XPost: comp.os.linux.networking   
   From: markhobley@yahoo.donottypethisbit.co   
      
   On Sun, 22 May 2011 11:40:16 +0100, Andy Furniss wrote:   
      
   > I see the same, but don't know what the behavior should be. If you set   
   > mtu on say eth0 then advertised tcp mss will be affected (which in a way   
   > is setting mtu plus mru for tcp) - maybe the route setting really just   
   > does mtu alone, which in a way is what you asked for   
      
   That would not be very good at all, because it breaks PMTUD. I would   
   obviously want the MTU to match the route.   
      
   > If you want to fix up your wan use iptables mss clamping on the gateway   
   > if you can.   
      
   I had a quick look through the router configuration settings and I could not   
   see such an option, so I guess that this facility is not provided.   
      
   > Using ping to try and work out isp behavior can be misleading - you may   
   > just be seeing the settings of the server/network you are pinging and   
   > the pings may get fragged/re-assembled without you knowing.   
      
   With PMTUD enabled, the Don't Fragment flag is set though, isn't it? So this   
   would mean that we have a single datagram end to end.   
      
   Mark.   
      
   --   
   Mark Hobley   
   Linux User: #370818  http://markhobley.yi.org/   
      
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