Configuring 802.1q trunk between UniFi AP and Juniper EX switch

Problem:

After configuring 802.1q VLAN trunking on port, according to UniFi Wireless Controller, AP is now in Disconnected or Adoption Failed state.

Diagnosis:

Tap the traffic (e.g. using port reflector). UniFi AP expects no VLAN tagging on native VLAN, tagged packets on management interface will get discarded. If you’ve a lot of DHCP Discover and DHCP Offer packets but no DHCP Request packets, check if your native VLAN packets are not tagged.

Running show ethernet-switching interfaces will probably describe default VLAN as tagged and untagged at the same time:

Interface    State  VLAN members        Tag   Tagging  Blocking 
ge-0/0/1.0        up     default             1     untagged unblocked
                    VLAN2               2   tagged   unblocked
                    VLAN3               3   tagged   unblocked
                    VLAN4               4   tagged   unblocked
                    default             1     tagged   unblocked

Solution:

802.1q VLAN members definition must not contain default VLAN, so ingress and egress packets in will not need and will not be tagged.

ge-0/0/1.0 {
    unit 0 {
        family ethernet-switching {
            port-mode trunk;
            vlan {
                members 2-4;
            }
            native-vlan-id default;
        }
    }
}