Starting from NetScaler 8.1, the concept of multi port tables was introduced and there are 16 tables by default allocated to each SNIP. Each SNIP will have 65k x 16 ports free for connections to the back end servers, which is equal to 1032192 free ports.

However it is important to note that:

• All these ports (1032192) might only be used when connections go to different destination addresses.

• This means, even if there are free ports available, they might not be used by the SNIP if the destination addresses of the backend servers are not unique.

For example:

• If there is 1 SNIP and only 1 Service, then the limit is 65k ports.

• If there is 1 SNIP and 5 unique services with different destination IP addresses then the possible limit is 65k x 5.
   

We can run the following commands to check the number of free ports available.
root@NS# nsapimgr -d freeports
Displaying all free ports of all MIPs...
Index IP              FreePorts
    0 0.0.0.1         16513536
    1 127.0.0.2       1031683
    2 241.0.0.2       1032096
    3 241.0.0.4       1032096
    4 241.0.0.5       16513536
    5 10.107.182.67   1032095
    6 10.107.182.76   1032080
 
root@NS# nsapimgr -d mappedip
Displaying all mapped IP info entries ...
Index   Devno UsedPorts FreePorts  Type IP
    0     651 4279485952  16513536 402   0.0.0.1
    1     653       510   1031682 LOOP  127.0.0.2
    2     657        96   1032096 NSIP  241.0.0.2
    3     661        96   1032096 LOOP  241.0.0.4
    4     659 4279485952  16513536 402   241.0.0.5
    5     649        97   1032095 NSIP  10.107.182.67
    6    9677       112   1032080 404   10.107.182.76
total       7         4264005519  38187121

To know number of free ports available for a specific MIP/SNIP we can run the below command.
> sh ns ip 10.107.182.76
 
        IP: 10.107.182.76
        Netmask: 255.255.255.224
        Type: SNIP
        Traffic Domain: 0
        state: Enabled
        arp: Enabled
        arpResponse: NONE
        icmp: Enabled
        icmpResponse: NONE
        vserver: NA
        management access: Disabled
          telnet: Enabled
          ftp: Enabled
          ssh: Enabled
          gui: Enabled
          snmp: Enabled
        Restrict access: Disabled
        dynamic routing: Disabled
        hostroute: Disabled
        # free ports: 1032080
        networkroute: Disabled
        ownerNode: ALL NODES
 

Port allocation error or running out of MIPs

We can run the below command to see if the port allocation counter is a non-zero value or not.
root@NS# nsconmsg -K /var/nslog/newnslog -d stats -g ip_err_portalloc_failed -g  tcp_err_ip_portalloc_failed
Displaying current counter value information
NetScaler V20 Performance Data
NetScaler NS11.1: Build 51.26.nc, Date: Jan 31 2017, 00:12:01
 
reltime:mili second between two records Thu Aug 31 21:41:04 2017
Index reltime     counter-value symbol-name&device-no
    1       0          57060984 ip_err_portalloc_failed Mapped_IP_10.107.182.76
    3       0          57060984 tcp_err_ip_portalloc_failed

SNMP OIDs

Free ports per IP address:
ipFreePorts  (1.3.6.1.4.1.5951.4.1.1.26.1.5)

Port allocation errors:
tcpErrIpPortFail - 1.3.6.1.4.1.5951.4.1.1.46.70
tcpErrAnyPortFail - 1.3.6.1.4.1.5951.4.1.1.46.69

Additional Resources

For more information please refer to NetScaler documentation or contact Citrix support.