Nat Mapping - Linksys SPA921 - Cisco - IP Phone Installation And Configuration Manual

Preparation
Network Setup Review
SPA9000 Voice System Installation and Configuration Guide for Setup Wizard

NAT Mapping

Network Address Translation (NAT) is a function that allows multiple devices to
share the same public, routable, IP address to establish connections over the
Internet. NAT is present in many broadband access devices to translate public and
private IP addresses. To enable VoIP to co-exist with NAT, some form of NAT
traversal is required.
Some ITSPs provide NAT traversal, but some do not. If your ITSP does not provide
NAT traversal, you have several options.
•
NAT mapping with SIP-ALG router: Use a router such as the WRV200, which
has a SIP ALG (Application Layer Gateway). With a SIP ALG in the router, you
have more choices in selecting an ITSP.
•
ITSP that supports NAT mapping through a Session Border Controller: With
NAT mapping provided by the ITSP, you have more choices in selecting a
router.
•
NAT mapping with the SPA9000 EXT IP setting: Configuring NAT mapping in
the SPA9000 is recommended only if the ITSP network does not provide a
Session Border Controller functionality. If this is the case, and if the external
(public) IP address is static, then Cisco recommends mapping a static
(permanent) IP address on the SPA9000. Instructions are available in the
SPA9000 Voice System Administration Guide
•
Configuring NAT Mapping with Simple Traversal of UDP through NAT (STUN):
Configuring NAT mapping in the SPA9000 is recommended only if the ITSP
network does not provide a Session Border Controller functionality. If this is the
case, and if the external (Public) IP address is assigned dynamically by the
network (and the router uses asymmetric NAT mechanism), it is possible to use
STUN as a mechanism to discover the NAT mapping in SPA9000. This method
is considered a practice of last resort and should be used only if the other
methods are unavailable. For more information, see the
Administration Guide
.
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SPA9000 Voice System
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