OS Hardening CHAPTER 2 27 EXAM WARNING Spend a few minutes reviewing port and protocol numbers for standard services provided in the network environment. This will help when you are analyzing questions that require configuration of ACL lists and determination of appropriate blocks to install to secure a network. The Security exam can ask specific questions about ports and what services they support. It's advisable to learn common ports before attempting the exam. 21 FTP 22 Secure Shell (SSH) 23 Telnet 25 Simple Mail Transfer Protocol (SMTP) 53 DNS 80 HTTP 110 Post Office Protocol (POP) 161 Simple Network Management Protocol (SNMP)