Cisco Show Commands Cheat Sheet
A quick-reference for the Cisco IOS show and troubleshooting commands you reach for most on routers and Catalyst switches — verifying interfaces, routing, Layer 2, device info, and connectivity. Every command is real IOS syntax; replace <angle-bracket> placeholders with your own values.
Part of the Network Services & Management learning hub
Interfaces & IP
'status' is a Catalyst switch command; the rest work on routers and switches.
| Command | What it does |
|---|---|
show ip interface brief | One line per interface: IPv4 address, admin status, and line/protocol state — the fast up/down check. |
show interfaces <if> | Full detail for one interface: line/protocol, duplex/speed, MTU, and error/drop counters (CRC, input/output errors). |
show interfaces status | Catalyst view: port status, access/trunk VLAN, duplex, speed, and media type. |
show interfaces description | Interface, line/protocol status, and the configured description text. |
show ip interface <if> | L3 detail for one interface: IP/mask, inbound/outbound ACLs, proxy-ARP, MTU, and helper address. |
Routing
Codes: C=connected, L=local, S=static, O=OSPF, D=EIGRP, B=BGP.
| Command | What it does |
|---|---|
show ip route | Full IPv4 routing table with source codes and administrative distance/metric. |
show ip route <net> | Details for one prefix: matching route, next hop, AD/metric, and route source. |
show ip protocols | Active routing protocols: timers, advertised networks, passive interfaces, AD, and neighbors. |
show ip ospf neighbor | OSPF adjacencies: neighbor ID, state (should reach FULL or 2WAY), address, and local interface. |
show ip eigrp neighbors | EIGRP neighbor table: neighbor address, local interface, hold time, and uptime. |
Layer 2
CDP is Cisco-only and link-local; LLDP is the open (802.1AB) equivalent and is often disabled by default.
| Command | What it does |
|---|---|
show vlan brief | VLAN IDs, names, status, and the access ports assigned to each VLAN. |
show mac address-table | Learned MACs mapped to VLAN and port; add 'address <mac>' or 'interface <if>' to filter. |
show interfaces trunk | Trunk ports, mode, encapsulation, native VLAN, and allowed/active/forwarding VLANs. |
show spanning-tree | Per-VLAN STP: root bridge, local bridge ID, and port roles/states; add 'vlan <id>' to scope. |
show cdp neighbors detail | Directly connected Cisco devices with mgmt IP, platform, and IOS version. |
show lldp neighbors | Directly connected LLDP devices (multi-vendor); add 'detail' for full data. |
Device & config
Narrow big configs with a pipe, e.g. 'show running-config | section <keyword>'.
| Command | What it does |
|---|---|
show version | IOS version, uptime, model, serial number, total memory, and configuration register. |
show running-config | Active configuration in RAM; add 'interface <if>' to view one interface. |
show startup-config | Saved configuration in NVRAM; compare against running to spot unsaved changes. |
show inventory | Hardware components with PID, VID, and serial number (SN) per module. |
show processes cpu sorted | CPU load (5s/1m/5m) sorted by top process; use 'show processes memory sorted' for RAM. |
Connectivity & troubleshooting
Run from privileged EXEC; scope every debug and turn it off when done.
| Command | What it does |
|---|---|
ping <ip> | Sends 5 ICMP echoes: '!' = reply, '.' = timeout, 'U' = unreachable. |
ping <ip> repeat <count> size <bytes> | Extended ping: adjust probe count and packet size (e.g., for MTU testing). |
traceroute <ip> | Hop-by-hop path with per-hop round-trip times to the destination. |
telnet <ip> <port> | TCP reachability test to a service port (e.g., 80, 443); use 'ssh -l <user> <ip>' for the SSH client. |
terminal monitor | Mirror console log/debug output to your current VTY (SSH/Telnet) session. |
debug <feature> | Real-time event output — CPU-heavy, use sparingly; stop with 'undebug all' (or 'no debug all'). |
Frequently asked questions
What's the difference between 'show ip interface brief' and 'show interfaces status'?
'show ip interface brief' is a Layer 3 view available on routers and switches — it lists each interface's IPv4 address plus admin and line/protocol state, ideal for a fast up/down check. 'show interfaces status' is a Catalyst switch command that shows Layer 2 port info instead: connected/notconnect status, the access or trunk VLAN, duplex, speed, and media type. Reach for brief to confirm IP and reachability; use status to confirm which VLAN and speed a switch port negotiated.
How do I safely run a debug over an SSH or Telnet (VTY) session?
Debug output goes to the console by default, so on a remote session first enter 'terminal monitor' to mirror it to your VTY line. Then enable only the specific debug you need (e.g., 'debug ip ospf adj') rather than a broad one — debug is CPU-intensive and can overload a busy device. When finished, always turn it off with 'undebug all' (or 'no debug all') and confirm nothing is left running with 'show debugging'.
When should I use 'show cdp neighbors' versus 'show lldp neighbors'?
Both discover directly connected devices, but CDP is Cisco-proprietary while LLDP (IEEE 802.1AB) is the open, multi-vendor standard. In an all-Cisco topology 'show cdp neighbors detail' gives you the neighbor's mgmt IP, platform, and IOS version. When non-Cisco gear is involved, use 'show lldp neighbors detail' — but note LLDP is frequently disabled by default and may need 'lldp run' enabled globally on both ends first.
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