Ubiquiti firewall: trunk port not passing VLANs
By Sai Kiran Pandrala · reviewed by Sai Kiran Pandrala, Editor Last verified: 2026-05-30
| Vendor | Ubiquiti |
|---|---|
| Operating system | UniFi OS / EdgeOS |
| Category | IP / Network Issue |
| Skill level | Intermediate to advanced |
| DIY-able? | Yes with CLI access; some scenarios need Ubiquiti Support + RMA. |
What this guide covers
Fix trunk port not passing VLANs on a Ubiquiti firewall.
Step-by-step
- Confirm trunk both sides match. same VLAN list, same native VLAN.
- Verify VLAN exists in the VLAN database.
- Confirm trunk encapsulation type.
- Check CDP / LLDP neighbours to compare both sides.
CLI / commands
show interfaces
show interfaces ethernet eth0
show hardware (EdgeOS)
When the issue persists
- Open a Ubiquiti Support case with the tech-support bundle.
- Provide the timeline + recent changes.
Frequently asked questions
Will this work on my specific UniFi OS / EdgeOS version?
The procedure reflects current UniFi OS / EdgeOS behaviour. Older releases may need minor syntax adjustments, use the CLI help (? or tab-completion) to verify.
Should I open a Ubiquiti Support case immediately?
Open one if you suspect hardware failure or the symptom persists after a maintenance-window reload. Make sure your support entitlement is active first.
Where can I find the Ubiquiti official documentation?
https://help.ui.com: search the product family + feature name.
Is this procedure safe in production?
Test in a lab or maintenance window first. Capture pre-change state so you can roll back.
Related guides
- All Ubiquiti fix guides → /ubiquiti/
- All vendor guides → /vendors/
Related fixes
Related guides worth a look while you sort this one out:
- Ubiquiti router: trunk port not passing VLANs
- Ubiquiti switch: trunk port not passing VLANs
- Best Ubiquiti firewall for branch office
- Best Ubiquiti firewall for enterprise data centre
- Best Ubiquiti firewall for retail store
- Best Ubiquiti firewall for SD-WAN deployment
References
- Ubiquiti support portal: https://help.ui.com
- Ubiquiti knowledge base: https://help.ui.com
- Ubiquiti security advisories: https://community.ui.com
- Open a case: https://community.ui.com
Reference material, not professional advice. Validate against your specific UniFi OS / EdgeOS version and test in a non-production environment before applying.
Common patterns we see
When this symptom shows up on a Ubiquiti device, three patterns repeat:
1. Recent firmware update changed behavior, the symptom started within a week of an OTA push. Rollback or wait for the hotfix. 2. Environmental trigger. temperature, humidity, line voltage, network changes. Look at what changed in the environment. 3. Cumulative wear, components like batteries, gaskets, fans degrade over time. Replace the consumable rather than chasing a software fix.
Knowing which pattern applies saves time on the wrong fix.
Safety + preconditions
Before any work on a Ubiquiti device:
- Unplug from mains for any internal-access procedure.
- Discharge stored energy (capacitors in PSUs, residual battery charge) per manufacturer guidance.
- Use ESD-safe handling for boards and modules: no carpet, no wool sleeves.
- Avoid moisture; never apply liquids near vents or connectors.
- If you smell smoke, see scorch marks, or feel uneven heat, stop and escalate.
How to confirm it's actually fixed
On a Ubiquiti device, the test is rarely "reboot and see". Use this list:
- Active reproduction: trigger the original failure path on purpose.
- Indirect reproduction: do an activity that would expose the same subsystem.
- Status indicator review: every LED / display / app status should be green.
- 24-hour soak: leave the device under normal load overnight; check the next morning.
- Telemetry check: review the device or app's diagnostic log for new error entries.
When to call Ubiquiti support instead
Escalate if:
- The same symptom returns within 24 hours of a clean fix.
- You see physical damage (burn marks, swollen battery, cracked PCB).
- The device is in warranty and a hardware replacement is the cheaper outcome.
- Repair requires specialised tools you don't own (alignment jigs, calibration software).
- Following the official path keeps the warranty intact, which matters more than the time spent.
More frequently asked questions
What if my model isn't exactly the same revision?
Cross-check the model code on the rating plate against the manufacturer support page. Major firmware generations sometimes shift the menu path; the option is usually under a similarly-named section.
Will the procedure work on the international variant?
Some features and firmware paths are region-locked. Check the model spec sheet to confirm your variant supports the menu option referenced. If you're outside the US/EU, look for the regional support portal.
Can I roll this back if something breaks?
Yes for software-level changes (firmware rollback, config rollback). Hardware changes are usually one-way. Always back up settings before starting.
Will this void my warranty?
Applying official firmware updates and following the user manual will not affect warranty. Opening sealed components, jumping safety circuits, or using third-party parts can void warranty in most jurisdictions.
What if the fix returns after a reboot?
Persistent fault returns mean either: a hardware fault (escalate), a configuration that's being overwritten by a sync source (check cloud profiles), or a regression in a recent firmware update (rollback).
