MTU, PMTU & DF flag

[Nathan Stratton Treadway]

On Thu, May 14, 2015 at 10:12:40 +0200, Florent B wrote:
> On 05/13/2015 05:00 PM, Guus Sliepen wrote:
> > I have no experience with Ubuntu, but I find it hard to believe it would
> > block ICMP Fragmentation Needed packets out of the box.
> 
> I can confirm you that this is the case. Ubuntu ignores those ICMP
> packets... :( (rp_filter settings)
> 
> You can see it here : https://mellowd.co.uk/ccie/?p=5662

As I read that page, Ubuntu has rp_filter on by default, which causes it
to ignore ICMP messages that arrive from an interface different from the
one it expects that sending IP to be using.

Does that actually apply to the Ubuntu client that is having problems
here?  From the original post, I got the impression that client was a
laptop moving between networks or something like that -- i.e. it didn't
seem like that client was likely to be one with multi-homed routing...

						Nathan

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