nat: tweak rfc7857 tcp connection tracking

The RFC7857 state machine introduced in 56c492a is a trade-off.
It tries to retain sessions as much as possible and also offers
some protection against spurious RST by re-establishing sessions if data
is received after the RST. From experience in the wild, this algorithm is
a little too liberal, as it leaves too many spurious established sessions
in the session table.

E.g. a oberserved pattern is:
client      server
         <- FIN, ACK
ACK      ->
ACK      ->
RST, ACK ->

With the current state machine this would leave the session in established state.

These proposed changes do:
 - require 3-way handshake to establish session.
   (current requires only to see SYNs from both sides)
 - RST will move session to transitory without recovery if data is sent after
 - Only a single FIN is needed to move to transitory

Fixes: 56c492aa0502751de2dd9d890096a82c5f04776d
Type: fix
Signed-off-by: Ole Troan <ot@cisco.com>
Change-Id: I92e593e00b2efe48d04997642d85bd59e0eaa2ea
Signed-off-by: Ole Troan <ot@cisco.com>

1 files changed, 3 insertions, 26 deletions

diff --git a/src/plugins/nat/nat44-ed/nat44_ed_format.c b/src/plugins/nat/nat44-ed/nat44_ed_format.c
index f643d1c6056..ee3e925e529 100644
--- a/src/plugins/nat/nat44-ed/nat44_ed_format.c
+++ b/src/plugins/nat/nat44-ed/nat44_ed_format.c
@@ -303,34 +303,11 @@ format_nat44_ed_tcp_state (u8 *s, va_list *args)
     case NAT44_ED_TCP_STATE_CLOSED:
       s = format (s, "closed");
       break;
-    case NAT44_ED_TCP_STATE_SYN_I2O:
-      s = format (s, "SYN seen in in2out direction");
-      break;
-    case NAT44_ED_TCP_STATE_SYN_O2I:
-      s = format (s, "SYN seen in out2in direction");
-      break;
     case NAT44_ED_TCP_STATE_ESTABLISHED:
-      s = format (s, "SYN seen in both directions/established");
-      break;
-    case NAT44_ED_TCP_STATE_FIN_I2O:
-      s = format (s, "FIN seen in in2out direction");
-      break;
-    case NAT44_ED_TCP_STATE_FIN_O2I:
-      s = format (s, "FIN seen in out2in direction");
-      break;
-    case NAT44_ED_TCP_STATE_RST_TRANS:
-      s = format (s, "RST seen/transitory timeout");
-      break;
-    case NAT44_ED_TCP_STATE_FIN_TRANS:
-      s = format (s, "FIN seen in both directions/transitory timeout");
-      break;
-    case NAT44_ED_TCP_STATE_FIN_REOPEN_SYN_O2I:
-      s = format (s, "FIN seen in both directions/transitory timeout/session "
-		     "reopening in out2in direction");
+      s = format (s, "established");
       break;
-    case NAT44_ED_TCP_STATE_FIN_REOPEN_SYN_I2O:
-      s = format (s, "FIN seen in both directions/transitory timeout/session "
-		     "reopening in in2out direction");
+    case NAT44_ED_TCP_STATE_CLOSING:
+      s = format (s, "closing");
       break;
     case NAT44_ED_TCP_N_STATE:
       s = format (s, "BUG! unexpected N_STATE! BUG!");