[fpc-devel] Re: [fpc-pascal] Website connectivity

Jonas Maebe jonas.maebe at elis.ugent.be
Tue Aug 18 10:35:19 CEST 2009

On 17 Aug 2009, at 18:34, Axel Scheepers wrote:

> On Mon, 2009-08-17 at 18:11 +0200, Michael Van Canneyt wrote:
>>> b) set the TCP maximum segment size of all *incoming* packets to  
>>> 1472. This
>>> means that setting the MTU on your computer to a low value (which  
>>> would then
>>> also be used by the server when replying) won't help, since the  
>>> server always
>>> sees an MTU of 1472 bytes.
>> It's a very common CISCO router :-)
>> The problem is not really the router itself, but the instructions  
>> we got from
>> the ISP on how to configure it :(
>> (totally braindead instructions in my opinion, but arguing didn't  
>> really help)
> Over here (isp) we have to use a lower mtu to be able to pass both  
> mpls
> and vlan tags around, it's not that braindead if you need that. Why  
> they
> need that for 'simple' access is indeed a bit strange.

The server is connected via adsl, probably using PPPoE. I guess the  
mss on incoming packets is set to the maximum mss that can be handled  
by the PPPoE connection (so that servers that reply won't use a higher  
mss). What does seem braindead to me is that the mss of incoming  
packets with a lower mss is increased to this maximum. And of course  
also that they drop ICMP type 3 code 4 messages ("fragmentation needed  
but don't-fragment bit set") and that they always set the "Don't  
Fragment" bit to outgoing packages.


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