diff -uar bgpd/bgp_network.c bgpd/bgp_network.c
--- bgpd/bgp_network.c	Sat Oct 29 22:44:50 2005
+++ bgpd/bgp_network.c	Tue Feb 13 13:15:38 2007
@@ -38,6 +38,56 @@
 extern struct zebra_privs_t bgpd_privs;
 
 
+#if defined(HAVE_TCP_MD5) && defined(GNU_LINUX)
+/* Set MD5 key to the socket.  */
+int
+bgp_md5_set (int sock, struct peer *peer, char *password)
+{
+  int ret;
+  struct tcp_rfc2385_cmd cmd;
+  struct in_addr *addr = &peer->su.sin.sin_addr;
+
+  cmd.command = TCP_MD5_AUTH_ADD;
+  cmd.address = addr->s_addr;
+  cmd.keylen = strlen (password);
+  cmd.key = password;
+
+  if ( bgpd_privs.change (ZPRIVS_RAISE) )
+    zlog_err ("bgp_md5_set: could not raise privs");
+
+  ret = setsockopt (sock, IPPROTO_TCP, TCP_MD5_AUTH, &cmd, sizeof cmd);
+
+  if (bgpd_privs.change (ZPRIVS_LOWER) )
+    zlog_err ("bgp_md5_set: could not lower privs");
+
+  return ret;
+}
+
+/* Unset MD5 key from the socket.  */
+int
+bgp_md5_unset (int sock, struct peer *peer, char *password)
+{
+  int ret;
+  struct tcp_rfc2385_cmd cmd;
+  struct in_addr *addr = &peer->su.sin.sin_addr;
+
+  cmd.command = TCP_MD5_AUTH_DEL;
+  cmd.address = addr->s_addr;
+  cmd.keylen = strlen (password);
+  cmd.key = password;
+
+  if ( bgpd_privs.change (ZPRIVS_RAISE) )
+    zlog_err ("bgp_md5_unset: could not raise privs");
+
+  ret = setsockopt (sock, IPPROTO_TCP, TCP_MD5_AUTH, &cmd, sizeof cmd);
+
+  if (bgpd_privs.change (ZPRIVS_LOWER) )
+    zlog_err ("bgp_md5_unset: could not lower privs");
+
+  return ret;
+}
+#endif /* defined(HAVE_TCP_MD5) && defined(GNU_LINUX) */
+
 /* Accept bgp connection. */
 static int
 bgp_accept (struct thread *thread)
@@ -238,6 +288,12 @@
   sockopt_reuseaddr (peer->fd);
   sockopt_reuseport (peer->fd);
 
+#ifdef HAVE_TCP_MD5
+  if (CHECK_FLAG (peer->flags, PEER_FLAG_PASSWORD))
+    if (sockunion_family (&peer->su) == AF_INET)
+      bgp_md5_set (peer->fd, peer, peer->password);
+#endif /* HAVE_TCP_MD5 */
+
   /* Bind socket. */
   bgp_bind (peer);
 
@@ -346,6 +402,10 @@
 	  continue;
 	}
 
+#ifdef HAVE_TCP_MD5
+      bm->sock = sock;
+#endif /* HAVE_TCP_MD5 */
+
       thread_add_read (master, bgp_accept, bgp, sock);
     }
   while ((ainfo = ainfo->ai_next) != NULL);
@@ -406,6 +466,9 @@
       close (sock);
       return ret;
     }
+#ifdef HAVE_TCP_MD5
+  bm->sock = sock;
+#endif /* HAVE_TCP_MD5 */
 
   thread_add_read (bm->master, bgp_accept, bgp, sock);
 
diff -uar bgpd/bgp_network.h bgpd/bgp_network.h
--- bgpd/bgp_network.h	Tue Jun 28 15:38:12 2005
+++ bgpd/bgp_network.h	Tue Feb 13 13:16:23 2007
@@ -21,6 +21,28 @@
 #ifndef _QUAGGA_BGP_NETWORK_H
 #define _QUAGGA_BGP_NETWORK_H
 
