Methods to determine link status of ethernet interfaces

- check /var/adm/messages (including when IPMP is used)

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checking link status with ndd

# ndd -set /dev/qfe instance 0 (instance set to "0" checks qfe0 status; "1" for qfe1,etc...)
# ndd   /dev/qfe link_status
  1
  ( 1 -up, 0 = down )                                                

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Checking link status for Gigaswift Ethernet(ce) is different from other Ethernet interfaces.   netstat
-k is used:

netstat -k ce0

link_up (1=up,0=down)                                                                                            

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checking with kstat (netstat -k)

# kstat qfe:0::link_up
module: qfe                                                         instance: 0
name:     qfe0                                                       class:       net
                  link_up                                                 1

# kstat eri |grep link_up
link_up                                                 1

# netstat -k qfe0 |grep link_up
  ......   link_up 1                                                                                                

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examining LED states

newer network interface adapters have light indicators.

on "qfe" quad fast ethernet and "ge" Sun Gigabit Ethernet 2.0 adapters

     LED           Status                 Description
--------------------------------------------------------------
LINK         Off                       Port not connected or Link partner down
                  Green Steady     Link detected & active                                                                                              

on "ce" Gigaswift:
  --------------------------------------------------------------
LINK QUALITY   Purple     Gigabit link quality good
  PHY 1000X       Green         Link 1Gbit/s up
  PHY 100X         Green         Link 100Mbit/s up
  PHY 10X           Green         Link 10Mbit/s up                                                                                              

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checking with SNMP ( requires snmp Software)
./snmpwalk netlab11 public interfaces.ifTable

...
interfaces.ifTable.ifEntry.ifDescr.1 = lo0
interfaces.ifTable.ifEntry.ifDescr.2 = ce3
interfaces.ifTable.ifEntry.ifDescr.3 = hme0
interfaces.ifTable.ifEntry.ifDescr.4 = qfe0
...
interfaces.ifTable.ifEntry.ifOperStatus.1 = up(1)
interfaces.ifTable.ifEntry.ifOperStatus.2 = up(1)
interfaces.ifTable.ifEntry.ifOperStatus.3 = up(1)
interfaces.ifTable.ifEntry.ifOperStatus.4 = down(2)