Hi Paiolfi,
I recon you are using roundrobin for load balancing. It is a normal senario for roundrobin since your alias name and server name not matched to each other.
If you want to use alias for admin portal login, you need to use h/w or s/w loadbalancer, which take your request, process that and send to available connection server.
But, if you like to stick with DNS based load balancing, then i think you need to stick with dedicated server name/Ip address.
Regards
Faisal