Subject: Re: IPsec PMTUD problem

From: Patrick McHardy <[email-masked]>
Date: Thu, 05 Apr 2007 14:09:20 +0200

Herbert Xu wrote:
> On Tue, Apr 03, 2007 at 06:32:07PM +0200, Patrick McHardy wrote:
> 
>>I'm not sure I understand how this would work, the ICMP message
>>looks the same in both cases. Or are you suggesting to
>>differentiate based on the source of the ICMP message?
> 
> 
> Actually you're right, this can't work in the general case.  Even
> if we had real devices for IPsec tunnels, there is still no way to
> reliably figure out which device we should attribute a given MTU
> event to if the same address appears on more than one device.
> 
> 
>>Yes, that would work as a workaround, but it still seems like
>>something worth fixing.
> 
> 
> One possible solution is to not send MTU errors to ourselves since
> we it wouldn't give us any new information.  We'd need to audit the
> users of icmp_send to make sure that there isn't a legitimate case
> where we'd want to do that.

One such case is delivery of errors to sockets. We'd need to make
sure the errors are delivered some other way.