VLAN offloading problem with bridge on hEX refresh

Hello.

Having a strange problem with hEX refresh using bridge.

The LAN port is configures as a hybrid VLAN port with LAN as untagged and GUEST and BASE network as tagged.

Implemented VLAN offloading on my hEX refresh by adding a bridge. Afterwords, internet via external WiFi access point is slow with IPv6, IPv4 works OK. Direct Ethernet connected devices is fast with both IPv4 and IPv6. Without bridge, direct Ethernet and WiFi works OK with both IPv4 and IPv6

Configuration Direct Ethernet WiFi (IPv4) WiFi (IPv6)
No Bridge 500 Mbps 450 Mbps 450 Mbps
With Bridge 500 Mbps 450 Mbps 100 Mbps

Have tried to disable hardware offload. Same result.

The bridge is named LAN to be able to reuse rules.

OS: 17.19.2

Fasttrack is enabled on IPv4 and IPv6. The LAN ip address is assigned to the bridge.

Before Bridge:

/interface ethernet set [ find default-name=ether2 ] name=LAN
/interface vlan add interface=LAN name=BASE vlan-id=192
/interface vlan add interface=LAN name=GUEST vlan-id=155
/ip address add address=10.2.5.1/24 interface=LAN network=10.2.5.0
/ip address add address=192.168.3.1/24 interface=BASE network=192.168.3.0
/ip address add address=192.168.155.1/24 interface=GUEST network=192.168.155.0

After bridge:

/interface bridge add name=LAN vlan-filtering=yes
/interface bridge port add bridge=LAN interface=ether2
/interface bridge vlan add bridge=LAN tagged=ether2 vlan-ids=192
/interface bridge vlan add bridge=LAN tagged=ether2 vlan-ids=155
/interface bridge vlan add bridge=LAN untagged=ether2 vlan-ids=1

/interface vlan add interface=LAN name=BASE vlan-id=192
/interface vlan add interface=LAN name=GUEST vlan-id=155

/ip address add address=10.2.5.1/24 interface=LAN network=10.2.5.0
/ip address add address=192.168.3.1/24 interface=BASE network=192.168.3.0
/ip address add address=192.168.155.1/24 interface=GUEST network=192.168.155.0

The usual culprit is MTU. The vlan tag adds 4 bytes to the packets, which then might exceed link mtu. Mtu on ipv6 is advertised as part or the RAs (router advertisements) - try decreasing it there by some amount, let’s say 50 and see if this fixes things. (50 is obviously over the top, but it’s okay for debugging.)

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