sec pkt failed we will notify trace */
+    CompareState *s = container_of(sec_rs, CompareState, sec_rs);
+
+    if (packet_enqueue(s, SECONDARY_IN)) {
+        trace_colo_compare_main("secondary: unsupported packet in");
+    }
 }
 
 /*
@@ -229,6 +327,15 @@ static void colo_compare_complete(UserCreatable *uc, Error **errp)
     net_socket_rs_init(&s->pri_rs, compare_pri_rs_finalize);
     net_socket_rs_init(&s->sec_rs, compare_sec_rs_finalize);
 
+    g_queue_init(&s->conn_list);
+    qemu_mutex_init(&s->conn_list_lock);
+    s->hashtable_size = 0;
+
+    s->connection_track_table = g_hash_table_new_full(connection_key_hash,
+                                                      connection_key_equal,
+                                                      g_free,
+                                                      connection_destroy);
+
     return;
 }
 
@@ -271,6 +378,8 @@ static void colo_compare_finalize(Object *obj)
     if (!QTAILQ_EMPTY(&net_compares)) {
         QTAILQ_REMOVE(&net_compares, s, next);
     }
+    qemu_mutex_destroy(&s->conn_list_lock);
+    g_queue_free(&s->conn_list);
 
     g_free(s->pri_indev);
     g_free(s->sec_indev);
diff --git a/trace-events b/trace-events
index ca7211b..703de1a 100644
--- a/trace-events
+++ b/trace-events
@@ -1916,3 +1916,6 @@ aspeed_vic_update_fiq(int flags) "Raising FIQ: %d"
 aspeed_vic_update_irq(int flags) "Raising IRQ: %d"
 aspeed_vic_read(uint64_t offset, unsigned size, uint32_t value) "From 0x%" PRIx64 " of size %u: 0x%" PRIx32
 aspeed_vic_write(uint64_t offset, unsigned size, uint32_t data) "To 0x%" PRIx64 " of size %u: 0x%" PRIx32
+
+# net/colo-compare.c
+colo_compare_main(const char *chr) ": %s"
