SIP NAT configuration example: destination address translation (destination NAT)

This configuration example shows how to configure the FortiGate to support the destination address translation scenario shown in the figure below. The FortiGate requires two SIP security policies:

l A destination NAT security policy that allows SIP messages to be sent from the Internet to the private network. This policy must include destination NAT because the addresses on the private network are not routable on the Internet. l A source NAT security policy that allows SIP messages to be sent from the private network to the Internet.

SIP destination NAT scenario part two: 200 OK returned to Phone B and media streams established

FortiGate HA cluster in NAT mode

General configuration steps

The following general configuration steps are required for this destination NAT SIP configuration. This example uses the default VoIP profile.

1. Add the SIP proxy server firewall virtual IP.
2. Add a firewall address for the SIP proxy server on the private network.
3. Add a destination NAT security policy that accepts SIP sessions from the Internet destined for the SIP proxy server virtual IP and translates the destination address to the IP address of the SIP proxy server on the private network.
4. Add a security policy that accepts SIP sessions initiated by the SIP proxy server and destined for the Internet.

Configuration steps – GUI

To add the SIP proxy server firewall virtual IP

1. Go to Policy & Objects > Virtual IPs.
2. Add the following SIP proxy server virtual IP.

VIP Type

IPv4

destination address translation (destination NAT)

Name	SIP_Proxy_VIP
Interface	port1
Type	Static NAT
External IP Address/Range	172.20.120.50
Mapped IP Address/Range	10.31.101.50

To add a firewall address for the SIP proxy server

1. Go to Policy & Objects > Addresses.
2. Add the following for the SIP proxy server:

Address Name	SIP_Proxy_Server
Type	Subnet
Subnet/IP Range	10.31.101.50/255.255.255.255
Interface	port2

To add the security policies

1. Go to Policy & Objects > IPv4 Policy.
2. Add a destination NAT security policy that includes the SIP proxy server virtual IP that allows Phone B (and other SIP phones on the Internet) to send SIP request messages to the SIP proxy server.

Incoming Interface		port1
Outgoing Interface		port2
Source		all
Destination Address		SIP_Proxy_VIP
Schedule		always
Service		SIP
Action		ACCEPT

3. Turn on NAT and select Use Outgoing Interface Address.
4. Turn on VoIP and select the default VoIP profile.
5. Select OK.
6. Add a source NAT security policy to allow the SIP proxy server to send SIP request messages to Phone B and the

Internet:

Incoming Interface

port2

SIP NAT configuration example: destination address translation (destination

Destination Address		all
Source		SIP_Proxy_Server
Schedule		always
Service		SIP
Action		ACCEPT

7. Turn on NAT and select Use OutgingInterface Address.
8. Turn on VoIP and select the default VoIP profile.
9. Select OK.

Configuration steps – CLI

To add the SIP proxy server firewall virtual IP and firewall address

1. Enter the following command to add the SIP proxy server firewall virtual IP. config firewall vip edit SIP_Proxy_VIP set type static-nat set extip 172.20.120.50 set mappedip 10.31.101.50 set extintf port1

end

2. Enter the following command to add the SIP proxy server firewall address. config firewall address edit SIP_Proxy_Server set associated interface port2 set type ipmask

set subnet 10.31.101.50 255.255.255.255

end

To add security policies

1. Enter the following command to add a destination NAT security policy that includes the SIP proxy server virtual IP that allows Phone B (and other SIP phones on the Internet) to send SIP request messages to the SIP proxy server.

config firewall policy edit 0 set srcintf port1 set dstintf port2 set srcaddr all set dstaddr SIP_Proxy_VIP set action accept set schedule always set service SIP set nat enable set utm-status enable set voip-profile default end

 

and RTP source NAT

2. Enter the following command to add a source NAT security policy to allow the SIP proxy server to send SIP request messages to Phone B and the Internet:

config firewall policy edit 0 set srcintf port2 set dstintf port1 set srcaddr SIP_Proxy_Server

set dstaddr all set action accept set schedule always set service SIP set nat enable set utm-status enable set voip-profile default end

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