How to Use Junos Show Commands to Troubleshoot a Network

When it comes to monitoring the network, the most essential CLI commands are show interfaces brief and show interface detail. For example, if you suspect that Gigabit Ethernet interface ge-0/0/0 is down, a simple show command reveals its status (which is indeed “Down”):

user@router>show interfaces ge-0/0/0 brief
Physical interface: ge-0/0/0, Enabled, Physical link is Down
  Link-level type: Ethernet, MTU 1514, Speed 1ge, Loopback: Disabled
  Source filtering: Disabled, Flow control: Enabled
  Device flags    : Present Running Down
  Interface flags : Hardware-Down SNMP-Traps Internal: 0x4000
  Link flags      : None

On the other hand, to see a lot more detail about the interface’s queues, input-output byte counts, and the same for packet counts, you can use the show interfaces ge-0/0/0 command to add this information:

user@router>show interfaces ge-0/0/0 detail
Physical interface: ge-0/0/0, Enabled, Physical link is Down
  Link-level type: Ethernet, MTU 1514, Speed 1ge, Loopback: Disabled
  Source filtering: Disabled, Flow control: Enabled
  Device flags    : Present Running Down
  Interface flags : Hardware-Down SNMP-Traps Internal: 0x4000
  Link flags      : None
  CoS queues      : 4 supported, 4 maximum usable queues
  Hold-times      : Up 0 ms, Down 0 ms
  Current address : 00:05:85:02:a4:00, Hardware address: 00:05:85:02:a4:00
  Last flapped    : 2010-12-15 14:30:58 PST (1w2d 23:03 ago)
  Statistics last cleared: Never
  Traffic statistics:
    Input bytes   :             0               0 bps
    Output bytes  :             0               0 bps 
    Input packets :             0               0 bps 
    Output packets:             0               0 bps
  IPv6 transit statistics:
    Input bytes   :             0               
    Output bytes  :             0               
    Input packets :             0               
    Output packets:             0               
  Egress queues: 4 supported, 4 in use
  Queue counters:    Queued packets  Transmitted packets   Dropped packets
    0 best-effort                 0                    0                 0
    1 expedited-fo                0                    0                 0
    2 assured-forw                0                    0                 0
    3 network-cont                0                    0                 0
  Active alarms   : LINK
  Active defects  : LINK

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