Description


This article addresses the challenge of running 802.1Q VLAN tagging and G.8275.1 Precision Time Protocol (PTP) simultaneously on multiple interfaces of Juniper ACX7024 devices. Initially, enabling VLAN tagging on interfaces caused PTP to fail, but a solution was found by adding a specific configuration.
 

Symptoms

  • PTP fails to pass when an interface is set to vlan-tagging/flexible-vlan-tagging or configured as a trunk with VLANs assigned.
  • No received PTP packets are recorded in statistics when VLAN tagging is enabled.
  • The device changes from Slave to Master state or remains in "Initializing" state when VLAN tagging is active.
  • PTP works correctly on untagged interfaces but fails on tagged interfaces.

Root Cause:
The default configuration for VLAN-tagged interfaces does not properly handle PTP traffic, causing it to be dropped or mishandled by the ACX7024.

 

Solution

Add an additional logical unit to each trunk interface with "vlan-id none" to allow PTP traffic to pass correctly.

Detailed Configuration:

Basic PTP and Interface Configuration:

set chassis fpc 0 pic 0 ptp-mode
set protocols ptp clock-mode boundary
set protocols ptp profile-type g.8275.1
set protocols ptp domain 24
set protocols ptp slave hybrid
set protocols ptp master interface et-0/0/7.0 multicast-mode transport ieee-802.3
set protocols ptp stateful interface et-0/0/22.0 multicast-mode slave-candidate
set protocols ptp stateful interface et-0/0/22.0 multicast-mode transport ieee-802.3
set vlans PTPoE vlan-id none
set vlans PTPoE interface et-0/0/22.0
set vlans PTPoE interface et-0/0/7.0
set interfaces et-0/0/22 speed 10g
set interfaces et-0/0/7 speed 10g
set chassis synchronization network-option option-2
set chassis synchronization selection-mode received-quality
set chassis synchronization clock-mode auto-select
set chassis synchronization quality-mode-enable
set chassis synchronization source interfaces et-0/0/22 quality-level prs
set chassis synchronization esmc-transmit interfaces et-0/0/7

VLAN Tagging Configuration:

For each interface that needs to support both VLAN tagging and PTP

set interfaces et-0/0/22 flexible-vlan-tagging
set interfaces et-0/0/22 unit 0 vlan-id 0
set interfaces et-0/0/22 unit 0 family ethernet-switching
set interfaces et-0/0/22 unit 1 vlan-id none
set interfaces et-0/0/22 unit 1 family ethernet-switching

Verification:

After applying the configuration, verify PTP operation:

Check PTP port status: > show ptp port brief

Expected output:
PTP port-data:
Local Interface : et-0/0/22.0
Local Address : bc:0f:fe:a8:23:80
Remote Address : 01:1b:19:00:00:00
Clock Stream : 5 Clock Identity : bc:0f:fe:ff:fe:a8:26:ad
Port State : Slave Delay Req Interval: -4
Announce Interval : -3 Announce Timeout : 3
Sync Interval : -4 Delay Mechanism : End-to-end
Port Number : 1 Operating Mode : Stateful
Local Priority : 128

Verify PTP lock status: >  show ptp lock-status detail

Expected output should show "PHASE ALIGNED" state.


Check chassis synchronization: > show chassis synchronization extensive

Verify that the clock is locked to the primary source.

Examine PTP statistics: > show ptp statistics brief

Ensure that both Received and Transmitted packets are non-zero for the relevant interfaces.
Additional Notes:

Modification History

2024-03-27 : Article Created