irule to create a hash of source and destination IPs

Maybe this will work.

when CLIENT_ACCEPTED {
    scan [IP::client_addr] "%u.%u.%u.%u" a b c d
    scan [IP::local_addr] "%u.%u.%u.%u" e f g h
    set src_dst_hash [ crc32 [ concat $a $b $c $d $e $f $g $h ] ]
    persist hash $src_dst_hash
}