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
62
Cisco IP Phone Installation
Determining Symmetric or Asymmetric NAT
