I've got an Asus RT-AC66U running Merlin 380.63_2. I'm trying to use an Alcatel MW40 hotspot (sold unblocked through Portuguese operator NÓS).
The router recognizes the device once plugged in via USB and I can access the internet. However, soon after setting it up, began to notice that some pages would hang, which seems like a symptom of an improper MTU setting (as found here: 1, 2, 3,
4).
I started debugging the issue by connecting my Mac's laptop's wifi directly to the USB modem, and determining the maximum MTU size I could send by doing ping tests as described here. A packet length of 1472 was the max I could send before I got the "message too long" error.
Since the page says to add 28 to that value, then that means that 1500 is the desired MTU size. But that just makes me think that my test is flawed-- that I am simply confirming the Mac's Wifi network MTU setting (which is, in fact, 1500). So then I tried the same test with my laptop wifi -> ASUS router -> USB modem. I got the same result-- 1472 was still the max I could send.
On the router, the default MTU I see on all interfaces is 1500 (br0, eth0, eth1, eth2, and usb0 -- the modem).
I can't reconcile the fact that, directly connected to the hotspot, my laptop's network interface is auto-set to MTU 1500, and things work fine, but adding the router in the middle, where all its interfaces are also set to 1500, things break.
When I see folks suggest to change the MTU value, I'm presuming they mean only the modem interface's MTU value. Although this can be done via the Web UI, I tried temporarily doing so on the command line:
I tried setting it to 1480 and 1472, per this message. And even tried 1502 per another message I found. None of it seems to make a difference. This message makes me worried I'm chasing a red herring.
A few notes about my config:
- Jumbo frames are disabled (seems to be the default)
- NAT acceleration is set to "Auto" (also seems to be the default)
Any help would be highly appreciated. I've donated to RMerlin before, but I'd totally make another donation if someone can help me get through this challenge.
The router recognizes the device once plugged in via USB and I can access the internet. However, soon after setting it up, began to notice that some pages would hang, which seems like a symptom of an improper MTU setting (as found here: 1, 2, 3,
4).
I started debugging the issue by connecting my Mac's laptop's wifi directly to the USB modem, and determining the maximum MTU size I could send by doing ping tests as described here. A packet length of 1472 was the max I could send before I got the "message too long" error.
Code:
ping -D -s 1473 192.168.0.1
PING 192.168.0.1 (192.168.0.1): 1473 data bytes
ping: sendto: Message too longSince the page says to add 28 to that value, then that means that 1500 is the desired MTU size. But that just makes me think that my test is flawed-- that I am simply confirming the Mac's Wifi network MTU setting (which is, in fact, 1500). So then I tried the same test with my laptop wifi -> ASUS router -> USB modem. I got the same result-- 1472 was still the max I could send.
On the router, the default MTU I see on all interfaces is 1500 (br0, eth0, eth1, eth2, and usb0 -- the modem).
I can't reconcile the fact that, directly connected to the hotspot, my laptop's network interface is auto-set to MTU 1500, and things work fine, but adding the router in the middle, where all its interfaces are also set to 1500, things break.
When I see folks suggest to change the MTU value, I'm presuming they mean only the modem interface's MTU value. Although this can be done via the Web UI, I tried temporarily doing so on the command line:
Code:
# ifconfig usb0 mtu XI tried setting it to 1480 and 1472, per this message. And even tried 1502 per another message I found. None of it seems to make a difference. This message makes me worried I'm chasing a red herring.
A few notes about my config:
- Jumbo frames are disabled (seems to be the default)
- NAT acceleration is set to "Auto" (also seems to be the default)
Any help would be highly appreciated. I've donated to RMerlin before, but I'd totally make another donation if someone can help me get through this challenge.
Last edited:
