The question mark is your best friend
Nobody remembers every command. On a router you press ? at any point:
show ?(with a space) lists every word that can come next, with a short description.sh?(no space) lists the commands that start with those letters.<cr>in the list means "you can press Enter now; the command is complete".
In NetLab
▶ R1 Router>enable Router#show ip ? arp IP ARP table interface IP interface status and configuration route IP routing table dhcp Show items in the DHCP database Router#sh? show
Short commands and Tab
You only need to type enough letters to be unique: sh ip int br is the same as show ip interface brief, and conf t is configure terminal. Press Tab to see the full word filled in. The ↑ key brings back earlier commands.
The three error messages
In NetLab
▶ R1 Router>enable Router#show ip interfase brief ^ % Invalid input detected at '^' marker. Router#show ip % Incomplete command. Router#co % Ambiguous command: "co"
| Message | What it means |
|---|---|
% Invalid input detected at '^' marker. | A word is wrong. The ^ points at the first bad character. |
% Incomplete command. | You stopped too early: the command needs more words. Add ? to see what. |
% Ambiguous command | You shortened too much: several commands start with those letters. |
The 'Translating...' trap
If you type a word that is not a command in EXEC mode, the router thinks it is the name of a computer you want to connect to, and tries to look it up with DNS. On real equipment this can freeze the console for many seconds:
In NetLab
▶ R1 Router>enable Router#shwo Translating "shwo"...domain server (255.255.255.255) % Unknown command or computer name, or unable to find computer address
Most engineers switch that look-up off on lab and branch routers:
In NetLab
▶ R1 Router>enable Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#no ip domain-lookup Router(config)#end *Mar 1 00:00:04.000: %SYS-5-CONFIG_I: Configured from console by console Router#shwo Translating "shwo" % Unknown command or computer name, or unable to find computer address
Filtering long output
Some show commands print a lot. Add | (a pipe) and a filter to keep only what you need: include keeps matching lines, exclude drops them, begin starts at the first match, and section shows a block and the lines indented under it. The text after the filter is a regular expression: | means "or", and _ matches a space or the end of the line, so include Fa0/1_ finds Fa0/1 but not Fa0/10.
In NetLab
▶ R1 Router>enable Router#show running-config | include hostname hostname Router Router#show running-config | section line line con 0 line aux 0 line vty 0 4 login