Cisco 7821 Administration Guide

Step 8 Click Submit All Changes.
What to do next
Configure the firewall settings on your router to allow SIP traffic.
Determining 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, 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 to receive syslog messages.
To Determine Whether the Router Uses Symmetric or Asymmetric NAT:
Procedure
Step 1 Verify that the firewall is not running on your PC. (It can block the syslog port.) By default, the syslog port
is 514.
Step 2 Click Voice > System and navigate to Optional Network Configuration.
Step 3 Enter the IP address for the Syslog Server, if the port number is anything other than the default, 514. It is not
necessary to include the port number if it is the default.
The address and port number must be reachable from the Cisco IP phone. The port number appears on the
output log file name. The default output file is syslog.514.log (if port number was not specified).
Step 4 Set the Debug Level to Error, Notice, or Debug.
Step 5 To capture SIP signaling messages, click the Ext tab and navigate to SIP Settings. Set the SIP Debug Option
to Full.
Step 6 To collect information about what type of NAT your router uses click the SIP tab and navigate to NAT
Support Parameters.
Step 7 Click Voice > SIP and navigate to NAT Support Parameters.
Step 8 Set STUN Test Enable to Yes.
Step 9 Determine the type of NAT by viewing the debug messages in the log file. If the messages indicate that the
device is using symmetric NAT, you cannot use STUN.
Step 10 Click Submit All Changes.
Cisco IP Phone 7800 Series Multiplatform Phones Administration Guide
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Cisco IP Phone Installation
Determining Symmetric or Asymmetric NAT

Cisco 7821 Specifications

General

Brand	Cisco
Model	7821
Category	IP Phone
Language	English