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FS#2062 - MTU is not set to 1508/1500 when using PPPoE #8425

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openwrt-bot opened this issue Jan 18, 2019 · 2 comments
Closed

FS#2062 - MTU is not set to 1508/1500 when using PPPoE #8425

openwrt-bot opened this issue Jan 18, 2019 · 2 comments
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@openwrt-bot
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alecrobertson13:

TP-LINK Archer C7, OpenWrt 18.06.1 r7258-5eb055306f / LuCI openwrt-18.06 branch (git-18.228.31946-f64b152).

Use PPPoE for WAN. Set MTU to 1508.

Observe ifconfig result. MTU is set at 1492, it should be 1500.

Add

config interface 'eth0'
option ifname 'eth0'
option mtu '1508'

to /etc/config/network, ensure PPPoE MTU (as above) is set to 1508 and restart the network/reboot the router.

Observe ifconfig result. MTU is set at 1500 as expected.

@openwrt-bot
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enryIT:

That's perfectly normal, openwrt automatically account for 8 byte of PPPoE overhead, thus 1500-8=1492.

If your ISP supports mini jumbo frames you could set MTU manually changing the MTU value on the pppoe interface.

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enyc:

I note, this is somewhat related to
https://bugs.openwrt.org/index.php?do=details&task_id=2667

In that case, VDSL driver "internally" does support larger MTUs and probably should be set to offer such 'automatically', whereas I can quite understand that in the case of PPPoE links, other modems' ethernet-links may-or-may-not support the larger MTU, and so may be best to set-up manually...

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