4IP Services

• 4.1NAT and PAT

  Covers the role of NAT in translating internal private addresses into global addresses, choosing among one-to-one static NAT, pool-based dynamic NAT, and PAT (overload) that collapses many hosts to one address using port numbers, the inside local / inside global terminology, and the judgment skill of isolating a fault from a mislabeled ip nat inside / ip nat outside or from the translation table.

• 4.2DHCP, DNS, and NTP

  Covers the DORA operation of DHCP for automatic IP assignment and the roles of server, client, and relay agent (ip helper-address); the role of DNS in resolving hostnames to IPs; and the stratum hierarchy and client/server configuration of NTP for time synchronization—building the judgment to isolate faults such as "hosts on a remote segment get no IP."

• 4.3SNMP and Syslog

  Covers the difference between SNMPv2c (community) and SNMPv3 (authentication and encryption) for monitoring and managing devices, the fire-and-forget trap versus the acknowledged inform, and the severity levels 0-7 (0 emergency to 7 debug) and facility of Syslog—learning to judge, from operational requirements, that a logging trap level captures "that value and everything more severe."

• 4.4QoS, SSH, and file transfer

  Covers the per-hop behavior of QoS (classification, marking (DSCP), queuing, congestion management, policing that drops excess, and shaping that buffers to smooth), the setup prerequisites of SSH (RSA key, domain name) for encrypted remote management versus Telnet, and choosing among TFTP, FTP, and SCP for transferring IOS images/configs—as practical judgment.