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labuwx
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RB450Gx4 switch does not tag incoming PPPoED

Tue Apr 19, 2022 12:38 am

Hi,

I have a RB450Gx4 (AR8327 switch) with ROS v7.2.1 . I use a similar switch/VLAN/bridge configuration: Basic VLAN switching: Other devices with a built-in switch chip.
My ISP's ONT is connected to an access port, so the switch chip should tag incoming frames before forwarding them to the CPU. The packet sniffer reveals that it tags most of them, except PPPoED (EtherType 0x8863). Thus PPPoE connections are impossible to set up.
A workaround I found is to diverge from the above-mentioned configuration and use a VLAN filtered bridge. With that (and frame-types=admit-all) I can add the missing tag in software.
Once the PPPoE connection is running, I can change the bridge port to frame-types=admit-only-vlan-tagged and the connection keeps working. Which confirms that the ether types the switch chip does not tag are only needed for the PPPoE setup phase.

Things I have also checked:
  • The ONT only sends untagged frames
  • The switch chip correctly tags frames with EtherType: IPv4, IPv6, ARP, PPPoE Session
 
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mkx
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Re: RB450Gx4 switch does not tag incoming PPPoED

Tue Apr 19, 2022 8:02 am

That's exactly what I observed on my hAP ac2. When I reported it to Mikrotik, they replied that they could identify the issue but that they had no ETA for the fix. This was around 3 years ago, so I lost all hope to see the fix. And my hAP ac2 happily runs in vlan-filtered bridge configuration. Another workaround is to connect WAN to third party VLAN--aware switch to do the tagging/untagging, works just fine.

This issue seems to be IPQ-401x related though. I've got a few RB951Gs which use (proper?) AR8327 switch chips and those don't experience same bug, they can tag/untag PPPoE packets just fine.

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