Re: [B.A.T.M.A.N.] Batman configuration and MTU

["Nicolás Echániz" <nicoechaniz@codigosur.org>]

On 04/17/2012 05:41 PM, HeXiLeD wrote:
> I have being doing some testing with several types of configurations
> with custom openwrt build and batman in oder to try to come with a basic
> default "plug & play" ready to deploy firmware evolving the least
> changes possible other than the router's ip and not much more.
> I have tried several configurations, more than one subnet and have being
> trying to see a way to make some nice HOW-Tos regarding this matter for
> several types of configurations.
> 
> So far and from what i seen all working and half working examples do not
> work for everyone or at least no one or very few post complete
> configurations of all files in /etc/config/  that actually fully work.
> 
> Then there is the question if bridging. Some say bridge this, others say
> do not bridge that. None supply a fully working example that can be
> replicated. (i am glad i access the routers over serial cable which i
> recommend to everyone if they are working on builds and configurations.

I can send you some sample configs if you wish, I copied some snippets
in this mail.


> config 'wifi-iface'
>         option 'device' 'radio0'
>         option 'hidden' '0'
>         option 'mode' 'adhoc'
>         option 'ssid' 'wireless'
>         option 'bssid' '02:16:b8:6b:0a:1a'
>         option 'encryption' 'none'
> 	#option 'network' 'lan' #is optional or must match bridge name
>         option 'mtu' '1528' #mtu seems to be ignored - needs fix


AFAIK mtu is set in config/network, not in config/wireless

> # cat batman-adv
> config 'mesh' 'bat0'
>         option 'ap_isolation' '0'
>         option 'bonding' '0'
>         option 'aggregation' '1'
>         option 'fragmentation' '1'
>         option 'gw_bandwidth' '3mbit/384kbit'
>         option 'gw_mode' 'client'
>         option 'gw_sel_class' '5'
>         option 'orig_interval' '1000'
>         option 'vis_mode' 'client'
>         option 'interfaces' 'wlan0 eth0.0'


I believe you have your bridges mixed up.

For a normal situation, you should make your batman interfaces members
of bat0 and then add bat0 to your br-lan, like so:


config 'mesh' 'bat0'
	option 'interfaces' 'wlan0-1 eth0'

config 'interface' 'lan'
	option 'type' 'bridge'
	option 'proto' 'static'
	option 'netmask' '255.255.248.0'
	option 'gateway' '10.5.0.1'
	option 'dns' '8.8.8.8'
	option 'mtu' '1500'
	option 'ipaddr' '10.5.0.2'
	option 'ifname' 'bat0 wlan0'

config 'interface' 'wlan0_1'
	option 'proto' 'none'
	option 'mtu' '1528'
	option 'ifname' 'wlan0-1'



In this example, wlan0 runs an open AP where clients can connect, while
other mesh nodes connect through eth0 and wlan0-1.

and this is the corresponding wireless config:

config 'wifi-device' 'radio0'
	option 'type' 'mac80211'
	option 'macaddr' '00:15:6d:3e:XX:XX'
	option 'hwmode' '11ng'
	option 'channel' '1'
	option 'country' 'US'
	option 'txpower' '27'
	option 'htmode' 'HT20'
    option 'noscan' '1'

config 'wifi-iface'
	option 'network' 'lan'
	option 'device' 'radio0'
	option 'encryption' 'none'
	option 'mode' 'ap'
	option 'ssid' 'quintanalibre.org.ar'

config 'wifi-iface'
	option 'device' 'radio0'
	option 'encryption' 'none'
	option 'mode' 'adhoc'
	option 'ssid' 'mesh.quintanalibre.org.ar'
	option 'bssid' '02:12:34:56:78:9A'
	option 'mcast_rate' '54000'


side note: experimenting with mcast_rate is an interesting to force bad
routes out of the picture.


I believe that the only time when you want a different bridge setup is
when you need to have batman and non-batman connections on the same
interface (a router's eth switch), then you'd use the setup described in
this document:
http://www.open-mesh.org/wiki/batman-adv/Bridge-loop-avoidance



> The last problem i now face (assuming that this configuration is valid)
> is the MTU settings which seem to be ignored no matter where i add them;
> including creating the following for the other interfaces:
> 
> config 'interface' 'wifi'
>         option 'proto' 'none'
>         option 'ifname' 'wlan0'
>         option 'mtu' '1528'

Here we use a similar method to get the MTU properly set (as you can see
in the previous config snippet).
This works well for us.


> I have lost quite a lot of sleep over these problems and it is natural
> that i might be missing something very simple.
> 
> batman_adv: bat0: The MTU of interface eth0.0 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 1528 would solve the problem.

have you tried setting the MTU from command line, like so:
# ifconfig wlan0 mtu 1528

does this succeed?

> 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 1528 would solve the problem.

we have found no solution for setting MTU above 1500 for wired
interfaces. If anyone has instructions about this, I'd also be very
interested.