Want to create a Irule in BIG-IP 11.5.1 Build 10.0.180 Hotfix HF10

Reformatting your rule for readability:

    when CLIENT_ACCEPTED {
    if {[TCP::remote_port] == 21} {
        pool Globalscape-HA-servers-SSH-pool      
    } elseif {[TCP::remote_port] == 23} {
        pool Globalscape-HA-servers-Telnet-pool         
    } elseif {[TCP::remote_port] == 990} {
        pool Globalscape-HA-servers-990-pool
    } elseif {[TCP::remote_port] == 443} { 
        pool Globalscape-HA-servers-SSL-pool 
    } else { 
        discard 
    }
}

Are you sure this is working in v12?

I ask because in the clientside contex, TCP::remote_port returns the client's source port, while the logic of your rule is interested in the client's destination port.

I suggest rewriting this rule with TCP::local_port, then testing to see if you are getting the desired outcome.

You might also want to look into replacing your if/else construct with the switch construct, for efficiency sake.

There are 2 better solutions:

• create one virtual server for each port... 4 VS is not so hard to create and let you manage configuration based on port
• create a LTM policy... easier than irule (not sure you can use port condition in version 11.5)

Rob already explained why your code don’t work!