+#if defined(HAVE_TCP_MD5) && defined(GNU_LINUX)
+/* setsockopt Number */
+#define TCP_MD5_AUTH 13
+
+/* Commands (used in the structure passed from userland) */
+#define TCP_MD5_AUTH_ADD 1
+#define TCP_MD5_AUTH_DEL 2
+
+struct tcp_rfc2385_cmd {
+  u_int8_t     command;    /* Command - Add/Delete */
+  u_int32_t    address;    /* IPV4 address associated */
+  u_int8_t     keylen;     /* MD5 Key len (do NOT assume 0 terminated ascii) */
+  void         *key;       /* MD5 Key */
+};
+#endif /* defined(HAVE_TCP_MD5) && defined(GNU_LINUX) */
+
+#ifdef HAVE_TCP_MD5
+int bgp_md5_set (int sock, struct peer *, char *);
+int bgp_md5_unset (int sock, struct peer *, char *);
+#endif /* HAVE_TCP_MD5 */
+
+
 extern int bgp_socket (struct bgp *, unsigned short);
 extern int bgp_connect (struct peer *);
 extern void bgp_getsockname (struct peer *);
diff -uar bgpd/bgp_vty.c bgpd/bgp_vty.c
--- bgpd/bgp_vty.c	Thu Sep 14 02:57:05 2006
+++ bgpd/bgp_vty.c	Tue Feb 13 13:15:38 2007
@@ -1479,6 +1479,46 @@
        "AS number used as local AS\n"
        "Do not prepend local-as to updates from ebgp peers\n")
 
+#ifdef HAVE_TCP_MD5
+DEFUN (neighbor_password,
+       neighbor_password_cmd,
+       NEIGHBOR_CMD2 "password LINE",
+       NEIGHBOR_STR
+       NEIGHBOR_ADDR_STR2
+       "Set a password\n"
+       "The password\n")
+{
+  struct peer *peer;
+  int ret;
+
+  peer = peer_and_group_lookup_vty (vty, argv[0]);
+  if (! peer)
+    return CMD_WARNING;
+
+  ret = peer_password_set (peer, argv[1]);
+  return bgp_vty_return (vty, ret);
+}
+
+DEFUN (no_neighbor_password,
+       no_neighbor_password_cmd,
+       NO_NEIGHBOR_CMD2 "password",
+       NO_STR
+       NEIGHBOR_STR
+       NEIGHBOR_ADDR_STR2
+       "Set a password\n")
+{
+  struct peer *peer;
+  int ret;
+
+  peer = peer_and_group_lookup_vty (vty, argv[0]);
+  if (! peer)
+    return CMD_WARNING;
+
+  ret = peer_password_unset (peer);
+  return bgp_vty_return (vty, ret);
+}
+#endif /* HAVE_TCP_MD5 */
+
 DEFUN (neighbor_activate,
        neighbor_activate_cmd,
        NEIGHBOR_CMD2 "activate",
@@ -8883,6 +8923,12 @@
   install_element (BGP_NODE, &no_neighbor_local_as_cmd);
   install_element (BGP_NODE, &no_neighbor_local_as_val_cmd);
   install_element (BGP_NODE, &no_neighbor_local_as_val2_cmd);
+
+#ifdef HAVE_TCP_MD5
+  /* "neighbor password" commands. */
+  install_element (BGP_NODE, &neighbor_password_cmd);
+  install_element (BGP_NODE, &no_neighbor_password_cmd);
+#endif /* HAVE_TCP_MD5 */
 
