Use of Wildcards instead of IP Addresses and Ports

When you configure a virtual server on the Citrix NetScaler, in some cases you can specify a wildcard for the IP address or port. The following situations may require this type of configuration:

  • When the NetScaler is configured as a transparent pass through.
  • If servers listen on ports that are not well known.
  • If servers change ports over time.
  • If you are reaching the limit for the number of IP addresses and ports that you can configure on a single NetScaler.
  • If you want to create virtual servers that listen for all traffic on a specific VLAN.

When the NetScaler receives traffic using a wildcard-based virtual server, it determines the actual IP address and port for the physical server and creates new records for the physical server. This is known as dynamically learned server information. A wildcard server can also use an asterisk as the port number. For example, a firewall load balancing configuration can use wildcards for both the IP address and port. If you bind a wildcard TCP server to this type of load balancing virtual server, the virtual server picks up all TCP traffic that does not match any other server or virtual server.

Order of Evaluation of Wildcards in Virtual Server Addresses and Ports.

The NetScaler attempts to locate virtual servers and servers by first attempting an exact match and if none is found, continuing to find a match based on wildcards, as follows:
1. Specific IP address and specific port number
2. Specific IP address and a * (wildcard) port
3. * (wildcard) IP address and a specific port
4. * (wildcard) IP address and a * (wildcard) port

If the NetScaler is unable to select a virtual server based on its IP address, it selects the virtual server based on the protocol used in a request, in the following order:
2. TCP
3. ANY

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