Ubiquiti firewall: MAC address flapping between ports

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 brief

Confirm 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 Bhubaneswar, 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.