diff --git a/scapy/layers/ipsec.py b/scapy/layers/ipsec.py
index 69e7ae3b..b35da2b1 100644
--- a/scapy/layers/ipsec.py
+++ b/scapy/layers/ipsec.py
@@ -518,12 +518,16 @@ class AuthAlgo(object):
         else:
             return self.mac(key, self.digestmod(), default_backend())
 
-    def sign(self, pkt, key):
+    def sign(self, pkt, key, trailer=None):
         """
         Sign an IPsec (ESP or AH) packet with this algo.
 
         @param pkt:    a packet that contains a valid encrypted ESP or AH layer
         @param key:    the authentication key, a byte string
+        @param trailer: additional data appended to the packet for ICV
+                        calculation, but not trnasmitted with the packet.
+                        For example, the high order bits of the exteneded
+                        sequence number.
 
         @return: the signed packet
         """
@@ -534,16 +538,20 @@ class AuthAlgo(object):
 
         if pkt.haslayer(ESP):
             mac.update(raw(pkt[ESP]))
+            if trailer:
+                mac.update(trailer)
             pkt[ESP].data += mac.finalize()[:self.icv_size]
 
         elif pkt.haslayer(AH):
             clone = zero_mutable_fields(pkt.copy(), sending=True)
             mac.update(raw(clone))
+            if trailer:
+                mac.update(trailer)
             pkt[AH].icv = mac.finalize()[:self.icv_size]
 
         return pkt
 
-    def verify(self, pkt, key):
+    def verify(self, pkt, key, trailer):
         """
         Check that the integrity check value (icv) of a packet is valid.
 
@@ -574,6 +582,8 @@ class AuthAlgo(object):
             clone = zero_mutable_fields(pkt.copy(), sending=False)
 
         mac.update(raw(clone))
+        if trailer:
+            mac.update(trailer) # bytearray(4)) #raw(trailer))
         computed_icv = mac.finalize()[:self.icv_size]
 
         # XXX: Cannot use mac.verify because the ICV can be truncated
@@ -757,7 +767,8 @@ class SecurityAssociation(object):
     SUPPORTED_PROTOS = (IP, IPv6)
 
     def __init__(self, proto, spi, seq_num=1, crypt_algo=None, crypt_key=None,
-                 auth_algo=None, auth_key=None, tunnel_header=None, nat_t_header=None):
+                 auth_algo=None, auth_key=None, tunnel_header=None, nat_t_header=None,
+                 use_esn=False):
         """
         @param proto: the IPsec proto to use (ESP or AH)
         @param spi: the Security Parameters Index of this SA
@@ -771,6 +782,7 @@ class SecurityAssociation(object):
                               to encapsulate the encrypted packets.
         @param nat_t_header: an instance of a UDP header that will be used
                              for NAT-Traversal.
+        @param use_esn: Use Extended Sequence Numbers
         """
 
         if proto not in (ESP, AH, ESP.name, AH.name):
@@ -782,6 +794,7 @@ class SecurityAssociation(object):
 
         self.spi = spi
         self.seq_num = seq_num
+        self.use_esn = use_esn
 
         if crypt_algo:
             if crypt_algo not in CRYPT_ALGOS:
@@ -827,6 +840,17 @@ class SecurityAssociation(object):
             raise TypeError('packet spi=0x%x does not match the SA spi=0x%x' %
                             (pkt.spi, self.spi))
 
+    def build_seq_num(self, num):
+        # only lower order bits are  transmitted
+        # higher order bits are used in the ICV
+        lower = num & 0xffffffff
+        upper = num >> 32
+
+        if self.use_esn:
+            return lower, struct.pack(">I", upper)
+        else:
+            return lower, None
+
     def _encrypt_esp(self, pkt, seq_num=None, iv=None):
 
         if iv is None:
@@ -835,7 +859,8 @@ class SecurityAssociation(object):
             if len(iv) != self.crypt_algo.iv_size:
                 raise TypeError('iv length must be %s' % self.crypt_algo.iv_size)
 
-        esp = _ESPPlain(spi=self.spi, seq=seq_num or self.seq_num, iv=iv)
+        low_seq_num, high_seq_num = self.build_seq_num(seq_num or self.seq_num)
+        esp = _ESPPlain(spi=self.spi, seq=low_seq_num, iv=iv)
 
         if self.tunnel_header:
             tunnel = self.tunnel_header.copy()
@@ -857,7 +882,7 @@ class SecurityAssociation(object):
         esp = self.crypt_algo.pad(esp)
         esp = self.crypt_algo.encrypt(self, esp, self.crypt_key)
 
-        self.auth_algo.sign(esp, self.auth_key)
+        self.auth_algo.sign(esp, self.auth_key, high_seq_num)
 
         if self.nat_t_header:
             nat_t_header = self.nat_t_header.copy()
@@ -884,7 +909,8 @@ class SecurityAssociation(object):
 
     def _encrypt_ah(self, pkt, seq_num=None):
 
-        ah = AH(spi=self.spi, seq=seq_num or self.seq_num,
+        low_seq_num, high_seq_num = self.build_seq_num(seq_num or self.seq_num)
+        ah = AH(spi=self.spi, seq=low_seq_num,
                 icv = b"\x00" * self.auth_algo.icv_size)
 
         if self.tunnel_header:
@@ -924,7 +950,8 @@ class SecurityAssociation(object):
         else:
             ip_header.plen = len(ip_header.payload) + len(ah) + len(payload)
 
-        signed_pkt = self.auth_algo.sign(ip_header / ah / payload, self.auth_key)
+        signed_pkt = self.auth_algo.sign(ip_header / ah / payload,
+                                         self.auth_key, high_seq_num)
 
         # sequence number must always change, unless specified by the user
         if seq_num is None:
@@ -955,11 +982,12 @@ class SecurityAssociation(object):
 
     def _decrypt_esp(self, pkt, verify=True):
 
+        low_seq_num, high_seq_num = self.build_seq_num(self.seq_num)
         encrypted = pkt[ESP]
 
         if verify:
             self.check_spi(pkt)
-            self.auth_algo.verify(encrypted, self.auth_key)
+            self.auth_algo.verify(encrypted, self.auth_key, high_seq_num)
 
         esp = self.crypt_algo.decrypt(self, encrypted, self.crypt_key,
                                       self.crypt_algo.icv_size or
@@ -998,9 +1026,11 @@ class SecurityAssociation(object):
 
     def _decrypt_ah(self, pkt, verify=True):
 
+        low_seq_num, high_seq_num = self.build_seq_num(self.seq_num)
+
         if verify:
             self.check_spi(pkt)
-            self.auth_algo.verify(pkt, self.auth_key)
+            self.auth_algo.verify(pkt, self.auth_key, high_seq_num)
 
         ah = pkt[AH]
         payload = ah.payload