[B.A.T.M.A.N.] MTU issue

[B.A.T.M.A.N.] MTU issue

[Wayne Abroue]

Hi All

We are having a small isue with mtu, on certain builds, could be only
the latest, we are getting this error in wrt.

batman_adv: bat0: The MTU of interface wlan0 is too small (1527) 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.

I had the same issue previously, but 1528 did not do it.
I have since changed build on that unit and can't remember the actual
value I used, But it was larger.

All I did was increase the value until the warning disappeared, and
everything started working as advertised.

Any idea's?

Wayne A

Re: [B.A.T.M.A.N.] MTU issue

[Marek Lindner]

Hi,

> I had the same issue previously, but 1528 did not do it.
> I have since changed build on that unit and can't remember the actual
> value I used, But it was larger.
> 
> All I did was increase the value until the warning disappeared, and
> everything started working as advertised.

what do you mean with "working as advertised" ? It should work even if you get 
this warning. All it does is fragmenting your traffic.

Setting the MTU to 1528 works for me. Without providing more information about 
your setup and giving us the number which seemingly "fixed" it for you nobody 
can help you.

Regards,
Marek

Re: [B.A.T.M.A.N.] MTU issue

[Marek Lindner]

Hi,

> However using the latest trunk Openwrt, batman-adv it simply does not
> communicate via the bat0 interface.
> 
> bat0 is up, batctl confirms correct interface, MTU set at 1527 or 1528
> or even a touch higher still does not produce batctl pings or
> originator lists.

in your previous mail you said increasing the MTU value helped and now it does 
not ? It is a bit confusing .. Would you mind to clarify ?
We had some bugs in the 2011.3.0 release which led to connection issues, 
therefore we released 2011.3.1. However, the originator list was unaffected.
You might want to give it a try.


> Thus I was wondering if anybody has had the same problem, to assist me
> compiling WRT trunk with a older version, I tried the Wiki procedure
> for older version editing makefile to 2010.2.0 which produced a error
> , " can;t remove /usr/sbin/batcl ;permissions at the build stage.

The location of the batctl binary changed. You can find the necessary changes 
in the OpenWrt repository.

Regards,
Marek

Re: [B.A.T.M.A.N.] MTU issue

[Wayne Abroue]

On Sun, Nov 6, 2011 at 7:27 PM, Marek Lindner <lindner_marek@yahoo.de> wrote:
>
> Hi,
>
>> However using the latest trunk Openwrt, batman-adv it simply does not
>> communicate via the bat0 interface.
>>
>> bat0 is up, batctl confirms correct interface, MTU set at 1527 or 1528
>> or even a touch higher still does not produce batctl pings or
>> originator lists.
>
> in your previous mail you said increasing the MTU value helped and now it does
> not ? It is a bit confusing .. Would you mind to clarify ?
> We had some bugs in the 2011.3.0 release which led to connection issues,
> therefore we released 2011.3.1. However, the originator list was unaffected.
> You might want to give it a try.
>
>
>> Thus I was wondering if anybody has had the same problem, to assist me
>> compiling WRT trunk with a older version, I tried the Wiki procedure
>> for older version editing makefile to 2010.2.0 which produced a error
>> , " can;t remove /usr/sbin/batcl ;permissions at the build stage.
>
> The location of the batctl binary changed. You can find the necessary changes
> in the OpenWrt repository.
>
> Regards,
> Marek
>

To answer your first question, Sorry for the confusion, When I tried a
trunk on a new UBNT , a few weeks ago I got the no comms result, so I
promptly compiled with Backfire and all was well.

However , a member of the VT-DEV list has the same problem while
trying to run from precompiled  trunk, on a new tp-link wr703 unit.

Unfortunately the wr703 is only supported on trunk, so with the
pre-compiled version he gets the same results I had.

I took this to be related, But if a patch is out, I reckon the only
way is to   build from a new svn update to solve?

Thanks for the help.

Wayne A

Re: [B.A.T.M.A.N.] MTU issue

[Sven Eckelmann]

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On Sunday 06 November 2011 20:05:23 Wayne Abroue wrote:
[...]
> To answer your first question, Sorry for the confusion, When I tried a
> trunk on a new UBNT , a few weeks ago I got the no comms result, so I
> promptly compiled with Backfire and all was well.
> 
> However , a member of the VT-DEV list has the same problem while
> trying to run from precompiled  trunk, on a new tp-link wr703 unit.
> 
> Unfortunately the wr703 is only supported on trunk, so with the
> pre-compiled version he gets the same results I had.

We are currently a little bit confused about your mail. It doesn't provide a 
good view on the actual problematic. There are small chunks of information 
here and there, but nothing which could help us to understand what it going 
on. Also references are only made as "somebody else said something" and not as 
link or citation. This makes it quite hard for us to help you.

So what we would need is a clear and consistent description:
 * what hardware/software is used?
 * what are the versions/revisions of everything (including branch
   informations)?
 * how looks the hardware (including network infrastructure) configuration?
 * how looks the software configuration?
 * can it be reproduced with the newest version? (include enough information
   to define "newest version")
 * do you know a version where it works and what is this version?
 * what tests did you use?
 * what result did you expect?
 * what was the actual result of the test?
 * when a workaround is known: what exact steps are necessary to work around
   the problem?
 * ...

Please also provide relevant information from the batman-adv debug(fs) 
interface [1] and packet dumps (please be aware that only relevant parts are 
interesting and that we have a limit of 200 KiB for mails).

Be aware that pre-compiled trunk of openwrt doesn't mean that you get the 
newest stuff in trunk or anything stable at all.

> I took this to be related, But if a patch is out, I reckon the only
> way is to   build from a new svn update to solve?

I cannot give a good answer to this question, but it would be a good idea to 
test the patches for batman-adv 2011.3.1 that are integrated in the openwrt 
trunk since r28779 [2].

Kind regards,
	Sven

[1] http://www.open-mesh.org/wiki/batman-adv/Understand-your-batman-adv-
network
[2] https://dev.openwrt.org/changeset/28575/packages/net/batman-adv

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[B.A.T.M.A.N.] MTU issue

[Saurabh Chakrabarti]

Following the Troubleshooting guide, I have changed the MTU for bat0 
interface to 1524. I'm getting this message in my syslog:

Jan  1 00:00:53 localhost kernel: [   26.899762] batman_adv: bat0: The 
MTU of interface wlan0 is too small (1524) 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.

I'm not seeing any apparent performance issues, but do I really need to 
make the MTU 1560?

-saurabh

Re: [B.A.T.M.A.N.] MTU issue

[cmsv]

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https://lists.open-mesh.org/pipermail/b.a.t.m.a.n/2014-January/011276.html

On 04/24/2014 04:34 AM, Saurabh Chakrabarti wrote:
> Following the Troubleshooting guide, I have changed the MTU for bat0
> interface to 1524. I'm getting this message in my syslog:
> 
> Jan  1 00:00:53 localhost kernel: [   26.899762] batman_adv: bat0: The
> MTU of interface wlan0 is too small (1524) 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.
> 
> I'm not seeing any apparent performance issues, but do I really need to
> make the MTU 1560?
> 
> -saurabh
> 

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