Monitor the free ports available on a NetScaler appliance for a new back-end connection

Last published : Sep 22, 2026
For communication with the physical servers or other peer devices, the NetScaler appliance uses a Citrix owned IP address as the source IP address. The NetScaler appliance maintains a pool of its IP addresses, and dynamically selects an IP address while connecting with a server. Depending on the subnet in which the physical server is placed, the appliance decides which IP address to use. This address pool is used for sending traffic and monitor probes.
You can display the total number of free ports available on the NetScaler owned IP addresses for a new back-end connection. This information helps you in deciding the need for more NetScaler owned IP addresses if the free ports available are nearing exhaustion.
You can provide the following information for the NetScaler appliance to calculate the total number of free ports available for a new back-end connection:
  • Citrix® owned IP address (optional)
  • Destination IP address
  • Destination port
  • TCP or non-TCP protocol
When you specify all the information except specifying a Citrix owned IP address:
  • The NetScaler appliance performs a route lookup for finding all the NetScaler owned IP addresses that can connect to the destination IP address. The appliance then finds and displays the total number of free ports available on these NetScaler owned IP addresses for the specified new back-end connection.
    Note:
    The NetScaler appliance does not perform ECMP lookup, or LLB lookup path, or PBR lookup path for finding the NetScaler owned IP addresses that can connect to the destination IP address.
When you specify all the information including specifying a Citrix owned IP address:
  • The NetScaler appliance displays the number of free ports available on the specified IP address for the specified new back-end connection.
Related information

Before you begin

Before you display the total number of free ports available for a new back-end connection, make note of the following points:
  • The NetScaler appliance does not perform ECMP lookup, or LLB lookup path, or PBR lookup path for finding the NetScaler owned IP addresses that can connect to the destination IP address.
  • The NetScaler appliance does not support displaying free ports available on a link local IP address.

Steps for displaying the number of free ports available on a NetScaler appliance for a new back-end connection

To display the total number of free ports available on a NetScaler appliance for a new back-end connection:
At the command prompt type:
  • show portallocation -destIP \&lt;ip_addr|ipv6_addr> -destPort \&lt;port> -protocol <1 for TCP, 0 for non-TCP protocol>
Example - total number of free ports available on a standalone NetScaler appliance:
> show portallocation -destip 198.51.100.30 -destport 80 -protocol 1

        Freeports available : 64505
 Done


> show portallocation -srcip 192.0.2.30 -destip 198.51.100.30 -destport 80 -protocol 1

        Freeports available for IPAddress 192.0.2.30 : 20505
 Done
Example - total number of free ports available on a Cluster setup:
The following example output displays the total number of free ports available on each node of a two node cluster setup.
> show portallocation -destip 198.51.100.30 -destport 80 -protocol 1

    Node Id: 1
    Freeports available : 32321

    Node Id: 0
    Freeports available : 32184

Done

Monitor the ports usage on a NetScaler appliance for back-end connections using SNMP

You can use the PORT-ALLOC-EXCEED SNMP alarm to monitor the ports usage on a NetScaler appliance for back-end connections.
PORT-ALLOC-EXCEED SNMP alarm includes the high-threshold and normal-threshold parameters, which specify the total allocated ports of the NetScaler owned IP addresses as percentages. For example, if the high-threshold parameter is set to 90, the NetScaler appliance generates and sends trap messages when the following event happens:
  • when the port allocation percentage exceeds 90 percent on any of the NetScaler owned IP address for the back-end connections
The SNMP alerts help you in deciding the need for more NetScaler® owned IP addresses if the free ports available are nearing exhaustion.
To Monitor the ports usage on a NetScaler appliance for back-end connections using SNMP
At the command prompt type:
  • set snmp alarm PORT-ALLOC-EXCEED -logging ( ENABLED | DISABLED ) -severity \&lt;severity> -state ( ENABLED | DISABLED ) -thresholdValue \&lt;positive_integer> -time \&lt;secs>
  • sh snmp alarm PORT-ALLOC-EXCEED
Example:
> set snmp alarm PORT-ALLOC-EXCEED -logging ENABLED  -severity Major -state ENABLED -thresholdValue 90 -time 1200
Done

> sh snmp alarm port-alloc-EXCEED

Alarm                   Alarm Threshold     Normal Threshold    Time    State       Severity        Logging
-----                   ---------------     ----------------    ----    --------    -------------   --------
1) PORT-ALLOC-EXCEED    80                  80                  7200    ENABLED     Major           ENABLED
Done
For more information on configuring SNMP alarms and SNMP trap listeners, see Configuring the NetScaler to generate SNMP traps.