Configuring SIP, SPCP, and NAT
Network Address Translation (NAT) and Cisco IP Phones
Cisco Small Business SPA300 Series, SPA500 Series, and WIP310 IP Phone Administration Guide 125
4
• Handle VIA received, Insert VIA received, Substitute VIA Addr: yes
• Handle VIA rport, Insert VIA rport, Send Resp To Src Port: yes
• EXT IP: Enter the public IP address for your router.
STEP 4 Click the Ext <number> tab. Configure the following:
• NAT Mapping Enable: Choose yes.
• NAT Keep Alive Enable: Choose yes (optional).
STEP 5 Click Submit All Changes.
NOTE You also need to configure the firewall settings on your router to allow
SIP traffic. See “Configuring SIP,” on page 101.
Configuring NAT Mapping with STUN
If the ITSP network does not provide a Session Border Controller functionality, and
if other requirements are met, it is possible to use STUN as a mechanism to
discover the NAT mapping. This option is considered a practice of last resort and
should be used only if the other methods are unavailable.
Requirements
• STUN is a viable option only if your router uses asymmetric NAT. See
“Determining Whether the Router Uses Symmetric or Asymmetric NAT,” on
page 126.
• You must have a computer running STUN server software. You can use a public
STUN server or set up your own STUN server.
NOTE Use NAT mapping only if the ITSP network does not provide a Session Border
Controller functionality.
STEP 1 Log in to the configuration utility.
STEP 2 Click Admin Login and advanced.
STEP 3 Click the SIP tab.
STEP 4 Under NAT Support Parameters, configure the following:
• Handle VIA received: yes
• Handle VIA rport: yes
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