Opened 3 years ago

Closed 3 years ago

#18869 closed defect (fixed)

Batman-adv MTU

Reported by: lbthomsen Owned by: developers
Priority: normal Milestone: Chaos Calmer 15.05
Component: packages Version: Trunk
Keywords: Cc:


I have been running a batman-adv mesh for a while. For the past couple of weeks I have seen this in the kernel log:

batman_adv: bat0: The MTU of interface wlan0 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1560 would solve the problem.

The MTU is set in the network configuration:

config interface 'mesh'
        option proto 'batadv'
        option mtu '1560'
        option mesh 'bat0'

Back in time (a couple of weeks ago) this would push the MTU of the wlan interface to 1560 but that no longer happens. The wlan0 interface got a MTU of 1500 and bat0 also got an MTU of 1500.

Question is - where is the right place to set the MTU?

Attachments (0)

Change History (5)

comment:1 follow-up: Changed 3 years ago by James

I have this issue too on the latest trunk but it was ok on r44070 so there must be an issue introduced at some point between r44070 and now.

The correct place is where you have it - in the network interface section.

Question (unrelated to the bug), why are you using 1560 MTU and not 1532 as documentated in the batman wiki?



comment:2 Changed 3 years ago by James

Possibly introduced in latest netifd?


comment:3 in reply to: ↑ 1 Changed 3 years ago by lbthomsen

Replying to James:

Question (unrelated to the bug), why are you using 1560 MTU and not 1532 as documentated in the batman wiki?

I think that is related to which flags batman-adv is compiled with. Notice the warning message from batman - it actually requests 1560 as MTU. If I remember correctly it was the multicast flag that tipped it over 1532.

comment:4 Changed 3 years ago by lbthomsen

Rolling back netifd to 0b0e5e2fc5b065092644a5c4717c0a03a9098dcf from Jan 12 fixes the issues, I will see if I can narrow that down further.

comment:5 Changed 3 years ago by nbd

  • Resolution set to fixed
  • Status changed from new to closed

fixed in r44461, thanks for tracking it down.

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