User Interfaces
Two CLI modes
Operational mode (prompt ends in >) is for monitoring: show, monitor, request, clear, ping, traceroute. Configuration mode (prompt ends in #) is entered with configure and edits the candidate configuration. From configuration mode, run executes a single operational command without leaving the mode; exit moves up one hierarchy level; top returns to the top of the hierarchy; up goes up one level. exit configuration-mode returns you to operational mode, and with uncommitted changes it warns and asks you to commit or discard.
Help and pipe filters
A question mark lists possible completions, Tab completes, and a space also completes. Pipe filters are heavily tested: | match, | except, | find, | count, | no-more, | display set, | display xml or json, | compare, | last. show configuration | display set prints the configuration as set commands, which is the quickest way to read a large config.
Other interfaces
J-Web (browser), NETCONF over SSH (port 830) and the Junos XML API for automation, plus console and AUX ports for out-of-band access. SSH is enabled by default; Telnet and J-Web are security decisions controlled under set system services.
Login classes
set system login user NAME class CLASS. Predefined classes are super-user, operator, read-only and unauthorized. root-authentication must be configured, and a commit fails without it, a classic exam trap. Local users, RADIUS and TACACS+ authentication are supported.
Traps
- Thinking exit in configuration mode silently discards edits; it prompts instead.
- Confusing | match (filters lines) with | find (jumps to the first match and keeps printing).
- Forgetting that changes made through NETCONF or J-Web still require a commit.
Rule of thumb
If the prompt ends in #, you are in configuration mode: prefix an operational command with run.