SA 520W How to have 1492 and 1500 MTU (WAN & LAN)

Unanswered Question
Dec 13th, 2009

Hi guys,

I recently got a new SA 520W and since this is my first Cisco router I am still learning my way through its administration etc. I would like to ask for your help ragarding the following problem:

I have PPPoE from ATT and its forced to 1492 MTU. Now I have a few NAS stations that stay on my LAN and they only support 1500 MTU. How can I have a WAN connection so I can get all sites to load with the 1492 MTU and at the same time connect to my NAS stations with 1500 MTU?

Can this be done with my SA 520W?

Your help is GREATLY appreciated.

Thanks.

LS

I have this problem too.
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CHRIS YEO Sun, 12/13/2009 - 20:37

Hi,

When the packet leaves your lan and goes to your wan the mtu on the SA will essentially instruct the packet to 'fragment' in order to go out on the wan at 1492.  Your pc will have the same constraints.  Some protocols will detect that you have a smaller mtu size and shrink the packet mtu appropriately.  If you look at this article:

http://en.wikipedia.org/wiki/Maximum_transmission_unit

Thanks!

Chris

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