Bridge not forwarding fragmented packets from PPPoE server

RouterOS General
1

I only have this problem on connections between pppoe server and client.
If I put the IP on the ethernet interfaces it works correctly.

I’ll explain. The pppoe server creates a session with the client with mtu 1480. Between the pppoe-server router and the client router there is a mikrotik router (ccr1072) which had a bridge between the physical interface of pppoe-server router and the client router in question.
Beyond this size I can’t pass packets, even if I don’t use the do-not-fragment option. Virtually any mtu greater than 1480 does not want to pass.
If I create an eoip tunnel with mtu declared 1500 on the virtual interfaces it doesn’t work the same, and get timeout on 1438.
CCR1072 Router (pppoe-server) 7.11.2 → CCR1072 Router (bridging) 6.48.4 → RB3011 (pppoe-client) 7.11.2

What can it be?
Has anyone solved it?

2

Check MTU size of bridge ports (L2MTU property). If I understand you right, bridge is passing PPOoE frames. So it won’t do fragmentation, no L2 device does fragmentation (only router / L3 device can), so you have to ensure that resulting frames are snall enough to pass all L2 entities. PPPoE comes with overhead that has to fit into L2 frame size as well.