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FS#4220 - MTU > 1500 settings are missing for WAN and LANx mt7621 #9201

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openwrt-bot opened this issue Jan 7, 2022 · 2 comments
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@openwrt-bot
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nicefile:

Dir878 /882 /882-r1 (mt7530)
OpenWrt SNAPSHOT, r18502-53b87a7a28 but seems linux 5.10 builds are afected as 5.4 kernel it's fine.

There is issue with setting MTU to 1508 for DSA driver to be rfc4638 compatibile

root@OpenWrt:# ifconfig br-lan mtu 1508
root@OpenWrt:
# ifconfig eth0 mtu 1508
root@OpenWrt:~# ifconfig LAN2 mtu 1508
ifconfig: SIOCSIFMTU: Invalid argument

But even then MTU > 1500 seem to work for lan side.

root@OpenWrt:~# fping -s -M -b 1473 192.168.1.3
192.168.1.3 is alive

But to be able to use rfc4638 pppoe WAN must be set to 1508
root@OpenWrt:~# ifconfig wan mtu 1508
ifconfig: SIOCSIFMTU: Invalid argument

PPPoE session is always connecting with MTU 1492

@openwrt-bot
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abajk:

@nicefile Changing the MTU value is supported since 5.11. Try to backport [[https://github.com/torvalds/linux/commit/9470174e7581e75a8ebd78964997314dfc2e706c#diff-35d2b0dd263dfe166663a9af8babdaebc5c43f0698cf6c73eb531079e0fbf4da|this commit]].

@abajk
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abajk commented Feb 22, 2022

Fixed in commit: 637a3aa.

@jow- jow- closed this as completed Feb 22, 2022
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