A structured lesson workspace with readable content, hands-on examples, and a clean path to completion.
R1# show ip interface brief | exclude unassignedR1# show interfaces | include (line protocol|errors)R1# show processes cpu sorted | head 20R1# show logging | include %LINK|%LINEPROTO
Those four commands give you more situational awareness than twenty minutes of scrolling through unfiltered output. Learning to filter `show` output is the difference between a five-minute diagnosis and a thirty-minute scroll. This lesson is about building the reflex.
| Command | Use case |
|---|---|
| `show ip interface brief` | Fast status of all interfaces — up/down/administratively down |
| `show interfaces` | Detailed per-interface counters, errors, statistics |
| `show interfaces status` | One-line summary per port on a switch |
| `show ip route` | Routing table — what the router knows and where it forwards |
| `show ip protocols` | Active routing protocols and their parameters |
| `show cdp neighbors detail` | Adjacent devices on each interface |
| `show logging` | Recent log messages — first place to look for clues |
| `show processes cpu sorted` | Top CPU-consuming processes |
| `show processes memory sorted` | Top memory consumers |
| `show version` | Uptime, IOS version, hardware info, last reload reason |
| `show environment` | Power, temperature, fan status |
| `show arp` | IP-to-MAC mappings |
! Include — show only lines matching a patternshow running-config | include vlan! Exclude — show lines NOT matchingshow interfaces | exclude 0 packets|0 bytes! Begin — start from first matchshow running-config | begin interface! Section — show only the config sections matchingshow running-config | section interface Gi0/1! Count matchesshow ip route | count! Multiple patterns (regex)show logging | include (LINK|LINEPROTO|OSPF)
The `section` filter is underused. `show running-config | section interface` gives you every interface config block without the noise. `show run | section ospf` shows just the OSPF config. It's the fastest way to audit a specific part of a config.
Debug commands generate enormous log volume on a busy device. `debug ip packet` on a router processing thousands of packets per second can lock the CPU and cause an outage. Before running any debug: check `show processes cpu` to know your baseline, and be prepared to `undebug all` immediately. In production, use debug only as a last resort — prefer `show` commands, logging, and packet captures.
! Safe debug workflowR1# show processes cpu | include CPU utilizationR1# terminal monitorR1# debug ip ospf adjacency! Wait a few secondsR1# undebug allR1# show processes cpu | include CPU utilization
If any debug shows as on when you didn't intend it, `undebug all` immediately. It's easy to forget a debug you enabled during troubleshooting — and leaving it on can crash a busy router. Make a habit of running `show debugging` before you log out of a device.
On a lab router: run `show ip interface brief` and identify any down interfaces. Use `show interfaces <intf>` to check error counters on each. Use `show logging` to see the last 20 log messages. Filter `show running-config` to show only the OSPF config with `| section ospf`.
Finish the lesson once you have worked through the material. This awards ★ 15 XP.