iRule with switch

you can also use this:

set port [TCP::local_port]
switch 1 \
[expr {$port>=10000 && $port<10025}] {pool pool-site1} \
[expr {$port>=10025 && $port<10050}] {pool pool-site2} \
[expr {$port>=10050 && $port<10075}] {pool pool-site3} \
default {pool default_pool}

Make sure you let 1 in switch value, each expression is evaluated and the result is compared with 1 until one success.

This switch command can't have curly brackets because of expression evaluation, that's why the \ is mandatory at the end of each line but the last.