[c-nsp] l2tp xconnect problem with packets > 1430

Gert Doering gert at greenie.muc.de
Thu Dec 8 05:14:38 EST 2011


On Wed, Dec 07, 2011 at 07:09:35PM -1000, Antonio Querubin wrote:
> Understood.  What I don't understand is why the large pings (in this case 
> large is anything > 1430) will sometimes work and sometimes not.  

Because sometimes fragmentation of the *outer* L2TP packet happens, and
sometimes not.  If fragmentation happens, anything will go through - and
the CPU load will go up through the roof.

> There is 
> no packet loss between the two routers and pmtud works between them.  They 
> can ping each other with large packets all day.  Not so the xconnected 
> hosts.

The routers will know how to fragment their pings.  The hosts won't.

USENET is *not* the non-clickable part of WWW!
Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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