This article explains how to configure the port speed to 1G on MPC7E line card, specifically MPC7E 3D 40XGE.

The default port speed on the line card type MPC7E 3D 40XGE is 10G, however there is a provision to modify the port speed to 1G via interface level config.

Port will remain Down,

When 1G Optic is inserted into the 10GE port on MPC7E 40XGE without configuring the port speed at interface level,

the interface flags will report like:

Interface flags: Hardware-Down <<<<

If the port needs to run in 1G speed,

Starting with Junos OS Release 20.4R1, you can configure 1-Gbps speed on 10-Gigabit Ethernet ports of the MPC7E-10G. You can configure the 10-Gigabit Ethernet ports to operate as 1-Gigabit Ethernet port using the speed statement at the edit interfaces <interface name> gigether-options hierarchy level.

lab@root# set interfaces xe-2/0/0 gigether-options speed ?

Possible completions:

 10g         Speed 10g

 1g          Speed 1g <<<<<<<<<

For Ex: 

before configuring the port speed:

Physical interface: xe-2/0/0, Enabled, Physical link is Down
  Interface index: 164, SNMP ifIndex: 554, Generation: 167
  Description: xyz:ge-1/1/5
  Link-level type: Ethernet, MTU: 1804, MRU: 1812, LAN-PHY mode, Speed: 10Gbps, BPDU Error: None, Loop Detect PDU Error: None, MAC-REWRITE Error: None, Loopback: None, Source filtering: Disabled, Flow control: Enabled, Speed Configuration: Auto  <<< Reports Auto
  
After configuring the port speed as 1g, the output looks like below

Physical interface: xe-2/0/0, Enabled, Physical link is Up
  Interface index: 164, SNMP ifIndex: 554, Generation: 167
  Description: xyz:ge-1/1/5
  Link-level type: Ethernet, MTU: 1804, MRU: 1812, LAN-PHY mode, Speed: 10Gbps, BPDU Error: None, Loop Detect PDU Error: None, MAC-REWRITE Error: None, Loopback: None, Source filtering: Disabled, Flow control: Enabled, Speed Configuration: 1G