Re: [B.A.T.M.A.N.] MTU/connection problem

[Sven Eckelmann <sven.eckelmann@gmx.de>]

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Clemens John wrote:
> Hi,
> 
> I have a problem to connect to the Internet. We are using Batman advanced
> 0.2.1 and IPv4 here in oldenburg. Our setup looks like this:
> 
> Laptop-[wifi]->Fonera-[wifi]->Dir300-->OpenVPN-->
> virtual OpenWrt machine-->internet.
> 
> The default route of the laptop goes to the virtual OpenWrt machine wich
> provides an Internet connection.
> 
> I can acces google (wget google.de) but not heise.de or golem.de. I´m not
> verry familar with network configurations but I heared that this might be
> an mtu problem.
> 
> All devices in the network (tap0, ath0, ath1, wifi0) have an mtu of 1524
> except bat0 and br-mesh which have an mtu of 1500.
> 
> Our routers are configured to bridge connections from non batman devices
> (like the laptop) to bat0. This is done in the device "br-mesh".
> 
> Everythink works fine, except I can´t connect to internet websites that are
> not google.de.
> 
> When I decrease the mtu of the wireless device of the laptop to 1476
> everything works fine.
> But I have to do this by hand and on a client this is bad.
> 
> Does anybody know what I´m doing wrong?

Sounds a little bit like a device is configured wrong. Lets go through the 
devices:

Laptop:
 * WiFi: MTU: 1500

Fonera:
 * Incoming (to Laptop) WiFi: MTU 1500
 * Outgoing (to Dir300) WiFi: MTU 1530
 * Bridge (has bat0 and Incoming WiFi included): MTU 1500
 * bat0 (has only Outgoing WiFi included): MTU 1500

Dir300:
 * Incoming (to Fonera) WiFi: MTU 1530
 * bat0 (only incoming device included): MTU 1500

This should work till Dir300. Now send 1500 Bytes large packets to each 
interesting partner (fonera, dir300) and check were it drops.

This can be done using `ping -M do -s 1472 $IP`.

If it works till dir300 and drops somewhere in the openvpn/virtual 
openwrt/internet connection then please check there. If it drops before then 
please check your configuration (running, not configuration files) and try to 
summarize those devices as I tried to do above.

How exactly is openvpn your connection to the internet configured? Do they 
work in an mode which adds extra headers? Do they fragment packets?

Best regards,
	Sven

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