2 & 3 Stateful packet filtering (using Linux IPTables), Plus, if you use the optional IPS and proxies (SMTP, HTTP, POP3, ...), you can get even more filtering and access control.
2 & 3 Stateful packet filtering (using Linux IPTables), Plus, if you use the optional IPS and proxies (SMTP, HTTP, POP3, ...), you can get even more filtering and access control.