1. Concepts
  2. Deployment Scenarios
  3. Network Address Translation Options

Network Address Translation Options

In the most common case, a load balancer is configured using destination NAT to provide a public IP address that clients use for communicating with one or more internal (private) Converged Application Server addresses. Load balancers may also be configured using source NAT, which modifies the Layer 3 address information originating from a private address to match the virtual IP address of the load balancer itself.

With the default route resolver behavior, a Converged Application Server engine originates UDP packets having a source IP address that matches the address of a local NIC (the private address). This can be problematic for applications that try to respond directly to the Layer 3 address embedded in the transport packet, because the local server address may not be publicly accessible. If your applications exhibit this problem, Oracle recommends that you configure the load balancer to perform source NAT to change the transport Layer 3 address to a publicly-accessible virtual IP address.

IP Masquerading Alternative to Source NAT

If you choose not to enable source NAT on your load balancer, Converged Application Server provides limited IP masquerading functionality. To use this functionality, configure a logical address on each engine tier server using the public IP address of the load balancer for the cluster. (Duplicate the same logical IP address on each engine tier server machine). When a local server interface matches the IP address of a configured load balancer (defined in the public address of a network channel), Converged Application Server uses that interface to originate SIP UDP messages, and the Layer 3 address contains a public address.

Caution:

Using the Converged Application Server IP masquerading functionality can lead to network instability, because it requires duplicate IP addresses on multiple servers. Production deployments must use a load balancer configured for source NAT, rather than IP masquerading, to ensure reliable network performance.

You can disable IP masquerading functionality by using the startup option:

-Dwlss.udp.lb.masquerade=false

See the Converged Application Server Administrator's Guide for more information on startup options.