AX-88U the wan eth0 is running at 576 MTU by default even i set 1500 in Web Gui

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New Around Here
the wan eth0 is running at 576 MTU by default even i set 1500 in Web Gui on my AX88U with ASUSWrt Merlin 384 and 386


how to fix it? cover it with wan-event manually?

how i use the wan-event script? i installed it in jffs/scripts ( it wasn't there by default)


Part of the Furniture
EDIT: There was an issue with the WAN MTU that Merlin fixed three days ago:
Asus started work on adding that MTU setting on their firmware, but it seems they haven't finished it yet. When moving to my firmware (which already had support for it), the router incorrectly ends up with no MTU value at all, which doesn't get properly handled. I changed the default value to 1500 in beta 1 (which is why alpha users must either fix it or do a factory default reset), however it's possible that the MTU configuration code I merged from Asus doesn't properly deal with blank values that get inherited when moving from one of their beta firmware (or my alpha firmware) with the issue.

So, looks like the issue can also be introduced by running their beta firmware, and then switching to my firmware without doing a factory default reset.

I'll see if I can make the router use a more sensible value of 1500 if that value is completely blank.

What kind of internet service do you have, e.g. cable, VDSL, etc?

Are you using IPv6 (on the WAN side)?

What is your WAN connection type, e.g. PPPoE?

How are you determining that the MTU is 576?
Last edited:


New Around Here
solved it. by clearing NVRAM (aka reset I guess)

it was a bug that was there because I upgraded from stock to merlin without doing it earlier

MTU of eth0 (my wan cable modem connection) was 576

I determined it by typing ifconfig eth0

and then saw
eth0 Link encap:Ethernet HWaddr 24:4B:FE:**:**:**
inet addr:84.108.*.* Bcast: Mask:
RX packets:12346831 errors:0 dropped:260 overruns:0 frame:0
TX packets:5684073 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:6372644807 (5.9 GiB) TX bytes:504400623 (481.0 MiB)

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