The problem seems to have become well known -- I had a router die on me two weeks ago. The German technical support team, once they heard I was in Switzerland, told me that "in Switzerland, the MTU should never be larger than 1252" [because Switzerland has special problems]. (Where did they get this magic number?)

So I had to wait for the heat problem in the router to subside so it would even boot at all, reset the ROM, set it up again with all my original settings plus an MTU of 1252, and wait for it to predictably lock up again after a few hours before the tedious bureaucrats would honour the guarantee. I'm still waiting for the router to come back -- it pays to have several backups. To their credit, the router company are having to do the usual dance with the CH customs, which always adds a few days to any repair under guarantee exercise.

I don't know why German-language tech support has become so noxious, but it's a well-known problem. German VCs I know have called it a problem of "daylight compatibility" (of the customer service workers).

But as far as the problem of the original poster is concerned, it would seem that somebody out there at Cablecom or elsewhere in the CH backhaul world is running around reconfiguring things in the middle of the data pipe with a lower MTU, which means that we at the endpoints have to follow suit. Probably they got a memo from some boss, believed it without thinking, and are just "doing their job."

Unfortunately, simply going along with the program and reducing your router's MTU limit is probably easier than figuring out for what misguided reason this practice was adopted.

Charles

-----Original Message----- From: Marcel Prisi [mailto:marcel@virtua.ch] Sent: Wednesday, May 02, 2007 11:36 AM To: swinog@swinog.ch Subject: Re: [swinog] Cablecom MTU issue ?

Hi,

We seem to suffer a similar trouble in Aubonne today, packets bigger than 1500 get lost somewhere, only via our Cablecom uplink ...

Could someone at Cablecom have a look ??

Thanks.

Le mardi 01 mai 2007 � 18:40 +0200, Francois Deppierraz a �crit :

Hi swinogers,

Anyone knows about some MTU issues in the Cablecom network (especially Morges area) ?

Packets bigger than 1492 bytes (sometimes even less) are dropped depending on the source IP and destination IP.

It looks as if some interfaces in a multipath route (using IP adresses hash) uses a MTU smaller than 1500 bytes.

That was experienced from AS6893 and AS559.

Thanks _______________________________________________ swinog mailing list swinog@lists.swinog.ch http://lists.swinog.ch/cgi-bin/mailman/listinfo/swinog

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