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Match Rules

When a match rule is configured you can specify that persistence methods for that match rule -- which supercede

those the persistence method specified for a cluster. This is the persistence type to be used when the match rules

conditions are met. For example, if you configured a match rule expression to redirect requests to Server A based

on the criteria configured in an expression, you can also configure the persistence type to be used when that

criteria is met.

To configure persistence with match rules select a configured match rule on the left navigational pane of the GUI.

Select the Persistence tab to display the configuration screen. It is configured the same as the configuration of

HTTP and HTTPS cluster persistence.

Changing the Spoof (SNAT) Setting Using Match Rules

By default, Equalizer uses the client IP address as the source address in the packets it forwards to server pools,

and then translates the server IP in server responses to Equalizer’s cluster IP. This is commonly called a

Half-

NAT

configuration, since Equalizer is

not

performing Network Address translation (or NAT) on client requests.

Because the server pools behind Equalizer see the source IP of the client, the server pools need to be configured

to route client requests back through Equalizer -- either by making Equalizer the default. This behavior is controlled

by the Spoof option, which is enabled by default. Half-NAT configurations are only a problem when a client is on

the same subnet as the servers behind Equalizer, since the servers will try to respond directly back to the client --

which will not recognize the server connection as a response to it’s original request and so refuse the connection.

This "local client" problem is solved by

disabling

the Spoof option. When Spoof is disabled, Equalizer translates

the source IP address in the request to one of Equalizer’s IP addresses before sending it on to the server. This is

called

Source Network Address Translation

, or

SNAT

-- and this configuration is often called

Full-NAT

, since

Equalizer is translating the client IP in packets from clients, as well as the server IP in packets from servers. In

this case, servers will send responses to Equalizer’s IP address, so no special routing or gateway is needed on the

server.

So, clusters with clients on a different subnet than the server pools behind it can have the spoof option enabled,

while clusters with only local clients should have spoof disabled.

But what do you do if you expect client requests to come to the cluster from the local server subnet as well as

other subnets?

In network configurations where Equalizer needs to be able to forward server responses to clients on the server

subnet as well as other subnets for the same virtual cluster IP, the Spoof option can be selectively enabled or

disabled by creating a Layer 7 match rule that looks for specific client IP addresses in incoming requests. When an

incoming request’s source IP matches the rule, Spoof will be set as appropriate for that connection. This is

commonly called

Selective SNAT

On Equalizer, implementing Selective SNAT using a Match Rule is the recommended method to allow local

access to Layer 7 clusters with Spoof enabled; other alternatives include:

l adding static routes on all your server pools to clients on the server’s local subnet

l creating two clusters -- one on the non-server subnet with spoof enabled, and one on the server subnet with

spoof disabled

Selective SNAT using a match rule is more easily implemented and maintained than either of the above methods,

but can be configured only for Layer 7 clusters. If you require Selective SNAT with a Layer 4 cluster, you’ll need to

use one of the above methods.

Selective SNAT Example

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