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>
diff --git a/test/test_nat44_ed.py b/test/test_nat44_ed.py
index f172dab..21eebb2 100644
--- a/test/test_nat44_ed.py
+++ b/test/test_nat44_ed.py
@@ -2609,8 +2609,8 @@
self.tcp_external_port)
# Wait at least the transitory time, the session is in established
- # state anyway. RST followed by a data packet should keep it
- # established.
+ # state anyway. RST followed by a data packet should move it to
+ # transitory state.
self.virtual_sleep(6)
p = (Ether(src=self.pg0.remote_mac, dst=self.pg0.local_mac) /
IP(src=self.pg0.remote_ip4, dst=self.pg1.remote_ip4) /
@@ -2624,15 +2624,6 @@
flags="P"))
self.send_and_expect(self.pg0, p, self.pg1)
- # State is established, session should be still open after 6 seconds
- self.virtual_sleep(6)
-
- p = (Ether(src=self.pg0.remote_mac, dst=self.pg0.local_mac) /
- IP(src=self.pg0.remote_ip4, dst=self.pg1.remote_ip4) /
- TCP(sport=self.tcp_port_in, dport=self.tcp_external_port,
- flags="R"))
- self.send_and_expect(self.pg0, p, self.pg1)
-
# State is transitory, session should be closed after 6 seconds
self.virtual_sleep(6)
@@ -3135,9 +3126,16 @@
# SYN out2in
p = (Ether(dst=self.pg1.local_mac, src=self.pg1.remote_mac) /
IP(src=self.pg1.remote_ip4, dst=self.nat_addr) /
- TCP(sport=self.tcp_external_port, dport=self.tcp_port_out))
+ TCP(sport=self.tcp_external_port, dport=self.tcp_port_out,
+ flags='SA'))
self.send_and_expect(self.pg1, p, self.pg0)
+ p = (Ether(dst=self.pg0.local_mac, src=self.pg0.remote_mac) /
+ IP(src=self.pg0.remote_ip4, dst=self.pg1.remote_ip4) /
+ TCP(sport=self.tcp_port_in, dport=self.tcp_external_port,
+ flags="A"))
+ self.send_and_expect(self.pg0, p, self.pg1)
+
# FIN in2out
p = (Ether(dst=self.pg0.local_mac, src=self.pg0.remote_mac) /
IP(src=self.pg0.remote_ip4, dst=self.pg1.remote_ip4) /
@@ -3152,17 +3150,8 @@
flags="F"))
self.send_and_expect(self.pg1, p, self.pg0)
- # SYN in2out
- p = (Ether(dst=self.pg0.local_mac, src=self.pg0.remote_mac) /
- IP(src=self.pg0.remote_ip4, dst=self.pg1.remote_ip4) /
- TCP(sport=self.tcp_port_in, dport=self.tcp_external_port))
- self.send_and_expect(self.pg0, p, self.pg1)
-
- # SYN out2in
- p = (Ether(dst=self.pg1.local_mac, src=self.pg1.remote_mac) /
- IP(src=self.pg1.remote_ip4, dst=self.nat_addr) /
- TCP(sport=self.tcp_external_port, dport=self.tcp_port_out))
- self.send_and_expect(self.pg1, p, self.pg0)
+ self.init_tcp_session(self.pg0, self.pg1, self.tcp_port_in,
+ self.tcp_external_port)
# 2 records should be produced - first one del & add
capture = self.pg3.get_capture(2)
@@ -3746,9 +3735,16 @@
p = (Ether(src=self.pg0.remote_mac, dst=self.pg0.local_mac) /
IP(src=self.pg0.remote_ip4, dst=self.pg1.remote_ip4) /
TCP(sport=in_port, dport=ext_port,
- flags="S", seq=101, ack=301))
+ flags="SA", seq=101, ack=301))
self.send_and_expect(self.pg0, p, self.pg1)
+ # send ACK packet out -> in
+ p = (Ether(src=self.pg1.remote_mac, dst=self.pg1.local_mac) /
+ IP(src=self.pg1.remote_ip4, dst=self.nat_addr) /
+ TCP(sport=ext_port, dport=out_port,
+ flags="A", seq=300, ack=101))
+ self.send_and_expect(self.pg1, p, self.pg0)
+
self.virtual_sleep(3)
# send ACK packet in -> out - should be forwarded and session alive
p = (Ether(src=self.pg0.remote_mac, dst=self.pg0.local_mac) /