Description

This article describes the root cause of LLDP packet drops from non-master members of EX4400 VC. 

Symptoms

The customer reported an LLDP adjacency failure with both the line card member of four member EX4400-48MP VC after a reboot or deletion/addition of the LLDP configuration. Whereas the LLDP adjacency from Primary and Backup members of the VC were working fine. This issue was locally recreated with the below topology while repeatedly moving between HiGig and HGoE VC modes along with LLDP configuration removal and addition.

Topology:

Peer1(ge-0/0/0) -------------(mge-2/0/0) EX4400-48MP/24MP [4 member VC] (mge-3/0/0) --------------(ge-0/0/1) Peer1
  
root> show virtual-chassis Preprovisioned Virtual Chassis
Virtual Chassis ID: b2ea.b4cb.8db3
Virtual Chassis Mode: Enabled
                                                Mstr           Mixed Route Neighbor List
Member ID  Status   Serial No    Model          prio  Role      Mode  Mode ID  Interface
0 (FPC 0)  Prsnt    ZG4321210016 ex4400-24mp    129   Master*      N  VC   3  vcp-255/1/0
                                                                           1  vcp-255/1/1
1 (FPC 1)  Prsnt    ZG4321210013 ex4400-24mp    129   Backup       N  VC   0  vcp-255/1/0
                                                                           2  vcp-255/1/1
2 (FPC 2)  Prsnt    ZF4321210011 ex4400-48mp      0   Linecard     N  VC   1  vcp-255/1/0
                                                                           3  vcp-255/1/1
3 (FPC 3)  Prsnt    ZF4321210006 ex4400-48mp      0   Linecard     N  VC   2  vcp-255/1/0
                                                                           0  vcp-255/1/1
Observation from the device during issue state:

At EX4400-VC: 
{master:1}
root@EX4400-VC> show interfaces terse | match ae12
mge-2/0/0.0             up    up   aenet    --> ae12.0
mge-3/0/0.0             up    up   aenet    --> ae12.0
ae12                    up    up
ae12.0                  up    up   eth-switch

{master:1}
root@EX4400-VC> show lldp neighbors
Local Interface    Parent Interface    Chassis Id          Port info          System Name
mge-2/0/0          ae12                ec:3e:f7:91:ac:c0   ge-0/0/0           Peer1        <<< From Peer1, LLDP packets are received.
mge-3/0/0          ae12                ec:3e:f7:91:ac:c0   ge-0/0/1           Peer1

At Peer:
{master:0}
root@Peer1> show interfaces terse | match ae0
ge-0/0/0.0              up    up   aenet    --> ae0.0
ge-0/0/1.0              up    up   aenet    --> ae0.0


{master:0}
root@Peer1> show lldp neighbors
Local Interface    Parent Interface    Chassis Id          Port info          System Name
                                                                                          <<<< No LLDP neighbour-ship from EX4400-VC 
root@Peer1>

Solution

In HGOE mode, the platform code calls an SDK API. In case of a speed change (for example with 40G SFP), the API resets VLAN membership check properties in the bitmap table for HIGIG ports. This table performs VLAN membership checks and drops the packet since HIGIG ports are not a member of control VLAN. The fix is to remove HIGIG ports from bitmap table and skip VLAN membership check.

Impact: There will be LLDP packet drops from Line card members of EX4400 VC.

Workaround: Until the issue is fixed, use LLDP neighbors from primary member of the VC.

Fix: This issue is fixed in the version 22.3R2-S2.10.

For more details, refer PR: https://prsearch.juniper.net/PR1747095

Modification History

2023-09-14: Initial Publication