* wabe <waben...@gmail.com> [160919 20:50]:
> Grant <emailgr...@gmail.com> wrote:
> > A while back I was having networking issues.  I eventually tried
> > drastically lowering the MTU of all the systems onsite and the issues
> > disappeared.  I always thought the issue was due to the MTU on our
> > modem/router.  Today I read that AT&T DSL requires a 1492 MTU so I
> > increased the MTU of our systems up to 1492 and haven't had any
> > issues.  Do certain ISPs require you to change the MTU of your entire
> > network, or is this likely due to our AT&T modem/router itself?
> AFAIK the MTU is defined for every network interface separately. For an
> ADSL connection it is common that a lower MTU is needed because of the 
> PPPoE header information that is encapsulated in the ethernet frames.
> But in that case it is sufficient to lower the MTU just for the WAN 
> interface that is connected to the DSL modem. 
> If you don't use protocol encapsulation in your LAN then there should
> be IMHO no reason for lowering the MTU of your internal interfaces.
> --
> Regards
> wabe

MTU is per network interface but you really don't want to end up having
your router fragment every IP packet because systems on your subnet are
using a larger MTU.


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