I85PREP
⌘ K
Cisco ENARSI 300-410 study materials
Cisco ENARSI 300-410 study resources

Cisco ENARSI 300-410: Infrastructure Services

Cisco ENARSI 300-410 · Work through your exam, one topic at a time.

All guide sections

Infrastructure Services

Infrastructure Services covers DHCP, NAT, NTP, SNMP, syslog, QoS, NetFlow, and IP SLA. ENARSI asks you to interpret operational output and fix service failures rather than configure every option from memory.

DHCP, NAT, and time

  • ip helper-address relays client broadcasts to a DHCP server; the relay adds giaddr so the server selects the correct pool. DHCP snooping and option 82 can affect relay behavior.
  • NAT order: inside-to-outside routes first, then translates; outside-to-inside translates first, then routes. Static NAT or PAT is useful for inbound access; overload enables PAT.
  • NTP stratum 1 is directly attached to a reference clock; stratum 16 means unsynchronized. Use ntp server, ntp authentication-key, and ntp trusted-key; ntp source sets the source address.

Monitoring and QoS

  • Syslog severity runs from 0 (emergency) to 7 (debugging); lower is more severe. logging trap sets the maximum severity sent.
  • SNMPv3 provides authentication and privacy; views restrict OIDs. Traps are unacknowledged; informs are acknowledged.
  • MQC uses class maps to match, policy maps to mark, queue, or police, and service policies to attach. NetFlow exports flow records; IP SLA probes measure delay, jitter, and loss.

Worked example

A branch DHCP pool is on a router that is not the default gateway; clients get no address. The gateway has ip helper-address 10.0.0.10, but the DHCP server has no route to 192.168.50.0/24. The relay packet carries giaddr 192.168.50.1, so the server selects the pool but cannot return the offer. Add a route on the server for 192.168.50.0/24 via 10.0.0.1, and confirm the gateway interface is up and the ACL permits UDP 67 and 68. This is a routing failure, not a pool failure.

Traps

  • The NAT ACL matches inside local addresses before translation.
  • Missing ip nat inside or ip nat outside on interfaces breaks NAT.
  • NTP stratum 16 is unsynchronized, not a valid clock source.
  • Syslog level 7 is the most verbose, not the most severe.
  • SNMP traps are not acknowledged; informs are.