Source NAT is typically used by internal users to access
the Internet; the source address is translated and thereby kept
private. There are three types of source NAT:
Dynamic IP and Port (DIPP)—Allows multiple hosts
to have their source IP addresses translated to the same public
IP address with different port numbers. The dynamic translation
is to the next available address in the NAT address pool, which
you configure as a Translated Address pool be
to an IP address, range of addresses, a subnet, or a combination
of these.
As an alternative to using the next address in
the NAT address pool, DIPP allows you to specify the address of
the Interface itself. The advantage of specifying
the interface in the NAT rule is that the NAT rule will be automatically
updated to use any address subsequently acquired by the interface.
DIPP is sometimes referred to as interface-based NAT or network
address port translation (NAPT).
(Affects
only PA-7000 Series firewalls that do not use second-generation
PA-7050-SMC-B or PA-7080-SMC-B Switch Management Cards) When you
use Point-to-Point Tunnel Protocol (PPTP) with DIPP NAT, the firewall
is limited to using a translated IP address-and-port pair for only
one connection; the firewall does not support DIPP NAT. The workaround
is to upgrade the PA-7000 Series firewall to a second-generation
SMC-B card.
Dynamic IP—Allows the one-to-one, dynamic translation
of a source IP address only (no port number) to the next available
address in the NAT address pool. The size of the NAT pool should
be equal to the number of internal hosts that require address translations.
By default, if the source address pool is larger than the NAT address
pool and eventually all of the NAT addresses are allocated, new
connections that need address translation are dropped. To override
this default behavior, use Advanced (Dynamic IP/Port
Fallback) to enable use of DIPP addresses when necessary.
In either event, as sessions terminate and the addresses in the
pool become available, they can be allocated to translate new connections.
Static IP—Allows the 1-to-1, static translation of
a source IP address, but leaves the source port unchanged. A common
scenario for a static IP translation is an internal server that
must be available to the Internet.
Beginning with PAN-OS 10.2.4, persistent NAT for DIPP is available
on all firewalls. VoIP, video, cloud-based video conferencing, audio conferencing, and
other applications often use DIPP and may require the Session Traversal Utilities for
NAT (STUN) protocol. DIPP NAT uses symmetric NAT, which may have compatibility issues
with applications that use STUN. To alleviate these issues, persistent NAT for DIPP
provides additional support for connectivity with such applications.
When persistent NAT for DIPP is enabled, the binding of a private
source IP address/port pair to a specific public (translated) source IP address/port
pair persists for subsequent sessions that arrive having that same original source IP
address/port pair. The following example shows three sessions:
In this example, original source IP address/port 10.1.1.5:2966 is
bound to the translated source IP address/port 192.168.1.6:1077 in Session 1. That
binding is persistent in Session 2 and Session 3, which have the same original source IP
address/port, but different destination addresses. The persistence of the binding ends
after all of the sessions for that source IP address/port pair have ended.
In Session 1 of the example, the Destination port is 3478, the
default STUN port.
When persistent NAT for DIPP is enabled, it applies to all NAT and
NAT64 rules; it is a global setting. Management
plane or dataplane logs will indicate NAT DIPP/STUN support has been enabled.
The persistent NAT for DIPP setting (enabled or disabled) survives
across firewall reboots.