•
A computer running STUN server software is available on the network. You can also use a public STUN
server or set up your own STUN server.
Procedure
Step 1
In the phone web user interface, navigate to
Admin Login
>
advanced
>
Voice
>
SIP
.
Step 2
In the
NAT Support Parameters
section, set
Handle VIA received
,
Insert VIA received
,
Substitute VIA
Addr
,
Handle VIA rport
,
Insert VIA rport
, and
Send Resp To Src Port
fields to
Yes
.
Step 3
In the
NAT Support Parameters
section, set
STUN Enable
field to
Yes
.
Step 4
Enter the IP address for your STUN server in the
STUN Server
field.
Step 5
Click the
Ext(n)
tab.
Step 6
In the
NAT Settings
section, set
NAT Mapping Enable
to
Yes
.
Step 7
(Optional) Set
NAT Keep Alive Enable
to
Yes
.
The service provider might require the phone to send NAT keep alive messages to keep the NAT ports open.
Check with your service provider to determine the requirements.
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).
Cisco IP Phone 8800 Series Multiplatform Phones Administration Guide
62
SIP and NAT Configuration
Summary of Contents for 8851
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