IP Services connects routing to the operational services users and administrators rely on. For each service, know the purpose, the packet-flow dependency, the configuration role, and the evidence that proves it works.
What to know and how to practise it
Inside-source NAT
Configure and verify static translation and dynamic translation with pools. Identify inside local, inside global, outside local, and outside global addresses from the packet’s perspective, and verify that interface roles, source matching, and the translation rule agree.
NTP, DHCP, and DNS
Use NTP to align device time, understand DHCP address allocation and relay behavior, and explain how DNS resolves names. A client symptom may depend on several of these services, so separate address assignment, gateway reachability, and name resolution.
SNMP, syslog, and QoS behavior
Recognize how SNMP supports monitoring, how syslog severity and timestamps support event analysis, and how classification, marking, queuing, policing, and shaping influence traffic. Understand per-hop behavior without treating QoS as extra bandwidth.
Secure remote access and file transfer
Configure secure CLI access with local credentials, domain and key prerequisites, VTY restrictions, and SSH. Distinguish TFTP and FTP use cases and recognize the security implications of clear-text or unauthenticated transfers.
Example service dependency chain
A branch client has an address but cannot reach a public service by name. Confirm the lease includes the correct gateway and DNS server, test the gateway, test a public IP, verify NAT translation, then test DNS. This isolates the failed service without random configuration changes.
show ip nat translations
show ip nat statistics
show clock
show logging
show running-config | section line vtyReadiness checklist
- Trace static and dynamic NAT from inside local to inside global.
- Separate DHCP allocation, relay, gateway, and DNS failures.
- Interpret syslog severity and timestamp usefulness.
- Explain classification, marking, queuing, policing, and shaping.
- Verify the prerequisites for an SSH management session.
Common mistakes to remove
- Applying NAT commands without marking the correct inside and outside interfaces.
- Treating a hostname failure as proof that general connectivity is down.
- Assuming QoS creates capacity instead of managing congestion behavior.