   /* "neighbor activate" commands. */
   install_element (BGP_NODE, &neighbor_activate_cmd);
diff -uar bgpd/bgpd.c bgpd/bgpd.c
--- bgpd/bgpd.c	Fri Dec  8 00:24:44 2006
+++ bgpd/bgpd.c	Tue Feb 13 13:55:11 2007
@@ -788,6 +788,7 @@
   peer->status = Idle;
   peer->ostatus = Idle;
   peer->weight = 0;
+  peer->password = NULL;
   peer->bgp = bgp;
   peer = peer_lock (peer); /* initial reference */
 
@@ -1202,6 +1203,18 @@
   peer->last_reset = PEER_DOWN_NEIGHBOR_DELETE;
   bgp_stop (peer);
   bgp_fsm_change_status (peer, Deleted);
+
+#ifdef HAVE_TCP_MD5
+  /* Password configuration */
+  if (peer->password)
+    {
+      if (! CHECK_FLAG (peer->sflags, PEER_STATUS_GROUP)
+          && sockunion_family (&peer->su) == AF_INET)
+      bgp_md5_unset (bm->sock, peer, peer->password);
+      free (peer->password);
+    }
+#endif /* HAVE_TCP_MD5 */
+
   bgp_timer_set (peer); /* stops all timers for Deleted */
   
   /* Delete from all peer list. */
@@ -1417,6 +1430,26 @@
   else
     peer->v_routeadv = BGP_DEFAULT_EBGP_ROUTEADV;
 
+#ifdef HAVE_TCP_MD5
+  /* password apply */
+  if (CHECK_FLAG (conf->flags, PEER_FLAG_PASSWORD))
+    {
+      if (peer->password)
+	free (peer->password);
+      peer->password = strdup (conf->password);
+
+      if (sockunion_family (&peer->su) == AF_INET)
+	bgp_md5_set (bm->sock, peer, peer->password);
+    }
+  else if (peer->password)
+    {
+      if (sockunion_family (&peer->su) == AF_INET)
+        bgp_md5_unset (bm->sock, peer, peer->password);
+      free (peer->password);
+      peer->password = NULL;
+    }
+#endif /* HAVE_TCP_MD5 */
+
   /* maximum-prefix */
   peer->pmax[afi][safi] = conf->pmax[afi][safi];
   peer->pmax_threshold[afi][safi] = conf->pmax_threshold[afi][safi];
@@ -3379,6 +3412,119 @@
   return 0;
 }
 
