Active-Passive NAT HA
=====================

Introduction
------------

One NAT node actively manages traffic while the other is synchronized
and ready to transition to the active state and takes over seamlessly
and enforces the same NAT sessions when failure occur. Both nodes share
the same configuration settings.

Configuration
-------------

NAT HA protocol
~~~~~~~~~~~~~~~

Session synchronization traffic is distributed through an IPv4 UDP
connection. The active node sends NAT HA protocol events to passive
node. To achieve reliable transfer NAT HA protocol uses acknowledgment
with re-transmission. This require the passive node to respond with an
acknowledgment message as it receives the data. The active node keeps a
record of each packet it sends and maintains a timer from when the
packet was sent. The active node re-transmits a packet if the timer
expires before receiving the acknowledgment.

Topology
~~~~~~~~

The two NAT nodes have a dedicated link (interface GE0/0/3 on both) to
synchronize NAT sessions using NAT HA protocol.

::

           +-----------------------+
           |    outside network    |
           +-----------------------+
            /                     \
           /                       \
          /                         \
         /                           \
        /                             \
   +---------+                   +---------+
   | GE0/0/1 | Active    Passive | GE0/0/1 |
   |         |                   |         |
   |  GE0/0/3|-------------------|GE0/0/3  |
   |         |   sync network    |         |
   | GE0/0/0 |                   | GE0/0/0 |
   +---------+                   +---------+
        \                             /
         \                           /
          \                         /
           \                       /
            \                     /
           +-----------------------+
           |    inside network     |
           +-----------------------+

Active node configuration
~~~~~~~~~~~~~~~~~~~~~~~~~

::

   set interface ip address GigabitEthernet0/0/1 10.15.7.101/24
   set interface ip address GigabitEthernet0/0/0 172.16.10.101/24
   set interface ip address GigabitEthernet0/0/3 10.0.0.1/24
   set interface state GigabitEthernet0/0/0 up
   set interface state GigabitEthernet0/0/1 up
   set interface state GigabitEthernet0/0/3 up
   set interface nat44 in GigabitEthernet0/0/0 out GigabitEthernet0/0/1
   nat44 add address 10.15.7.100
   nat ha listener 10.0.0.1:1234
   nat ha failover 10.0.0.2:2345

Passive node configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~

::

   set interface ip address GigabitEthernet0/0/1 10.15.7.102/24
   set interface ip address GigabitEthernet0/0/0 172.16.10.102/24
   set interface ip address GigabitEthernet0/0/3 10.0.0.2/24
   set interface state GigabitEthernet0/0/0 up
   set interface state GigabitEthernet0/0/1 up
   set interface state GigabitEthernet0/0/3 up
   set interface nat44 in GigabitEthernet0/0/0 out GigabitEthernet0/0/1
   nat44 add address 10.15.7.100
   nat ha listener 10.0.0.2:2345