Interesting issue: MTU limits and RPi3 wifi NIC

Raspberry Pi 2

Interesting issue: MTU limits and RPi3 wifi NIC

Postby atamisk » Sun Jul 03, 2016 2:21 pm

Hey everyone,

I ran into an issue when using my Pi3 over SSH when on the internal wifi. Basically, whenever i made a lot of output with the pi (i.e. dmesg), the ssh connection would stall. I investigated the issue using tcpdump and noticed that all packet traffic to/from the pi stopped when this issue occurred. However, if i started a parallel connection to the pi, it would respond (so long as output was kept small!!).

All connections over the ethernet NIC could process unlimited amounts of output.

After some research, i tracked the issue down to an MTU sizing/fragmentation problem. I raised the default MTU setting on my router from 1500 to 1800, and all issues went away.

In addition to just posting this process for someone else that might run into it in the future, i'm curious about something: What makes the RPi wireless NIC "different"? I've never had fragmentation issues on any of my hardware before, and even a different interface on the same device yields acceptable results at the default MTU. I'd always assumed a packet was a packet, but could something be different be happening that is specific to my setup?

For reference, my network is served by a Linksys WRT 1200AC running OpenWRT 15.05
atamisk
 
Posts: 1
Joined: Sun Jul 03, 2016 2:10 pm

Return to Broadcom

Who is online

Users browsing this forum: No registered users and 4 guests