+#ifdef HAVE_TCP_MD5
+/* Set password for authenticating with the peer. */
+int
+peer_password_set (struct peer *peer, const char *password)
+{
+  struct peer_group *group;
+  struct listnode *nn, *nn2;
+
+  if (peer->password && strcmp (peer->password, password) == 0
+      && ! CHECK_FLAG (peer->sflags, PEER_STATUS_GROUP))
+	return 0;
+
+  SET_FLAG (peer->flags, PEER_FLAG_PASSWORD);
+  if (peer->password)
+    free (peer->password);
+  peer->password = strdup (password);
+
+  if (! CHECK_FLAG (peer->sflags, PEER_STATUS_GROUP))
+    {
+      if (peer->status == Established)
+          bgp_notify_send (peer, BGP_NOTIFY_CEASE, BGP_NOTIFY_CEASE_CONFIG_CHANGE);
+      else
+        BGP_EVENT_ADD (peer, BGP_Stop);
+
+      if (sockunion_family (&peer->su) == AF_INET)
+	bgp_md5_set (bm->sock, peer, peer->password);
+      return 0;
+    }
+
+  group = peer->group;
+  for (ALL_LIST_ELEMENTS(group->peer, nn, nn2, peer))
+    {
+      if (peer->password && strcmp (peer->password, password) == 0)
+	continue;
+
+      SET_FLAG (peer->flags, PEER_FLAG_PASSWORD);
+      if (peer->password)
+        free (peer->password);
+      peer->password = strdup (password);
+
+      if (peer->status == Established)
+        bgp_notify_send (peer, BGP_NOTIFY_CEASE, BGP_NOTIFY_CEASE_CONFIG_CHANGE);
+      else
+        BGP_EVENT_ADD (peer, BGP_Stop);
+
+      if (sockunion_family (&peer->su) == AF_INET)
+	bgp_md5_set (bm->sock, peer, peer->password);
+    }
+
+  return 0;
+}
+
+int
+peer_password_unset (struct peer *peer)
+{
+  struct peer_group *group;
+  struct listnode *nn, *nn2;
+
+  if (! CHECK_FLAG (peer->flags, PEER_FLAG_PASSWORD)
+      && ! CHECK_FLAG (peer->sflags, PEER_STATUS_GROUP))
+    return 0;
+
+  if (! CHECK_FLAG (peer->sflags, PEER_STATUS_GROUP))
+    {
+      if (peer_group_active (peer)
+	  && CHECK_FLAG (peer->group->conf->flags, PEER_FLAG_PASSWORD))
+	return BGP_ERR_PEER_GROUP_HAS_THE_FLAG;
+
+      if (peer->status == Established)
+        bgp_notify_send (peer, BGP_NOTIFY_CEASE, BGP_NOTIFY_CEASE_CONFIG_CHANGE);
+      else
+        BGP_EVENT_ADD (peer, BGP_Stop);
+
+      if (sockunion_family (&peer->su) == AF_INET)
+	bgp_md5_unset (bm->sock, peer, peer->password);
+
+      UNSET_FLAG (peer->flags, PEER_FLAG_PASSWORD);
+      if (peer->password)
+	free (peer->password);
+      peer->password = NULL;
+
+      return 0;
+    }
+
+  UNSET_FLAG (peer->flags, PEER_FLAG_PASSWORD);
+  if (peer->password)
+    free (peer->password);
+  peer->password = NULL;
+
+  group = peer->group;
+  for (ALL_LIST_ELEMENTS(group->peer, nn, nn2, peer))
+    {
+      if (! CHECK_FLAG (peer->flags, PEER_FLAG_PASSWORD))
+	continue;
+
+      if (peer->status == Established)
+        bgp_notify_send (peer, BGP_NOTIFY_CEASE, BGP_NOTIFY_CEASE_CONFIG_CHANGE);
+      else
+        BGP_EVENT_ADD (peer, BGP_Stop);
+
+      if (sockunion_family (&peer->su) == AF_INET)
+	bgp_md5_unset (bm->sock, peer, peer->password);
+
+      UNSET_FLAG (peer->flags, PEER_FLAG_PASSWORD);
+      if (peer->password)
+        free (peer->password);
+      peer->password = NULL;
+    }
+
+  return 0;
+}
+#endif /* HAVE_TCP_MD5 */
+
 /* Set distribute list to the peer. */
 int
 peer_distribute_set (struct peer *peer, afi_t afi, safi_t safi, int direct, 
@@ -4416,6 +4562,16 @@
 	    ! CHECK_FLAG (g_peer->flags, PEER_FLAG_SHUTDOWN))
 	  vty_out (vty, " neighbor %s shutdown%s", addr, VTY_NEWLINE);
 
+#ifdef HAVE_TCP_MD5
+      /* Password. */
+      if (CHECK_FLAG (peer->flags, PEER_FLAG_PASSWORD))
+	if (! peer_group_active (peer)
+	    || ! CHECK_FLAG (g_peer->flags, PEER_FLAG_PASSWORD)
+	    || strcmp (peer->password, g_peer->password) != 0)
+	  vty_out (vty, " neighbor %s password %s%s", addr, peer->password,
+		   VTY_NEWLINE);
+#endif /* HAVE_TCP_MD5 */
+
       /* BGP port. */
       if (peer->port != BGP_PORT_DEFAULT)
 	vty_out (vty, " neighbor %s port %d%s", addr, peer->port, 
@@ -4943,6 +5099,9 @@
   bm->port = BGP_PORT_DEFAULT;
   bm->master = thread_master_create ();
   bm->start_time = time (NULL);
+#ifdef HAVE_TCP_MD5
+  bm->sock = -1;
+#endif /* HAVE_TCP_MD5 */
 }
 
