L2 MTU issues - is BFD proper solution?

[David Sinn]

Hello,

On Aug 15, 2014, at 12:00 AM, Mathias Wolkert <tias at netnod.se> wrote:

> Hi
> 
>> 3 jul 2014 kl. 11:43 skrev Bartosz Radwan <b.radwan at citypartner.pl>:
>> 
>> We experienced recently several times issues caused by eg. EAPS path swich in one of our L2 transmission providers (new path MTU was not big enough due to jumbo frames not enabled - that's what they told us, but in fact it does not meter - it's out of our control).
>> 
>> From our point of view this situation sucks - we have several BGP sessions, terminated on 2 different BGP routers in different data centers, but problems as descripbed above in just one L2 provider network may cause our all services are not fully operational - especially when afeccted BGP sessions provides best routes for some popular services like FB, YT or… redtube.com ;).
>> 
>> So, the question: is BFD able to detect broken L2 MTU and if detected - disable affected BGP sessions?

BFD does not send MTU frames, so it would not be able to.

>> If not BFD, any other ideas?
> 
> ISIS hello packets are padded to MTU or close to it. 
> 
> It might not be useful for you, but anyway. 
> 
> /Tias
> 
>> 
>> It's possible to detect L2 problems outside bird and then disable protocols, but this may be complicated and error prone, so in fact - i do not want to to that.

You could write a script that would send pings at MTU with the DF bit set and react to failed responses.  

David


>> 
>> 
>> -- 
>> A: Because it messes up the order in which people normally read text.
>> Q: Why is top-posting such a bad thing?
>> Bartosz Radwan
>>