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Router Security Configuration Guide UNCLASSIFIED 26 UNCLASSIFIED Version 1.0g allows routers to only share information with nearest neighbors. It is used as an interior gateway protocol. 2.5.5.    Session Layer 5, Presentation Layer 6, and Application Layer 7 These protocols are labeled (TCP) or (UDP) depending on which layer 5 protocol they are based upon. Telnet – (TCP) Enables terminal oriented processes to communicate. FTP – File Transfer Protocol (TCP) enables transfers of files between hosts. SMTP – Simple Mail Transport Protocol (TCP) is pretty much self-explanatory. DNS – Domain Name System (both TCP and UDP) performs naming resolution service by translating host names into IP addresses. TFTP – Trivial File Transfer Protocol (UDP) provides file transfers without any authentication or security. SNMP – Simple Network Management Protocol (UDP) enables a management station to trap certain information messages from network devices.