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Grant <emailgrant@×××××.com> wrote: |
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> >> A while back I was having networking issues. I eventually tried |
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> >> drastically lowering the MTU of all the systems onsite and the |
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> >> issues disappeared. I always thought the issue was due to the MTU |
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> >> on our modem/router. Today I read that AT&T DSL requires a 1492 |
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> >> MTU so I increased the MTU of our systems up to 1492 and haven't |
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> >> had any issues. Do certain ISPs require you to change the MTU of |
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> >> your entire network, or is this likely due to our AT&T |
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> >> modem/router itself? |
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> > |
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> > AFAIK the MTU is defined for every network interface separately. |
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> > For an ADSL connection it is common that a lower MTU is needed |
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> > because of the PPPoE header information that is encapsulated in the |
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> > ethernet frames. But in that case it is sufficient to lower the MTU |
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> > just for the WAN interface that is connected to the DSL modem. |
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> > If you don't use protocol encapsulation in your LAN then there |
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> > should be IMHO no reason for lowering the MTU of your internal |
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> > interfaces. |
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> |
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> |
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> So I should be OK with 1492 MTU on the modem/router and 1500 inside |
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> that LAN? That hasn't been my experience but I haven't tried in a |
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> while. Wouldn't that lead to fragmentation issues? Admittedly, my |
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> understanding of this is weak. |
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FWIR it is sufficient when all interfaces that are connected to a |
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layer 2 network are using the same MTU for the respective layer 3 |
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protocols. So it should be ok when the MTU of the (logical) ppp |
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interface is set to 1492 even when the MTU of the (physical) Ethernet |
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interface is set to 1500. This is the case for my router that is |
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connected to my DSL modem. I don't have any network problems and |
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always maximum internet speed. |
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I'm not a network expert and don't understand all the details. Also |
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my English is not good enough to explain it in a better way. |
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But to be honest, I'm not sure that I could explain it better in my |
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native language. ;-) |
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Probably there are other members on this ML that can give your more |
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useful information about this topic. |
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-- |
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Regards |
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wabe |
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