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FS#3990 - lantiq: gswip: packets larger than 1496 bytes dropped when VLAN is used #9076

openwrt-bot opened this issue Aug 23, 2021 · 0 comments


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openwrt-bot commented Aug 23, 2021


This issue occurs with current master on a Fritzbox 7412 and 7362 SL.

When a switch port is using tagged VLAN, any packets sent from the device which are larger than 1496 bytes are dropped. Incoming packets are received correctly.

Comparison of the old swconfig driver with the new DSA driver shows that a lower value is now written to the GSWIP_MAC_FLEN register. Now it is 1526 (VLAN_ETH_FRAME_LEN + 8), while it was 1534 before (1518 + 8 + 4 * 2, which corresponds to "MAC frame + 8-byte special tag + 4-byte VLAN tag * 2" according to comments in the vendor driver). Increasing this to the old value seems to fix the issue.

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