Description

This article describes a scenario seen where port stayed down after replacing a MX with an ACX.

The customer migrated an MX router to a Juniper ACX device. After the migration, they noted that port ge-0/0/20 on EX4600 showed as down. 

 

Symptoms

Old setup:

EX4600 ge-0/0/20 no-auto-negotiation ---- MX

 

New setup:

EX4600 ge-0/0/20 no-auto-negotiation ---- ACX

 

Solution

Port ge-0/0/20 on the primary switch was down due to a missing auto-negotiation command present on the secondary switch config but disabled on the primary. 

 

[edit]

labroot@switch# set interfaces ge-0/0/20 ether-options auto-negotiation  

 

Auto Negotiation: 

Auto-negotiation is a protocol used in Ethernet networks to allow two connected devices (such as computers, switches, or routers) to automatically determine the best settings for communication.

Modification History

2026-08-13 : Article Created