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ENARSI 4.0 Infrastructure Services (25%)

Infrastructure Services is a quarter of the ENARSI exam, and every objective uses the verb troubleshoot. You will not be asked to recite what SNMP is. You will be shown show snmp group output, a DHCP relay config or an IP SLA statistics screen and asked what is broken. The skill to build this week is reading diagnostic output fast: know which show command proves each layer works, and know what the output looks like when one piece is missing.

Objective Verb Page
4.1 Device management: console and VTY, Telnet, HTTP, HTTPS, SSH, SCP, (T)FTP Troubleshoot Device Management
4.2 SNMP v2c and v3 Troubleshoot SNMP
4.3 Logging: local, syslog, debugs, conditional debugs, timestamps Troubleshoot Logging and Debugs
4.4 IPv4 and IPv6 DHCP: client, IOS server, relay, options; SLAAC, stateless and stateful DHCPv6 Troubleshoot DHCPv4 and DHCPv6
4.5 IP SLA: jitter, tracking objects, delay, connectivity Troubleshoot IP SLA and Object Tracking
4.6 NetFlow v5, v9 and Flexible NetFlow; 4.7 Catalyst Center Assurance Troubleshoot NetFlow and Catalyst Center Assurance

Time budget: week 21 of the study plan. A workable split is one day each for 4.1 with 4.2, 4.3, 4.4 (the largest), 4.5, and 4.6 with 4.7, then a sixth day for the labs you skipped and the practice questions.

How these objectives are tested

  • Exhibit questions dominate. Expect a running-config fragment plus one show command, and four answers that each name a different missing line. The trick is to know the full dependency chain (for SSH: hostname, domain name, RSA key, transport input, login method) so you can spot the gap.
  • Defaults matter. Syslog trap level informational, IP SLA frequency 60 seconds, DHCP lease one day, Flexible NetFlow active timeout 1800 seconds. Questions are built around a value someone forgot to change.
  • Services depend on each other. Logging timestamps are useless without NTP. IP SLA one-way delay needs synchronised clocks. SNMP traps and NetFlow export need a reachable source interface. A fault in one service often shows up as a symptom in another.

Module lab topology

The page labs reuse one small topology. Build it once in CML and save a baseline (copy running-config flash:baseline.cfg) before each break/fix exercise.

graph LR
  H1["HOST1 IOSv<br/>DHCP client"] -- "Gi0/0 to R1 Gi2  10.10.10.0/24" --- R1["R1 C8000v<br/>Lo0 10.255.255.1"]
  R1 -- "Gi1 .1  10.1.2.0/30  .2 Gi0/0" --- R2["R2 IOSv<br/>DHCP server, SLA responder"]
  R1 -- "Gi3 .1  10.1.3.0/30  .2 Gi0/0" --- R3["R3 IOSv<br/>backup path"]
  R3 -- "Gi0/1 .2  10.2.3.0/30  .1 Gi0/2" --- R2
  R2 -- "Gi0/1 .1  192.168.100.0/24" --- NMS["NMS Ubuntu .50<br/>syslog, SNMP, NetFlow"]
Device Interface IPv4 IPv6
R1 Gi1 10.1.2.1/30 2001:db8:1:2::1/64
R1 Gi2 (branch LAN) 10.10.10.1/24 2001:db8:10::1/64
R1 Gi3 10.1.3.1/30
R1 Lo0 10.255.255.1/32
R2 Gi0/0 10.1.2.2/30 2001:db8:1:2::2/64
R2 Gi0/1 (management LAN) 192.168.100.1/24 2001:db8:100::1/64
R2 Gi0/2 10.2.3.1/30
R2 Lo0 10.255.255.2/32
R3 Gi0/0, Gi0/1 10.1.3.2/30, 10.2.3.2/30
NMS ens2 192.168.100.50/24, gateway .1

Run OSPF area 0 on every router link and loopback (except the host-facing LAN, which is passive) so the NMS can reach every device. See Lab Setup for images and the addressing convention.

When you finish, take the Infrastructure Services practice questions. Aim for 80% or better before moving on.