Working with SIP Signaling Groups and NAT

In this section:

Overview

In the WebUI Signaling Group options, when when the Outbound NAT Traversal field is set to Static NAT, the name of the Signaling/Media Source IP option changes to Signaling /Media Private IP. For details on these fields, refer to Creating and Modifying SIP Signaling Groups.

This article describes the SG Signaling/Media Source IP and NAT Traversal configuration.

When an INVITE is sent from the SBC to a SIP destination:

The call route specifies the egress SG.
If the SG Signaling/Media Source IP is set to Auto, the egress Ethernet is selected by the best match in the IP Routing Table.
If the SG Signaling/Media Source is set to a specific Ethernet/IP interface, the INVITE is forwarded out that specified port; however, the IP Route Table must have an IP Route to the destination network. Even when a specific port is selected, the IP Routing engine must still be able to route the packet towards the destination IP network.

The Signaling/Media IP Source configuration overrides the IP Routing Table for selecting a particular egress Ethernet interface. Regardless, the IP Route Table must contain the appropriate routing entries for the SBC to send the packet towards the destination IP network.

SG Signaling/Media Source IP Configuration

Signaling/Media Source IP Set to Auto

Below is a configuration example for Signaling/Media Source IP set to Auto.

In a call from the phone to SIP Server 10.3.1.253:

The call route specifies the Network 1 SG Destination Signaling Group.
The Network 1 SG Signaling Group specifies that calls be sent to the destination server configured in the Network 1 SIP Servers Table.
The Network 1 SIP Server Table specifies the SIP Server IP 10.3.1.253.
With the Network SG 1's Signaling/Media Source IP configured to Auto, the IP Route Table is consulted and the Ethernet 1 IP (Next Hop) is selected because 10.3.1.0/24 is the best matching route.
The INVITE is sent out Ethernet 1 to the SIP Server.

Calls with Signaling/Media set to a specific Ethernet/IP interface

Below is a configuration example for Signaling/Media set to Specific Ethernet/IP interface.

In a call from the phone to SIP Server 50.2.2.201:

The call route specifies the Network 2 SG Destination Signaling Group.
The Network 2 SG Signaling Group specifies that calls be sent to the destination server configured in the Network 2 SIP Servers Table.
The Network 2 SIP Server Table specifies the SIP Server IP 50.2.2.201.
With the Network SG 2's Signaling/Media Source IP configured to Ethernet 2 IP (50.2.2.1) , the INVITE confined to egress on Ethernet Port 2.
IP Routing Table is consulted to ensure there is an IP route to the 50.2.2.0/24 network.
The INVITE is sent out Ethernet 2 to the SIP Server.

In a call from the phone to SIP Server 50.3.3.153:

The call route specifies the Network 2 SG Destination Signaling Group.
The Network 2 SG Signaling Group specifies that calls be sent to the destination server configured in the Network 2 SIP Servers Table.
The Network 2 SIP Server Table specifies the SIP Server IP 50.3.3.153.
With the Network SG 2's Signaling/Media Source IP configured to Ethernet 2 IP (50.2.2.1) , the INVITE confined to egress on Ethernet Port 2.
IP Routing Table is consulted to ensure there is an IP route to the 50.3.3.0/24 network.
The INVITE is not sent as there is no IP Route to the 50.3.3.0/24 network.

Calls to a SIP Server Not On the Specified Signaling/Media Interface

Below is a configuration example for a SIP Server on a different interface than the one set in the SG Signaling/Media configuration.

In a call from the phone to SIP Server 10.3.1.253:

The call route specifies the Network 2 SG Destination Signaling Group.
The Network 2 SG Signaling Group specifies that calls be sent to the destination server configured in the Network 2 SIP Servers Table.
The Network 2 SIP Server Table specifies the SIP Server IP 10.3.1.253.
With the Network SG 2's Signaling/Media Source IP configured to Ethernet 2 IP (50.2.2.1) , the INVITE confined to egress on Ethernet Port 2.
IP Routing Table is consulted to ensure there is an IP route to the 10.3.1.0/24 network. The IP Route table specifies the 10.3.1.253 SIP Server is on Ethernet/IP port 1.
The INVITE is not transmitted because the Signaling/Media IP is configured for Ethernet 2 IP (50.2.2.1) while the destination SIP Server is on Ethernet/IP port 1.

Setting a NAT Public IP Address

Below is a configuration example for a NAT Public IP.