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:
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.
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.
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.
Beginning
with PAN-OS 10.1.6, persistent NAT for DIPP is available on VM-Series
firewalls and single-dataplane firewalls. Beginning with PAN-OS 10.1.7,
it 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's 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.