[Chilli] Best way to enforce MTU 1480?

[Ben West]

Thanks for the feedback Derek.  My original experience was that possible
MTU issues w/ coovachilli seemed to occur on devices that were *below* a
node on an OLSRd-managed mesh (e.g. a sub-mesh of OLSR nodes connected to
the LAN port of a node in a larger OLSR mesh).  I hope to repeat that
configuration soon to see if the command line param for chilli addresses it.

My value of MTU 1480 comes from the docs provided with OLSRd (section 5.4)
http://olsr.org/git/?p=olsrd.git;a=blob_plain;f=README-Olsr-Extensions;hb=release-0.6.5

I was assuming the need for maximum MTU 1500, as I must have packets
originating on a mesh forwarded through ethernet, e.g. for Internet
gateway. Thus, 1480 from (ethernet max - OLSRd tunnel overhead).

Indeed, the OLSRd overhead might compound with multiple layers of mesh, so
I will also be testing with MTU 1440 too, if needed.  My hair falls out on
its own, if you were curious. ;)



On Thu, Mar 27, 2014 at 4:38 PM, Derek Conniffe <derek at hssl.ie> wrote:

>  Hi Ben,
>
> I use a MESH as well (with UBNT M radios & ATH9K with an AdHoc VAP) but
> what I did was set the MTU of the MESH I/F to something like 1528 so that
> standard (1500) packets get though OK.  Last year I was trying to clamp MTU
> on a couple of I/Fs (for a different reason - it was on an EC2 instance
> with VPN & Squid and not MESH related) and it nearly broke my spirit and
> cost me a couple of days in hair-pulling!
>
> Derek
>
>
> On 27/03/2014 20:52, David Bird wrote:
>
> The MTU option will send the MTU value in DHCP, but doesn't mean it's
> always respected. You might refer to
> http://lartc.org/howto/lartc.cookbook.mtu-mss.html
>
>
> On Thu, Mar 27, 2014 at 12:30 PM, Ben West <ben at gowasabi.net> wrote:
>
>>  I'm running coovachilli v1.3.0 under OpenWRT AA on Ubiquiti Nanostation
>> gear, with only 32Mbytes of RAM.  Since these are nodes in a mesh managed
>> by OLSR, I need to enforce MTU=1480 for all client sessions authorized by
>> chilli.
>>
>>  From the online Changlog, it appears I can do this by adding a parameter
>> to the start-up command in coovachilli's init script:
>>
>> /usr/sbin/chilli --mtu 1480
>>
>>  However, the tap interface which I believe is what chilli sets up to
>> manage bandwidth throttling on client sessions still reports MTU 1500:
>>
>> tun0      Link encap:UNSPEC  HWaddr
>> 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
>>           inet addr:101.232.44.1  P-t-P:101.232.44.1  Mask:255.255.255.0
>>           UP POINTOPOINT RUNNING  MTU:1500  Metric:1
>>           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
>>           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
>>           collisions:0 txqueuelen:100
>>           RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
>>
>>  ... where 101.232.44.1 is the NAP IP of the device where I quoted this
>> from.
>>
>>  Is there a way I can ensure proper MTU settings on chilli client
>> sessions?
>>
>> --
>> Ben West
>> http://gowasabi.net
>> ben at gowasabi.net
>> 314-246-9434
>>
>> _______________________________________________
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>>
>>
>
>
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>
>


-- 
Ben West
http://gowasabi.net
ben at gowasabi.net
314-246-9434
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