 
diff -uar bgpd/bgpd.h bgpd/bgpd.h
--- bgpd/bgpd.h	Thu Sep 14 02:57:05 2006
+++ bgpd/bgpd.h	Tue Feb 13 13:24:36 2007
@@ -52,6 +52,11 @@
 #define BGP_OPT_NO_FIB                   (1 << 0)
 #define BGP_OPT_MULTIPLE_INSTANCE        (1 << 1)
 #define BGP_OPT_CONFIG_CISCO             (1 << 2)
+
+#ifdef HAVE_TCP_MD5
+  /* bgp receive socket */
+  int sock;
+#endif /* HAVE_TCP_MD5 */
 };
 
 /* BGP instance structure.  */
@@ -346,6 +351,8 @@
 #define PEER_FLAG_DYNAMIC_CAPABILITY        (1 << 5) /* dynamic capability */
 #define PEER_FLAG_DISABLE_CONNECTED_CHECK   (1 << 6) /* disable-connected-check */
 #define PEER_FLAG_LOCAL_AS_NO_PREPEND       (1 << 7) /* local-as no-prepend */
+#define PEER_FLAG_PASSWORD                  (1 << 8) /* password */
+
 
   /* NSF mode (graceful restart) */
   u_char nsf[AFI_MAX][SAFI_MAX];
@@ -370,6 +377,9 @@
 #define PEER_FLAG_MAX_PREFIX_WARNING        (1 << 15) /* maximum prefix warning-only */
 #define PEER_FLAG_NEXTHOP_LOCAL_UNCHANGED   (1 << 16) /* leave link-local nexthop unchanged */ 
 
+  /* MD5 password */
+  char *password;
+
   /* default-originate route-map.  */
   struct
   {
@@ -916,6 +926,11 @@
 
 extern int peer_maximum_prefix_set (struct peer *, afi_t, safi_t, u_int32_t, u_char, int, u_int16_t);
 extern int peer_maximum_prefix_unset (struct peer *, afi_t, safi_t);
+
+#ifdef HAVE_TCP_MD5
+int peer_password_set (struct peer *, const char *);
+int peer_password_unset (struct peer *);
+#endif /* HAVE_TCP_MD5 */
 
 extern int peer_clear (struct peer *);
 extern int peer_clear_soft (struct peer *, afi_t, safi_t, enum bgp_clear_type);
diff -uar configure.ac configure.ac
--- configure.ac	Fri Dec  8 20:31:44 2006
+++ configure.ac	Tue Feb 13 13:15:38 2007
@@ -233,6 +233,8 @@
 [  --enable-isis-topology        enable IS-IS topology generator])
 AC_ARG_ENABLE(capabilities,
 [  --disable-capabilities        disable using POSIX capabilities])
+AC_ARG_ENABLE(tcp-md5,
+[  --enable-tcp-md5  enable TCP MD5 Signature Option (RFC2385)])
 AC_ARG_ENABLE(gcc_ultra_verbose,
 [  --enable-gcc-ultra-verbose    enable ultra verbose GCC warnings])
 AC_ARG_ENABLE(gcc-rdynamic,
@@ -281,6 +283,11 @@
   AC_DEFINE(HAVE_OPAQUE_LSA,,OSPF Opaque LSA)
   AC_DEFINE(HAVE_OSPF_TE,,OSPF TE)
 fi
+
+if test "${enable_tcp_md5}" = "yes"; then
+  AC_DEFINE(HAVE_TCP_MD5,,Linux TCP MD5 Signature Option)
+fi
+
 
 AC_MSG_CHECKING(if zebra should be configurable to send Route Advertisements)
 if test "${enable_rtadv}" != "no"; then