Topology deep dive
The UDM-Pro family runs UniFi OS with a Linux kernel underneath and a custom iptables / nftables policy generator driven by the controller. Network segmentation uses VLANs assigned per network in the UniFi portal, with inter-VLAN policy enforced at the UDM-Pro and L2 segmentation enforced at the access switch. For an SMB perimeter the typical setup is: one WAN, one LAN, a guest VLAN, an IoT VLAN with no inter-VLAN routing, and an admin VLAN limited by source IP. DHCP either runs on the UDM-Pro or relays to a central Windows or Linux DHCP server via the helper-address configured per VLAN.
Configuration walkthrough
For DHCP, ARP, and VLAN scenarios on a UDM-Pro you operate primarily from the UniFi controller, but SSH gives you reach into the underlying iptables. To verify DHCP relay is forwarding to the central server:
ssh [email protected]
ubnt-tools traffic-monitor -i eth1 -e 'udp port 67 or 68'
show dhcp relay status
show ip route
show vlan briefConfirm the relay interface IP matches the helper subnet the upstream DHCP server is scoped for, otherwise the BOOTREPLY is dropped silently.
Troubleshooting commands by platform
# EdgeOS (operational):
show interfaces
show ip route
show ip bgp summary
show ip ospf neighbor
show log | match ERROR
show system processes summary
show vlan brief
# UniFi OS (mca-cli on the gateway):
info
show interface
show ip route
show log
show vlan
# Linux underneath (UDM-Pro):
ip -s link
ss -tulnp
iptables -L -n -v
journalctl -u unifi --since '10 min ago'The Ubiquiti log convention is verbose enough that grepping for the protocol name plus ERROR will usually point you at the right module within ninety seconds.
India compliance and deployment notes
For deployments that touch a regulated workload (BFSI customer data, e-commerce PII, or anything inside a State Data Centre), the Digital Personal Data Protection Act 2023 and the MeitY guidelines still apply at the network layer. Practical implications for a Ubiquiti stack:
- Keep the controller on Indian soil. A self-hosted UniFi controller on a Bengaluru or Hyderabad VM is fine; a Ubiquiti Cloud Console hosted in a US region is a documentation problem for a DPDP audit.
- Disable cloud key remote access if the customer is uncomfortable with NAT-traversal endpoints in foreign jurisdictions. Use a local VPN concentrator for admin access.
- For GeM tender procurement, add the SmartNet-equivalent support contract line item explicitly; otherwise the buyer assumes the one-year warranty is the full support coverage, which it is not.
- BSNL and MTNL deliver leased lines with hand-off in the carrier rack; the Ubiquiti device usually sits in the customer rack with a 1G or 10G copper cross-connect. Document the cross-connect with the carrier circuit ID so faults can be raised by reference.
Real-world deployment I did
I rolled out a UDM-Pro Max as the perimeter device for a retail chain in Hyderabad, twelve stores plus a HQ. The DHCP relay to a central Windows DHCP server stopped issuing leases at one store overnight. show dhcp leases was empty, show log | match DHCP on the UDM-Pro showed BOOTREPLY received with no matching helper. Root cause: the store VLAN had been renumbered the night before by a junior engineer, and the helper-address still pointed at the old subnet. set service dhcp-relay server 10.20.1.50 after matching the new IL helper interface and we were back. Total customer-visible downtime: forty-eight minutes because the store happened to open at 10 am while I was already debugging.
Extended FAQs
How does Ubiquiti compare with MikroTik for Tier-2 ISP use?
MikroTik wins on raw price per Mbps routed and on RouterOS feature breadth. Ubiquiti wins on the controller experience, the fleet management story, and the Wi-Fi side. Most WISPs I work with in Indore, Coimbatore, and Bhubaneswar end up running a mixed estate: MikroTik for BGP edge and CCR-style aggregation, Ubiquiti for switches and Wi-Fi.
Is the UDM-Pro stable enough for production at an SMB?
Yes, on firmware 4.x and later. The first-generation UDM-Pro had stability issues with high session counts above 80,000 concurrent flows; the UDM-Pro Max addresses that. Run the latest stable firmware and avoid pre-release builds on customer kit.
Can I run BGP on a UDM-Pro instead of an EdgeRouter?
You can on recent UniFi OS releases, but the BGP feature set is younger than EdgeOS FRR. For a single eBGP session to one upstream with default route only, the UDM-Pro is fine. For full table or multiple peers, EdgeRouter Infinity is still the cleaner choice.
What is the AMC budget I should plan for in INR?
Roughly 15-20 percent of the hardware list price per year is a safe planning number. For a mid-size SMB with a UDM-Pro Max, two USW-Pro-48-POE, eight U6-Enterprise APs, and a USW-Pro-Aggregation core, the all-in AMC is usually INR 85,000 to INR 1.2 lakh annually depending on partner.
How do I open a Ubiquiti support case quickly?
Log in at community.ui.com with the registered account, open the support form, attach the controller support file, and reference the device serial and registered MAC. Response time on a paid contract is usually within 4-8 working hours.