About balancing server-to-NetCache traffic over interfaces

Implication of source IP address on server-to-appliance traffic

The source address of the outbound request determines which interface the origin server replies to and, therefore, is the IP address to which the server sends the requested object. If the NetCache appliance has multiple interfaces, you can configure their IP addresses as outbound IP addresses so that traffic can be shared across the interfaces. Because the outbound traffic is spread over multiple IP addresses, incoming packets in response to the request are directed to the appropriate interface based on the source IP address and, therefore, are balanced over the NetCache interfaces.

Option you can use for load balancing server-to appliance traffic

You can use the Load Balancing Interfaces option to specify all interfaces through which the NetCache appliance communicates when initiating outgoing connections. Each interface listed participates in the load balancing of outbound traffic by splitting traffic across outbound links. The end result is that the incoming traffic is split over NetCache interfaces.

Restrictions for using this option are as follows:

Do not list any interfaces in this option that you have listed in the Disabled Outgoing Interfaces option, which identifies interfaces that NetCache is not to use for outgoing traffic. See About restricting interfaces for connecting to servers for more information about the Disabled Outgoing Interfaces option.
You cannot use the Load Balancing Interfaces option if your NetCache appliance is part of a takeover pair.

The Load Balancing Interfaces option is on the Network - General page (Setup tab > Network > General).

Topology example

The advantage of configuring NetCache so that requests are sent out with different source interfaces is that responses from origin servers are distributed over multiple lines on their way to the NetCache appliance. In the following example, an ISP has multiple lines to the Internet and needs to balance the traffic load across those lines. Because transferring objects from the origin server generates the most traffic, the ISP needs to balance the traffic being sent to the NetCache appliance from the Internet.

In this example:

NetCache is configured to have one interface in the Load Balancing Interfaces option for each line to the Internet. In this case, three IP addresses are required.
NetCache sends requests to origin servers, cycling through the interfaces in the Load Balancing Interfaces list as source addresses.
The origin servers respond by sending the requested object to the IP address where the request originated.