inserting already existent values

["Fernando T. Martins Mano" <fernando@cpts.pucrs.br>]

I got an objectClass that allows multivalued attributes, as follows:

dn:               cn=test, dc=myExample, dc=com
objectClass: myObjectClass  SUP top
site:            www.google.com
site:            www.altavista.com
site:            www.lycos.com
port:            80
port:            80 (when I try to add this already existent value, I get an
error message)
protocol:    TCP
protocol:    UDP
protocol:    TCP (same occurs here)

I would like to know if it is possible to add repeated values, if yes...
how?