Description

Traffic forwarding continues even after VLAN is deleted. This is due to "family ethernet-switching" config being present under the interface unit. This scenario is specifically seen on QFX5110.

Symptoms

On QFX5110 running Junos 17.3R2.10 with the following IFL config: 

{master:0}
user@switch> show configuration groups CONFIG interfaces ae3000
description ServiceProvider4;
flexible-vlan-tagging;
mtu 9192;
encapsulation flexible-ethernet-services;
aggregated-ether-options {
    minimum-links 1;
    lacp {
        active;
        periodic fast;
    }
}
unit 802 {
    encapsulation vlan-bridge;
    vlan-id-list 100-4094;
    input-vlan-map push;
    output-vlan-map pop;
    family ethernet-switching;
}

And the IFL is part of the bridge domain: 

{master:0}
user@switch> show vlans v802
 
Routing instance        VLAN name             Tag          Interfaces
default-switch          v802                  NA
                                                           ae3000.802*
                                                           ae90.2002*

user@switch> show vlans v802 detail
 
Routing instance: default-switch
VLAN Name: v802                           State: Active
Tag: NA
Internal index: 13, Generation Index: 14, Origin: Static
MAC aging time: 300 seconds
VXLAN Enabled : No
Interfaces:
    ae3000.802*,tagged
    ae90.2002*,tagged
Number of interfaces: Tagged 2    , Untagged 0
Total MAC count: 2

After removal of the bridge domain, it shows as Destroyed but the forwarding still continues: 

user@switch# delete vlans v802
{master:0}
user@switch> show vlans v802 detail
 
Routing instance: default-switch
VLAN Name: v802                           State: Destroyed
Tag: NA
Internal index: 13, Generation Index: 14, Origin: Static
MAC aging time: 300 seconds
VXLAN Enabled : No
Interfaces:
    ae3000.802*,tagged
    ae90.2002*,tagged
Number of interfaces: Tagged 2    , Untagged 0
Total MAC count: 2


user@switch> show vlans v802
 
Routing instance        VLAN name             Tag          Interfaces
default-switch          v802                  NA
                                                           ae3000.802*
                                                           ae90.2002*

Solution

The issue occurs due to ' family ethernet-switching ' on the 'vlan-bridge' encapsulated IFL.

For example, a warning message appears when we commit the configuration. But the VLAN still passes traffic. 

{master:0}[edit]
user@switch# commit check 
[edit interfaces]
  'ge-0/0/2'
    Configuration vlan-tagging is not supported with ifl family ethernet-switching
[edit interfaces]

The workaround is to remove 'family ethernet-switching' on the 'vlan-bridge' encapsulated IFL.