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morrownr / 88x2bu

Linux Driver for USB WiFi Adapters that are based on the RTL8812BU and RTL8822BU Chipsets
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(can't fix) MTU cannot be set to more than 1500 #80

Closed backahasten closed 2 years ago

backahasten commented 2 years ago

MTU cannot be set to more than 1500 When configuring the ad-hoc based mesh network of Batman adv, i need to use the command: sudo ifconfig wlan0 mtu 1532 However, I found that when the MTU is set to be more than 1500, an error will be reported: SIOCSIFMTU: Invalid argument Is this a chip problem?

morrownr commented 2 years ago

I did a little snooping around in the code to see what I could see. It appears 1500 is a hard coded limit in the driver. It isn't obvious why. I suspect making a change would result in breakage. Let me do a little reading about BATMAN so as to make a recommendation.

Can you give me an idea of your setup so I know what you are trying to accomplish?

backahasten commented 2 years ago

I'm just trying to use 88x2 network card to build Batman adv network. You can https://www.open-mesh.org/projects/batman-adv/wiki Find more information.

backahasten commented 2 years ago

It is an OSI layer 2 protocol, so MTU needs to be modified

morrownr commented 2 years ago

After a little reading and testing...

BATMAN seems interesting. I may have to look harder at this.

I have experience with various USB WiFi adapters and drivers. My main box almost always has at least 2 usb wifi adapters connected. I decided to test the adapters I currently have attached:

$ sudo ifconfig wlan0 mtu 1532

$ sudo ifconfig wlan1 mtu 1532

$ ifconfig| grep -i MTU enp2s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1532 wlan1: flags=4099<UP,BROADCAST,MULTICAST> mtu 1532

I did not see an error and the system is reporting the MTU of both adapters has increased to 1532. And everything is working well.

Now, what is the difference between what I tested and your adapter? Both of the adapters I tested are using the in-kernel Mediatek drivers (MT76). One adapter uses a mt7612u chipset (AC1200) and the other uses a mt7610u chipset (AC600).

You can find more information at the following site:

https://github.com/morrownr/USB-WiFi

Overall thoughts: My testing has shown that the 88x2 driver is not bad for managed mode. It has gaps in capability such as no WPA3 support but overall not bad. On the other hand. monitor mode and master mode support is not good at all. You would probably be well served by finding another job for your 88x2 adapter while getting an a adapter based on a mt7612u chipset for this BATMAN project. I can make a specific recommendation if you explain your use case.

Let me know how it goes.

backahasten commented 2 years ago

Finally, I used Qualcomm's chip, and they seemed to do well. Many functions of WiFi chips are not commonly used, and Qualcomm has done a good job in these uncommon functions.

morrownr commented 2 years ago

I agree. Qualcomm Atheros generally does a pretty job making sure less commonly used functions work well. The only problem is that we need them to released chipsets for the usb adapter market. If a project can use a card instead of an adapter, that opens up more options as wireless chipsets from Atheros, Mediatek and Intel are well supported in-kernel. Mediatek does a good job with less common features as well. I monitor the Linux Wireless mailing list.

I would avoid Realtek products. Period.