Determining Whether The Router Uses Symmetric Or Asymmetric Nat - Linksys RTP300 - Broadband Router With 2 Phone Ports Administration Manual

Configuring Your System for ITSP Interoperability
4. Click Voice tab > Line N, where N is the number of the line interface.
5. Scroll down to the NAT Settings section.
• NAT Mapping Enable: Choose yes.
• NAT Keep Alive Enable: Choose yes (optional).
NOTE: Your ITSP may require the SPA device to send NAT keep alive messages to keep
the NAT ports open permanently. Check with your ITSP to determine the requirements.
6. Click Submit All Changes.
NOTE: You also need to configure the firewall settings on your router to allow SIP traffic. See
"Firewalls and SIP, " on page

Determining Whether the Router Uses Symmetric or Asymmetric NAT

STUN does not work on routers with symmetric NAT. With symmetric NAT, IP addresses are
mapped from one internal IP address and port to one external, routable destination IP address
and port. If another packet is sent from the same source IP address and port to a different
destination, then a different IP address and port number combination is used. This method is
restrictive because an external host can send a packet to a particular port on the internal host
only if the internal host first sent a packet from that port to the external host.
This procedure assumes that a syslog server is configured and is ready
Note
to receive syslog messages.
1. Make sure you do not have firewall running on your PC that could block the syslog port
(port 514 by default).
2. Connect to the administration web server, and choose Admin access with Advanced
settings.
Linksys ATA Administration Guide
Network Address Translation (NAT) and Voice over IP (VoIP)
Voice tab > SIP > NAT Support Parameters
Voice tab > Line N > NAT Settings
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