There are several methods, pick the most appropriate:
1/ on M/T/MX – If you have 1GE copper with autoneg enabled , then
test interface ge-x/y/z restart-auto-negotiation
2/ on any JUNOS platform (example below for 10GE interface, substitute for your interface name):
start shell user root ifconfig xe-y/z/w down ifconfig xe-y/z/w up exit
WARNING – if You abort command sequence after “ifconfig .. down” and forget to bring interface up in shell, then Your interface will display as & stay DOWN in JUNOS CLI printouts and MIB without apparent reason.
3/ in PFE shell, works for 10 GE XFP:
start shell pfe network fpc<number> show xfp list test xfp <index> laser off test xfp <index> laser on
IMPORTANT: XFP index begins from 1, not 0. Hence, XFP in port xe-0/0/0 will have index 1 locally in FPC 0 shell.